UNIT IV

Part A(2 Marks)

1. What do you understand by the processing of waste?[N/D-16A/M-15]

Any method, system, or other means designated to change the physical form or chemical content of solid wastes.

2. Write the merits and demertits of Incineration.[N/D-16,A/M-15]

Merits There are a number of advantages to using incineration as a waste management method. Two of the primary advantages of incineration are that waste volumes are reduced by an estimated of 80-95%, and the need for land and landfill space is greatly reduced². For urban areas, this can be especially important, as urban land is often at a premium. Demerits Smoke and ash emitted by the chimneys of incinerators include acid gases, nitrogen oxide, heavy metals, particulates, and dioxin, which is a carcinogen. While incineration pollution control technology is evolving to reduce these pollutants, it has been found that even with controls in place, some remaining dioxin still enters the atmosphere 3. What are the four main ways to treat organic biodegradable waste?

[A/M-17]

Composting, aerobic digestion, anaerobic digestion and Incineration

4. What is Municipal solid waste composting? [A/M-17,N/D-10]

Composting is the biochemical degradation of organic fraction of the solid waste material into a stable, humus-like end product under controlled conditions. This humus-like end product is called compost and is primarily used for soil conditioning. Bacterial decomposition of municipal solid waste may be accomplished either aerobically or anaerobically but since anaerobic processes are extremely slow and offensive odours associated with these processes may be difficult to control, most composting operations are aerobic. 5. Mention the process parameters of composting? [N/D-11,M/J-10] 1. Particle size 2. Seeding 3. Mixing/turning 4. Air requirements 5. Moisture content 6. Temperature

control 7. C/N ratio 8. pH 9. Heat evolution 10. RQ, respiratory quotient

6. Define in-vessel composting? [N/D-11] In-vessel composting uses a completely enclosed system to treat feedstock materials, control odours

and optimise compost processing conditions. In-vessel composting systems can consist of metal or plastic tanks or concrete bunkers in which air flow and temperature can be controlled, using the principles of a "bioreactor". Generally the air circulation is metered in via buried tubes that allow fresh air to be injected under pressure, with the exhaust being extracted through a biofilter, with temperature and moisture conditions monitored using probes in the mass to allow maintenance of optimum aerobic decomposition conditions.

7. What are the off-site processes? [A/M-13,N/D-12] The off-site processes of solid waste are 1. Incineration 2.Pyrolysis 3.Composting 4. Anaerobic digestion

5.Incineration-pyrolysis (Purox system)

8. List any four recoverable products from off-site processing of solid waste? [A/M-13,N/D-10]

1. Compost, a rich bio-manure from composting process 2. Heat recovery from Incineration 3. Methane from pyrolysis and purox system

Part B(16Marks)

1. (a)Describe the incineration Technologies and air emissions and its Control in detaiL (16)

[N/D-16,A/M-17,N/D-10]

Combustion products and residues:

2. (b)Write briefly about the composting facilities and various types of composting techniques.(16)[N/D-16,A/M-17,A/M-13] Composting is the biochemical degradation of organic fraction of the solid waste material into a

stable, humus-like end product under controlled conditions. This humus-like end product is called

compost and is primarily used for soil conditioning. Bacterial decomposition of municipal solid waste

may be accomplished either aerobically or anaerobically but since anaerobic processes are extremely

slow and offensive odours associated with these processes may be difficult to control, most

composting operations are aerobic.

The organic fraction of most municipal solid wastes can be classified as follows:

1. Water-soluble constituents, a group which includes sugars, starches, amino-acids, and various

organic acids.

2. Hemicellulose, a condensation product of five and six carbon sugars.

3. Cellulose, a condensation product of six carbon sugars, glucose.

4. Fats, oils and waxes, which are esters of alcohols and higher fatty acids.

5. Lignin. a material the exact chemical nature of which is still not known (present in some paper

products such as newsprint and fibreboard)

6. Lignocellulose, a combination of lignin and cellulose.

7. Proteins, which are composed of chains of amino acids.

If these materials are subjected to bacterial decomposition, the end product remaining after

dissimilatory and assimilatory bacterial activity is called humus. Most composting operations consist of

three basic steps, preparation of the solid wastes, decomposition of the solid wastes and product

preparation and marketing.

1. Receiving, sorting, separation of organic fraction, size reduction and moisture & nutrient

addition are part of preparation.

2. To accomplish decomposition step, several techniques and methods have been developed.

(eg. Windrow method, aerated static pile, In-vessel and vermicomposting)

3. Product preparation and marketing include fine grinding, blending with various additives,

granulation, bagging, storage, shipping and in some cases direct marketing.

The entire process involving both the seperation and the bacterial conversion of the organic solid

wastes is known as composting.

"Typical process flow diagram of composting process"

Although they are extremely diverse, the principal microorganisms involved in the aerobic

decomposition of solid wastes can be identified as bacteria, fungi, yeasts and actinomycetes. While

members of each of these groups can be found that are capable of decomposing all the raw materials

in solid wastes, as a group they prefer different compounds. Typically, bacteria prefer simple water-

soluble sugars, while fungi, yeasts and actinomycetes are particularly effective in the decomposition of

cellulose and hemicelluloses.

Initially, the material being composted heats up as a result of the release of energy accompanying

the degradation of the readily convertible organic food wastes and simple sugars. When the

temperature rises above 20oC, the mesophilic organisms begin to predominate. These organisms will

predominate upto about 45oC, after which the thermophils grow and dominate. The temperature of the

compost may reach 70oC due to thermophils wherein most pathogens are destroyed (ie. if maintained

at 70oC for 24 hours). Once the substrate becomes limiting, the temperature once again falls down to

mesophilic range, a stage called curing of compost.

In windrow composting, prepared solid wastes are placed in windrows in an open field. The

windrows are turned once or twice per week for a composting period of about 5 weeks. The material is

usually cured for an additional 2 to 4 weeks to ensure complete stabilization, a process called curing.

By controlling the operation carefully in a mechanical system, it is possible to produce a humus within

5 to 7 days in a controlled environment but it is often followed up by curing in open windrows for an

additional period of 3 weeks. Once the solid waste have been converted into humus like material, they

are ready for the third step of product preparation and marketing.

3.Explain the classification of composting technologies and discuss briefly the basic steps involved in the composting practise.[N/D-11,A/M-14,A/M-15]

The various classification of composting are 1. Windrow composting 2. Static pile composting 3. In-vessel Composing 4. Vermicomposting

4.Explain about Explain about In-vessel composting and vermin- composting. [N/D-12,A/M-13,N/D-14] In-vessel composting generally describes a group of methods that which confine the composting materials within a building, container, or vessel. In-vessel composting systems can consist of metal or

plastic tanks or concrete bunkers in which air flow and temperature can be controlled, using the principles of a "bioreactor". Generally the air circulation is metered in via buried tubes that allow fresh air to be injected under pressure, with the exhaust being extracted through a biofilter, with temperature and moisture conditions monitored using probes in the mass to allow maintenance of optimum aerobic decomposition conditions. This technique is generally used for municipal scale organic waste processing, including final treatment of sewage biosolids, to a safe stable state for reclamation as a soil amendment. Offensive odors are caused by putrefaction (anaerobic decomposition) of nitrogenous animal and vegetable matter gassing off as ammonia. This is controlled with a higher carbon to nitrogen ratio, or increased aeration by ventilation, and use of a coarser grade of carbon material to allow better air circulation. Prevention and capture of any gases naturally occurring (volatile organic compounds) during the hot aerobic composting involved is the objective of the biofilter, and as the filtering material saturates over time, it can be used in the composting process and replaced with fresh material. In-vessel composting is a vital tool in the management of BMW(Biodegradable Municipal Waste). It uses a completely enclosed system to treat feedstock materials, control odours and optimise compost processing conditions. By source separating BMW into garden and kitchen wastes, and utilising natural composting process, the biodegradable waste can be reduced in weight by up to 50% and converted into a soil conditioner rich in nutrients and humus. The technique of in-vessel composting occurs within a contained vessel. This technique allows the operator to maintain close control over the process. Other advantages of this technique compared to other composting techniques are: the effects of weather are diminished, the quality of the resulting product is more consistent, less manpower is required to operate the system and public acceptance of the facility may be better. In addition, due to the smaller space requirement, in-vessel technology is more suitable in suburban and urban technologies compared to the other composting technologies. In addition, the in-vessel system allows for detailed containment and treatment of air to remove odors before release. Disadvantages of this technique are that it is generally more costly than the other methods, particularly with respect to capital expenditures. The higher level of mechanization with this technique also results in more maintenance requirements which increases operational costs.

Vermicomposting: Vermicompost is the product or process of composting using various worms, usually red wigglers, white worms, and other earthworms to create a heterogeneous mixture of decomposing vegetable or food waste, bedding materials, and vermicast. Vermicast, also called worm castings, worm humus or worm manure, is the end-product of the breakdown of organic matter by an earthworm. These castings have been shown to contain reduced levels of contaminants and a higher saturation of

nutrients than do organic materials before vermicomposting. Containing water-soluble nutrients, vermicompost is an excellent, nutrient-rich organic fertilizer and soil conditioner. This process of producing vermicompost is called vermicomposting. Composting is the only the first step in the process of breaking down organic matter. Earthworms finish this process. By feeding on the microrganisms which feed on organic waste, earthworms convert “garbage” into a nutrient rich substance which provides many benefits to plants. Through vermicomposting we contribute to soil preservation and waste reduction.Vermicomposting involves mixing a bedding substance, such as shredded newspaper, peat moss, coir, or composted manure, a small amount of soil, organic matter, and moisture. Once added, the worms will need to be fed organic matter. Unlike your family dog, worms don't need everyday feeding, and in fact less is often better.Over a short period of time (usually 2 – 3 months) the worms will break down the organic matter in the vermicomposting unit, and leave behind nutrient rich "castings". These castings are the best imaginable soil amendment for your plants, but worms cannot tolerate too high a concentration of castings. After this period of time the worms will need to be transferred to fresh bedding, and you will be able to harvest a bin full of "Black Gold"

Advantages of vermicompost include enriching soil, increasing harvest yields and suppressing plant disease. 1.Vermicompost is superior to most composts as an inoculant in the production of compost. 2.Worms have a number of other possible uses on farms, including value asa high-quality animal feed. 3.It restores microbial population which includes nitrogen fixers, phosphate solubilizers etc. 4.Provides major and micro- nutrients to the plants. 5. Improves soil texture and water holding capacity of the soil. 6. Provides good aeration to soil, thereby improving root growth and proliferation of beneficial soil microorganisms. 7. Decreases the use of pesticides for controlling plant pathogens. 8. Improves structural stability of the soil, thereby preventing soil erosion. 9. Enhances the quality of grains/ fruits due to increased sugar content. Disadvantages: 1. Ratios Between Waste and Time: Vermicomposting requires waste to be applied in thin layers because of temperature concerns. If you

apply too much waste to the bin in a short amount of time, the temperature will rise too fast and kill off the worms. Large quantities of waste must be spread out over large areas of ground to maintain the correct temperature. 2. Temperature Limits: Vermicomposting requires a low temperature to be maintained in the compost operation so the worms do not lose moisture and dry out. The normal temperature for vermicomposting is between 55 and 80 degrees F. 3. Care: Vermicomposting requires greater care than regular composting methods. The worms used in vermicomposting require care, food, heat and moisture at proper levels to remain healthy and create the compost material. It requires more space because worms are surface feeders and won’t operate in material more than a meter in depth. It is more vulnerable to environmental pressures, such as temperature, freezing conditions and drought. 4. Cost: Vermicomposting is more expensive to set up than regular compost piles or batch composters. Vermicomposting needs special materials to start, such as plastic or metal containers and red worms. Regular composting requires nothing but a hill or barrel to start. Vermicomposting also requires lime to stabilize the acid levels created by the waste in the new soil. 5. Size Scales: Vermicomposting requires more space than regular composting. Eventually, you will need several bins to get the same compost yield as you would from one traditional composting bin. 6. Concerns: Vermicomposting does not destroy any weed seeds which may have entered the bedding area with the food supply. There is not enough evidence to show that pathogens would be destroyed if large amounts of pathogens are present in organic material. Bedding must be provided that allows the worms to breed away from their food.

5. Write short notes on (i) Shredding and pulverizing: [N/D-12,A/M-14]

There are four types of shredders used for the shredding or pulverizing of solid waste: hammermills, drum pulverizers, crushers, and wet pulverizers. Each type of equipment has a variety of designs, advantages, and disadvantages. Major considerations in selecting a shredder are its capacity, speed, power requirements, maintenance needs, ability to produce the end product desired, and, most important, reliability. These characteristics will differ significantly for various types of solid waste and differing end products. In choosing a type and particular design of a shredder, it is desirable to obtain information on the performance of the shredder in circumstances similar to those for which the machine is to be used.