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5th European Water & Wastewater Management Conference

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PRESENTING A NEW WASTEWATER TREATMENT TECHNOLOGY BASED ON A CASE

STUDY OF A FULL-SCALE PLANT IN HUNGARY

Szilágyi, N.1,2, Kovács, R.1, Kenyeres, I.1, Csikor, Zs.2 1Organica Technologies, Hungary,

2 Budapest University of Technology and Economics, Hungary

Corresponding Author: Tel.: +3630-386-15-27 Email:

Abstract

Modern society is rapidly placing new demands on the wastewater treatment field, which has

changed little in the past several decades; included in these new demands is reducing footprint

and operational costs while increasing treatment efficiency. The technologies which suit these

requirements best are biofilm-based. In this paper a biofilm-based system is introduced based

on experiments conducted within a full-scale industrial plant treating the wastewater of a

cheese factory in Hungary. The results showed excellent performance; the technology provided

94.7% COD removal efficiency and 96.6% ammonia-N removal efficiency during the 118-day

monitoring campaign. Additionally, the total beneficial biomass quantity in the reactors was

much higher compared to conventional technologies; a biomass amount of 15-20 kg/m3 was

observed.

Keywords

biofilm technology, industrial wastewater, nitrogen removal, organic matter removal

Introduction

In the field of industrial wastewater treatment, anaerobic technologies are the most widely used

since these are more suitable for treating high organic matter loading rates. In general aerobic

systems are suitable for biodegradable COD concentrations lower than 1000 mg/l (Chan et al.

(2009)). However according to Cakir and Stenstrom (2005) there is a range in influent BOD5

concentration where anaerobic and aerobic technologies are both suitable.

In considering both aerobic and anaerobic treatment technologies, an increasing trend of

biofilm-based technologies is emerging. Biofilm-based systems have several advantages such as

smaller footprint, better process stability, enhanced sludge settleability, and in addition,

reduced solids loading on the secondary clarifier (Tchobanoglous et al, 2004). Moreover, in

biofilm-based technologies a significantly higher observable sludge residence time (SRT) can be

achieved compared to conventional treatment technologies such as activated sludge systems

(AS) (Shieh et al. 1981).

In this paper an aerobic biofilm-based wastewater treatment technology is introduced founded

on the operational experiences observed in a full-scale industrial plant. The examined

technology consists of aerobic reactors in series filled with biofilm carriers. The general

components of the reactors can be seen in Fig. 1. Plants are placed on the top of each reactor (1

– numbers are according to Fig. 1) with their roots (2) extending under the water level.

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Figure 1: General structure of a reactor

The plant roots functionas natural biofilm carriers. Into the deeper parts of the reactors where

plant roots do not grow, artificial carriers are installed (3) to mimic their function. The aeration

is provided by fine bubble diffusers. Due to the plants located on the top of the reactors the

whole system is enclosed in a greenhouse to maintain a minimum ambient air temperature.

The examined plant treats the wastewater of a cheese factory in Szarvas, Hungary. The COD

concentration of the wastewater is approximately 1000 mg/l, thus aerobic treatment is suitable

for this case.

Materials and methods

The full scale plant treating industrial wastewater of a cheese factory has been in operation

since 2008 as an activated sludge plant. The plant was upgraded to a biofilm-based technology

for performance enhancement.

Figure 2: The simplified process scheme of the wastewater treatment plant





The process scheme of the upgraded plant can be seen in Fig. 2. The influent water arrives to

the equalization basin (1 – numbers in brackets are according to Fig. 2.). From the equalization

basin the water is pumped (Robot Pumps RW2110DA-150, Robot Pumps B.V., The Netherlands)

to the physical-chemical pre-treatment unit (2) with aluminium-sulfate, lime and

polyelectrolyte. Leaving the pre-treatment unit, the water flows to the reactor cascade which

consists of eight biological reactors (3) in series. All reactors are aerated (blower type: Robuschi

Robox ES65/2P, Robuschi S.p.A., Italy) through fine bubble diffusers (Flygt Sanitaire 9”, ITT,

Sweden) (6). The first six tanks are equipped with specially-designed biofilm carriers (4) (inside

the reactors in addition to plants (5) on the top of each tank. The oxygen level was monitored in

situ in reactor 5 (OT). The biological reactor cascade is followed by a secondary clarifier (7). The

settled sludge is forwarded to the sludge treatment step, from where the leachate is directed

back to the first reactor stage for treatment. The effluent from the secondary clarifier is

disinfected (8) and then flows to the receiver. The physical and operational parameters of the

plant are represented in Tables 1 and 2.

Table 1: The physical parameters of the plant

Reactor V (m3) Carrier area (m2)

Reactor #1 67.5 537.6

Reactor #2 64 268.8

Reactor #3 63.6 268.8

Reactor #4 63.2 268.8

Reactor #5 62.7 268.8

Reactor #6 65.1 268.8

Reactor #7 60.4 -

Reactor #8 23.4 -

Table 2: The operational parameters of the plant

Parameter Value Unit

Influent flow 164 m3/d

Dissolved oxygen in reactors 2 mg/l

Temperature 26 °C

The monitoring campaign lasted for 118 days, during which the average temperature was 26°C.

The oxygen level was maintained at 2 mg/l in the reactors, and the air flow was controlled with

a frequency converter installed on the blower. The system was operated with no internal

recirculation since the effluent TN limit was 50 mg/l.

COD, TN, ammonia-N, nitrate-N and TSS were measured from the influent (after the physical

treatment), from each reactor stage and from the effluent (from the disinfection tank). COD





measurements were made according to DIN ISO 15705:2003 using tube tests from Macherey-

Nagel. TN, Ammonia-N and nitrate-N were measured using tube tests from Macherey-Nagel, the

results were evaluated photometrically. TSS was measured according to APHA (1997).

Results and discussion

Description of developed biofilm structure and biomass amount in reactors

The main elements of the technology are the installed artificial biofilm carriers. These carriers

provide especially good habitat for microbes to attach and form biofilm. Besides these artificial

carriers, plant roots are used as natural carriers. These natural carriers are the roots of the

plants located on the top of each reactor stage. Due to the special carrier structure, the

developed biofilm has a strikingly different structure than the commonly known biofilms (see

Fig. 3).

Figure 3: Structure of the dipped and taken out biofilm

The biofilms widely recognized in the industry have a compact structure. Contrarily, the biofilm

developed in this technology has a fluffy structure and is significantly thicker compared to other

biofilms. Due to these facts, a significantly higher biomass amount can be observed in the

biological reactors compared to that of conventional technologies (see Table 3).





Table 3: Biomass amount in different biofilm-based technologies

Technology Biomass amount (kg/m3) Reference

Conventional activated sludge max. 5 ATV (2000)

MBBR 3-4

4.9

Odegaard et al. (1999)

Li et al. (2011)

MBR

15

9.9-10.3

11

11.6

Melin et al. (2006)

Khan et al. (2011)

Sahar et al. (2011)

Delrue et al.(2011)

Presented technology 15-20 this paper

In the MBBR technology, a thin layer of biofilm can develop only in the inner part of the carriers,

due to the high shear stress caused on the moving carriers. The maximum achievable biomass

amount is in the same range as it is for conventional activated sludge systems. In MBR

technology a higher MLSS (mixed liquor suspended solids) concentration is also achievable, but

full-scale plants are operated in the range of 10-12 kg/m3 for different operational and

maintenance reasons. Using the presented technology a biomass amount of 15-20 kg/m3 is

achievable with no clogging problems or higher operational costs.

Evaluating overall performance

The wastewater treatment plant performance was well within the effluent limit parameters

after upgrading to the presented biofilm-based technology. Table 4 shows the effluent limits for

the plant and the average effluents.

Table 4: The effluent limits and the measured average effluent values

Parameter Effluent limit Measured effluent Unit

COD 75 44 mg/l

TN 50 20 mg/l

Ammonia-N 10 1.5 mg/l

TSS 50 40 mg/l

Taking into consideration all parameters, the average measured effluent was significantly below

the effluent limits.





Evaluating organic matter removal

The technology’s organic matter removal performance shows extremely good results. However

the influent COD was showing high fluctuations since the activity of the cheese factory was

varying, the effluent COD stayed constant and was always below the effluent limit (see Fig. 4).

Figure 4: The influent and effluent COD data with the effluent limit

The average influent COD was 844 ± 326 mg/l, while the effluent was 44 ± 11 mg/l. The results

showed that the available 2.8 days HRT was extremely high for this wastewater, demonstrated

by the fact that already at the 5th reactor the COD was below the effluent limit (see Fig. 5). This

means that a 1.9 days HRT was adequate to provide appropriate effluent in terms of COD.

Figure 5: COD profile through the reactor system

The data shows that the overall COD removal was 94.7%., while already a 94.6% removal was

achieved after the 5th stage.





Evaluating nitrogen removal

The technology also performed well in terms of nitrogen removal. The average effluent

ammonia-N was 1.5 mg/l.

Figure 6: Ammonia-N profile through the reactor system

Nitrification takes place mainly in the first four reactors. However, in the second reactor the

ammonia-N removal efficiency is 22%, however in the third reactor it reaches 55%. At the fourth

stage the ammonia-N concentration is 5 mg/l which is below the effluent limit and the removal

efficiency is already 88%. From this point on the ammonia-N concentration is below 2 mg/l, at

the end of the reactor train the overall removal efficiency was 96.6%. Based on these results it

can be concluded, that an HRT of 1.9 days is adequate for treating the wastewater of the cheese

factory.

Differentiation of microbe population through the reactor system

From the different degradation rates of COD and ammonia-N the differentiation of the microbial

population in each reactor stage can be deduced. The COD removal efficiency was already above

80% at the second stage, while the ammonia-N removal efficiency was only 20% (see Fig. 7); this

phenomenon indicates that the first two reactors are mainly responsible for organic matter

degradation, where autotrophic bacteria are outcompeted by the dominating heterotrophs.

From the third stage the ammonia-N removal efficiency increases, the autotrophic bacteria are

not outcompeted; since most of the readily biodegradable COD is consumed in the first two

reactors, heterotrophs cannot overgrow autotrophs.





Figure 7: Removal efficiencies for COD and ammonia-N

The differentiation of microbial population within the reactors is made possible by the fixed

biomass. With longer residence time in the reactors, the attached microbes can adapt to the

environment in the specific reactor stage, thus a population can develop which is most suitable

for the conditions in each stage.

Conclusions

A biofilm-based aerobic wastewater treatment technology was successfully implemented for a

full-scale industrial application. The performance of the plant was excellent, as all measured

parameters were much below the required effluent limit. In terms of COD the average effluent

concentration was 44 mg/l while the effluent limit is 75 mg/l. The COD removal efficiency was

94.7%. In terms of ammonia-N the effluent concentration was 1.5 mg/l, while the effluent limit

is 10 mg/l. The removal efficiency was 96.6%.

In each reactor stage a special microbial population developed according to the different

environmental conditions. In the first stages heterotrophic microbes dominate, while at the

later reactors autotrophs develop.

Besides for the more complex microbial ecology within the reactors, a completely new biofilm

structure developed on the biofilm carriers. Owing to the fluffy structure, a total biomass

amount of 15-20 kg/m3 could be achieved in the system which is 1.5-2 times higher compared to

conventional biofilm-based treatment technologies. Due to this fact, the technology has the

potential to allow for the design of wastewater treatment plants with a smaller footprint and

appropriate removal efficiency with no increased operational costs.

Acknowledgements

The authors thank the National Research and Development Office (NKTH) Hungary for financial

support (project IDs: TECH_08-A4/2-2008-0161; TET-09-1-2009-0014; KMOP-1.1.1-08/1-2008-

0049)





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