Solid waste Part-II

L-48SOLID WASTE MANAGEMENT PART-II

ENVIRONMENTAL ENGINEERING-II

HAZARDOUS WASTE : INTRODUCTION

Definition

Solid wastes are considered a hazardous waste if it exhibits one of the four characteristics

IGNITABILITY CORROSIVITY REACTIVITY TOXICITY

Ignitability

Ignitable wastes can create fires under certain conditions, are spontaneously combustible, or have a flash point less than 60 °C (140 °F).

Examples: waste oils and used solvents.

Corrosivity

Corrosive wastes are acids or bases (pH less than or equal to 2, or greater than or equal to 12.5) that are capable of corroding metal containers, such as storage tanks, drums, and barrels.

Example: Battery acid

Reactivity

Reactive wastes are unstable under "normal" conditions.

They can cause explosions, toxic fumes, gases, or vapors when heated, compressed, or mixed with water.

Examples : lithium-sulfur batteries and explosives.

Toxicity

Toxicity - Toxic wastes are harmful or fatal when ingested or absorbed (e.g., containing mercury, lead, etc.).

When toxic wastes are land disposed, contaminated liquid may leach from the waste and pollute ground water.

Toxicity is defined through a laboratory procedure called the Toxicity Characteristic Leaching Procedure (TCLP)

Examples: wastes containing heavy metals Pb, hg etc

STORAGE AND TRANSPORTATION

Indian scenario

MSWM is a major problem in Indian cities Average waste generated in India is 500

gram /person /day according to pollution control board(PCB 2000)

Typical rate of waste generation increase in India is 1.3% annually

Studies reveal that 90% of municipal wastes is disposed of unscientifically in open dumps.

Onsite storage

Storage of wastes before final disposal is done at three levels:

1) At sourceSolid wastes are often stored at the source in containers until they are picked up by waste collectors (collection crew) or taken out to be thrown into an open space or a community bin.

2) At community levelCommunity bins are used in crowded and narrow market areas, which is a common feature of most developing countries.

Because of the high cost of door to door collection many waste management authorities have introduced community bins.

3) At transfer stationsTransfer stations are established, for economic reasons in cities, which have long haulage distances to final disposal sites.

Smaller collection vehicles bring in the wastes collected at their source of generation or from the community bins and larger vehicles transport them away to final disposal sites.

Transfer stations are also used as collection and sorting points for recycling materials

Most of the collection systems followed in India are:

1) Door to door collectionThis system is used in narrow streets where a collection truck cannot reach individual houses.

The house places the filled containers outside their doors when the waste collectors arrive.

2) Curbside collectionThis method is used in wider streets, where the collection trucks can pass through conveniently.

The house owners leave the waste containers at the edge of the pavement.

The waste collectors collect the waste from the curbside or empty the containers into the vehicle as it passes through the street at a set time and day and return the containers.

3) Block collectionThe collection vehicles arrive at a particular place or a set day and time to collect waste from the households. Households bring their waste containers and empty directly into the vehicle.

4) Community binsCommunity storage bins are placed at convenient locations, where the community members carry their waste and throw it.

Community bins

Transport of solid waste

1. Autorikshaws :- these are 3 or 4 wheelers have covered bodies. Capacities are limited to ½ to ¾ tonnes are used for narrow localities where large vehicles can not go.

Small - collecting vehicles

2. Trailors

Capacity – 2 to 3 tonnesUsed for localities where trucks can not

goLoading is done manuallyThey are of tilting tipping type, hence

unloading can be done automatically.

3. Trucks

Capacity- 5 to 10 tonnesThey are of tilting tipping type so

unloading is automatic

Disposal of refuseRefuse or solid waste can be finally

disposed of by the following methods

1.Controlled tipping

2.Filling of low lying area (Land-filling)

3.Dumping into the sea

4.Pulverization

5.Incineration

6.Composting

1. Controlled tippingThis method is adopted where there is

adequate Land is available.Refuse is tipped in hollows of depth 1 to 2

m.Coarse material is tipped at the bottom while

fine material is tipped on the top surface.Tips are covered with soil so as to seal the

top surface.After 12 months decomposition is complete.Area of 0.3 to 0.5 m2/cap/yr is required

2. Filling of low lying area (LANDFILL)

A landfill is the place where we dispose our waste by burying them inside the earth.

It is the most common and oldest method to dispose our waste.

It is used to dispose hazardous as well as non –hazardous waste and solid municipal waste.

This kind of waste disposal is eco- friendly.

Garbage is dumped into low lying areas.

Dumping is done in the layers of 1-2 m and each layer is covered by thickness of good earth (0.2 m thick)

A rest of 2-3 weeks is given before dumping the second layer

Each layer is compacted

Land filling

Advantagesi. Simplest and economical

ii. No plant/ equipment are required

iii. Separation of solid waste is not required

iv. No byproducts are generated

v. Low lying area can be reclaimed

Disadvantages

i. Proper sites may not be available nearby

ii. Large land area are required

iii. Leachate problems in rainy season

iv. Leachate may pollute the ground water

3. INCINERATION:Incineration is the process of removal

of waste through thermal combustion.

Wastes are collected and burnt them in incinerators (boilers) at temperatures greater than 6000C

During burning, the heat is converted into energy.

Only thing we have to consider is during this process is there is a chance of release of some toxic substances during burning.

This method destroys the waste instead of disposing or storing it, and offers better solution.

Volume of waste reduces considerably.

Advantagesi. Most hygienic method

ii. No odour trouble or dust nuisance

iii. Heat generated can be used to generate power

iv. Lesser space required for disposal of residues

v. No effect of weather conditions.

vi. Can burn variety of refuses

vii. Clinker can be used in road construction

Disadvantages

1. Large initial cost

2. Problem of air pollution

3. Special attention shall be given to dispose residues

4. High stacks are needed to dispose flue gases.

4. Trenching This method is adopted when low lying aera is

not available. Trench size – length= 4 to 10 m, width =2 to

3 m and depth = 1 to 2 m Trenches are filled with refuse/garbage in the

layers of 15 cm. On the top of each layer 5 cm thick layer of

night soil or animal dung is placed in semi liquid form

On the top local soil is placed After 6 months compost is available for use.

5. Dumping into the seaSolid waste can also be disposed into the

sea.Waste has to be carried 15 to 20 km into

the sea.The depth at disposal point should not be

less than 30 mSolid waste may float on the top surface of

water.During stormy weather disposal is not

possible.

6. Pulverization

Dry refuse is pulverized to powdered form without changing its chemical form.

Powdered refuse can be used as manure.

Not commonly practiced in India.

7. COMPOSTING

COMPOSTING:Composting is the oldest form of solid

waste treatment method. The municipal waste consists of 50 – 60 % of organic matters.

These organic wastes are converted into usable forms by using micro organisms such as fungi, bacteria. The fungi or bacteria convert the organic waste into humus.

The humus is rich in carbon and nitrogen content, can be used as natural fertilizing medium for growing plants.

This method is cheap as well as safe.

performed by aerobic microorganisms;

decomposition of organic matter; (organic acids, amino acids, sacharides) occurs;

consuming of O2 and release of CO2 and energy;

high rate of composting process; temperature - up to 55-60° С.

I. First stage: active (thermophilic)

Decomposing of more complicated organic molecules;

Most of the microorganisms die from lаck of “food”; Lower rate of the process; Temperature - up to 40 - 45° С; Duration – few weeks

humification!

Waste appearance before and after composting process

II. Second stage: cooling

III. Third stage: maturation Temperature is equal to the ambient;

A completely disinfected high quality compost is formed as a result

1. Temperature Thermophilic (45 –750C) and Mesophillic (10-

450C). Above this temperature Microorganisms

inactivated or die off. Affected by its climatic surroundings and

method of aeration. In a windrow highest temperature reached in

centre, lower at edges.

Environmental Factors Affecting Composting

2. pHAnaerobic digestion the pH level covers a

narrow range (pH 6.5 to 7.5)Aerobic- pH so broad difficulties rarely

encountered with too high or too low pH in composting.

During the early stages the pH usually drops (down to about pH 5.0) because of organic acid formation.

3. Aeration (Anaerobic & Aerobic)Anaerobic: Advantages

a) minimisation of the loss of nitrogenb) less costly

Disadvantages include:a) Slowness of decompositionb) Absence of high temperaturesc) The presence of un-decomposed intermediatesd) The un-pre-processed appearance of the product

AerobicAerobic composting benefits from:

a) A rapid rate of degradation

b) Elevated temperature levels

c) Absence of putrefactive matter

Oxygen uptake reflects intensity of microbial activity.

4. Moisture ContentMoisture content and oxygen availability

are closely related If the moisture content of the mass is so

high as to displace the air from the interstices (voids between particles) anaerobic conditions will develop within the mass .

Woodchips, straw and hay can be as high as 75 to 80% whereas paper (upon becoming wet, collapses and forms mats) has a permissible moisture content of 55 to 60%.

5. Substrate

The waste (referred to as the substrate) should contain all necessary nutrients.

  Macronutrients Micronutrients Carbon (C) Cobalt (Co) Nitrogen (N) Manganese (Mn) Phosphorous (P) Manganese (Mg) Potassium (K) Copper (Cu)

Only available if they are in a form that can be assimilated by the microbes.

Certain groups of microbes have an enzymatic complex that permits them to attack, degrade and utilize the organic matter found in freshly generated waste.

Others can only utilize decomposition products (intermediates) as a source of nutrients.

Carbon: Nitrogen Ratio (C: N) The C: N ratio of the waste to be

composted is the most important factor that requires attention.

A large percentage of the carbon is oxidized to carbon dioxide by the microbes in their metabolic activities .

The C: N of the substrate should fall within the range of 20-25:1.

Mmicroorganisms such as bacteria and fungi grow best with the proper level of Carbon and Nitrogen.

METHODS OF COMPOSTING

1. Composting by trenching

Trench is 4 to 10 m long, 2 to 3 m wide, 0.7 to 1 m deep.

Trenches are filled with garbage/refuse layers of 15 cm thick.

On the top of each layer night soil/ animal dung is spread in semi liquid form.

On the top layer 10 cm thick local soil is laid

Within 2 to 3 days decomposition process starts.

Because of decomposition temperature raises up to 750C

Refuse gets stabilized after 4 to 5 months and turns brown in colour

Manure is sieved through 12.5 mm sieve to separate out stones, bricks etc

Sieved manure is applied to farms

2. Open windrow composting In India, 50-60% of municipal solid waste is

organic waste. Considering the climatic conditions and other

factors, composting of organic waste is excellently suited for India and Windrow composting is the best option to deal with the huge volume of bio-degradable waste.

Windrow composting is the available best model for stabilization of the biodegradable portion of the MSW.

Refuse is dumped on ground in the form of 0.6m to 1 m high, 6 m long and 1 to 2 m wide piles at about 60% moisture content.

Pile is covered with night soil, cow dung, cattle urine etc.

Temperature during process is 750C After this pile is reversed (turned up)Within 4-6 weeks compost/manure is

ready

Windrow turner

Static pile composting

3. Indore method Refuse, night soil, animal dung etc are

placed in small brick lined pit 3m x 3 m x 1 m deep in alternate layers of 7.5 cm to 10 cm height so as to take total height of 1.5 m

DDT or any other insecticide can be added to prevent flies breeding

The material is turned regularly for period of 8-12 weeks. Water is sprayed on dried material during overturning

Manure/compost is ready after 4 months

3 m

3 m

The advantages of this method are:

1. the process can be kept under control and runs smoothly, because the heap is turned regularly;

2.compost is produced in a short time.Disadvantages of this method are:

1. it requires much water;

2. it is very labour intensive.

4. Bangalore method In Bangalore method refuse is stabilized

anaerobically.Earthen trenches of size 10m x 1.5m x

1.5m deep are filled up in alternate layers of refuse and night soil or animal dung.

The material is covered up with 15 cm layer of good earth and left for decomposition for 4-5 months.

The compost is ready after 4-5 months

10 m

1.5 m

1.5 m

1.5 m

The major advantages of the Bangalore Method are:

1.a saving of water;

2. it requires less labour, because the heap is not turned over during the decomposition process.

Disadvantages of the Bangalore Method are:

1. more disease germs and weed seeds survive due to the temperature during decomposition;

2. the decomposition process is more difficult to control because the heap has to be kept continually covered;

3. it is a less suitable method for those with little or no experience in composting.

5. Mechanical composting Indore and Bangalore methods are suitable

for small cities and towns to decompose the garbage.

Mechanical compost plants of 200 tonnes/day and above capacity have been made for converting the city waste into compost.

Before that, the non compostable material such as bricks, stones, iron pieces, broken glass pieces, rubber, plastics etc. are removed.

Advantages of composting

Reduces mass and volume

- lower hauling costs

• Reduces odour

• Pathogens are destroyed

• Kills weed seeds

• Improves transportability as volume gets reduced

• Good Soil conditioner

• Improves nutrient qualities

- the nutrients from compost are

released slowly and steadily

• Decreases pollutants

- stabilizes the volatile nitrogen into

large protein particles, reducing losses

• Land application when convenient

Saleable product

• Increases water retention of soil

Disadvantages

• Loss of ammonia (N)• Time and labour involved• More Cost of equipment (initial and

operating)• Land required for composting• Marketing required for sale

Theory QuestionsQ1. Explain theory of composting.

Q2. Enlist different methods of composting and explain any one method in detail.

Q3. Discuss factors affecting composting process.

Q4. What are advantages and disadvantages of composting?

Q5. Draw a neat sketch of ‘Landfill’.

Q6. Write short notes on

1. Landfill

2. Effects of solid waste on human and environment

3. Bangalore method of composting

4. Indore method of composting 5. Incineration of MSW