REMOVAL OF HEAVY METALS FROM INDUSTRIAL SLUDGE … · GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCIES ... for removal of heavy metals from industrial sludge and the effect of inorganic

DOKUZ EYLÜL UNIVERSITY

GRADUATE SCHOOL OF NATURAL AND APPLIED

SCIENCIES

REMOVAL OF HEAVY METALS FROM INDUSTRIAL SLUDGE

by

Işıl AKSAKAL

February, 2005

İZMİR


A Thesis Submitted to the

Graduate of Natural and Applied Sciences of Dokuz Eylül University

In Partial Fulfillment of the Requirement for the Degree of Master of Science in

Environmental Engineering, Environmental Technology Program

by

Işıl AKSAKAL

February, 2005

İZMİR

ii

M.Sc THESIS EXAMINATION RESULT FORM

We have read the thesis entitled “REMOVAL OF HEAVY METALS FROM

INDUSTRIAL SLUDGE” completed by IŞIL AKSAKAL under supervision of

Instructor Dr. NURDAN BÜYÜKKAMACI and we certify that in our opinion it is

fully adequate, in scope and in quality, as a thesis for the degree of Master of Science.

Supervisor

(Jury Member) (Jury Member)

Prof.Dr. Cahit HELVACI Director

Graduate School of Natural and Applied Sciences

iii

ACKNOWLEDGMENTS

I would like to express my gratitude to my supervisor Instructor Dr. Nurdan

Büyükkamacı for her guidance and motivation.

I also would like to thank Prof. Dr. Ayşe Filibeli, Instructor Dr. Zihni Yılmaz,

Res. Ass. Azize Ayol and Nazlı Baldan for their valuable helps in my thesis.

I am very grateful to the personnel of wastewater treatment plant of Atatürk

Organized Industrial District, Sahan Dyestuff Industry, Norm Cıvata and Cevher

Döküm for their assistance during taking samples for this study. Also, I thank to the

personnel of DEÜ Wastewater Laboratory for their assistance during my

experiments.

I am particularly grateful to Özgür Aksakal and Sibel Şen, my husband and my

sister for their helps and morale motivations.

Finally, I thank to my father, Erol Şen, and my mother, Habibe Şen, for their

moral support, and patience during my education.

Işıl AKSAKAL

iv


ABSTRACT

In this thesis, solid-to-liquid extraction method at lab scale conditions was used

for removal of heavy metals from industrial sludge and the effect of inorganic acid

and organic acid addition was compared. For this purpose, inorganic acid

(HF+HClO4) and organic acids (citric acid, oxalic acid, and acetic acid) were directly

added to sludge samples as an extraction reagent. Three different extraction reagent

concentrations (1 mol, 2 mol, and 5 mol) in organic acid applications were used. In

order to evaluate the effects of extraction time on extraction efficiency, four different

extraction time (1 h, 3 h, 24 h, and 72 h) were examined.

The heavy metal extraction studies were carried out using four different industrial

sludges, which were taken from a dyestuff industry, two metal industries, and an

organized industrial district. The extraction efficiencies were determined depending

on the concentration of extracting reagent and extraction time. The most effective

extraction reagent was determined for each heavy metal of each sludge sample. In

the case of one of the organic acid was the most effective reagent, the most effective

extraction time was also determined.

Keywords: Sludge, heavy metal, extraction

v

ENDÜSTRİYEL ÇAMURLARDAN AĞIR METAL GİDERİMİ

ÖZET

Bu tez kapsamında, endüstriyel çamurlardan ağır metal giderimi laboratuvar

koşullarında incelenmiştir. Bu amaçla katı-sıvı ekstraksiyon metodu kullanılmış ve

inorganik ve organik asit ilavesinin etkisi karşılaştırılmıştır. Deneysel çalışmalarda

ekstraksiyon ayıracı olarak inorganik asit (HF+HClO4) ve organik asitlerin (sitrik

asit,oksalik asit ve asetik asit) etkisi incelenmiştir. Organik asitlerle yapılan

çalışmalarda asit konsantrasyonun etkisinin belirlenebilmesi amacıyla üç farklı

konsantrasyonda asit ilavesi (1 mol, 2 mol ve 5 mol ) ile çalışılmış ve ekstraksiyon

süresinin ağır metal giderim verimi üzerine etkisini değerlendirmek için de dört farklı

ekstraksiyon süresi (1 saat, 3 saat, 24 saat ve 72 saat) uygulanmıştır.

Farklı endüstriyel nitelikli çamurlarda metal ekstraksiyon veriminin

incelenebilmesi için boya endüstrisi, organize sanayi bölgesi ve iki farklı metal

endüstrisine ait atıksu arıtma tesisinden alınan dört farklı endüstriyel çamur ile

çalışılmıştır. Her bir çamur örneğinde bulunan her bir ağır metal için en etkili

ekstraksiyon ayıracı belirlenmiştir. Organik asitlerden birinin inorganik aside göre

daha etkili sonuç vermesi durumunda ise, en etkili ekstraksiyon ayıracı

konsantrasyonu ve en etkili ekstraksiyon süresi tespit edilmiştir.

Anahtar Kelimeler: çamur, ağır metal, ekstraksiyon

vi

CONTENTS

Page

THESIS EXAMINATION RESULT FORM……………………………………………ii

ACKNOWLEDGEMENTS……………………………………………………………..iii

ABSTRACT……………………………………………………………………………..iv

ÖZET……………………………………………………………………………………..v

CHAPTER ONE – INTRODUCTION………………………………………………...1

1. Introduction………………………………………………………………………...1

CHAPTER TWO – GENERATION AND NATURE OF SLUDGE………………...3

2. Generation and Nature of Sludge…………………………………………………..3

2.1 Introduction…………………………………………………………………....3

2.1.1 Sludge Sources…………………………………………………………...3

2.1.2 Sludge Handling and Disposal Methods………………………………....6

2.1.3 Ultimate Disposal and Fertilizer Value of Sludge………………………..9

2.2 Industrial Sludge……………………………………………………………...11

CHAPTER THREE – HEAVY METAL EXTRACTION………………………….14

3. Heavy Metal Extraction…………………………………………………………...14

3.1 Chemistry of Heavy Metals…………………………………………………..14

3.2 Removal Methods of Heavy Metals from Solid Wastes……………………..16

3.2.1 Solid-to-Liquid Extraction………………………………………………17

3.2.2 Physical Separation Processes…………………………………………..20

3.3 Extraction from Sludge……………………………………………………….23

3.3.1 Extraction Reagents……………………………………………………..25

3.3.1.1 Organic Acids……………………………………………………...26

3.3.1.2 Standard Methods………………………………………………….29

3.3.1.3 Sequential Extraction Method……………………………………..29

vii

3.3.1.4 Summary of Case Studies………………………………………….30

3.3.2 Extraction Conditions…………………………………………………...31

3.4 Legislation about Heavy Metal Content of Sludge…………………………..34

3.4.1 Legislations of EU, EPA, and Other Countries…………………………34

3.4.2 Legislations of Turkey…………………………………………………..38

CHAPTER FOUR – MATERIALS AND METHODS……………………………...41

4. Materials and Methods…………………………………………………………....41

4.1 Materials……………………………………………………………………...41

4.1.1 The Characteristics of the Sludge Samples……………………………..41

4.2 Methods………………………………………………………………………46

4.2.1 Analytical Methods……………………………………………………..46

4.3 Experimental Procedure……………………………………………………...47

4.3.1 Elutriation Test………………………………………………………….47

4.3.2 Extraction Procedure with Organic Acids………………………………47

CHAPTER FIVE – RESULTS AND DISCUSSION………………………………...49

5. Results and Discussion……………………………………………………………49

5.1 Results of Experimental Studies with Sludge A……………………………...49

5.1.1 Zinc Extraction Studies…………………………………………………49

5.1.2 Copper Extraction Studies………………………………………………51

5.1.3 Nickel Extraction Studies……………………………………………….53

5.1.4 Iron Extraction Studies………………………………………………….55

5.2 Results of Experimental Studies with Sludge B………………………………57


5.2.2 Copper Extraction Studies……………………………………………....59


5.2.4 Chromium Extraction Studies…………………………………………..63


5.3 Results of Experimental Studies with Sludge C………………………………67

viii



5.3.3 Chromium Extraction Studies…………………………………………..71



5.4 Results of Experimental Studies with Sludge C……………………………...77




5.4.4 Lead Extraction Studies…………………………………………………85


5.4.6 Cadmium Extraction Studies……………………………………………90

5.5 Cost Analysis…………………………………………………………………92

CHAPTER SIX – CONCLUSIONS AND RECOMMENDATIONS………………94

6. Conclusions and Recommendations………………………………………………94

6.1 Conclusions…………………………………………………………………..94

6.2 Recommendations……………………………………………………………96

REFERENCES………………………………………………………………………...98

APPENDICES………………………………………………………………………...103

1

CHAPTER ONE

INTRODUCTION

Sludge is produced during the water and wastewater treatment operations.

Industrial sludge is generated at an industrial facility during the treatment of

industrial wastewater. Industrial sludges have often higher concentration of heavy

metals than domestic sludge. The ultimate disposal of heavy metal containing

sludges has been a headache for years. Conversion of sewage sludge into organic

fertilizer for agricultural use is an option for sludge disposal. However, the existence

of concentrated heavy metals in dewatered sewage sludge, especially from industrial

wastewater treatment plant, is a big concern for land application of sludge-made

fertilizer. Heavy metals remaining in the fertilizer may migrate into the subsurface

and eventually cause contamination of soils and groundwater. Due to high heavy

metal contents in sludge, especially in the industrial sludge, the removal of heavy

metal from sludge should perform before composting or land application.

Heavy metal extraction from sludge can be carried out either with solid-to-liquid

extraction or physical separation method. Solid-to-liquid extraction methods are

widely used method. This process is based on the extraction of metals from the solid-

waste to an aqueous-liquid phase followed by separation of the solid and liquid

phase. To promote solubilisation, an extracting agent is added directly (chemical

extraction) or is produced by microorganisms (microbiological leaching).

Several inorganic acids (HNO3, HCl, H2SO4) and strong complexing agents

(NTA, EDTA) have been commonly used for extraction of heavy metals from the

sludge up to now. However, Veeken & Hamelers, 1999 designate that organic

complexing acids (OCAs) such as citric and oxalic acid can be more promising.

Organic acids are more cost effective reagents and also harmless to the environment.

The variable extraction conditions, such as extracting time, reagent concentration,

solids concentration and type of mixing, the ambient temperature, pH are important

2

parameters in the extraction process. The heavy metal transform from solid to liquid

requires good contact between solids and liquid. Therefore, sufficient extracting time

is very important.

In this thesis, solid-to-liquid extraction method was used and the effect of

inorganic acid and organic acid addition was compared. For this purpose, inorganic

acid (HF+HClO4) and organic acids (citric acid, oxalic acid, and acetic acid) were

directly added as an extraction reagent.

The heavy metal extraction studies were carried out using four different industrial

sludges, which were taken from a dyestuff industry, two metal industries, and an

organized industrial district. The extraction efficiencies were determined depending

on the concentration of extracting reagent and extraction time. The most effective

extraction reagent was determined for each heavy metal of each sludge sample. In

the case of one of the organic acid was the most effective reagent, the most effective

extraction time was also determined.

3

CHAPTER TWO

GENERATION AND NATURE OF SLUDGE

2.1 Introduction

Sludge originates from the process of treatment of water/wastewater. “The treatment of

wastewaters invariably produces a residual which must be disposed of into the environment.

Most often this residual is a semisolid, odiferous, unmanageable and dangerous material

commonly termed sludge” (Vesilind, 1979, chap. 1). “Wastewater sludge is a suspension of

both organic and inorganic solids, usually between 1 and 5%, mixed in a liquid that has an

infinity variety of dissolved solids” (Vesilind & Spinosa, 2001, chap. 1).

2.1.1 Sludge Sources

Sewage sludge is generated from urban wastewater treatment plants, septic tank sludge is

generated from septic tanks which contain human excreta and domestic wastewater from

single or multiple human dwellings, and industrial sludge is generated from the treatment of

industrial wastewater of the sectors.

In the water/wastewater treatment, a variety of processes have been used but overall results

of them have the same effective. In essence, the aim of these processes is to separate the waste

into two streams - a clarified water containing around 20-30 mg/L of suspended solids and a

sludge stream of 1-3% solids dry weight. Both streams must be discharged to the

environment. Although the sludge stream has much smaller volume than the other, the

damage, it gives to the environment, has a much greater potential (Priestley, bt).

The properties of sludge originating from the processes of water/wastewater treatment

plant are given respectively as follows.

4

1. Raw sludge is untreated non-stabilized sludge, which can be taken from

wastewater treatment plants. It tends to acidify digestion and produces odour

(http://www.lenntech.com).

2. “Primary sludge is produced in the primary clarifier or settling tank and has

some particularly obnoxious characteristics. It is highly odiferous, it contains

identifiable solid matter that makes it aesthetically unpleasing, and it is

dangerous” (Vesilind & Spinosa, 2001, chap. 1). The composition of this

sludge depends on the characteristics of the catchments area. Primary sludge

consists to a high portion of organic matters, as faeces, vegetables, fruits,

textiles, paper etc. The consistence is a thick fluid with a water percentage

between 93 % and 97 %.

3. The removal of dissolved organic matter and nutrients from the wastewater

takes place in the biological treatment step. It is done by the interaction of

different types of bacteria and microorganisms, which require oxygen to live,

grow and multiply in order to consume the organic matter. The resulting

sludge from this process is called activated sludge. The activated sludge

exists normally in the form of flakes, which besides living and dead biomass

contain adsorbed, stored, as well as organic and mineral part.

4. Primary sludge is often digested to make less objectionable and is then

known as primary digested sludge. Digested sludge accrues during the

anaerobic digestion process. It has a black colour and smells earthy. As a

function of the stabilization degree of anaerobic sludge exhibits an organic

portion of the solid from 45 to 60 % (http://www.lenntech.com).

An alternative to anaerobic digestion is aerobic digestion, which is simply

an extension of the aeration system. Waste activated sludge is aerated in a

separate tank for several days and thus is stabilized in terms of its oxygen

demand and fraction of volatile solids. The resulting sludge is referred to as

aerobically digested sludge.

5

5. Trickling filters are widely used as a biological treatment method for BOD.

The solids that slough off the filter rocks are captured in the final clarifier.

This sludge is called filter humus. Both filter humus and waste activated

sludge are often mixed with raw primary sludge and digested. The resulting

material, called mixed digested sludge, usually is dewatered before its final

disposal.

6. An additional source of sludge in sanitary engineering is the waste from

water treatment. Aluminum sulfate (alum), the most widely used chemical for

coagulation and flocculation in water treatment, produces a sludge known

waste alum sludge (Vesilind, 1979, chap. 1).

Some of the physical characteristics of sludge and corresponding data on the

sludge concentrations to be expected from various processes are given in Table 2.1

(Metcalf & Eddy, 1991, chap. 12).

Table 2.1 Characteristics of sludge and expected sludge concentrations from various treatment

operations and processes. Sludge solids concentration,

% dry solids

Operation or

process

application Range Typical

Characteristics

Primary Sludge 4,0-10,0 5,0

gray and slimy, extremely

offensive odor, digested

under suitable conditions.

Waste Activated

Sludge 0,8-2,5 1,3

has a brownish, flocculant

appearance, is dark under

septic condition, in good

condition inoffensive odor.

6

Sludge solids concentration,

% dry solids

Operation or

process

application Range Typical

Characteristics

Trickling-Filter

Humus Sludge 1,0-3,0 1,5

brownish, flocculant,

inoffensive when fresh,

slowly decomposition,

contains many worms.

Anaerobically

Primary Digested 5,0-10,0 8,0

Anaerobically

*Mixed Digested 2,5-7,0 3,5

Anaerobically digested

sludge is dark brown to

black, contains large

quantity of gas, as sludge

dries, the gasses escape,

musty but not offensive

after digested.

Aerobically

Waste Activated

Sludge

0,8-2,5 1,3

Aerobically

*Mixed Digested 1,5-4,0 2,5

Aerobically digested

sludge is dark brown,

flocculant, not offensive

after digested, dewaters

easily on drying beds

after well – digested.

**Waste Alum 0,5-1,5 gray-yellow, odorless,

very difficult to dewater

* “Mixed” means waste activated sludge + primary sludge

** Source: Vesilind, 1979, pp 5

2.1.2 Sludge Handling and Disposal Methods

Especially, in modern society, amount of sludge that is handled in the wastewater

treatment processes are amazing. Sludge handling is performed for two main

purposes:

7

• Stabilization of the sludge by use of different methods such as biological

(anaerobic and aerobic digestion and composting), chemical (mainly using

lime) and thermal (heat drying, incineration and melting) techniques.

• Volume reduction by use of thickening (gravity thickening, flotation and

centrifugation), de-watering (use of centrifugation, filters and presses),

drying (natural and heat drying) and incineration and melting methods.

(http://www.balticuniv.uu.se)

These methods are described briefly below:

1. Stabilization Methods: Stabilization is used to obtain a sludge that does not

change with time, i.e. a stable sludge that does not cause odour problems.

Biological methods are quite common as the others because of less energy

consuming (http://www.balticuniv.uu.se).

Anaerobic digestion is an appropriate technique for the treatment of sludge

before final disposal and it is employed worldwide as the oldest and most

important process for sludge stabilization. It is a biological process that

produces a gas principally composed of methane (CH4) and carbon dioxide

(CO2) otherwise known as biogas. These gases are produced from organic

wastes such as livestock manure, food processing waste, etc. During the

process, energy rich biogas containing about 2/3 methane gas and 1/3 carbon

dioxide, is produced. The biogas may be used for the aim of energy

production, heating, and electricity production.

Aerobic digestion of sludge is quite common method and aerobic

digestion process aerates the sludge containing biodegradable organic

material for 15 to 20 days. Aerobic digestion requires supplying oxygen to

the sludge. Aerobic digestion has therefore mainly come to be used at small

treatment plants.

8

The other stabilization methods are lime stabilization; heat treatment. The

lime stabilization is performed by addition of lime to untreated sludge in

suitable quantity. As for heat treatment, untreated sludge is heated in a

pressure vessel to temperatures up to 2600C at pressures up to 2760 kN/m2

(Metcalf & Eddy, 1991, chap. 12).

2. Volume Reduction Methods: A significant decrease in moisture content will

greatly reduce the volume of sludge. Thickening is the widely used volume

reduction method. A volume reduction of approximately 30 – 80 % can be

reached with sludge thickening before a further treatment. Metcalf & Eddy

(1991) defines it that is a procedure used to increase the solids content of

sludge by removing a portion of the liquid fraction (chap. 12). Typical sludge

thickening methods are gravity, flotation and centrifugal thickening.

Wastewater sludge thickener performance varies widely, but some typical values are

given in Table 2.2 (Scales, Lester, Dixon, 2001, chap. 17).

Table 2.2. Typical performance of gravitational thickeners

Sludge Type Feed Solids (%) Underflow Solids

(%)

Solids Loading

(kg/m2/d)

Primary

Waste Activated

Anaerobically

digested

2-7

1-3

8

5-10

2-5

12

20-30

7-10

24

According to Pandit & Das (1998), gravity thickening is used for types of sludge

as softening and coagulation sludge. The changes in solids concentration for these

sludges are illustrated in Table 2.3.

9

Table 2.3 Solids concentration before and after thickening for two different sludges

Sludge type Original solids concentration

Solids after gravity thickening

Thickener loadings, lb/day-ft2 (kg/day-m2)

Lime softening 1% 30% 12.5 (61)

Alum coagulation 1% 2% 4 (20)

In the study of Pandit & Das (1998), water treatment sludge is categorized as

softening and coagulation sludge. According to them, coagulation sludges have a

gelatinous appearance are produced from clarifier operations and from the

backwashing of filters. As for softening sludges, these sludges contain mainly

calcium carbonate and magnesium hydroxide precipitates with some organic and

inorganic substances. These sludges dewater easily and processing for ultimate

disposal is common and feasible.

2.1.3 Ultimate Disposal and Fertilizer Value of Sludge

The ultimate disposal of sludge entails two techniques:

1. Landfilling

2. Land application

“Landfills may be on public land such as a municipality owned landfill, or on

private land. Landfill operators commonly require 15 to 30 % sludge (solids). The

minimum concentration required is often determined by local sanitary landfill

regulations” (Pandit & Das, 1998). Landfilling sludge has become expensive because

of the high costs associated with burial in properly constructed landfills. Landfilling

also concentrates organic wastes and may result in point-source contamination for

future generations to deal with (http://lancaster.unl.edu).

Land application of sludge has been used successfully for decades. “Sludges may

be applied to (1) agricultural land, (2) forest land, (3) disturbed land, and (4)

dedicated land disposal sites” (Metcalf & Eddy, 1991, chap.12). The sludge from

10

wastewater treatment is increasingly used as a fertilizer, as it has some advantages,

including the fact that it is often supplied free or cheaply and it contains nutrients

and organic matter. Land disposal is generally considered more environmentally

sound than all other disposal options (Antoniadis, 1998).

Conversion of sewage sludge into organic fertilizer for agricultural use is an

option for sludge disposal. However, the existence of concentrated heavy metals in

dewatered sewage sludge, especially from industrial wastewater treatment plant, is a

big concern for land application of sludge-made fertilizer. Heavy metals remaining in

the fertilizer may migrate into the subsurface and eventually cause contamination of

soils and groundwater. The use of sludge shall be carried out in such a way as to

minimize the risk of negative effects to

(http://europa.eu.int/comm/environment/waste/sludge):

– human, animal and plant health,

– the quality of groundwater and/or surface water,

– the long-term quality of the soil, and

– the bio-diversity of the micro-organisms living in the soil.

The technology for applying sludge is advanced and includes surface spreading

and injection of the material into the soil, a practice which helps reduce the odour

problems and helps the sludge to be more properly incorporated into the soil. The

optimum dose of application is difficult to determine, because there are restrictions

depending on soil parameters, such as pH, clay content and the contaminant and

nitrogen contents in the sludge (Antoniadis, 1998).

Costs can be an important concern in waste disposal and often play an important

part in determining the disposal method used. Also, agricultural use of sludge is often

regarded as the best alternative if the pollutants in the sludge are below guidance and

limiting values. However, the potential problems in land application of sludge

sometimes can occur. The source of these problems can be organic matter,

11

emulsified oil and grease, bacteria and virus, nutrients such as nitrate and phosphate,

and, a legacy of industrial age, heavy metals and organochlorines.

Due to the physical-chemical processes involved in the treatment, the sludge tends

to concentrate heavy metals and poorly biodegradable trace organic compounds as

well as potentially pathogenic organisms (viruses, bacteria, etc.) present in waste

waters. Sludge is, however, rich in nutrients such as nitrogen and phosphorous and

contains valuable organic matter that is useful when soils are depleted or subject to

erosion. The organic matter and nutrients are the two main elements that make the

spreading of this kind of waste on land as a fertilizer or an organic soil improver

suitable (http://europa.eu.int/comm/environment/waste/sludge/index.htm).

A major limiting factor on the application of sludge to agricultural land is the

presence of heavy metals. Even in sludges from non-industrial regions problems can

arise from zinc (phytotoxicity), copper, lead and even cadmium. Cadmium in

particular has been found to accumulate in the food chain and strict limits have been

placed on the level acceptable in sludge (Priestley, bt). Cadmium has had a wide

range of uses in industry, including electroplating, paints and pigments, silver -

cadmium batteries and plastic stabilizers. Nickel is widely used in industry, as it is a

metal which does not corrode as much as Fe. It is, therefore, used in the production

of alloys, on which it confers them stain and corrosion protection. Lead is used as an

absorber of high energy X and γ rays and in roofing, while PbO is used in crystal

glass because it dispenses light spectrally. Industrial uses of Zn include corrosion

protecting coating and manufacture of brass and other alloys. Zinc has a very

similar environmental chemical behavior to Cd, as both elements normally occur

together (Antoniadis, 1998).

2.2 Industrial Sludge

Sludge can be categorized into two main groups: 1) domestic sludge, 2) industrial

sludge. “Industrial sludge is defined as semi-liquid residue or slurry remaining from

treatment of industrial water and wastewater” (http://www.epa.gov).

12

In addition to chemical sludges formed in water and wastewater treatment, many

industries produce waste sludges that must be disposed of. Industrial sludges are

often of little value as soil conditioners and, in fact, are often highly toxic. The

ultimate disposal of such sludges has been a headache for years... The origins of this

sludge vary with the industries producing them. For example, metal-finishing plants

often produce sludges high in zinc, chromium and other heavy metals (Vesilind,

1979, chap. 9).

These components usually occur in small amounts not harmful to plants. Some

heavy metals, including zinc and copper, are micronutrients that are necessary for

plant growth. Excessive amounts of some heavy metals (zinc, copper, nickel) can be

damaging to plants, resulting in reduced yield or even plant death (Muse, 1991)

The most common industrial sources of some heavy metals are shown in the

Table 2.4 (Antoniadis, 1998).

Table 2.4 Most common industrial uses of Cd, Ni, Pb and Zn.

Industry Type Cd Ni Pb Zn

Electroplating x x

Paint pigments x x x

Plastic stabilisers x

Silver-Cd batteries x x x

Coinage x

Water pipes x

Car fuel x

Galvanisation x

Metal antirust coating x x

Roofing x

Absorber of high energy

radiation x

Mining x x x x

Cable coating x

13

Due to high heavy metal contents in sludge, especially in the industrial sludge, the

extraction of heavy metal from sludge should perform before composting or land

application. Chaney and Ryan (1993) have sequenced the negative effects of heavy

metal contents in soil systems as follows:

• Leaching of heavy metal to groundwater systems,

• Heavy metal uptake by plants and animals which introduces more heavy

metals into various vital life-cycles,

• Inhibition of plant growth and of the activity of soil microorganisms.

After removal of heavy metal:

• Sludge can be disposed to landfills with lower risk of heavy metals leaching to

surface and groundwater or uptake by plants,

• Sludge can be used as soil improver,

• Sludge can be applied with lower risk as energy source in co-incineration. In

addition, the off-gas treatment system would be less complex than when the

sludge is metal polluted,

• Dewatered sludge or sludge fly ashes can be applied with lower risk as raw

material for Portland cement and bricks production (Veeken, 2004).

14

CHAPTER THREE

HEAVY METAL EXTRACTION

3.1 Chemistry of Heavy Metals

The heavy metals are metallic chemical element and they have a relatively high

density and are toxic or poisonous at low concentrations. Examples of heavy metals

include mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl),

and lead (Pb).

Heavy metals are natural components of the Earth's crust. Heavy metals are

present in large quantity and enter the water cycle through a variety of geochemical

processes. They cannot be degraded or destroyed. To a small extent they enter our

bodies via food, drinking water and air. As trace elements, some heavy metals (e.g.

copper, selenium, zinc) are essential to maintain the metabolism of the human body.

However, at higher concentrations they can lead to poisoning. Heavy metal

poisoning could result, for instance, from drinking-water contamination (e.g. lead

pipes), high ambient air concentrations near emission sources, or intake via the food

chain.

Heavy metals are dangerous because they tend to bioaccumulate.

Bioaccumulation means an increase in the concentration of a chemical in a

biological organism over time, compared to the chemical's concentration in the

environment. Compounds accumulate in living things any time they are taken up and

stored faster than they are broken down (metabolized) or excreted.

Heavy metals can enter a water supply by industrial and consumer waste, or even

from acidic rain breaking down soils and releasing heavy metals into streams, lakes,

rivers, and groundwater (www.lenntech.com). Many metals are also introduced to

water by man-induced activities such as manufacturing, construction, agriculture,

and transportation. Although some metals are not toxic at low concentrations, soluble

metal compounds may be harmful to health and subsequent water use at high

15

concentrations. Water quality conditions such as pH, temperature, hardness, CO2

content and turbidity affect the toxicity levels of heavy metals.

The regulatory agencies have limited the heavy metals discharged to surface

streams from industrial and municipal sources, because of the negative effects of

heavy metals to water supplies. Many industrial establishments discharge wastewater

through the public collection system to the wastewater treatment plant. These

discharges may contain significant quantities of heavy metal that can effect the

collection and treatment system. If any industrial facility discharges wastewater to

the wastewater treatment plant, they should provide pretreatment requirements. Due

to increased environmental legislation, heavy metals need to be removed from

wastewater down to an extremely low residual concentration. The toxic heavy metals

tend to accumulate in the biological systems and thus tend to concentrate. Namely,

what was a low concentration in the influent may be converted to a concentration as

much as twenty to thirty times greater in the solids produced as sludge (Ronald &

Robert, 1981).

In the presence of ambient ligands such as HCO3-, CO3

2-, Cl-, SO42-, an aqueous

divalent contaminant metal (MaqII) can speciate in various free and complex forms:

Maq = M2+ + M (OH)x(2-x) + Mx (OH)y

(2x-y) + M (HnCO3)z2(1-x+n) + MClx

(2-x)

+ M (SO4)x(2-x)

The solubilities of metals are typically too small to effect satisfactory results by

washing with water alone. The solubilites of contaminant metals are controlled by

predominant mineral phases depending upon the pH and/or ambient ligands

available. Commonly observed metal mineral phases include those of oxide,

hydroxide, carbonate, and hydroxy-carbonate, such as MO(s), M (OH)2(s), MCO3(s),

and Mx (OH)y (CO3)z.

16

When the amounts of heavy metals of interest e.g. Pb, Cd, Cu, Zn, Ni exceed the

solubilities of their corresponding hydroxides, carbonates, and/or hydroxy-carbonate

mineral phases at a given pH value, the metals will be precipitated as solids. Hence

these solid minerals will be entrapped in the soil or sediment matrix (Peters, 1999).

At the interaction of solid with metals, effect of pH usually is that, heavy metals

are dissolved under acidic conditions and precipitated under alkaline conditions. The

increasing in the pH of a metal-containing solution should induce precipitation of the

dissolved metal. The increasing pH performs by the addition of alkali such as NaOH

(caustic) or Ca(OH)2 (lime) to provide the hydroxide ions. Thus, the heavy metal

ions in solution react with the hydroxide ions to form solid particles. This specific pH

differs in terms of the other components in the solution such as chelating agents,

surfactants and the other conditions such as temperature (Ronald & Robert, 1981).

The metals adsorbed to the solid phase or present as heavy metal precipitates are

transferred from the solid phase to the liquid phase under acidic condition. Therefore,

the several of acids such as inorganic acids, chelating agents, organic acids are added

to heavy metal – containing sludge. The contact time of acid with sludge and

temperature are significant parameters in the transfer of heavy metals to liquid phase.

3.2 Removal Methods of Heavy Metals from Solid Wastes

Although several studies have been carried out by several researchers, there is no

full scale process for the removal of heavy metals from the organic wastes up to now.

The developed technologies can be classified in to two main groups:

• Solid-to-liquid extraction. This process is based on the extraction of metals

from the solid-waste to an aqueous-liquid phase followed by separation of the

solid and liquid phase. To promote solubilisation, an extracting agent (or

extractant) is added directly (chemical extraction) or is produced by

microorganisms (microbiological leaching).

17

• Physical separation. This process is based on the physical separation of a

specific fraction of the solid waste in which the heavy metals are

concentrated. Physical separation processes are based on differences in

physical properties of different fractions of the solid waste stream (Veeken,

2004).

3.2.1 Solid-to-Liquid Extraction

Extraction scheme for the removal of heavy metals from solid wastes is given in

Figure 3.1. As it is seen from the figure, the extraction process used for the removal

of heavy metals from solids wastes normally performs at three steps.

1. The actual extraction process

2. Separation of the solid and liquid phase

3. Cleaning and recycling of the heavy metal enriched liquid phase (extracting

liquid) (Veeken & Hamelers, 1999).

extracting reactor

solid-liquidseparation

“polluted” waste

extractingreagent “cleaned” waste

heavy metal removal

heavy metal sludge

liquid discharge

recyclingextracting

liquid

Figure 3.1 Extraction scheme for the removal of heavy metals from solid wastes (Veeken, 2004).

18

The applicability of the extraction process for solid wastes or sludge is firstly

determined by the extraction efficiency of the used extracted agent. The extraction

efficiency is defined as the percentage of heavy metals extracted from the solid to the

aqueous phase. Other factors determining the possibilities of the extraction process

are of economical, technological and environmental concern:

1. Costs of the process:

• costs of the extracting reagent,

• number of process units,

• wastewater treatment for liquid discharge.

2. Minimisation of the production of hazardous emissions:

• air emissions,

• water emissions,

• final inert waste.

3. Possible negative effects of the leaching process of the cleaned solid waste on:

• the structure of the waste,

• the bioavailability of essential nutrients in subsequent biological

processes,

• toxicity of heavy metals in subsequent biological processes (Veeken,

2004). Veeken (2004) explains the main mechanisms for the retention of heavy metals in

the solid phase as follows:

1. Adsorption to the organic and inorganic solid phases, e.g. Fe-(hydr)oxides,

clay minerals, organic debris, humic substances

2. Presence as inorganic precipitates, e.g. CdCO3, Cu3(PO4)2, PbS

Two types of reagents for chemical extraction of heavy metals from solid wastes

or sludge are used. These reagents are acids and complexants (chelating agents). Acid

extraction of heavy metals is brought about by the exchange of protons for heavy

metals adsorbed to the solid phase and by the solubilisation of heavy metal

19

precipitates. The protons can either be supplied directly by addition of a strong acid

(e.g. HCl, HNO3, H2SO4, citric acid) or be produced by microorganisms. Extraction

through the production of acids by bacteria or fungi is referred to as microbiological

leaching (Veeken, 2004). For instance, strong organic acids, such as citric acid and

oxalic acid, can be produced by fungi (Burgstaller & Schinner, 1993). H2SO4 can be

produced by the oxidation of reduced sulphur compounds by Thiobacilli strains

(Wong & Henry, 1988). Weak organic acids such as acetic acid and lactic acid can

be produced by a variety of anaerobic consortia (Schlegel, 1993).

According to Veeken (2004), at heavy metal extraction by complexants, because

of the high affinity of the anion for heavy metals, heavy metals adsorbed to the solid

phase or present as heavy metal precipitates are dissolved. The most common

chelating agents, used for the extraction of heavy metals from solid wastes or sludge,

are ethylenediaminoacetic acid (EDTA) and nitrotriacetic acid (NTA). The other

processes, which are more or less based on these two types of reagents, are extraction

with lye, ion exchange and electro-reclamation.

• Extraction with lye (e.g. NaOH): At high pH values humic substances are

solubilised, thus enhancing the solubilisation of heavy metals.

• Ion exchange: The solid ion-exchanger is suspended in the liquid phase and

the metal ions are transported from the contaminated solid waste to the

complexing ion-exchanger.... This process is very complex and rate-limited by

mass transport of heavy metal ions from the bulk solution to the surface of the

ion-exchange particles and by transport of the metal ions from the solid phase

to the liquid phase.

• Electro-reclamation: Mostly applied for in-situ removal of heavy metals from

soils by electrically charging the system through the application of several

electrode arrays; generally the process is promoted by acidification of the soil

(Veeken, 2004).

According to Peters (1999), each conjugate acid / base of the chelating agent may

form a strong complex with the metal, resulting in the formation of various

20

complexes. He designated in his study that total metal solubility with chelators is

much higher than the metal solubility without chelators and for target heavy metals

extraction application, the chelating agents should satisfy the following criteria:

• The chelating agents (with and without the chelated metal) will be compatible

with the foam and will display no adverse effects on the stability of the foam.

• The ligands possess high metal complexing abilities toward heavy and

transition metals as opposed to hard sphere cations such as Ca or Mg. The

relative magnitudes of the equilibrium complexation constants toward heavy

metals and toward alkali metals are an indicator.

• The ligands containing sulfur and nitrogen as donor atoms are generally

preferred for higher selectivity toward metals of interest, which are transition

metals (e.g. Cu2+, Ni2+) and B-type (soft sphere) cations (e.g. Zn2+, Cd2+,

Pb2+, Hg2+). Ligands containing sulfur or nitrogen as donor atoms generally

form more stable complexes with soft sphere metals, whereas ligands

containing oxygen as the donor atom prefer hard sphere cations.

• Multidentate ligands are preferable because they contain multiple

coordinating sites capable of forming more stable complexes with metals

(Peters, 1999).

3.2.2 Physical Separation Processes

If heavy metals are concentrated in specific solid fractions of a solid waste, the

selective removal of these particles from the solid waste generally results in a small

fraction that is highly contaminated and a large fraction that is relatively clean. The

separation of a specific fraction is achieved by means of physical separation

processes. The term 'physical' is added to distinguish this process from molecular

separation processes, such as distillation and dialysis. The processes are widely used

in soil remediation, the mining industry and mineral processing. Until now,

21

adaptations of mining technologies in the field of environmental technology have

been applied only in the cleaning of polluted soils and sediments, where "non-

polluted" sand is separated from polluted smaller size fractions. The separation of a

specific fraction of the solid waste by a solid-solid separation process is established

by differences in particles properties (Veeken, 2004).

The wet solid-solid separation processes widely used in environmental

applications, together with the principal properties on which the separation is based

are shown in Table 3.1. For instance, De Waaij & Van Veen (1990) examined the

heavy metal seperation by hydrocyclones, which is one of the process, at several

types of sediment.

Table 3.1 Waste properties that determine separation in various wet solid-solid separation processes

(Veeken, 2004).

Process Size Density Hydro- phobicity

Shape Magnetic properties

Screening (sieving)

+ (+)1

Elutriation + + (+)

Hydrocyclones + + (+) Air flotation + Magnetic separation

+

1brackets indicate secondary importance

The polluted waste can be qualified by a clean solid stream and a contaminated

solid stream at the physical wet-separation processes used as an environmental

technology. A schematic projection interested in a physical wet-separation process

where the contaminated waste (influent flow) is separated into a “clean fraction” and

a “contaminated fraction” (Figure 3.2). The flows are characterised as follows:

F : the flow rate of the liquid (in m3.s-1),

S : the total solids concentration (in kg.m-3),

C : the concentration of contaminant in the solids (in mg.kg-1 dry matter).

22

The subscripts 'in' and 'con' refer to the incoming flow and contaminated flow,

respectively (Veeken, 2004).

input

FinSinCin

contaminated fraction

FconSconCcon

clean fraction

Figure 3.2. Schematic presentation of physical separation process for environmental applications (Veeken, 2004).

The separation efficiency (ES) with respect to the total contaminated flow is

defined as the total solids mass flow of the contaminated fraction as a fraction of the

total solids feed mass flow rate:

Scon con

in inE =

F SF S

The efficiency of the solid-solid separation process is determined not only by the

total separation efficiency but also by the distribution of the contaminant over the

clean and contaminated flows. The separation efficiency with respect to the

contaminants (EC) is defined as:

C

con con con

in in inS

con

inE =

F S CF S C

= ECC

The removal efficiency of a solid-solid wet-separation process is high when ES is

low and EC is high.

23

The solid waste has to be characterised with respect to particle size distribution

and level of contamination before a separation technology is applied on a pilot-plant

or practical scale.... After the classification, the heavy metal content of the separated

fractions is determined. In this way, it becomes clear to which constituents of the

solid waste the heavy metals are bound. On the basis of these results a separation

technology has to be selected to separate the most contaminated fractions. Most

often a single separation process is insufficient for the separation of a contaminated

solid waste into a clean and a contaminated fraction. Instead a cascade of

separation units is necessary.

There is still a wide gap between the theory and practice of solid-solid separation

processes because the primary properties of a system cannot be easily translated into

equipment. Selection and sizing of the equipment can only be done on the basis of

small-scale tests either in a laboratory or on a pilot-plant scale (Veeken, 2004).

3.3. Extraction from Sludge

The existence of concentrated heavy metals in dewatered sewage sludge,

especially from industrial wastewater treatment plant, is a big problem. Typical metal

content in wastewater sludge and potential heavy metals in sludge and ways to

control them are summarized in Table 3.2 and Table 3.3, respectively.

Table 3.2 Typical metal content in wastewater sludge (Medcalf & Eddy, 1991).

Dry Sludge, mg/kg Metal

Range Median

Arsenic 1,1-230 10

Cadmium 1-3410 10

Chromium 10-99000 500

Cobalt 11,3-2490 30

Copper 84-17000 800

Iron 1000-154000 17000

Lead 13-26000 500

24

Dry Sludge, mg/kg Metal

Range Median

Manganese 32-9870 260

Mercury 0,6-56 6

Molybdenum 0,1-214 4

Nickel 2-5300 80

Selenium 1,7-17,2 5

Tin 2,6-329 14

Zinc 101-49000 1700

Table 3.3 Potential heavy metals in sludge and ways to control them (Muse, 1991).

Heavy Metals Potential Concern Solution

Copper, Zinc, and Nickel Accumulation in topsoil; toxic to plants at high levels

Reduce source of metal in sludge; apply according to soil loading limits; lime soil

Cadmium Accumulation in topsoil; taken up by plant and accumulates in leafy material; accumulates in animal organs; human health


Lead Accumulation in topsoil: Potentially harmful if excessive amounts are ingested with soil particles by animals


Mercury, Chromium, Selenium, Arsenic, and Antimony

Little concern unless present in extremely high amounts

Extraction of heavy metals from sludge typically consists of three steps. In the

first step of the extraction process the heavy metals are transferred from the solid

phase to the aqueous phase. This requires good contact between solids and liquid

which is brought about by intensive mixing. In the second step the aqueous phase is

separated from the ‘cleaned’ sludge by a solid-liquid separation process, e.g.

decanting centrifuge. In the third step the (heavy) metals are removed from the

25

extracting solution to recover the economical value of the extracting agent and

prevent environmental impact associated with discharge of extracting liquid. The

most appropriate and economically feasible technologies for removal of heavy

metals from solutions are chemical sulphide precipitation and/or selective ion-

exchange (Veeken & Hamelers, 1999).

3.3.1. Extraction Reagents

Various inorganic acids (HNO3, HCl, H2SO4) and strong complexing agents

(NTA, EDTA) are proposed in literature. Inorganic acids and complexing agents

however are not applicable on a practical scale due to (1) the costs of the process

and (2) the negative environmental impacts of the discharged solid and liquid waste

streams (Wong & Henry 1988). Veeken & Hamelers (1999) designate depending on

the following reasons that organic complexing acids (OCAs) such as citric and oxalic

acid can be more promising.

1. Heavy metal extraction is partly due to the acidic character but for the greater

part to the complexing behaviour of OCAs; therefore extraction can be

performed at mildly acidic conditions (pH 3-5),

2. OCAs are readily biodegradable under both aerobic and anaerobic

conditions. This implies that the ‘cleaned’ sludge does not have to be

conditioned, thus leading to a substantial reduction of wastewater. Moreover,

wastewater can be treated (an)aerobically,

3. Heavy metals can be removed from OCAs solution. In this way, the extraction

liquid can be recycled, reducing the costs of the process.

Like inorganic acids and strong complexing agents, organic acids are not

selective and also metals other than heavy metals are simultaneously extracted from

the sludge. The major cations competing with heavy metals for citric acid are Ca,

Mg, Fe and Al (here referred to as ‘competing’ metals). Therefore, citric acid has to

be dosed to sewage sludge in an equimolar amount to the cumulative content of

26

complexing metals. This last point is often overlooked in relation to heavy metal

extraction by complexing agents. Moreover, for recovery of OCAs not only heavy

metals but also competing metals have to be removed from the extracting liquid.

Otherwise, the competing metals are accumulated in the extraction reactor, in this

way lowering the heavy metal extracting capacity of OCAs.

3.3.1.1. Organic Acids

The structure and properties of organic acids (citric, oxalic, and acetic) are

described below in detail:

1. Citric acid (C6H8O7): It is a weak organic acid found in citrus fruits. It is a

good, natural preservative and is also used to add an acidic (sour) taste to

foods and soft drinks. In biochemistry, it is important as an intermediate in

the citric acid cycle and therefore occurs in the metabolism of almost all

living things. It also serves as an environmentally friendly cleaning agent and

acts as an antioxidant (http://en.wikipedia.org/wiki/Citric_acid). Its structure

is shown in Figure 3.3.

Figure 3.3 The chemical formula of citric acid.

The acidity of citric acid results from the three carboxy groups (COOH)

which can lose a proton in solution. If this happens, the resulting ion is the

citrate ion. Citrates make excellent buffers for controlling the pH of acidic

solutions. Citrate ions form salts called citrates with many metal ions. An

important one is calcium citrate or "sour salt… Additionally, citrates can

27

chelate metal ions, which gives them use as preservatives and water

softeners.... Similarly, citric acid is used to regenerate the ion exchange

materials used in water softeners by stripping off the accumulated metal ions

as citrate complexes.

At room temperature, citric acid is a white crystalline powder....

Chemically, citric acid shares the properties of other carboxylic acids. When

heated above 175°C, it decomposes through the loss of carbon dioxide and

water.... Citric acid is recognized as safe for use in food… It is naturally

present in almost all forms of life, and excess citric acid is readily

metabolized and eliminated from the body

(http://en.wikipedia.org/wiki/Citric_acid).

2. Oxalic Acid (ethanedioic acid): It is a bi-carboxylic acid with structure

(HOOC)-(COOH). Because of the joining of two carboxyl groups, this is one

of the strongest organic acids. The anions of oxalic acid as well as its salts

and esters are known as oxalates. Oxalic acid and oxalates are mild toxins

found in many plants. Oxalic acid is a strong acid that irritates the lining of

the gut when consumed, and can prove fatal in large doses. Oxalic acid also

combines with metals such as calcium in the body to form oxalates which

further irritate the gut and kidneys. The most common kind of kidney stone is

made of calcium oxalate.

Because it binds vital nutrients such as calcium, long-term consumption of

foods high in oxalic acid can lead to nutrient deficiencies. Healthy

individuals can safely consume such foods in moderation, but those with

kidney disorders, gout, or rheumatoid arthritis are typically advised to avoid

foods high in oxalic acid or oxalates….In addition to its natural occurrence

in plants, oxalic acid may also be found in household chemical products such

as some bleaches, rustproofing treatments and wood restorers - where the

acid dissolves away a layer of dry surface wood to expose fresh material

underneath (http://en.wikipedia.org/wiki/Oxalic_acid).

28

3. Acetic Acid: It is a carboxylic acid with chemical formula C2H4O2, often

written as CH3COOH to better reflect the structure is shown in Figure 3.4.

Acetic acid is a molecule central to biochemistry, and is produced in some

amount by nearly all forms of life…. Acetic acid is produced naturally as

fruits and some other foods spoil, and it is one of the oldest chemicals known

to humanity.

Figure 3.4 The chemical formula of acetic acid.

Pure acetic acid is a colorless, corrosive, flammable liquid that freezes at

16.6 °C. Because pure acetic acid freezes only slightly below room

temperature and has an ice-like appearance when it does so, it is often called

glacial acetic acid. In aqueous solution, acetic acid can lose the proton of its

carboxyl group, turning into the acetate ion CH3COO-. The pKa of acetic

acid is about 4.8 at 25 °C, meaning that about half of the acetic acid

molecules are in the acetate form at a pH of 4.8. As a vapor, acetic acid does

not consist of individual acetic acid molecules. Instead, it consists mostly of

pairs of acetic acid molecules hydrogen bonded to one another. As a result,

acetic acid vapors behave in a way that grossly violates the ideal gas law.

Most acetic acid made for industrial use is made by one of three chemical

processes: methanol carbonylation, butane oxidation, or acetaldehyde

oxidation. In the form of vinegar, acetic acid is used directly as a condiment,

and also in the pickling of vegetables and other foodstuffs…. The glacial

acetic acid produced by the chemical industry is used in the manufacture of

photographic films and stop bath and sometimes in the production of the

plastic polyethylene terephthalate (PET)…. Dilute solutions (4% - 6%) of

acetic acid are extremely useful in treating the sting of the box jellyfish; the

29

acid disables the stinging cells of the jellyfish, and can prevent serious injury

or death if immediately applied. Some of the esters of acetic acid are

commonly used solvents and artificial flavorings.

Concentrated acetic acid is corrosive and has to be handled with care,

since it can cause skin burns, permanent eye damage, and irritation to the

mouth, nose, throat, and lungs. It can penetrate the skin, and it may not

produce burns or blisters for several hours after exposure. Dilute acetic acid

(in the form of vinegar) is harmless and has been consumed for millennia.

However, ingestion of stronger solutions or the glacial acid is dangerous,

resulting in severe damage to the digestive system, and a potentially lethal

change in the acidity of the blood. Acetic acid poses no known cancer risk

(http://en.wikipedia.org/wiki/Acetic_acid).

3.3.1.2. Standart Methods

According to Standart Methods, to reduce interference by organic matter and to

convert metal associated with particulates to a form (usually the free metal) that can

be determined by atomic absorption spectrometry or inductively-coupled plasma

spectroscopy, use one of the digestion techniques. These techniques are as follows

(APHA, AWWA, WEF, 1992):

• nitric acid digestion (section 3030 E)

• nitric acid-hydrochloric acid digestion (section 3030 F)

• nitric acid-sulfuric acid digestion (section 3030 G)

• nitric acid-perchloric acid digestion (section 3030 H)

• nitric acid- perchloric acid-hydrochloric acid digestion (section 3030 I)

3.3.1.3. Squential Extraction Method

Heavy metals occur in sludges in various abiotic (physicochemical) forms, such

as, soluble, adsorbed, exchangeable, precipitated, organically complexed, and

30

residual phases. Heavy metals may also exist in biotic forms, such as extracellular

and intracellular species. The variety of heavy metal forms significantly influences

their environmental mobilities and bioavailability, and finally determines the

potential for environmental contamination. If heavy metals exist as loosely bound

fractions, such as, soluble, exchangeable and adsorbed forms, they tend to be easily

moved and dispersed. However, metals associated with organic ligands or in crystal

lattices are not easily seperated or mobilized (Kim et al., 2002).

Therefore, to determine the speciation of heavy metals is very important.

Sequential extraction analysis is one of the digested methods have been suggested.

This sequential extraction scheme consists of several extraction steps. Bound

fractions of heavy metals to sludge in each step are retained by additional of a variety

of chemical extract ants. The researcher, examine determination of heavy metal

contents from sludge, usually modify and utilize from the sequential extraction

procedure described by Tessier et al. (1979), Ure et al. (1993), Quevauviller et al.

(1997) and the others (Fuentes et al., 2004; Kim et al., 2002; Scancar et al., 2000).

For example, Scancar et al. (2000) examined various heavy metal extractions using

sequential extraction method according to procedure given by Quevauviller (1997).

They used four steps: At first step, metals present in ionic form, bound to carbonates

and the exchangeable fraction are extracted. At second step, metals bound to

amorphous iron and manganese oxides and hydroxides are leached. At third step,

metals bound to organic matter and sulphides are extracted. At last step, metals

bound to silicate lattice or crystalline iron and manganese oxides.

3.3.1.4. Summary of Case Studies

The extraction of heavy metals from sewage sludge has been studied extensively.

Ito et al. (1999) examined the removal of heavy metals from anaerobically digested

sewage sludge by using ferric sulfate as extracting regeant. They observed that the

addition of ferric sulfate to the sludge caused the subsequent elution of heavy metals

such as Cd, Cu and Zn from the sludge due to the acidification of the sludge. The

elution percentage of these metals increased with an increase in the amount of iron

31

added and with a decrease in the sludge concentration. This study resulted with the

elution percentage of cadmium, copper and zinc was more than 80%.

A compilation of literature data regarding the extraction efficiencies of Cd, Cu, Pb

and Zn from sewage sludge is demonstrated in

Table 3.4. The table shows a very broad range of extraction efficiencies for heavy

metals given follow. “The broad range in extraction efficiencies is due to differences

in sludge composition, differences in pretreatment of the sludge and differences in

extracting conditions” (Veeken, 2004).

Table 3.4. Extraction efficiency of heavy metals from sewage sludge (in %)(Veeken, 2004).

Extracting reagent Cd Cu Pb Zn Reference

0.5 M acetic acid 40 0 5 25

Bloomfield & Pruden,

1975

HCl, pH 1.5 10-90 0-70 5-100 50-90 Oliver & Carey, 1976

H2SO4 10-70 <2 10-15 35-70 Jenkins, 1981

HCl, pH 1.5 80-100 80-100 40-100 100 Wozniak &

Huang, 1982

HCl, pH 1 90 50 - 90 Ried, 1988 H2SO4, pH 1.5 - 50-75 50-60 80-95 Tyagi et al.,

1988

HCl, pH 1 22-90 2-90 30-100 50-95 Rulkens et al., 1989

H2SO4, pH 1.5 95-99 8-10 35-65 50-99 Lo & Chen,

1990

3.3.2. Extraction Conditions

The variable extraction conditions, such as extracting time, reagent concentration,

solids concentration and type of mixing, the ambient temperature, pH are important

parameters in the extraction process.

32

According to Veeken and Hamelers (1999), as might be expected, the extraction

efficiency increases for lower pH values. Besides, they reached in their study that the

rate of extraction increases for Cu and Zn at higher temperatures and citric acid

concentrations. The lower solubility is caused by the reduction of sulphate to

sulphide and the subsequent precipitation of heavy metal sulphides. Heavy metal

sulphides, especially CuS and PbS, are very difficult to solubilise, even at low pH

values. Also, the lower solubility of Cu is due to the stronger binding of Cu to sludge

biomass (Veeken, 2004).

Veeken and Hamelers (1999) obtained in their study as regards OCAs those

extractions were performed for oxalic acid and citric acid at various concentrations in

pH range 2-6 for Cu, Zn, Ca and Fe. Both acids increased the heavy metal extraction

efficiency at mildly acidic pH. Citric acid had higher extraction efficiencies

compared to oxalic acid because oxalic acid is removed from solution by

precipitation as calcium oxalate and citrate anion is protonated. At low pH, the

extraction can be assisted to the action of the protons. Besides, binding degree of

metal ions to the sludge is important.

33

0

20

40

60

80

100

0 3 6 9 12

time (d)

extra

ctio

n (%

)

12.6 5 1.3

Ca

0

20

40

60

80

100

0 3 6 9 12

Zn0

20

40

60

80

100

0 3 6 9 12

extra

ctio

n (%

)

Cu

0

20

40

60

80

100

0 3 6 9 12

time (d)

12.6 5 1.3

Fe

Figure 3.5 Kinetics of extraction of Cu, Zn, Ca and Fe from sewage sludge at various citric acid

concentrations (Veeken & Hamelers, 1999).

The kinetics of the extraction process were studied for citric acid extraction at

various concentrations at pH 3 (Figure 3.5). The course of extraction showed a

distinct difference between heavy metals (Cu, Zn) and competing metals (Ca, Fe).

The extraction of Cu and Zn as a function of time is typical for the extraction of

heavy metals from sewage sludge: less strongly bound heavy metals (Zn) are

extracted more rapidly from the sludge than strongly bound heavy metals (Cu).

Heavy metals are predominantly incorporated in sludge flocs and the extraction

takes time because the heavy metals have to diffuse from the sludge matrix to the

bulk solution. The metals Ca and Fe are extracted much more rapidly from sewage

sludge because these metals are present as precipitate (e.g. Fe(OH)3, FePO4,

CaCO3) or very weakly adsorbed to sludge flocs (Ca). The dissolution of precipitates

is a relatively fast process compared to the diffusion of metal ions from within the

sludge flocs to the bulk solution. The extraction was also studied at 10, 20 and 30 oC

for the extraction with 0.1 M citric acid at pH 3.5. The increase in rate of extraction

for both Cu and Zn with increasing temperature confirms the hypothesis that the rate

34

of extraction is controlled by diffusion of metal ions from the sludge flocs to the bulk

solution.

Heavy metals and competing metals both have to be removed from the extracting

liquid to prevent accumulation of these metals in the process. Citric acid is a

moderately strong complexing agent and both heavy and competing metals can

possibly be removed from the liquid phase by a combination of chemical sulphide

precipitation and specific ion exchangers.

Extraction of heavy metals from organic wastes by citric acid could be an

attractive option because the extraction can be performed at mildly acidic conditions

(pH 3-5). As citric acid is biologically degradable, the extraction process is

compatible with composting and wastewater treatment. The extraction was studied

for heavy metals Cu and Zn and for competing metals Ca and Fe from polluted

sewage sludge. The rate of extraction increases for increasing temperature and citric

acid concentration. Cu can be extracted for 60-70% and Zn for 90-100% by citric

acid at pH 3-4. However, the process is still critical with respect to the removal of

competing and heavy metals from the recycling liquid. Moreover, the process results

in a highly toxic metal sludge that has to be landfilled. A first economic valuation of

the extraction process showed that the total costs of the treatment process are high

and comparable to the costs of incineration, approx. €400 per ton of dry matter

(Veeken, 2004).

3.4 Legislations about Heavy Metal Content of Sludge

3.4.1 Legislations of EU, EPA, and Other Countries

The purpose of using sludge in agriculture is partly to utilise nutrients such as

phosphorus and nitrogen and partly to utilise organic substances for soil

improvement. However, an important consideration in this application is the heavy

metal content of the sludge. At a pH greater than 6, heavy metals will exchange for

Ca+2, Mg+2, Na+ and K+. This natural ability to Exchange heavy metals by the soil is

35

called the Cation Exchange Capacity (CEC) and is expressed in milliequivalents per

hundred grams of dry soil. The U. S. Department of Agriculture has listed the

maximum amount of heavy metals that can be applied to the land , as shown in Table

3.5 (Eckenfelder, 1989). Maximum loadings of heavy metals have been tentatively

adopted by the EPA.

Table 3.5 Suggested maximum heavy metals can be applied .

Soil Cation Exchange Capacity, milliequivalents/ 100 g

0-5 5-15 >15 Metals

The Amount of Heavy metal (lbre/acre)*

Zn 225 450 900

Cu 110 225 450

Ni 45 90 180

Cd 4,5 9 18

Pb 450 900 1 800 * lbre/acre = 0,112 g/m2 = 1,12 kg/ha

Table 3.6 gives comparative data from a number of countries on the maximum

allowable concentrations of heavy metal in sludge (Priestley, bt).

Table 3.6 Maximum permitted concentrations of heavy metals in sewage sludge used for land

application (mg/kg dry solid).

Heavy

Metals

The

Netherlands France Sweden Japan NSW

Arsenic 10 - - 50 15

Mercury 5 10 8 2 10

Cadmium 5 40 15 5 8-20

Chromium 500 1 000 1 000 - 500

Lead 500 800 300 - 500

Nickel 100 200 500 - 100

Zinc 2 000 3 000 10 000 - 1 800

Copper 600 1 000 3 000 - 1 200

36

Table 3.7 demonstrates sewage sludge metal level standards proposed by

European Council.

Table 3.7 European Council Directive 86/278/EEC sewage sludge metal level standards (Hutton&

Meeus, 2001).

Metals

Limit Values for Concentrations of Heavy Metals in

Soil Soil with pH of 6-7

mg/kg

Limit Values for Heavy-Metal

Concentrations in Sludge for Use in

Agriculture mg/kg

Limit Values for Amounts of Heavy

Metals which may be Added Annually to Agricultural Land (Based on 10-Year

Avg.) kg/ha/yr

Cadmium

1 to 3 20 to 40 0.15

Copper

50 to 140 1 000 to 1750 12

Nickel

30 to 75 300 to 400 3

Lead

50 to 300 750 to 1 200 15

Zinc

150 to 300 2 500 to 4 000 30

Mercury

1 to 1.5 16 to 25 0.1

Chromium 100 to 150 1 000 to 1 500 4

Table 3.8 is given in a study performed by EPA (1994). This document explains

the requirements applicable to land appliers of sewage sludge. 40 CFR 503.13 means

40 Code of Federal Regulations Part 503. Ceiling concentration establishes the

maximum concentration of each pollutant that sewage sludge can contain and still be

land applied. Cumulative Pollutant Loading Rates establish the maximum amount

(mass) of each regulated pollutant that can be applied to a site during the life of the

site. Annual Pollutant Loading Rates establish the maximum amount (mass) of

pollutants in sewage sludge that can be applied to a site during a 365-day period.

37

Table 3.8 Pollutant limits for the land application of sewage sludge (EPA, 1994).

Concentration Limits

Pollutant Ceiling Concentrations

(Table 1 of 40 CFR 503.13) mg/kg,dry weight

Pollutant Concentration (Table 3 of 40 CFR 503.13)

mg/kg,dry weight Arsenic 75 41

Cadmium 85 39

Chromium 3000 1200

Copper 4300 1500 Lead 840 300

Mercury 57 17 Molybdenum* 75 --

Nickel 420 420 Selenium 100 36

Zinc 7500 2,800 Loading Rates

Cumulative Pollutant Loading Rates

(Table 2 of 40 CFR 503.13)

Annual Pollutant Loading Rates

(Table 4 of 40 CFR 503.13) Pollutant

kg/he, dry weight

libre/acre, dry weight

kg/he/365 days,

dry weight

libre/acre/365 days,

dry weight Arsenic 41 37 2,0 1,8

Cadmium 39 35 1,9 1,7

Chromium 3000 2677 150 134

Copper 1500 1339 75 67 Lead 300 268 15 13

Mercury 17 15 0,85 0,76 Molybdenum* -- -- -- --

Nickel 420 375 21 19 Selenium 100 89 5,0 4,5

Zinc 2800 2500 140 125 * The pollutant concentration limit, cumulative pollutant loading rate, and annual pollutant loading rate for molybdenum were deleted from Part 503 effective February 19, 1994. EPA will reconsider establishing these limits at a later date.

Table 3.9 gives the limit values for concentrations of heavy metals in soil

depending on the European Union Directives. When the concentration value of an

element in a specific land area is higher than the concentration limit as set in the

38

table, the competent authority may allow the use of sludge on that land on a case-by-

case basis and after evaluation of the following aspects:

• uptake of heavy metals by plants,

• intake of heavy metals by animals,

• groundwater contamination,

• long term effects on bio-diversity, in particular on soil biota.

Table 3.9 Limit values for concentrations of heavy metals in soil (http://europa.eu.int).

Limit Values (mg/kg DM) (Directive 86/278/EEC)

Elements 6<pH<7 5≤pH<6 6≤pH<7 pH≥7

Cd 1-3 0,5 1 1,5

Cr - 30 60 100

Cu 50-140 20 50 100

Hg 1-1,5 0,1 0,5 1

Ni 30-75 15 50 70

Pb 50-300 70 70 100

Zn 150-300 60 150 200

3.4.2 Legislations of Turkey

The directives about sludge are given in Legislations of Solid Waste Management

(Official Gazette, 1991), Legislations of Hazardous Waste Management (Official

Gazette, 1995), and Legislations of Soil Contamination Management (Official

Gazette, 2001) in Turkey. The directives related with heavy metal given in these

Legislations are summarized in the Table 3.10 - 3.12.

39

Table 3.10 Limit values of heavy metals in soil for Turkey as different years.

Soil Contamination Control Directive (2001) Heavy

Metal PH ≤ 6

mg/kg DS

PH>6 mg/kg DS

Soil Contamination Control Directive

(1991) (pH is not denoted)

Lead 50 ** 300 ** 100

Cadmium 1 ** 3 ** 3

Chrome 100 ** 100 ** 100

Copper * 50 ** 140 ** 100

Nickel * 30 ** 75 ** 50

Zinc * 150 ** 300 ** 300

Mercury 1 ** 1,5 ** 2

* If pH value is higher than 7, the heavy metal levels can be increased up to 50% by Ministry ** The heavy metal levels can be increased if it is proved to be harmless for human health in cropland by the scientific studies.

Table 3.11 Maximum allowable heavy metal content in sewage sludge used in agriculture for Turkey

as different years

Heavy Metal Limit value for 2001 (mg/kg DS)

Limit value for 1991 (mg/kg DS)

Lead 1200 1200

Cadmium 40 20

Chromium 1200 1200

Copper 1750 1200

Nickel 400 200

Zinc 4000 3000

Mercury 25 25

40

Table 3.12 Maximum heavy metal loadings which may be added annually to agricultural land (based

on 10-Year Avg.) in Turkey as different years.

Heavy Metal Limit loading value**

for 2001 (g/ha/yr)

Limit loading value for 1991 (g/ha/yr)

Lead* 1500 2000

Cadmium 15 33

Chromium* 1500 2000

Copper* 1200 2000

Nickel* 300 330

Zinc* 10 42

Mercury 3000 5000

* The limit loading values of heavy metals except for Cd and Hg can be increased up to 5% by Ministry respecting suggestions of related Institutions in the case of three months duration between sludge applications to the land and harvesting (for 2001) ** These values can be exceeded in the case of it is used at animal food growing land and scientific studies are proved that it is not harmful for human and environment.

41

CHAPTER FOUR

MATERIALS AND METHODS

4.1. Materials

4.1.1 The Characteristics of the Sludge Samples

Lab-scale experiments were carried out with four different industrial sludges. The sludges

were taken from a dyestuff industry (Sahan Dyestuff Industry, Torbali), two metal industries

(Norm Cıvata and Cevher Döküm), and an Organized Industrial District (Atatürk Organized

Industrial District). The first metal industry, the dyestuff industry, the Organized Industrial

District (OID), and the second metal industry sludge is named as “Sludge A”, “Sludge B”,

“Sludge C”, and “Sludge D”, respectively, in the thesis. All of the sludges were dewatered

sludge.

Before extraction studies with organic acids were started, general properties of each sludge

sample had been determined. In these characterization experiments, total solids (TS) and total

volatile solids (TVS) of the samples were taken into consideration. In addition, the heavy

metal contents of sludge were determined using HF+HClO4 digestion method depending on

the procedure described in Section 4.3. The results of the characterization studies are given in

Table 4.1 – 4.4.

42

Table 4.1 General properties of “Sludge A” taken from a metal industry.

Parameter Unit Value

Total Solids, TS mg/g 350

Total Volatile Solids, TVS mg/g 82

Dry Matter % 34,96

Organic Matter % 8,23

Total Fe

mg/kg

mol/kg

92 220

1,65

Zn2+

mg/kg

mol/kg

65 000

1,00

Cu2+

mg/kg

mol/kg

4,8

0,000075

Total Cr

mg/kg

mol/kg

99

0,0019

Ni+

mg/kg

mol/kg

1 820

0,031

Na+

mg/kg

mol/kg

7 600

0,33

K+

mg/kg

mol/kg

200

0,0051

Ca2+

mg/kg

mol/kg

536

0,0134

Mg2+

mg/kg

mol/kg

2 100

0,086

Total Metal Content* 0,34

*sum of heavy and competing metals in mol/kg DM

43

Table 4.2 General properties of “Sludge B” taken from a dyestuff industry.




Dry Matter % 68,30

Organic Matter % 17

Total Fe

mg/kg

mol/kg

80 200

1,43

Zn2+ mg/kg

mol/kg

24 120

0,37

Cu2+ mg/kg

mol/kg

311

0,0049

Total Cr mg/kg

mol/kg

694

0,013

Ni+ mg/kg

mol/kg

244

0,0041

Na+ mg/kg

mol/kg

36 400

1,58

K+ mg/kg

mol/kg

600

0,015

Ca2+ mg/kg

mol/kg

75 400

1,885

Mg2+ mg/kg

mol/kg

12 860

0,53



44

Table 4.3 General properties of “Sludge C” taken from an OID.




Dry Matter % 20,10


Total Fe

mg/kg

mol/kg

83 940

1,498

Zn2+

mg/kg

mol/kg

9 680

0,149

Cu2+

mg/kg

mol/kg

702

0,011

Total Cr

mg/kg

mol/kg

1 093

0,021

Ni+

mg/kg

mol/kg

368

0,0062

Pb2+

mg/kg

mol/kg

7,8

0,00038

Na+

mg/kg

mol/kg

61 200

2,66

K+

mg/kg

mol/kg

2 600

0,066

Ca2+

mg/kg

mol/kg

48 000

1,2

Mg2+

mg/kg

mol/kg

11 200

0,461



45

Table 4.4 General properties of “Sludge D” taken from a metal industry.




Dry Matter % 40,20


Total Fe

mg/kg

mol/kg

2 232

0,0398

Zn2+

mg/kg

mol/kg

8 532

0,1313

Cu2+

mg/kg

mol/kg

237,6

0,0037

Total Cr

mg/kg

mol/kg

---

---

Ni+

mg/kg

mol/kg

152

0,0026

Na+

mg/kg

mol/kg

78 000

3,3913

K+

mg/kg

mol/kg

2 800

0,0718

Ca2+

mg/kg

mol/kg

120 000

3,0

Mg2+

mg/kg

mol/kg

4 200

0,173



46

4.2. Methods

4.2.1 Analytical Methods

Industrial sludge collected from the four wastewater treatment plants placed in

Izmir was examined in this study. The collected sludge samples were stored at 4°C

until used. The general characteristics of the sludge were determined before heavy

metal extraction with organic acids.

To determine composition of the sludge samples, total solid content (TS) and total

volatile solids (TVS) were determined according to procedure given in Standard

Methods (APHA, AWWA, WEF; 1992). The total metal concentrations were

measured after digestion of samples with strong acids including HF and HClO4

treatment (APHA, AWWA, WEF; 1992). The concentrations of heavy metals and

Fe, Ca, and Mg in the final solutions were determined by an atomic absorption

spectrometer (AAS) (UNICAM 929). Na+ and K+ were measured using a flame

photometer (JENWAY PFP 7).

Total solid is the sum of the dissolved and suspended solids in the sludge and is

determined by drying a sample at 105oC and weaving the residue. The determination

of the total solids of a sludge sample is required for determining the moisture content

of the sludge, usually expressed as percentage of wet weight, and for expressing

other constituents on a dry weight basis.

The volatile solids content of sludge, generally expressed as a percentage, is used

as a measure of the organic content of sludge. Volatile solids reduction is used as a

measure of the performance of the digester. The volatile solids are determined by the

loose in weight when the sludge is combusted by heating a sample to 550oC

(Lue-Hing, Zenz, & Kuchenrither, 1992).

47

4.3 Experimental Procedure

4.3.1 Elutriation Test

The total heavy metals contents of industrial sludge samples were determined

using HF-HClO4 digestion method. At the beginning of the experiment, a platinum

container was carefully cleaned and heated in a furnace at 800oC for 15-20 minutes

and then weighed. After sludge sample was dried and ground, 0,5 gram of the sample

was put in the platinum container. And then, 1 ml HClO4 and certain amount of HF

acid were added in the sample. In order to obtain pre-degradation, prepared sample

was placed above a heater. When the level in the platinum container decreased, HF

acid was added again.

In the meantime, 100 ml pure water and 5 ml HCl acid were added into 250 ml of

a beaker at a different place. When the level in the platinum container decreased

again, the platinum container was put in the beaker. When the level in the beaker

abated three times, the beaker was taken from the heater. The solution in the beaker

was conducted from a blue filter band and the filtrate was completed to 100 ml by

pure water. The prepared filtrate for heavy metals analysis was kept in the

refrigerator at 4oC until they were analyzed by atomic absorption spectrometer

(UNICAM 929).

4.3.2 Extraction Procedure with Organic Acids

The sludges, which were taken from different industrial sources, were stored at

+4°C until analysed. After then, each sludge sample was dried in an oven at 103-

105oC for 1-2 days, depending on the structure of sludge. In order to get ready the

sludge sample to extraction analyses with organic acid, dried sludge was ground.

Although citric acid and oxalic acid were used as main organic acids at this study,

acetic acid was also applied to the sludge sample originating from a metal industry

(Sludge D) used at the end of this study.

48

The amount of the extracting reagent applied during the organic acid extraction

was determined from the sum of heavy metals of raw sludge samples, which were

determined using HF+HClO4 digestion method. The amount of organic acid was

adjusted as it is larger than the sum of them and at this study, 1 mol, 2 mol, and 5

mol citric, oxalic acid, and acetic acid was examined at room temperature.

5 gram of dried sludge sample was placed in a shaken flask with selected amount

of extracting reagent. pH was measured before stirring. Flasks were kept in stirring

conditions (70 rpm) at room temperature using a shaker (Roto-Torque, heavy duty

rotator). The samples, which were taken after 1 h, 3 h, 24 h, and 72 h of extraction

time, were centrifuged at 5000 rpm during 30 minutes and filtered over firstly a black

filter band and secondly a blue filter band. The filtrate was completed to 100 ml with

pure water and then, stored at 4oC before analysis. Na+ and K+ were analyzed by a

flame photometer and the other heavy metals were determined by atomic absorption

spectrometer as mg/l. These values were transformed to mg/kg by considering

dilutions.

49

CHAPTER FIVE

RESULTS AND DISCUSSION

The results of experimental studies carried out with organic acids for four

different sludges are discussed below. In addition, all results are also given as table

form at Appendix.

5.1 Results of Experimental Studies with Sludge A

Sludge A was taken form a Metal Industry. The characteristics of the sludge

sample are given in Chapter 4 (see Table 4.1). Comparisons of extraction results

carried out using different organic acids-citric acid, oxalic acid- and the conventional

HF + HClO4 digestion method for Sludge A are debugged in the following

subsections. The extraction of heavy metals accomplished by different organic acids

was performed at different extraction times for 1 h (0,04 d), 3 h (0,125 d), 24 h (1 d),

and 72 h (3 d).

5.1.1 Zinc Extraction Studies

Citric Acid Results

Citric acid (C6H8O7) with three different concentrations (1, 2, and 5 mol) and the

conventional HF + HClO4 digestion were applied to Sludge A for the extraction of

heavy metals. The results for this application and the conventional method are

depicted in Figure 5.1.

50

0

10000

20000

30000

4000050000

60000

70000

80000

90000

1 mol CA 2 mol CA 5 mol CA HF+HClO4

Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.1 Zn extraction results vs. citric acid additions for Sludge A

In the comparison of the citric acid application with conventional method, citric

acid application was found to be more effective than HF + HClO4 for Zn extraction

of the sample. Increases in extraction time have led to enhancements in the

efficiencies for all citric acid concentrations. For example, 55 455 mg/kg, 67 287

mg/kg, 77 092 mg/kg, and 78 971 mg/kg were achieved at 1 h, 3 h, 24 h, and 72 h

extraction time, respectively, when 5 mol citric acid was applied.

Oxalic Acid Results

1 mol, 2 mol, and 5 mol oxalic acid (C2H2O4) were examined for the extraction of

Zn from Sludge A. Figure 5.2 shows the extraction results of these experiments. On

the contrary to citric acid results, oxalic acid was not effective reagent for Zn

extraction except for 1 mol oxalic acid at 1 hour extraction time. The conventional

HF + HClO4 digestion method produced better results than the oxalic acid extraction.

Therefore, the oxalic acid reagent is not preferred for the exctration of Zn from

Sludge A.

51

0

10000

20000

30000

40000

50000

60000

70000

1mol OA 2 mol OA 5 mol OA HF+HClO4

Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.2 Zn extraction results vs. oxalic acid additions for Sludge A

As a conclusion, citric acid is more effective organic acid reagent than oxalic acid

for Zn removal from Sludge A. Besides, when comparing with inorganic acid result,

citric acid is shown up a successful reagent as well as HF + HClO4.

5.1.2 Copper Extraction Studies

Citric Acid Results

1 mol, 2 mol, and 5 mol citric acid and HF + HClO4 digestion methods were

applied for Cu removal from Sludge A. Results of these experiments are plotted in

Figure 5.3.

52

0

1

2

3

4

5

6

7

8


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.3 Cu extraction results vs. citric acid additions for Sludge A

Among the applications, the most succesful result was obtained at 1 hour

extraction time with 2 mol citric acid. Moreover, the extraction efficiency of Cu at 1

day extraction time with 5 mol citric acid is higher than inorganic acid (HF + HClO4)

application. Conversely, 1 mol citric acid application did not affect the extraction

efficiency as high as the others. It could not be obtained consistent results while the

extraction times were changed. It was not found any linear relationship between the

time and the efficiency at this application. When 1 mol citric acid was used,

efficiency increased with increasing extraction time; however, removal efficiency

decreased while extraction time increased in the case of 2 mol citric acid was

applied.

Oxalic Acid Results

In order to evaluate the effect of oxalic acid application on Cu extraction from

Sludge A, three different oxalic acid concentrations were used as 1, 2, and 5 mol,

respectively. The results of these experiments are given in Figure 5.4. As noted from

this figure, Cu extraction with oxalic acid was only effective when 1 mol oxalic acid

53

was used at 1 hour of extraction time. Even though very high extraction efficiency

was obtained with this application, other applications did surprisingly not yield any

effectual results for Cu extraction. On the other hand, 1 mol oxalic acid application at

1 hour was as effective as HF + HClO4 application. However, the result is not

satisfactory to use oxalic acid reagent for extraction of Cu from Sludge A.

0

1

2

3

4

5


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.4 Cu extraction results vs. oxalic acid additions for Sludge A

In brief, it can be said that citric acid application is more successful than oxalic

acid application for Cu removal from Sludge A. Consequently, it could be made a

preference between citric acid and conventional method from the economical point

view of in the removal of Cu from Sludge A.

5.1.3 Nickel Extraction Studies

Citric Acid Results

To assess the effeciency of citric acid for Ni removal from Sludge A, citric acid

with three different concentrations as 1 mol, 2 mol, and 5 mol was applied. The

results of citric acid and HF + HClO4 applications are shown in Figure 5.5.

54

0200400600800

100012001400160018002000


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.5 Ni extraction results vs. citric acid additions for Sludge A

The experimental results have demonstrated that the citric acid was as effective

as HF + HClO4 digestion method. The maximum extraction efficiency for Ni was

obtained at 3 days extraction time with 2 mol citric acid (1 822 mg/kg Ni was

measured), but there was no colossal difference between the efficiencies of citric acid

application and HF + HClO4 digestion (1 820 mg/kg Ni was measured). As can be

seen from Figure 5.5, extraction efficiencies increased with the increasing extraction

time. For instance, 1 652 mg/kg, 1 692 mg/kg, 1 722 mg/kg, and 1 822 mg/kg Ni

were measured for 1 h, 3 h, 24 h, and 72 h of extraction time for 2 mol citric acid

application, respectively.

Oxalic Acid Results

1 mol, 2 mol, and 5 mol oxalic acid concentrations were applied to assess the

effect of oxalic acid for Ni extraction from Sludge A. Oxalic acid performances are

given in Figure 5.6 together with HF + HClO4 application performance. From this

figure, it is clearly seen that Ni extraction with oxalic acid was only effective at 1

hour extraction time with 1 mol oxalic acid as in Cu extraction studies. The

extraction efficiency for Ni is quite low as compare with inorganic acid application

55

for the other concentrations of oxalic acid. The maximum Ni removal efficiency was

achieved with HF + HClO4 extraction reagent (1 820 mg Ni/kg DM). It is therefore

more reasonable to use inorganic acid extraction for Ni removal from Sludge A.

If oxalic acid is preferred for Ni extraction, required reaction time should be taken

into consideration. Depending on the experiments, it was found that the efficiency

was inversely proportional to the extraction time.

0200400600800

100012001400160018002000


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.6 Ni extraction results vs. oxalic acid additions for Sludge A

5.1.4 Iron Extraction Studies

Citric Acid Results

In the comparison of citric acid application to the HF + HClO4 extraction method,

it is noticeable that Fe extraction efficiency with citric acid is rather lower at all

applications (Figure 5.7). Although maximum 15 211 mg/kg Fe was extracted among

the all citric acid concentrations, 92 220 mg/kg Fe was obtained in the case of

inorganic acid was applied.

56

0100002000030000400005000060000700008000090000

100000


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.7 Fe extraction results vs. citric acid additions for Sludge A

Oxalic Acid Results

Fe removal from Sludge A was also examined with oxalic acid addition and the

results are illustrated in Figure 5.8. Although oxalic acid gave high extraction

efficiency (40 031 mg Fe/kg DM) at 24 h extraction time with 5 mol concentration,

very low extraction performance was obtained with the other applications. Inorganic

acid was more effective than oxalic acid for Fe extraction from Sludge A, as in citric

acid practices.

As a concequence, oxalic acid is more effective than citric acid for iron removal

form Sludge A, as organic acid. However, HF + HClO4 digestion method is the most

appropriate method for Fe extraction; therefore, inorganic acid should be preferred

rather than organic acids.

57

0100002000030000400005000060000700008000090000

100000


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.8 Fe extraction results vs. oxalic acid additions for Sludge A

5.2 Results of Experimental Studies with Sludge B

Sludge B as in sludge cake form was taken successively a mechnical dewatering

unit of a dyestuff industry wastewater treatment plant. The characteristics of the

sludge sample are given in Chapter 4 (Table 4.2). To investigate the heavy metal

removal from this type of sludge, organic acids (citric acid, oxalic acid) and

inorganic acid (HF + HClO4) were examined as in Sludge A experiments. This

subsection gives the experimental results in detail. The extraction of heavy metals

with organic acids for Sludge B was performed at 1 h (0,04 d), 3 h (0,125 d), 24 h (1

d), and 72 h (3 d) of extraction time.


Citric Acid Results

The effect of citric acid on Zn removal from Sludge B can be seen from Figure

5.9. It is obviously apparent that 2 mol and 5 mol of citric acid applications were

quite better than HF + HClO4. Maximum Zn removal efficiency was obtained at 24 h

58

extraction time with 5 mol citric acid application. pH of the solution ranged from 2 to

4, and lowest pH value as 2 belonging to 5 mol citric acid application. Lower pH

values have led to higher efficiency, which indicates the importance of pH on

extraction process with organic acids. Increases in citric acid concentrations have

also enhanced the removal efficiency.

0

10000

20000

30000

40000

50000

60000


Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.9 Zn extraction results vs. citric acid additions for Sludge B

Oxalic Acid Results

Results of oxalic acid experiments for Zn extraction are shown in Figure 5.10. 5

mol oxalic acid applications at 1 h reaction time seem to be the most efficient

experiment. Due to the other experiments are not successful as it is, the maximum

removal can not be seen as considerable result and it should be negligible. That is

why inorganic acid should effectively be used for Zn extraction from Sludge B.

59

0

10000

20000

30000

40000

50000

60000


Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.10 Zn extraction results vs. oxalic acid additions for Sludge B

As a conclusion, citric acid could be priorly preferred to remove Zn from Sludge

B. If it is not suitable to use citric acid, HF + HClO4 digestion can be choosen.

Oxalic acid is ineffective extraction reagent for Zn removal from Sludge B.


Citric Acid Results

The highest Cu extraction efficiency (950 mg Cu/kg DM) was achieved at 72 h

extraction time with 5 mol citric acid addition. At 1 mol and 2 mol citric acid

additions, almost Cu extraction could not be obtained. At 5 mol citric acid addition,

increasing removal efficiency was obtained with the increasing extraction time.

When comparing citric acid and inorganic acid digestion methods (311 mg Cu/kg

DM), citric acid extraction application produced three times better results than

conventional method (Figure 5.11).

60

0100200300400500600700800900

1000


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.11 Cu extraction results vs. citric acid additions for Sludge B

Oxalic Acid Results

Figure 5.12 summarizes the experimental results of Cu removal with different

amounts of oxalic acid additions. Similar results were also obtained with citric acid.

Experimental results have shown that the oxalic acid was more efficient than HF +

HClO4 digestion at higher extraction time and higher extraction reagent

concentrations. The maximum removal efficiency was obtained at 24 h extraction

time with 5 mol oxalic acid addition (565 mg Cu/kg DM).

As a summary, it can be said that organic acid extraction method at higher

extraction reagent concentrations and higher extraction time is more effectual than

HF + HClO4 digestion. Consequently, citric acid could be first choosen to remove Cu

from Sludge B. Oxalic acid additions could be also used for the same purpose; but, it

is not expected the results would be as succesfull as citric acid application.

61

0

100

200

300

400

500

600


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.12 Cu extraction results vs. oxalic acid additions for Sludge B


Citric Acid Results

Results of citric acid application for Ni removal from Sludge B are given in

Figure 5.13. Citric acid is very successful as it is for Sludge A. It is observed that

higher extraction times and citric acid concentrations have commonly led to

increases in the removal efficiencies. The results obtained with citric acid application

at especially high concentrations are close to the result of HF + HClO4 digestion

application. Besides, Figure 5.13 shows that 5 mol citric acid addition at 24 h

extraction time has more effectual than HF + HClO4.

62

0

50

100

150

200

250

300


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.13 Ni extraction results vs. citric acid additions for Sludge B

Oxalic Acid Results

Figure 5.14 illutrates the effects of oxalic acid and HF + HClO4 application on Ni

removal from Sludge B. It can be said that the oxalic acid application is not as

effective as HF + HClO4 for Ni extraction from Sludge B. Although, the most

efficient result was achieved at 1 hour extraction time with 5 mol oxalic acid, HF +

HClO4 digestion method gave similar result.

In consequence, citric acid and HF + HClO4 applications are more effective than

oxalic acid for Ni removal from Sludge B. Therefore, by considering economical

feasibilities, inorganic acid digestion or citric acid extraction should be used for this

purpose.

63

0

50

100

150

200

250

300

350


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.14 Ni extraction results vs. oxalic acid additions for Sludge B

5.2.4 Chromium Extraction Studies

Citric Acid Results

Figure 5.15 shows the results of chromium extraction studies with different

amounts of citric acid additions. As noted from this figure, the conventional

inorganic acid digestion method is more effective than citric acid extraction

application. While maximum 305 mg Cr could be extracted from dried sludge with

citric acid application, 694 mg Cr/ kg DM was obtained with HF+HClO4 addition.

64

0

100

200

300

400

500

600

700

800


Extraction Reagent

Ext

ract

ed C

r (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.15 Cr extraction results vs. citric acid additions for Sludge B

Oxalic Acid Results

As can be seen from Figure 5.16, oxalic acid is not successful for Cr extraction

from Sludge B, like citric acid. However, the performance of oxalic acid was slightly

lower than citric acid. Increases in oxalic acid concentrations have led to better

efficienciens. Cr extraction could not be acquired at 1 mol and 2 mol of oxalic acid

additions; even though, Cr extraction at 1 mol acid addition was almost zero. The

most efficienct extraction was achieved at 72 h of extraction times for 5 mol oxalic

acid (336 mg Cr/kg) addition.

65

0

100

200

300

400

500

600

700

800


Extraction Reagent

Ext

ract

ed C

r (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.16 Cr extraction results vs. oxalic acid additions for Sludge B

In brief, when comparing the both organic acids with inorganic acid, the effects of

organic acids were rather low. Therefore, HF+HClO4 digestion method should be

used for the removal of Cr from Sludge B.


Citric Acid Results

Fe removal studies from Sludge B were carried out with 1 mol, 2 mol, and 5 mol

citric acid additions and the results are given in Figure 5.17. Approximately 80 000

mg Fe/kg DS was extracted in the case of inorganic acid addition. However,

maximum 19 825 mg Fe/kg DS, 49 860 mg Fe/kg DS, and 63 718 mg Fe/kg DS

could be removed with 1 mol, 2 mol, and 5 mol of citric acid additions, respectively.

66

0

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20000

30000

40000

50000

60000

70000

80000

90000


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.17 Fe extraction results vs. citric acid additions for Sludge B

Oxalic Acid Results

Results of oxalic acid application for Fe removal from Sludge B are shown in

Figure 5.18. While there is no effect of 1 mol oxalic acid application, the application

of 2 mol oxalic acid has slightly better effect on the removal of Fe. But, the

extraction with 5 mol oxalic acid gave superior results than the others. In particular,

the most effective value for this addition was obtained at 1 hour of extraction time.

At this application, almost the same extraction efficiency was achieved with

inorganic acid.

67

0100002000030000400005000060000700008000090000


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.18 Fe extraction results vs. oxalic acid additions for Sludge B

In conclusion, oxalic acid at high concentrations should be preferred instead of

citric acid as organic acid for Fe extraction from Sludge B. When oxalic acid is used

for this aim, low extraction time should be chosen.

5.3 Results of Experimental Studies with Sludge C

Sludge C is a dewatered sludge originating from an Organized Industrial District.

The characteristics of Sludge C were given in previous Chapter (see Table 4.3). In

order to examine removal efficiencies of some heavy metals from this sludge,

organic acids (citric acid and oxalic acid) and inorganic acid (HF + HClO4) were

used as applied to other sludge samples. The extraction studies of heavy metals with

the organic acids for Sludge C were performed for 1 h (0,04 d), 3 h (0,125 d), 24 h (1

d), and 72 h (3 d) of extraction time. Evaluations of these studies are given in

following sections.

68


Citric Acid Results

The results belonging to Zn extraction studies utilized citric acid application are

demonstrated in Figure 5.19. Higher extraction efficiency was obtained with certain

organic acids treatment while 9 680 mg Zn could be only extracted with inorganic

acid addition. For all citric acid additions, the most effective results were achieved at

high extraction time (72 h). The lowest extraction efficiency at this extraction time

was 2 767 mg Zn in the case of 1 mol citric acid added. However, it was gone up

until 11 134 mg and 12 626 mg at 2 mol and 5 mol acid additions, respectively.

0

2000

4000

6000

8000

10000

12000

14000


Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.19 Zn extraction results vs. citric acid additions for Sludge C

Oxalic Acid Results

Figure 5.20 shows the results obtained with oxalic acid application for Zn removal

from Sludge C. The highest extraction was achieved with HF + HClO4 application.

69

Oxalic acid is not effective as HF + HClO4. Maximum Zn was measured as 4 503 mg

when oxalic acid applied.

0100020003000400050006000700080009000

10000


Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.20 Zn extraction results vs. oxalic acid additions for Sludge C

As a conclusion, citric acid is the most effectual reagent for Zn removal from

Sludge C. Oxalic acid did not exhibit similar performance on the Zn extraction for

this sample. If Zn removal is required for any sludge that will be stored either in a

landfill or agricultural usage, citric acid extraction method should be applied.


Citric Acid Results

Results of Ni extractions with various concentrations of citric acid for Sludge C

are shown in Figure 5.21. HF+HClO4 digestion method yielded better results in the

comparison of citric acid application. Among the citric acid additions, the most

efficient extraction was performed at 72 h of extraction time when 5 mol citric acid

was added. This value (328 mg Ni/kg) is quite near the result obtained with

HF+HClO4 digestion method, 368 mg Ni/kg. Higher extraction times for citric acid

70

application gave better efficiencies, which comfirmed the previous results obtained

for other sludge samples.

050

100150200250300350400450


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.21 Ni extraction results vs. citric acid additions for Sludge C

Oxalic Acid Results

Figure 5.22 summarizes the experimental studies carried out with oxalic acid for

the removal of Ni from Sludge C. HF+HClO4 extraction gave fairly better result than

oxalic acid application. Increased oxalic acid concentrations have enchanced the

removal efficiencies. The extraction efficiencies surprisingly decreased at higher

extraction times, in particular, after 24 h.

71

050

100150200250300350400450


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.22 Ni extraction results vs. oxalic acid additions for Sludge C

As a result, for removing Ni from Sludge C, organic acids are not superior

solution since the inorganic acid (HF+HClO4) extraction is more sensible method for

this purpose.

5.3.3 Chromium Extraction Studies

Citric Acid Results

The results obtained with citric acid application for Cr removal from Sludge C are

depicted in Figure 5.23. As can be seen from this figure, inorganic acid application

gave better results than citric acid additions. The maximum Cr extraction was

determined as 1 093 mg Cr/kg DM at the inorganic acid application (HF+HClO4).

It was found a linear relationship between extraction time and efficiency at citric

acid application. For example; 133 mg Cr, 352 mg Cr, 730 mg Cr, and 815 mg Cr

could be extracted at 1 h, 3 h, 24 h, and 72 h of extraction time, respectively, when 5

mol acid was used. Similarly, at 2 mol acid addition, the amount of extracted Cr

increased from 112 mg to 704 mg when extraction time increased from 1 h to 3 days.

72

On the other hand, higher citric acid concentrations improved the efficiency. The

best result between citric acid additions was achieved at 72 h of extraction time with

5 mol citric acid.

0

200

400

600

800

1000

1200


Extraction Reagent

Ext

ract

ed C

r (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.23 Cr extraction results vs. citric acid additions for Sludge C

Oxalic Acid Results

The following figure shows the obtained results from oxalic acid extraction

studies of Cr from Sludge C (Figure 5.24). Oxalic acid is not satisfactorily effective

for Cr removal. Inorganic acid gave much better effect than oxalic acid.

As in citric acid application, increases in oxalic acid concentrations improved the

removal efficiency. More effective results were obtained for the highest oxalic acid

addition (5 mol) comparing with the other concentrations.

73

0

200

400

600

800

1000

1200


Extraction Reagent

Ext

ract

ed C

r (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.24 Cr extraction results vs. oxalic acid additions for Sludge C

Consequently, Cr extraction with organic acids from Sludge C is not reasonable.

Anyhow, if organic acids preferred, high extraction time should be required. But, the

most suitable method for this purpose is inorganic acid digestion.


Citric Acid Results

Figure 5.25 depicts the results of experimental studies of Fe extractions with

various concentrations of citric acid for Sludge C. The maximum Fe extraction (77

368 mg) could be obtained using 5 mol citric acid at 24 h of extraction time.

Following this, the best result was 75 412 mg Fe for 2 mol acid application at 72 h of

extraction time. The experimental studies have showed that increasing citric acid

concentrations have led to improved extraction efficiencies.

74

0

10000

2000030000

40000

50000

6000070000

80000

90000


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.25 Fe extraction results vs. citric acid additions for Sludge C

Oxalic Acid Results

As in citric acid application, oxalic acid application is also not effective for

removal of Fe from Sludge C (Figure 5.26) at low concentrations (1 mol and 2 mol).

However, more successful results were obtained at 5 mol acid addition. Especially

higher extraction times at 5 mol addition caused much more Fe removal from Sludge

C. Although 83 940 mg Fe could be removed with inorganic acid, 5 mol oxalic acid

at 72 h of extraction time gave the best removal as over than 90 000 mg Fe.

Although higher extraction times increased the extraction efficiency at 5 mol

citric acid addition, it was ascertained that reverse relationship was found between

extraction time and removal efficiency at lower oxalic acid concentrations.

75

0100002000030000400005000060000700008000090000

100000


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.26 Fe extraction results vs. oxalic acid additions for Sludge C

As a result, organic acids, both citric and oxalic, or inorganic acid (HF+HClO4)

should be used for Fe extraction from Sludge C. In the case of organic acids are

preferred for this aim, higher acid concentrations and higher extraction times should

be applied.


Citric Acid Results

Figure 5.27 shows the results obtained with citric acid for Cu removal from

Sludge C. Surprisingly, any effects of citric acids on Cu extractions were detected at

the applied experimental conditions.

76

0

100

200

300

400

500

600

700

800


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.27 Cu extraction results vs. citric acid additions for Sludge C

Oxalic Acid Results

Oxalic acid additions were also not effective of Cu removal from Sludge C as in

citric acid experiments. A small amount of Cu could be extracted from the sludge at

only 5 mol oxalic acid applications (Figure 5.28).

0100200300400500600700800


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.28 Cu extraction results vs. oxalic acid additions for Sludge C

77

In brief, it is questionably understood that organic acids are not effective for Cu

removal from Sludge C. In comparison of inorganic acid method with organic acids,

HF+HClO4 digestion method is very effective. Therefore, HF+HClO4 elutriation

method should be used for this purpose.

5.4 Results of Experimental Studies with Sludge D

Sludge D is a dewatered sludge originating from a metal industry, which is

different from the sources of Sludge A. The characteristics of Sludge D were given in

previous Chapter (see Table 4.4). Effects of organic acids (citric, oxalic, and acetic)

and inorganic acid (HF+HClO4) on several heavy metal extractions from sludge D

were investigated and results of these studies are discussed below. At this study,

acetic acid was also examined different from previous studies carried out with

Sludge A, B, and C.


Citric Acid Results

The following figure shows the effect of citric acid on Zn removal from Sludge D

(Figure 5.29). When comparing citric acid and HF+HClO4 digestion methods, citric

acid extraction application produced about eight times lower extraction efficiencies

than inorganic acid digestion method.

78

0

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2000

3000

40005000

6000

7000

8000

9000


Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.29 Zn extraction results vs. citric acid additions for Sludge D

Oxalic Acid Results

Figure 5.30 summarizes the experimental results of Zn removal from Sludge D

with different amounts of oxalic acid additions. At this application, almost the same

extraction efficiency was achieved with citric acid. Higher than 8 000 mg Zn was

extracted with HF+HClO4, while lower than 1 000 mg Zn could be only extracted

with oxalic acid additions.

79

0100020003000400050006000700080009000

10000


Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.30 Zn extraction results vs. oxalic acid additions for Sludge D

Acetic Acid Results

Figure 5.31 shows the results of experimental studies carried out with acetic acid

for Zn removal from Sludge D. The experimental results have demonstrated that the

acetic acid was not effective as in citric and oxalic acid applications. But, acetic acid

is most effective extraction reagent among the applied organic acids. Higher

extraction times for citric acid application gave better Zn extraction efficiencies at all

acetic acid additions.

80

0100020003000400050006000700080009000

10000

1 mol Ac 2 mol Ac 5 mol Ac HF+HClO4

Extraction Reagent

Ext

ract

ed Z

n (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.31 Zn extraction results vs. acetic acid additions for Sludge D

As a conclusion, organic acids application is not good alternative for Zn

extraction from Sludge D. Inorganic acid digestion method is the most ideal solution

for Zn removal from Sludge D.


Citric Acid Results

The following figure shows the obtained results from citric acid extraction studies

of Ni from Sludge D (Figure 5.32). The maximum extraction efficiency was

achieved with inorganic acid. Although increases in the extraction time and the

concentration of acid have led to increases in the efficiencies, very low extraction

performance was obtained with the citric acid additions.

81

0

20

40

60

80

100

120

140

160


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.32 Ni extraction results vs. citric acid additions for Sludge D

Oxalic Acid Results

Figure 5.33 depicts the results of experimental studies of Ni extractions with

various concentrations of oxalic acid for Sludge D. Increases in both the extraction

time and the oxalic acid concentration have led to increases in the efficiencies. But,

the highest extraction efficiency of oxalic acid is lower than the extraction efficiency

obtained with inorganic acid. As a result of the study, if oxalic acid is used for Ni

extraction, high amount of oxalic acid concentrations and high extraction time should

be chosen.

82

0

20

40

60

80

100

120

140

160


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.33 Ni extraction results vs. oxalic acid additions for Sludge D

Acetic Acid Results

Figure 5.25 depicts the results of experimental studies of Ni extractions with

various concentrations of acetic acid for Sludge D. Acetic acid additions gave more

successful results than HF+HClO4 reagent. Increasing removal efficiency was

obtained with the increasing extraction time.

0

50

100

150

200

250

300


Extraction Reagent

Ext

ract

ed N

i (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.34 Ni extraction results vs. acetic acid additions for Sludge D

83

As a result, among other organic acids and inorganic acid applications, acetic acid

gave higher extraction efficiency. Therefore, it could be preferred for removal of Ni

from Sludge D.


Citric Acid Results

Figure 5.35 summarizes the results of experimental studies of Cu removal with

different amounts of citric acid additions. From this figure, it is clearly seen that Cu

extraction with inorganic acid produced five times better results than citric acid

extraction for Sludge D. At all citric acid applications, 3 h of extraction time gave the

best result.

0

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100

150

200

250


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.35 Cu extraction results vs. citric acid additions for Sludge D

Oxalic Acid Results

As in citric acid addition, oxalic acid was not successful for Cu extraction from

Sludge D. The extraction efficiency of oxalic acid at applied conditions for Cu is

84

quite low as compare with inorganic acid application. HF+HClO4 digestion method

gave better result than oxalic acid additions like citric acid.

0

50

100

150

200

250


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.36 Cu extraction results vs. oxalic acid additions for Sludge D

Acetic Acid Results

Figure 5.37 summarizes the results of experimental studies of Cu removal with

different amounts of acetic acid additions. As in Ni extraction studies, acetic acid

gave the best results among organic acid applications. The maximum Cu extraction

was obtained at 3 h extraction time with 2 mol acetic acid addition (128 mg Cu/kg).

As a conclusion, HF+HClO4 digestion method is the best extraction method for

Cu removal from Sludge D. In the case of organic acids are preferred for this aim,

acetic acid should be choosen.

85

0

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150

200

250


Extraction Reagent

Ext

ract

ed C

u (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.37 Cu extraction results vs. acetic acid additions for Sludge D

5.4.4 Lead Extraction Studies

Citric Acid Results

Performances of citric acid on Pb removal form Sludge D are shown in Figure

5.38. Surprisingly, any effects of 1 mol citric acids and HF+HClO4 on Pb extractions

were detected at the applied experimental conditions. However, 2 mol and 5 mol

citric acid additions could be extracted Pb from Sludge D. It was not found any linear

relationship between the extraction time and the extraction efficiency at this

application. The highest Pb concentration was measured at 1 hour extraction time

with 5 mol citric acid addition (about 180 mg Pb/kg DS).

86

020406080

100120140160180200


Extraction Reagent

Ext

ract

ed P

b (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.38 Pb extraction results vs. citric acid additions for Sludge D

Oxalic Acid Results

The high concentrations of oxalic acid additions were more effective for Pb

extraction from Sludge D as it is seen from Figure 5.39. The highest performance

was obtained at 24 h of extraction time with 5 mol oxalic acid addition (135 mg

Pb/kg DS) and this result is lower than the maximum result obtained with citric acid.

It was not ascertained any linear relationship between the extraction time and the

extraction efficiency.

87

020

406080

100120

140160


Extraction Reagent

Ext

ract

ed P

b (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.39 Pb extraction results vs. oxalic acid additions for Sludge D

Acetic Acid Results

Figure 5.40 depicts the results of Pb extraction studies with various concentrations

of acetic acid for Sludge D. Acetic acid was very successful for Pb removal. The best

result (436 mg Pb/kg DS) was obtained at 72 h of extraction time with 1 mol acetic

acid addition.

050

100150200250300350400450500


Extraction Reagent

Ext

ract

ed P

b (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.40 Pb extraction results vs. acetic acid additions for Sludge D

88

As a result, organic acid is more succesfull extraction reagent comparing with

inorganic acid for Pb removal from Sludge D. It was found that, acetic acid is the

most effective acid among applied organic acids.


Citric Acid Results

The results of Fe extraction studies carried out with citric acid are given in Figure

5.41. The citric acid additions were not effective as HF+HClO4 as. Increases in

extraction time and acid concentration have led to enhancements in the efficiencies at

all citric acid concentrations. The most extraction efficiency was obtained at 72 h

extraction time with 5 mol citric acid addition (837 mg Fe/kg DS).

0

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1500

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2500


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.41 Fe extraction results vs. citric acid additions for Sludge D

Oxalic Acid Results

Although the oxalic acid additions gave similar results with citric acid for Fe

removal from Sludge D (Figure 5.42), the maximum Fe extraction efficiency

89

obtained with oxalic acid (657 mg Fe/kg DS) was lower than the maximum of citric

acid (837 mg Fe/kg DS).

0

500

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1500

2000

2500

1mol OA 2 mol OA 5 mol OA HF+HClO4Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.42 Fe extraction results vs. oxalic acid additions for Sludge D

Acetic Acid Results

The following figure shows the obtained results from 1 mol, 2 mol, and 5 mol

acetic acid extraction studies of Fe from Sludge D (Figure 5.43). The best extraction

efficiency was obtained at 72 h of extraction time with 1 mol acetic acid addition. It

is seen from this figure that increases in acetic acid concentration have decreased the

efficiency. Moreover, in some cases acetic acid affected the extraction efficiency

better than inorganic acid application.

90

0500

100015002000250030003500400045005000


Extraction Reagent

Ext

ract

ed F

e (m

g/kg

DM

)1 h3 h24 h72 h

Figure 5.43 Fe extraction results vs. acetic acid additions for Sludge D

In conclusion, acetic acid is the most suitable extraction reagent among the

examined acids for Fe extraction from Sludge D and it could be preferred rather than

citric, oxalic and HF+HClO4 application.

5.4.6 Cadmium Extraction Studies

Citric Acid Results

Similar to Pb extraction, HF+HClO4 digestion method was not responsible for Cd

extraction from Sludge D. However, citric acid is also effective at only three

experimental studies. The most efficient removal (3,55 mg Cd/kg DS) was achieved

at 1 hour extraction time with 5 mol citric acid, but at 72 h of extraction time with 1

mol acid gave comparable result with it.

91

0

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3

4


Extraction Reagent

Ext

ract

ed C

d (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.44 Cd extraction results vs. citric acid additions for Sludge D

Oxalic Acid Results

Figure 5.45 shows the results achieved with oxalic acid for Cd removal from

Sludge D. The highest result (6,35 mg Cd/kg DS) was achieved at 1 hour extraction

time with 2 mol oxalic acid.

0

1

2

3

4

5

6

7


Extraction Reagent

Ext

ract

ed C

d (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.45 Cd extraction results vs. oxalic acid additions for Sludge D

92

Acetic Acid Results

Acetic acid effects on the removal of Cd are shown in Figure 5.46. Particularly, in

the application of 1 mol acetic acid, the best extraction efficiencies were obtained.

The best Cd extraction (32 mg Cd/kg DS) with acetic acid was obtained at 72 h of

extraction time when 1 mol acetic acid was applied.

0

5

10

15

20

25

30

35


Extraction Reagent

Ext

ract

ed C

d (m

g/kg

DM

)

1 h3 h24 h72 h

Figure 5.46 Cd extraction results vs. acetic acid additions for Sludge D

In brief, the value obtained with acetic acid is about seven times more than citric

acid. 3,55 mg, 6,35 mg, and 32 mg Cd could be extracted with citric, oxalic, and

acetic acid application, respectively. Therefore, acetic acid should be preferred for

Cd removal from Sludge D.

5.5. Cost Analysis

The cost analyses of applied extraction methods were also performed. The costs

were calculated on unit dry matter of sludge and unit analysis.

93

The costs were calculated based on chemical material consumptions. The result of

this study will be useful to assess the potential value for application of extraction

processes at a full-scale plant.

Table 5.1 gives the cost analyses results and it is seen from the table that HF +

HClO4 digestion method is the most expensive method following by acetic acid,

oxalic acid, and citric acid addition. Veeken (1999) reported that inorganic acids and

complexing agents are not applicable on a practical scale due to the costs of the

process. The cost analyses of this study also confirm this result.

Table 5.1 Cost analysis of the extraction methods used this study.

Method Cost ($/kg DM) Cost ($/analysis)

HF + HClO4 560 0,28

Citric Acid 24 0,12

Oxalic Acid 32 0,16

Acetic Acid 48 0,24

94

CHAPTER SIX

CONCLUSIONS AND RECOMMENDATIONS

6.1. Conclusions

The aim of this study was to investigate the effects of inorganic and organic acids

on extraction of heavy metals from treatment plant sludges. For this purpose, four

different industrial sludges were taken from a dyestuff industry, two metal industries,

and an organized industrial district. After characterization of raw sludges, extraction

studies were carried out with inorganic acid (HF+HClO4) and organic acids (citric

acid, oxalic acid, and acetic acid). In extraction studies with organic acids, three

different concentrations of acids (1 mol, 2 mol, and 5 mol) and four extraction times

(1 h, 3 h, 24 h, and 72 h) were examined.

According to the experimental results, the conclusion remarks from this study

could be given as follows:

• Citric acid is more effective organic acid reagent than oxalic acid for Zn

removal from Sludge A. Besides, when comparing with inorganic acid results,

citric acid is shown up a successful reagent as well as HF + HClO4.

• Citric acid application is more successful than oxalic acid application for Cu

removal from Sludge A. Consequently, it could be made a preference between

citric acid and conventional method from the economical point view of in the

removal of Cu from Sludge A.

• The maximum Ni removal efficiency from Sludge A was achieved with HF +

HClO4 extraction reagent (1 820 mg Ni/kg DM). The experimental results have

demonstrated that the citric acid was also as effective as HF + HClO4 digestion

method.

• Oxalic acid is more effective than citric acid for iron removal form Sludge A.

However, HF + HClO4 digestion method is the most appropriate method for Fe

extraction; therefore, inorganic acid should be preferred rather than organic

acids.

95

• Citric acid could be priorly preferred to remove Zn from Sludge B. If it is not

suitable to use citric acid, HF + HClO4 digestion can be chosen. Oxalic acid is

ineffective extraction reagent for Zn removal from Sludge B.

• Organic acid extraction method at higher extraction reagent concentrations and

higher extraction time is more effectual than HF + HClO4 digestion.

Consequently, citric acid could be first chosen to remove Cu from Sludge B.

Oxalic acid additions could be also used for the same purpose; but, it is not

expected the results would be as successful as citric acid application.

• Citric acid and HF + HClO4 applications are more effective than oxalic acid for

Ni removal from Sludge B. Therefore, by considering economical feasibilities,

inorganic acid digestion or citric acid extraction should be used for this

purpose.

• When comparing the both organic acids with inorganic acid, the effects of

organic acids were rather low. Therefore, HF+HClO4 digestion method should

be used for the removal of Cr from Sludge B.

• Oxalic acid at high concentrations should be preferred instead of citric acid as

organic acid for Fe extraction from Sludge B. When oxalic acid is used for this

aim, low extraction time should be chosen.

• Citric acid is the most effectual reagent for Zn removal from Sludge C. Oxalic

acid did not exhibit similar performance on the Zn extraction for this sample. If

Zn removal is required for any sludge that will be stored either in a landfill or

agricultural usage, citric acid extraction method should be applied.

• For removing Ni from Sludge C, organic acids are not superior solution since

the inorganic acid (HF+HClO4) extraction is more sensible method for this

purpose.

• Cr extraction with organic acids from Sludge C is not reasonable. Anyhow, if

organic acids preferred, high extraction time should be required. But, the most

suitable method for this purpose is inorganic acid digestion.

• Organic acids, both citric and oxalic, or inorganic acid (HF+HClO4) should be

used for Fe extraction from Sludge C. In the case of organic acids are preferred

for this aim, higher acid concentrations and higher extraction times should be

applied.

96

• It is questionably understood that organic acids are not effective for Cu

removal from Sludge C. In comparison of inorganic acid method with organic

acids, HF+HClO4 digestion method is very effective. Therefore, HF+HClO4

elutriation method should be used for this purpose.

• Organic acids application is not good alternative for Zn extraction from Sludge

D. Inorganic acid digestion method is the most ideal solution for Zn removal

from Sludge D.

• Among other organic acids and inorganic acid applications, acetic acid gave

higher extraction efficiency. Therefore, it could be preferred for removal of Ni

from Sludge D.

• HF+HClO4 digestion method is the best extraction method for Cu removal

from Sludge D. In the case of organic acids are preferred for this aim, acetic

acid should be chosen.

• Organic acid is more successful extraction reagent comparing with inorganic

acid for Pb removal from Sludge D. It was found that, acetic acid is the most

effective acid among applied organic acids.

• Acetic acid is the most suitable extraction reagent among the examined acids

for Fe extraction from Sludge D and it could be preferred rather than citric,

oxalic and HF+HClO4 application.

• The value obtained with acetic acid is about seven times more than citric acid.

Therefore, acetic acid should be preferred for Cd removal from Sludge D.

• The estimation of cost of heavy metal extraction from sludge is a part of the

research. Depending on the calculations, HF+HClO4 application is more

expensive than organic acid applications.

6.2. Recommendations

• Extraction efficiencies of organic acids should also be monitored depending on

the temperature and pH.

• Heavy metal extraction studies will also be carried out in a larger scale plant

like pilot scale or full scale plant.

97

• As acetic acid was usually more successful reagent than citric acid and oxalic

acid and because acetic acid naturally occurs during anaerobic decomposition,

heavy metal removal may be investigated in an anaerobic stabilization of

sludge containing heavy metal.

98

REFERENCES

Acetic acid, (b.t.). Retrieved September 16, 2004, from

http://en.wikipeida.org/wiki/Acetic_acid.

Antoniadis, V. (1998). Heavy metal availability and mobility in sewage sludge-

treated soils. Retrieved December 21, 2004, from

www.aegean.gr/environment/antoniadis/PhD/phdab.pdf.

APHA, AWWA, WEF (1992). Standard Methods for the Examination of Water and

Wastewater. (18th ed.). Standart method.

Burgstaller, W., & Schinner, F. (1993). Leaching of metals with fungi, J. Biotechnol.

27, 91-116.

Chaney, R., & Ryan, J. (1993). Heavy metals and toxic organic pollutants in MSW

composts: Research results on phytoavailability, bioavailability, fate, etc. Science

and Engineering of Composting: Design, Environmental, Microbiological and

Utilization Aspects. 451-506. Ohio: Renaissance Publications.

Citric acid, (b.t.). Retrieved September 16, 2004, from

http://en.wikipeida.org/wiki/Citric_acid.

De Waaij, A. C., & Van Veen, H. J. (1990). Processing of Contaminated Sediments

in the Netherlands. Contaminated Soil '90, Third International KfK/TNO

Conference on Contaminated Soil. Dordrecht: Kluwer Academic Publishers.

Eckenfelder, Jr. W. W. (1989). Industrial water pollution control (2nd ed.). Mexico:

McGraw-Hill.

EPA, (1994). Land application of sewage sludge. Retrieved May 10, 2004, from

http://www.epa.gov/owm/mtb/biosolids/sludge.pdf.

99

Fuentes, A., Llorens, M., Saez, J., Soler, A., Aguilar, M. I., Ortuno, J. F., et al.

(2004). Simple and sequential extractions of heavy metals from different sewage

sludges. Chemosphere, 54, 1039-1047.

http://europa.eu.int/comm/environment/waste/sludge 2003

http://europa.eu.int/comm/environment/waste/sludge/index.htm

http://lancaster.unl.edu/factsheets/014.htm. Land Application of Wastewater Solids:

Is Sludge Safe? Barb Ogg, Extension Educator. Retrieved February 10, 2005

http://www.epa.gov/OCEPAterms/iterms.html. Terms of Environment. Retrieved

February 12, 2005, Last updated on Tuesday, January 6th, 2004.

http://www.lenntech.com. Water treatment & Air Purification. Sludge Treatment

Hutton, M., & Meeus, C., (2001). For and behalf of environmental resources

management, analysis and conclusions from Member States. Assessment of the

Risk to Health and the Environment from Cadmium in Fertilisers.

Ito, A., Umita, T., Aizawa, J., Takachi, T., & Morinaga, K. (2000). Removal of

heavy metals from anaerobically digested sewage sludge by a new chemical

method using ferric sulfate. Water Research, 34 (3), 751-758.

Kim, S. O., Moon, S. H., Kim, K. W., & Yun, S. T. (2002). Pilot scale study on the

ex situ electrokinetic removal of heavy metals from municipal wastewater

sludges. Water Research, 36, 4765-4774.

Lue-Hing, C. H., Zenz, D. R., & Kuchenrither, R. (Eds.). (1992). Municipal sewage

sludge management processing, utilization and disposal. Water Quality

Management Library, Vol. 4. Technomic Publishing Company.

100

Metcalf & Eddy, (1991). Design of facilities for the treatment and disposal of sludge.

Wastewater engineering, treatment, disposal, reuse (3rd ed.) (765-915).

Singapore: McGraw-Hill

Muse, J. K. (1991). Land application of sludge. Retrieved Junuary 11, 2005, from

http://www.aces.edu/department/crd/publications/ANR-607.html.

Official Gazete (1991). Legislations of Solid Waste Management. Date: 14.3.1991,

No: 20814.

Official Gazette (1995). Legislations of Hazardous Waste Management. Date: 27

Ağustos 1995, No: 22387.

Official Gazette (2001). Legislations of Soil Contamination Management. Date:

10.12.2001, No: 24609.

Oxalic acid, (b.t.). Retrieved September 16, 2004, from

http://en.wikipeida.org/wiki/Oxalic_acid.

Pandit, M., & Das, S. (1998). Sludge Disposal. Retrieved November 12, 2004, from

http://ewr.cee.vt.edu/environmental/teach/wtprimer/sldg/sldg.html#EPA.

Peters, R.W. (1999). Chelant extraction of heavy metals from contaminated soils.

Journal of Hazardous Materials, 66, 151-210.

Priestley, A. J. (b.t). Report on sewage sludge treatment and disposal -

environmental problems and research needs from an Australian perspective.

Retrieved Junuary 11, 2005, from

http://www.eidn.com.au/ukcsirosewagesludge.htm.

101

Reynolds, T. D., & Richards, P. A. (1995). Unit operations and processes in

environmnetal engineering (2nd ed.). Boston: PWS Publishing Company.

Ronald, A. T., & Robert, H. E. (1981). Heavy metals removal. Pretreatment of

industrial wastes manual of practice (89-108).

Scales, P.J., Lester, D., Dixon, D.R. (2001). Thickening. Spinosa, L. & Vesilind,

P.A., (Ed.). Sludge into Biosolids. Processing, Disposal, and Utilization (1st ed.)

(315-339). IWA Publishing.

Scancar, J., Milacic, R., Strazar, M., & Burica, O. (2000). Total metal concentrations

and partitioning of Cd, Cr, Cu, Fe, Ni and Zn in sewage sludge. The Science of

the Total Environment, 250, 9-19.

Schegel, H.G. (1993). General Microbiology. Cambridge: Cambridge University

Pres.

Sludge handling, (b.t). Retrieved November 15 2004, from

http://www.balticuniv.uu.se/swm/Lektion17/Moment17b.htmSludge.

Veeken, A. (2004). Remediation technologies for conversion of heavy metal polluted

organic wastes into compost Wageningen University, Wageningen, The

Netherlands.

Veeken, A. H. M., & Hamelers, H. V. M. (1999). Removal of heavy metals from

sewage sludge by extraction with organic acids. Water Science and Technology,

40, 129-136.

Vesilind, P. A. (1979). Treatment and disposal of wastewater sludges (Revised

Edition). Michigan: Ann Arbor Science

102

Vesilind, P.A., & Spinosa, L. (2001). Production and Regulations. Spinosa, L. &

Vesilind, P.A., (Ed.). Sludge into Biosolids. Processing, Disposal, and Utilization

(1st ed.) (3-18). IWA Publishing.

Wong, L. T. K., & Henry, J. G. (1988). Bacterial Leaching of Heavy Metals from

Anaerobically Digested Sludge. Biotreatment Systems, 3, Boca Raton: CRC Pres.

103

APPENDICES

Table A 1 The results of Zn extraction carried out with citric acid for Sludge A

Extracted Zn Concentration (mg/kg DM)

at different extraction times

Citric Acid

Concentration

for kg DM 1 h 3 h 24 h 72 h

1 mol CA 6 605 59 204 66 497 64 265

2 mol CA 62 202 60 702 67 658 70 762

5 mol CA 55 455 67 287 77 092 78 971

Table A 2 The results of Zn extraction carried out with oxalic acid for Sludge A



Oxalic Acid

Concentration


1 mol OA 51 363 4 773 4 836 4 827

2 mol OA 796 653 104 131

5 mol OA 1 799 1 244 154 22

Table A 3 The results of Ni extraction carried out with citric acid for Sludge A

Extracted Ni Concentration (mg/kg DM)


Citric Acid

Concentration


1 mol CA 465 1 547 1 608 1 673

2 mol CA 1 652 1 692 1 722 1 822

5 mol CA 1 345 1 415 1 455 1 706

104

Table A 4 The results of Ni extraction carried out with oxalic acid for Sludge A



Oxalic Acid

Concentration


1 mol OA 1 531 292 217 127

2 mol OA 160 118 23 21

5 mol OA 635 446 137 115

Table A 5 The results of Cu extraction carried out with citric acid for Sludge A

Extracted Cu Concentration (mg/kg DM)


Citric Acid

Concentration


1 mol CA 1,16 1,5 2,1 3

2 mol CA 7 4,9 5,4 4,4

5 mol CA 3,8 0,27 5,4 1,5

Table A 6 The results of Cu extraction carried out with oxalic acid for Sludge A



Oxalic Acid

Concentration


1 mol OA 4,7 - - -

2 mol OA - - - -

5 mol OA - - - -

105

Table A 7 The results of Fe extraction carried out with citric acid for Sludge A

Extracted Fe Concentration (mg/kg DM)


Citric Acid

Concentration


1 mol CA 6 733 3 200 3 683 4 200

2 mol CA 5 052 5 555 6 314 8 362

5 mol CA 7 591 7 516 6 388 15 211

Table A 8 The results of Fe extraction carried out with oxalic acid for Sludge A



Oxalic Acid

Concentration


1 mol OA 3 535 4 211 2 323 1 070

2 mol OA 8 487 10 274 9 122 7 112

5 mol OA 15 143 34 500 40 031 21 200

Table A 9 The results of Zn extraction carried out with citric acid for Sludge B



Citric Acid

Concentration


1 mol CA 18 564 18 167 16 413 9 810

2 mol CA 30 012 32 487 36 212 33 373

5 mol CA 36 723 41 469 51 410 4 898

106

Table A 10 The results of Zn extraction carried out with oxalic acid for Sludge B



Oxalic Acid

Concentration


1 mol OA 3 230 2 624 1 242 675

2 mol OA 15 767 16 500 10 435 3 844

5 mol OA 54 745 2 983 7 330 3 634

Table A 11 The results of Ni extraction carried out with citric acid for Sludge B



Citric Acid

Concentration


1 mol CA 107 130 156 156

2 mol CA 145 184 218 236

5 mol CA 190 241 285 130

Table A 12 The results of Ni extraction carried out with oxalic acid for Sludge B



Oxalic Acid

Concentration


1 mol OA 29 50 45 45

2 mol OA 114 105 87 72

5 mol OA 292 134 136 76

107

Table A 13 The results of Cu extraction carried out with citric acid for Sludge B



Citric Acid

Concentration


1 mol CA - - - -

2 mol CA - - - 96

5 mol CA 44 73 636 950

Table A 14 The results of Cu extraction carried out with oxalic acid for Sludge B



Oxalic Acid

Concentration


1 mol OA - - - -

2 mol OA 50 54 42 16

5 mol OA 52 82 565 460

Table A 15 The results of Cr extraction carried out with citric acid for Sludge B

Extracted Cr Concentration (mg/kg DM)


Citric Acid

Concentration


1 mol CA 119 112 107 100

2 mol CA 195 197 226 221

5 mol CA 180 253 305 140

108

Table A 16 The results of Cr extraction carried out with oxalic acid for Sludge B



Oxalic Acid

Concentration


1 mol OA - - - -

2 mol OA 9 7,8 6,3 3,1

5 mol OA 24 28 227 336

Table A 17 The results of Fe extraction carried out with citric acid for Sludge B



Citric Acid

Concentration


1 mol CA 14 378 17 436 16 652 19 825

2 mol CA 36 254 38 192 49 860 43 731

5 mol CA 61 453 49 906 63 718 52 517

Table A 18 The results of Fe extraction carried out with oxalic acid for Sludge B



Oxalic Acid

Concentration


1 mol OA 84 71 51 68

2 mol OA 13 000 17 363 1620 182

5 mol OA 80 511 68 792 63 500 63 817

109

Table A 19 The results of Zn extraction carried out with citric acid for Sludge C



Citric Acid

Concentration


1 mol CA 1 187 1 617 1 816 2 767

2 mol CA 1 690 3 183 7 535 11 134

5 mol CA 2 981 4 412 4 295 12 626

Table A 20 The results of Zn extraction carried out with oxalic acid for Sludge C



Oxalic Acid

Concentration


1 mol OA 1 515 1 314 250 320

2 mol OA 3 087 3 954 4 120 1 234

5 mol OA 3 587 1 803 4 503 583

Table A 21 The results of Ni extraction carried out with citric acid for Sludge C



Citric Acid

Concentration


1 mol CA 107 120 160 197

2 mol CA 147 194 257 251

5 mol CA 196 264 221 328

110

Table A 22 The results of Ni extraction carried out with oxalic acid for Sludge C



Oxalic Acid

Concentration


1 mol OA 100 103 40 27

2 mol OA 161 184 170 50

5 mol OA 201 215 227 81

Table A 23 The results of Cu extraction carried out with citric acid for Sludge C



Citric Acid

Concentration


1 mol CA - - - -

2 mol CA - - - 0,59

5 mol CA - - - 0,62

Table A 24 The results of Cu extraction carried out with oxalic acid for Sludge C



Oxalic Acid

Concentration


1 mol OA - -- - -

2 mol OA - - - 3,26

5 mol OA - - 13 62

111

Table A 25 The results of Cr extraction carried out with citric acid for Sludge C



Citric Acid

Concentration


1 mol CA 81 130 290 372

2 mol CA 112 295 606 704

5 mol CA 133 352 730 815

Table A 26 The results of Cr extraction carried out with oxalic acid for Sludge C



Oxalic Acid

Concentration


1 mol OA 83 66 43 70

2 mol OA 172 182 207 172

5 mol OA 238 366 690 760

Table A 27 The results of Fe extraction carried out with citric acid for Sludge C



Citric Acid

Concentration


1 mol CA 28 284 44 450 57 650 60 208

2 mol CA 50 000 45 492 56 576 75 412

5 mol CA 34 933 56 281 77 368 67 051

112

Table A 28 The results of Fe extraction carried out with oxalic acid for Sludge C



Oxalic Acid

Concentration


1 mol OA 25 400 15 863 5 571 1 621

2 mol OA 34 188 17 646 27 658 15 884

5 mol OA 27 700 30 594 71 377 92 045

Table A 29 The results of Zn extraction carried out with citric acid for Sludge D



Citric Acid

Concentration


1 mol CA 88 145 275 285

2 mol CA 103 177 390 520

5 mol CA 93 175 464 675

Table A 30 The results of Zn extraction carried out with oxalic acid for Sludge D



Oxalic Acid

Concentration


1 mol OA 125 133 146 163

2 mol OA 211 231 250 295

5 mol OA 249 336 526 624

113

Table A 31 The results of Zn extraction carried out with acetic acid for Sludge D



Acetic Acid

Concentration


1 mol Ac 540 798 1 920 2 585

2 mol Ac 586 938 1 778 2 085

5 mol Ac 680 1 130 1 570 1 868

Table A 32 The results of Ni extraction carried out with citric acid for Sludge D



Citric Acid

Concentration


1 mol CA 16 18 26 32

2 mol CA 27 29 39 57

5 mol CA 69 64 85 87

Table A 33 The results of Ni extraction carried out with oxalic acid for Sludge D



Oxalic Acid

Concentration


1 mol OA 15 18 19 21

2 mol OA 34 35 39 41

5 mol OA 68 78 97 105

114

Table A 34 The results of Ni extraction carried out with acetic acid for Sludge D



Acetic Acid

Concentration


1 mol Ac 88 106 152 222

2 mol Ac 97 104 158 241

5 mol Ac 106 132 157 259

Table A 35 The results of Cu extraction carried out with citric acid for Sludge D



Citric Acid

Concentration


1 mol CA 8 11 3 4

2 mol CA 8 24 8 10

5 mol CA 26 42 18 5

Table A 36 The results of Cu extraction carried out with oxalic acid for Sludge D



Oxalic Acid

Concentration


1 mol OA 15 18 3 6

2 mol OA 26 22 23 1

5 mol OA - - - 24

115

Table A 37 The results of Cu extraction carried out with acetic acid for Sludge D



Acetic Acid

Concentration


1 mol Ac 31 100 98 25

2 mol Ac 49 128 122 38

5 mol Ac 59 97 39 69

Table A 38 The results of Pb extraction carried out with citric acid for Sludge D

Extracted Pb Concentration (mg/kg DM)


Citric Acid

Concentration


1 mol CA - - - -

2 mol CA 24 105 - -

5 mol CA 178 49 90 114

Table A 39 The results of Pb extraction carried out with oxalic acid for Sludge D



Oxalic Acid

Concentration


1 mol OA 6 5 - 26

2 mol OA 54 39 - 16

5 mol OA 89 80 135 43

116

Table A 40 The results of Pb extraction carried out with acetic acid for Sludge D



Acetic Acid

Concentration


1 mol Ac 71 74 144 436

2 mol Ac 241 291 303 269

5 mol Ac 91 174 298 60

Table A 41 The results of Cd extraction carried out with citric acid for Sludge D

Extracted Cd Concentration (mg/kg DM)


Citric Acid

Concentration


1 mol CA - - - 3

2 mol CA 0,21 - - -

5 mol CA 3,55 - - -

Table A 42 The results of Cd extraction carried out with oxalic acid for Sludge D



Oxalic Acid

Concentration


1 mol OA 0,68 - - -

2 mol OA 6,35 - 0,67 -

5 mol OA - - - 5,54

117

Table A 43 The results of Cd extraction carried out with acetic acid for Sludge D



Acetic Acid

Concentration


1 mol Ac - - 11 32

2 mol Ac - 1,48 - -

5 mol Ac - 0,56 - -

Table A 44 The results of Fe extraction carried out with citric acid for Sludge D



Citric Acid

Concentration


1 mol CA 69 144 338 339

2 mol CA 85 140 478 680

5 mol CA 93 213 555 837

Table A 45 The results of Fe extraction carried out with oxalic acid for Sludge D



Oxalic Acid

Concentration


1 mol OA 102 96 123 97

2 mol OA 196 254 267 285

5 mol OA 236 342 576 657

118

Table A 46 The results of Fe extraction carried out with acetic acid for Sludge D



Acetic Acid

Concentration


1 mol Ac 194 504 2 213 4 438

2 mol Ac 468 853 2 193 2 805

5 mol Ac 486 1 033 577 44

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