Transcript
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
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