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Waste management is a burning problem in the urban, industrial and rural areas.
Hazardous wastes contaminate the environment in various ways. Even before such wastes are safely of they pollute the air, water and soil and pose a constant danger to human life.
Improper handling of hazardous wastes contaminates the atmosphere and the surrounding environment.
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The discharge of hazardous substances into water bodies often kills aquatic life. Uncontrolled disposal of wastes on land can easily pollute the soil and groundwater. Therefore the careful management of hazardous wastes is one of the most important concerns of the modern society.
Wastes management involves the following steps:
1. Reduction of wastes
2. Recycling of wastes
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3. Treatment of wastes
4. Disposal of wastes
1. Reduction of Wastes:
The first concept of waste management involves the reduction in the quantity of wastes.
This can be achieved by the following steps:
Source reduction:
In this the industrial processes are modified in such a way that there is optimum use of raw materials and the amount of hazardous wastes generated is reduced to a bare minimum.
Concentration:
The wastes that are generated during various industrial processes are concentrated using modem methods, such as precipitation or decantation techniques. Thus, the volume of wastes is reduced, which can be manage easily.
Segregation:
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The wastes are segregated according to their chemical composition, hazard potential and physical nature. This helps in their eventual disposal.
2. Recycling of Wastes:
Many types of wastes contain some useful substances. Recycling is the method by which the wastes can be further used through reprocessing.
Recycling commonly refers to two things:
Reuse:
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This refers to the case where certain wastes can be again used with very little reprocessing. For example, discarded bottles and containers, certain chemicals, lubricants, etc. can be put to further use with minimum processing.
Recycling:
It differs from reuse in the sense that the wastes must be thoroughly treated and re-processed before it can be used again. Some recycling processes use materials for the same purposes; for example, metal scraps, cans, bottles, etc. are usually melted and recast into the original material. Other recycling processes turn old materials into entirely new products for example, wood remains are used in the paper industry. Recycling encourages awareness and responsibility for waste management.
3. Treatment of Wastes:
Hazardous wastes can be treated by a number of processes to change the physical and chemical composition of the wastes so as to reduce and neutralize their toxicity. The treatments vary depending on the physical state and chemical nature of the hazardous wastes. The treatment of wastes can be divided into three broad types:
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Physical treatment:
Physical treatment of solid wastes includes mechanical separation and segregation so as to facilitate the disposal. In case of liquid wastes, physical treatment mainly involves phase separation. This involves the process of sedimentation, whereby sand, silt and other particulates settle at the bottom of the tank. Extremely fine colloidal particles are combined by the process of coagulation and then settled.
Chemical treatment:
The hazardous wastes are treated with different chemicals, so as to neutralize them and remove their toxicity. This treatment involves the modification of the chemical properties of the wastes through oxidation, reduction, precipitation, neutralization, etc.
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Biological treatment:
This involves the action of microorganisms on the wastes products as you know, the microorganisms like bacteria and fungi are known as nature’s scavengers which break down the organic substances present in the wastes.
Biological treatment involves the processes of:
1. Conditioning:
The wastes are exposed to the atmosphere for a specific period.
2. Digestion:
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The action of microorganisms breaks the complex organic compounds into simpler forms.
3. Composting:
The organic matter is converted into useful manures.
4. Disposal of Wastes:
The final step in hazardous waste management involves the safe disposal of wastes.
However there are certain steps that are necessary before disposal which are as follows:
1. Collection of wastes:
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2. Provisional storage of wastes
3. Transport of wastes
After the above pre-requisites are fulfilled, the wastes are finally disposed of depending on their nature and chemical properties.
Processes involved in Solid Waste Management:
The different steps involved in the management of solid waste from its generation to final disposal are as follows (Fig. 17.2).
Waste generation:
Material that is discarded because it has served its purpose or is no longer useful; becomes the waste.
Storage and Processing:
The activities which are associated with the handling storage and processing of solid waste at the point of generation.
Collection:
The activities concerned with the collection of solid wastes at specific locations.
Transfer and Transport:
Activities involve the transfer of wastes from the collection points to the vehicles and then transport of wastes to the disposal sites.
Processing and Recovery:
Methods and facilities that are used to recover the wastes for recycling and other treatments.
Disposal:
The final step is the disposal of solid wastes to a landfill site.
Solid wastes are mostly generated in the urban areas and hence, solid waste disposal is primarily an urban problem. Huge amounts of wastes are produced by different activities, which need to be properly handled.
The common methods of solid waste disposal include:
1. Open dumps
2. Sanitary landfills
3. Ocean dumping
4. Drainage
5. Incineration
6. Composting
Open dumps:
Open dumps are the oldest, simplest and most common method of disposing solid wastes. Open, unregulated dumping is the predominant method of waste disposal in most of the developing countries. In developed countries, however, open dumping is banned. Open dumps are located wherever land is available. The wastes are dumped on the vacant lands which take the shape of huge piles. Sometimes, the wastes are ignited and burnt.
Disadvantages:
Though open dumping is a cheapest method of solid wastes disposal, it has the following drawbacks:
1. Open dumps are aesthetically revolting.
2. They breed pests and microorganisms.
3. Pollute the air, surface water and groundwater (by leaching).
Sanitary landfills:
The developed countries now dump their solid wastes in sanitary landfills. A sanitary landfill is a disposal site that does not create a hazard for public health and where solid waste disposal is regulated and controlled (Fig. 17.3). The waste damped into the sanitary landfills are compacted to reduce the volume and then covered with a layer of soil at the end of each operation. This soil cover discourages breeding of pests, decreases offending odours and minimizes leaching.
Precautions:
Before operating a sanitary landfill the following precautions are required:
1. Proper site selection for a landfill is important.
2. Landfill should be located far from rivers, lakes, flood plains and groundwater recharge zones.
3. The topographic relief, depth of groundwater table and the soil and rock type should be taken into consideration.
4. The bottom of the landfill should have an impermeable lining of clay or plastic material.
5. Proper drainage systems should be installed around the landfills so as to check water accumulation.
6. Monitoring wells to evaluate potential groundwater pollution should be installed.
Advantages:
1. No open burning
2. Less odour
3. Less cost
4. Accommodates huge amount of wastes
5. Landfills can be used for other purposes
Disadvantages:
1. More noise pollution
2. More dust
3. Space problem
4. Emits greenhouse gases (methane)
5. Ground water pollution
6. Slow decomposition
Ocean Dumping:
Oceans are the biggest reservoirs. Every year approximately 25000 metric tonnes of solid wastes including packaging materials, bottles, cans, containers, etc. are dumped into the sea.
This careless dumping of wastes into the oceans has many disadvantages which are as follows:
i. It has littered many coastal areas with non-biodegradable wastes.
ii. Reduction of the dissolved oxygen content of marine environment.
iii. Eutrophication caused by nutrient rich wastes especially in shallow waters, such as estuaries.
iv. Habitat change of the organisms adversely affecting the marine ecosystem.
Drainage:
It is one of the most common practices in which the wastes are drained directly into the water bodies like rivers, lakes, ponds, oceans, etc. Although it is economical, it pollutes the water making it unfit for use. This practice is now avoided in most of the affluent countries and other safe disposal methods are being implemented.
Incineration:
As space for sanitary landfills is decreasing day-by-day, burning is the most modem method of solid waste disposal. This process is called incineration, in which the hazardous wastes are destroyed through high temperature burning (1300°C). The plant in which the wastes are burnt IS called incinerator (Fig. 17.4). In some incinerators, the resultant steam is generated which is used to drive a turbine to generate electricity. In advanced countries especially designed municipal incinerators are capable of burning thousands of tones of wastes per day.
There are two tunes of incinerators:
i. Refuse derived:
The wastes are segregated to remove un-combustible materials before combustion.
ii. Mass burn:
In which all the solid wastes are burnt without sorting. During the process of incineration, the volume of garbage is reduced by 80 to 90% and the weight by 75%, thus making disposal an easier task. In India, incinerators are not successful because of the huge costs involved and also because the wastes produced in the Indian cities contain less percentage of combustible matter.
Composting:
Composting is a biochemical process in which organic materials are decomposed to form humus. It involves partial decomposition of moist solid organic wastes under aerobic conditions by the action of microorganisms. The organic material present in the wastes are not buried or burnt but are thus converted to useful manures.
During the process of composting the organic wastes like food products, leaves, paper, saw dust, etc. are deposited in a trench, layer by layer. When the trench is filled, the pile of wastes is dampened and covered by a layer of soil. By the action of microorganisms, some amount of heat is generated, which helps in the decomposition of the wastes. After a time of three to four months, the wastes are converted into nutrient rich compost.
The benefits of composting include:
1. Compost acts as manure.
2. Conversion of household organic wastes into manure.
3. Nutrient-rich compost increases the water holding capacity of soil and improves crop yields.
4. It is an easy, inexpensive and eco-friendly fertilizer.
