INTEGRATED SOLID WASTE MANAGEMENT

One of the frustrating problems confronting environmental scientists and environmental engineers lies in trying to determine the characteristics of solid wastes. Solid wastes are simply solid materials that have lost value for their owner and are discarded. It does not mean that the solid wastes being discarded have no value. It simply means that the solid wastes have no value for the current owner. It may well have value for another owner. If the solid wastes have value for a new owner, these materials are no longer solid wastes, but rather raw materials for further use with renewed value until the new owner decides to discard them as solid wastes. All material goods that society makes and uses will become solid wastes in time.

Solid wastes cannot be characterized by their chemical composition or their size or their weight alone. Solid wastes are characterized by many parameters. Chemical composition is an important parameter, along with size and weight. Bio-stability is also an important parameter for solid wastes that has largely been ignored. Bio-stability is the parameter that defines how the solid waste materials react to microorganisms and the rate of that reaction. Most solid wastes currently being produced are largely bio-stable, showing little to no reaction with microorganisms. Food wastes are the least bio-stable solid wastes, undergoing rapid reaction with microorganisms. Grass clippings and leaves are seasonal solid wastes that are not very bio-stable. From a practical point of view environmental microbiologists are only interested in the solid wastes having the least bio-stability.

There are many ways to characterize solid wastes. No one classification is perfect. Classifications tend to start with the major sources of solid wastes.

A. SOLID WASTE TYPES

Source	Typical waste generators	Types of solid wastes
Residential	Single and multifamily dwellings	Food wastes, paper, cardboard, plastics, textiles, leather, yard wastes, wood, glass, metals, ashes, special wastes (e.g., bulky items, consumer electronics, white goods, batteries, oil, tires), and household hazardous wastes.).
Industrial	Light and heavy manufacturing, fabrication, construction sites, power and chemical plants.	Housekeeping wastes, packaging, food wastes, construction and demolition materials, hazardous wastes, ashes, special wastes.
Commercial	Stores, hotels, restaurants, markets, office buildings, etc.	Paper, cardboard, plastics, wood, food wastes, glass, metals, special wastes, hazardous wastes.
Institutional	Schools, hospitals, prisons, government centers.	Same as commercial.
Construction and demolition	New construction sites, road repair, renovation sites, demolition of buildings	Wood, steel, concrete, dirt, etc.
Municipal services	Street cleaning, landscaping, parks, beaches, other recreational areas, water and wastewater treatment plants.	Street sweepings; landscape and tree trimmings; general wastes from parks, beaches, and other recreational areas; sludge.
Process (manufacturing, etc.)	Heavy and light manufacturing, refineries, chemical plants, power plants, mineral extraction and processing.	Industrial process wastes, scrap materials, off-specification products, slay tailings.
Agriculture	Crops, orchards, vineyards, dairies, feedlots, farms.	Spoiled food wastes, agricultural wastes, hazardous wastes (e.g., pesticides).

Municipal solid wastes

Municipal solid wastes include the residential SW, the commercial SW, institutional SW and limited industrial SW generated within the municipality Table 1. Examination of the different groups of municipal solid wastes indicates that glass and plastics are the most biostable with metals being relatively biostable. Paper, wood, rubber, leather and textiles are slowly biodegradable under specific conditions. Food wastes and yard wastes are biodegradable. One of the key parameters for biodegradability is moisture content. Food wastes contain up to 80% moisture, averaging about 70% moisture. Yard wastes average about 60% moisture with grass clippings having the most moisture and dead branches having the least moisture. Paper and cardboard normally contain less than 10% moisture. Wood can contain up to 40% moisture. Rubber, leather, and textiles usually contain less than 10% moisture. These materials are not biodegradable without the addition of water to increase their moisture level. Dry metal objects are bio-stable except in the presence of water. Microorganisms can slowly react with wet metal products, if the end products of the microbial-metal reactions are not toxic to the microorganisms. Glass and plastics have very low moisture content and are bio-stable even when immersed in water. For the most part municipal solid wastes reflect the lifestyle of the people within the municipality and the changes in the local economy.

Table 1: General Composition of Municipal Solid Wastes

Paper 7.4%

Yard Waste 2.0%

Plastics 10.7%

Food Wastes 11.2%

Metals 7.8%

Rubber, Leather, and Textiles 6.7%

Glass 5.5%

Wood 5.5%

Other 3.2%

Industrial solid wastes

Industrial solid wastes consist of hazardous solid wastes and non-hazardous solid wastes. The hazardous solid wastes are dangerous for the environment and are controlled by separate federal legislation than the non-hazardous solid wastes. The characteristics of industrial solid wastes are highly variable, depending upon the specific industrial processes and the workers within specific plants. Industrial solid wastes range from inorganic materials to organic materials.

Construction and demolition solid wastes

The construction of new houses and new commercial buildings results in the production of construction solid wastes in direct proportion to the materials employed in the construction project. The characteristics of the construction solid wastes will vary with each project. Normally, construction wastes will include the residual materials that could not be incorporated into the finished building. The construction of houses will include pieces of wood, wallboard fragments, partial shingles, and excess roofing paper. If the house has a cinder block foundation and/or a brick front, broken cinder blocks and broken bricks will also be included. The amounts of construction wastes produced are directly proportional to the number of houses and buildings constructed. As a net result, the construction waste quantities and characteristics are highly variable and not easily estimated.

Street sweepings

The quantity of street sweepings collected is a function of the size of the city and the rainfall characteristics. Large cities produce more street sweepings than small cities. The close examination of street sweepings indicates they are composed of dirt, sand, grit, paper products of various types, plastic materials, broken glass, rubber particles, and miscellaneous materials too difficult to identify and measure. Most of the street sweepings are relatively inert material that can be used as fill or placed into a sanitary landfill. One of the problems with street sweepers is their tendency to suspend fine particles around the street sweeper rather than capturing the fine particles. There are no uniform analyses for street sweepings. Every community must determine its own characteristics of street sweeping wastes, both as to quantities produced and their chemical characteristics.

Water and waste water sludge

Every community that has a water treatment plant and/or a wastewater treatment plant will have water treatment sludge and/or wastewater treatment sludge. The water treatment plants generate preliminary sludge, alum sludge and calcium carbonate sludge. The characteristics of water treatment plant sludge are quite similar from plant to plant as far as chemical characteristics are concerned. The quantity of sludge produced varies with the magnitude of treatment required to remove the contaminants. Alum treatment of surface water produces an aluminum hydroxide floe that removes the suspended solids in the water. Water plants that soften the water will produce calcium carbonate sludge. A few plants may produce magnesium hydroxide in addition to the calcium carbonate. Wastewater treatment plants produce screenings and grit in addition to the sludge generated every day. Most plants collect the screenings and dispose of them with the other municipal solid wastes. Grit is largely sand and dense organic particles. Wastewater treatment plants handling large quantities of industrial wastes will produce even more excess sludge. The activated sludge generated is quit biodegradable and contains many pathogenic microbes.

Agricultural solid wastes

Farms produce large quantities of solid wastes. The quantities of solid wastes produced are a function of the specific crops grown on the farm. Farmers have long recognized that manure from farm animals and crop residues after harvest must be returned to the land to help maintain the soil quality for future crop production. Farmers are among the oldest of the recyclers in our society. The residue left by farmers after processing the crop plants like wheat, grasses, pesticides, fertilizers and many other products. Synthetic fertilizers and pesticides are more harmful than any other waste generated from agriculture. However most of the waste thus generated is highly biodegradable which can be used to make manure for recycling.

B. IMPACT OF SOLID WASTE

The Impact of solid waste in human health due to improper management and handling is one of the main emerging problems of today in urban areas. Besides environmental pollution, it has many adverse impacts on human beings.

The main risks to human health arise from the breeding of disease vectors primarily flies and rats. A common transmission route of bacillary dysentery, amoebic dysentery and diarrhoeal disease is from human faecal matter by flies to food or water and thence to humans. It has been estimated that in warm climates exposed garbage produces as many as 70,000 flies per 0.03 m3 in a week.

The refuse dumps also serve as a source of food for the rats and small rodents which quickly proliferate and spread to neighboring areas. Rats destroy property, infect by direct bite and spread various diseases like plague, endemic typhus, Salmonellosis, trichinosis etc. Apart from the diseases for which insects and rats are carriers, the handling and transfer of biological wastes pose a threat to the worker and those he contacts. Disease transmission may occur through direct contact with the waste, through infection of open sores or through vectors.

The hazardous wastes are injurious to human health: some have acute effects while others pose a health hazard after prolonged period of exposure. Improper disposal of such wastes has resulted in the death of humans and animals through contamination of crops and waters supplies.

The environmental damage caused by solid wastes is mostly aesthetic in nature. Uncontrolled dumping of urban wastes destroys the beauty of countryside: also there is the danger of water pollution when the leachate from the refuse dump enters surface water or ground water resources. In addition uncontrolled burning of open dumps can cause firing and air pollution.

Solid waste disposal is at present limited to land and surface water in contest to our country. Therefore besides its impact on our health it also degrades soil and may cause loss of fertile soil during surface runoff. Dumping at hill side may cause erosion of land.

C. SOLID WASTE MANAGEMENT

Effective solid waste management is more than just cleaning the streets or collecting waste and dumping of the collected waste, as practiced by most municipalities. It requires efficient combination of various components of solid waste management in an integrated manner. Integrated solid waste management is therefore a process of optimizing the waste management system as a whole with application of a variety of suitable technologies. This includes the following activities:

• Reduction of the amount of waste generated


• Proper segregation and storage of waste at source


• Efficient waste collection


• Street sweeping


• Waste transfer from preliminary collection vehicles to haulage vehicles/Transportation of waste


• Waste composting and recycling


• Hazardous waste management


• Public education and participation


• Formulation and enforcement of policies and regulations


• Organizational and Financial management

The management of waste comprises various stages which are given as:-

1. Collection

2. Transfer

3. Disposal

4. Potential methods of disposal and recycling

1. COLLECTION METHODS

Proper collection and transportation processes are essentials part of solid waste management system. Nearly 70-80% of total cost is required for collection and transportation of waste. Therefore, properly designed and executed waste collection systems can result in significant savings and reduction in environmental and public health risks. The following issues generally need to be considered in designing a waste collection system:

• Containerization and on-site storage of waste


• Source separation


• Collection mechanism (roadside collection, door-to-door collection, communal containers, on-time collection etc.)


• Time of collection


• Type of vehicles used for collection


• Frequency of collection


• Route planning


• No. of staff used for collection


• Special collection for bulk waste generators


• Separate collection for special waste such as medical waste and household hazardous waste


• Transfer of waste from primary collection vehicles to larger vehicle for secondary transport

The basic collection method in developing countries is from community collection point. The basic collection methods in Nepal are to collect in metal containers placed at several places in the city. However, metropolitan cities are also provided facilities to collect the waste to waste management unit. This facility is provided in some wards of Kathmandu, Pokhara and Biratnagar.

The simple and best methods to collect the waste comprise the daily collection of the waste especially during summer and rainy seasons. If wastes are not collected daily, it generates odor problem and chances of spreading of microbes into the environment (air and water).

In developed countries block collection and curbside collection are common methods.

A. Block Collection

Individuals bring waste in containers to a carryings vehicle which travels a regular route twice or thrice a week. The containers are emptied by vehicle crew and returned to the individuals.

B. Curbside Collection

The Waste is brought in containers and placed on the footway at special places, which is collected later by cranes of solid waste management department and leave the containers at sample place.

For transportation in a developing countries simple hard carte are effective in many places due to lack of manpower, wide streets and vehicles. However, special vehicles are in compound practice to collect the waste from containers and solid waste collection centre.

The waste in the tractors and trucks are covered with plastics in order to prevent spreading of waste into the air and transported to final disposal place.

In the developed countries, government provides containers to the individuals in order to collect biodegradable and non-biodegradable wastes separately. Peoples themselves separate the recyclable waste and non-recyclable and transfer it to the collection containers. This practice makes an easy economical disposal method / Recycle method.

2. TRANSPORTATION

Once waste is collected in primary collection vehicles such as handcarts, rickshaws or tractors, it often needs to be transferred to larger vehicles for transportation to treatment or disposal sites. This transfer process is usually inefficient and ineffective because the waste from the primary collection vehicle is normally dumped on the ground and then loaded on to the haulage vehicle manually or using a loader. A more effective method is to transfer the waste from the primary vehicle directly on to the secondary transport vehicle by collecting the waste in detachable containers, such as sacks or bins within the primary vehicle which can be lifted manually and emptied into the secondary vehicle without having to put the waste on the ground during the transfer process. Another method is to use a split-level transfer process, where the primary collection vehicle is tipped to allow waste to fall in to the secondary vehicle that is placed at a lower level. Such transfer operations are practiced in a few locations in Kathmandu.

3. DISPOSAL OF WASTE

The process of selection of right solid waste disposal method is a complex one due to heterogeneity of the urban waste, but an appropriate method can save money as well as reduces the chances of problems occurs in future.

The disposal methods should be selected in such a way that the present situations are fulfilled and future situations are anticipated. The methods should also provide opportunity for recycling of materials if possible and should not pollute the air, ground water, surface water and the land water.

Several disposal methods are being using the various parts of the world. Among the various methods, sanitary landfill is applied in developed countries while open dumping is practiced in developing countries.

A. Hog feeding

B. Open dumping

C. Incineration

D. Sanitary landfills

E. Composting

F. Pyrolysis

G. Pulverization

H. Controlled tipping

I. Pulverization combined with controlled tipping

J. Ocean Dumping and River Dumping

A. Hog feeding

It is the oldest method of solid waste (particularly kitchen waste) management practiced in many countries especially in countryside. Properly controlled waste can be converted into the wealth. Previously hogs were used as scavengers of raw garbage. They were feed with kitchen waste. But it leads to the spread of several bacterial, viral and parasitic diseases to other animals and human beings. This problem is overcome by steaming of garbage for ½-1 hours before feeding to the hogs. This method is applicable in the cities covered with rural areas where hog farming is possible. In many Terai regions of Nepal, hogs are still fed with human excreta and raw garbage.

B. Open Dumping

Open dumping of solid waste is practiced extensively in developing countries because it is cheap and requires no planning. Generally low lying areas and out skirts of town and cities are used for this purpose. Open dumps causes public health problems by encouraging the breeding of files, rats, mosquitoes and other pests. Files can transmit typhoid, fever, cholera, dysentery, tuberculosis, anthrax and other disease; rats which can transmit typhoid, leptospirosis, rickettsial pox, plague, and cockroaches and mosquitoes transmit malaria, yellow fever, dengue, encephalitis, filarial etc. They also become a source of objectionable odors and results in air pollution when the wastes are burned in order to reduce their volume and conserve space.

C. Incineration

Incineration is also a commonly used method which involves the burning of waste at a high temperature. After burning ashes, glass, metals and other unburned materials account for 25% of total waste. The remaining materials which are also known as ashes are safely disposed by the methods such as sanitary landfill or by dumping or recycling. Incineration leads to ambient air pollution if incinerators are not properly designed, equipped and operated properly. This method is useful when availability of land is limited as well as safe disposal of hazardous waste such as waste from nursing homes, hospitals, laboratories. Incineration results into the formation of some air pollutants which are ash, SO₂, Hydrogen chloride and organic acids. New techniques for the handling of waste involves the separation of non-combustible part by magnetic or gravity separation methods and recycle them. This technique encourages the recycling of waste as well as it reduces the total cost needed for incineration. Incineration is widely applied techniques for the disposal of solid waste generated in the industries. The design of incinerator used is depend upon combustibility and nature of waste to be disposed. Another term commonly used for this technology is energy recovery or waste to energy because the heat derived from incineration of refuse is a useful resource. The heat energy liberated could be used to generate electricity. Internationally, over 1500 waste to energy plants in Brazil, Japan and Western Europe generate electricity and reduce the investments needed for landfilling. Various types of incinerators are widely used in the .

Advantages	Disadvantages
1. Energy generation. 2. Volume reduction by 90% 3. Suitable for aesthetic hygienic and stand point 4. Requires small land area. 5. Inert materials such as ash is recovered,	1. Initial investment is high. 2. Required skilled manpower. 3. High Maintenance cost 4. Air pollution

D. Sanitary landfill

The landfill operation is essentially a biological method of waste treatment. The stabilization of waste may be divided into five distinct phases within overall process. During first phase of operation aerobic bacteria are dominant which consume oxygen. As a result of metabolism of bacteria, temperature of the environment increases. In the second phase, anaerobic condition is established, and hydrogen and CO₂ gas are evolved due to fermentation of organic substrates. In the third phase, growth of methanogens starts to produce methane and CO₂ gas. In the fourth phase, the methanogenic activity becomes stabilized. In the fifth phase, the methanogenic activity decreases representation depletion of the organic matter and alternately the system returns to aerobic conditions within the landfills. The duration of each phase of landfill depends on the prevailing environmental conditions and the nature of the waste. The end products of decomposition of wastes during the third and fourth phases are mostly CO₂ and CH₄ gas along with a small amount of H₂S, NH₃ and water. During first year, the amount of N₂ decreases as air cannot penetrate the soil to the sealed waste. Methane production can usually be observed around 200 days after reduce disposal. During construction the landfills site must be designed in such a way that leachate should be drained from there in proper manner to avoid surface and ground water pollution. Escape rents for gases should be provided so that they couldn’t build up to dangerous levels. Landfills gas is renewable source of energy and which can be used for cooking purpose.

Advantages

Disadvantages

1. Most economical method where land is available. 2. Minimum public health problem because flies, rats and other pests are unable to breed in the covered waste. 3. Minimum fire hazards. 4. Can receive all types of waste, eliminating the necessity of separation of waste into degradable and non-biodegradable. 5. Finished landfills sites can be used for the development of parks, playground, golf courses etc.

1. Unavailability of suitable land especially near the crowded area. 2. Proper operation and skilled manpower are needed for daily operation. 3. Danger of surface and ground water pollution if site aren’t properly selected and designed. 4. Sealing materials used do not remain effective permanently 5. Leakage of gases may cause odor problems.

E. Composting

Composting of organic waste appears to offer an attractive alternative to landfill for decomposition of domestic solid waste and agricultural waste. In contrast to a sanitary landfill, composting of refuse is an aerobic method of decomposing solid waste. It is microbial process that converts putrescible organic materials into stable humus like product that is reduced in bulk and can be used for soil improvement. The organisms included are bacteria which predominate at all stages, fungi which often appear after first week and actinomycetes which assist during final stages.

Initially the process starts with the mesophilic bacteria which oxidize the organic matter in the refuse to carbondioxide and release heat which rises the temperature to about 45°C. At that point the thermophilic bacteria take over and continue the decomposition. During this phase temperature further rises to about 60°C. During the operation the refuse is periodically turned over to allow the sufficient oxygen to penetrate to all parts of the material to support the aerobic life. After about 3 weeks the compost is stabilized and the end point of composting operation can be measured by a drop in temperature.

Composting process can be categorized into two types

1. Aerobic process

2. Anaerobic Fermentation process

E1. Aerobic process

In aerobic decomposition process microorganisms utilize oxygen to feed on the organic matter in the waste to produce stable end product as well as their own biomass. The end product is humus like material which is extremely useful as plant nutrient. The aerobic fermentation process occurs very widely in nature and is the main way in which waste products from field and forest are converted into humus. Composting is accomplished in Static piles, Aerated piles or Continuous feed reactors.

The static pile process is simple but relatively slow, requiring many months for stabilization. Insects breeding and odor problem during static pile method can be controlled by covering the piles with a layer of soil, finished compost or wood chips. Under the favorable conditions, self heating causes to rise in temperature to 55-60° C or above in 2-3 days. After few days temperature is gradually decreased. Oxygen concentration in the compost pile is five times lower than ambient air. Periodic turning of the compost piles help to saturate the waste with oxygen and uniform mixing. After thermophilic process, a curing phase at mesophilic temperature starts for several month. Hence, large land area is required due to slowness of the process.

The aerated pile process is substantially faster process through improved aeration. The aerated pile process involves the suction of air through perforated pipes buried inside the compost pile. This design, Beltsville process, achieves at least partial oxygenation of pile, but temperature control is inadequate. The temperature rises unto 70-80°C. This model is improved by Rutgers model which reverses the airflow from suction to injection. Thermostats placed inside the pile controls blower operation, starting when temperature exceeds 60°C. The injection at air not only oxygenates the pile but cools it sufficiently to avoid temperature rises. The heat generated by the biodegradation process is effectively used in evaporating water which results into dried and stable compost. The aerated pile process completes in three weeks.

In continuous feed reactor process composting is carried out in a bioreactor. It requires about 20,000 cubic feet of air per ton of organic matter/day for efficient composting. This process forms a uniform and stable product but also requires a high initial investment. Composting in a reactor is accomplished in 2-4 days. A part or the entire reactor is maintained at thermophilic temperature using the heat produced in the composting process. After processing in the reactor, the product requires “curing” for about a month prior to packaging.

Regardless of the process design, conducting the composting process in the thermophilic temperature range is desirable because it speeds the process and destroys pathogens that may be present in feacal matter and in sewage sludge. The aerobic oxidation process catalyzed by microorganisms produce heat which increases temperature to 76-78°C. This temperature is inhibitory to biodegradation process i.e. for microbes because the maximal thermophilic activity of microbes occurs between 52-63°C. Aeration or turning or periodic cool water spraying can reduce temperature to an optimum level.

The composting process is initiated by mesophilic heterotrophs. As temperature rises, they are replaced by thermophilic forms. Thermophilic bacteria predominating compost piles are B. steriothermophilus, Thermomonospera, Thermoactinomyces, Clostridrum, and Thermocellum. Important fungi in composting process are Geotrichum condidum, Aspergillus fumigatus, Mucor pusillus, Chaetomium thermophile, Thermoascus auranticus and Torula thermophila etc.

Factors affecting composting:-

1. Moisture: Optimum 50-60% moisture is essential. Above 70% or more interferes with aeration and lowers self heating capacity.

2. C:N ratio(Carbon: nitrogen ration): Should not be greater than 40:1. Lower nitrogen content should not permit formation of sufficient microbial biomass. Excessive nitrogen content (25:1) tends to volatilization of ammonia causing odor problems and lowers the fertilizer value of compost. So optimum is about 27 to 30:1.

3. Temperature: Optimum is around 60°C at which thermophilic activity is favoured. Temperature above 50-60°C is an essential to operate thermophilic activity and to kill pathogens (cells and cysts).

4. Aeration: It is important to maintain temperature and hence most stable compost.

Steps in composting:

E1. Separation of compostible and non-compostible:

Organic- compostible, inorganic – non-compostible

Magnetic device separates tin, iron and other metals.

Manual or gravity separation method is used to separate glasses, bottles, rubber, plastic etc.

Separation at source is more economical than separation at collection centre or composting centre.

E2. Shredding: -

Once most of non-compostible materials have been removed, the rest is shred. This is necessary to give the materials a sufficiently large area for the microbial attack to proceed readily. Hammer mills are generally employed for shredding which reduce the size.

E3. Blending for composting:-

Blending causes to adjust C: N ratio. Some materials with poor nitrogen content (waste plant products, saw dust etc.) are blended with materials having very high C: N ratio (human or animal excreta, slaughterhouse waste, etc). Soil is also added to adjust the moisture.

E4. Composting:-

Aerated piles or bioreactors (mentioned above).

Nusoil process: - The pulverized matter then goes to a vertical digester where decomposition takes place. The digester is a circular unit having seven sections. The waste moves down through each section of the digester. It is kept for about one day in each section and air flow rate and water addition are regulated so that decomposition takes place under optimum condition. The digestion process is completed in seven days and the resultant compost is satisfactory for direct field application without addition of supplementary nutrients.

E5. Curing and packaging:-

F. Pyrolysis: -

Pyrolysis is a method of solid waste disposal which results into chemical conversion of refuse to get new chemical compounds. Pyrolysis is operated using intense heat to cause chemical changes but not combustion. In Pyrolysis, the refuse is heated in an oxygen free environment during which most organic substrates can be split through a combination of thermal cracking and condensation reactions into gaseous, liquid and solid fractions. Pyrolysis is carried out in different reactors and three major component fractions resulting from pyrolysis are;

a. A gas stream generated by pyrolysis may contain primarily hydrogen, methane, carbon monoxide etc. depending upon organic characteristics of the material being pyrolysed.

b. A fraction that consists of tar and/or oil stream that is liquid at room temperature. It consists of chemicals like acetic acid, acetone and methanol.

c. Solid fraction containing pure carbon plus inert materials.

G. Pulverization: -

Pulverization is really a step involved in disposal of refuse by sanitary landfill, composting or other techniques. It is the process of making small pieces of solid waste by pressing or cutting. The separation is conducted by the use of rotating drum machines. The pulverized waste can be easily disposed by applying other techniques.

G1. Rotating drum machines: - These pulverize the waste by attrition. Water is added to the crude refuse and mixes, is then passed into the revolving drums which have a circular, an octagonal or a hexagonal crops section. The drums operate either in a batch or continuous basis with number of rotations depending upon types of refuse. The drums usually contain a separation device for materials which cannot be broken down: -mainly plastics, rubbers and metals etc. The final materials that come out of drums normally contain a moisture 50-60% and density of 0.5-0.6kg/dm³_, much higher than the original density of refuse. Drum-type pulverizers usually have a capacity of about 10-12 tons/hr and require about 35 Kw of power to operate. It is provided with magnetic separation to remove iron and tin.

G2. Hamper mills: - Hammer milling is operated either a dry or wet process. Hammer mills are of two types i.e. fixed hammer and swing-hammer type. The hammer mills can process maximum about 30 tons/day. It consists basically a horizontal rotor which carries a number of swinging or fixed hammers. It consists of impact plates and grates through which the processed refuse is finally ejected. Size of pulverized particles is about 5-8 cm in diameter. Metals are separated by shredding and iron is recovered by magnetic separators. Power consumption is about 150-200 Kw.

H. Controlled tipping: -

This method allows permanent deposition of waste on land, sealed in cells isolated from the surface with layers of earth. Controlled tipping is generally practiced in conjugation with land reclamation schemes, to reclaim marshes, exhausted quarries and gravel pits for agricultural, industrial and recreational uses. If not properly designed it will create water pollution problem and invoke the breeding of pests. If the reclaimed area is to be used for agriculture purpose, non-biodegradable compounds should be removed.

I. Pulverization and controlled tipping:-

Although cost is high it has few advantages: -

a) Less earth cover with required than unpulverized waste.

b) Rat, mice, insect larvae destroyed.

c) Land can be used for agriculture purpose.

d) Very less time will required for complete degradation of waste.

J. Ocean dumping/River dumping: -

It is one of the oldest methods and nowadays it is completely restricted.

4. POTENTIAL METHODS OF DISPOSAL

1. Utilization.

2. Recovery and recycling: - paper, metal, plastic, glass.

5. SELECTION OF DUMPING SITES

The criteria for selecting a dumping site are almost similar all over the world with some constraints related to locality. The selection of the dumping site (landfill) is a big question that faces local authorities because it represents a point of confluence of science, social science, and planning. Urban planners and city managers throughout the world are now confronting this issue within a much broader social development context. Before selection of dumping site, the following parameters should be considered.

1. Far from community or local area

2. No drinking water resources nearby it (to prevent surface water and groundwater contamination due to leachate)

3. Not at hill side (better if the sites are deep, the wind velocity may deliver all waste to down hill into locality)

4. Barren land or unfertile land (No fertile soil is degraded)

5. Cold climate (where vectors breeding will be low)

6. Economical factors such as dumping site should be at minimum distance from roads so that collection vehicles can travel through the optimum route.

7. Environmental factors such as noise contamination due to trucks movement and atmospheric contamination due to emission of carbon dioxide (CO₂) and methane (CH₄).

6. EDUCATION AND AWARENESS

Education and awareness in the area of waste and waste management is increasingly important from a global perspective of resource management . The Talloires Declaration is a declaration for sustainability concerned about the unprecedented scale and speed of environmental pollution and degradation , and the depletion of natural resources . Local, regional, and global air pollution; accumulation and distribution of toxic wastes; destruction and depletion of forests, soil , and water ; depletion of the ozone layer and emission of "green house" gases threaten the survival of humans and thousands of other living species, the integrity of the earth and its biodiversity , the security of nations, and the heritage of future generations. Several universities have implemented the Talloires Declaration by establishing environmental management and waste management programs, e.g. the waste management university project. University and vocational education are promoted by various organizations, e.g. WAMITAB and Chartered Institution of Wastes Management . Many supermarkets encourage customers to use their reverse vending machines to deposit used purchased containers and receive a refund from the recycling fees. Brands that manufacture such machines include Tomra and Envipco.