The waste is delivered to fixed storage bins usually built from concrete blocks to the location from where the collection vehicle will ultimately transport it to the site of disposal. Daily collection is essential because the organic matter in the waste tends to decompose rapidly in the hot climate.
2. Disposal of Solid Waste:
As cities are growing in size with a rise in the population, the amount of waste generated is increasing becoming unmanageable. The local corporations have adapted different methods for the disposal of waste – open dumps, landfills, sanitary landfills, composting and incineration plants.
3. Open Dumps:
Open dumping of solid waste is done in low lying areas and outskirts of the towns and cities. Being comparatively cheaper and required no planning, this method of disposal is used extensively in India.
Open dumps refer to uncovered areas that are used to dump solid waste of all kinds. The waste is untreated, uncovered, and not segregated. It is the breeding ground for flies, rats, and other insects that spread disease.
The rainwater run-off from these dumps contaminates nearby land and water thereby spreading disease. They also become a source of objectionable odours and cause air pollution when the wastes are burned in order to reduce their volume and conserve space.
Landfills are generally located in urban areas where a large amount of waste is generated and has to be dumped in a common place. Unlike an open dump, it is a pit that is dug in the ground. The garbage is dumped and the pit is covered thus preventing the breeding of flies and rats.
At the end of each day, a layer of soil is scattered on top of it and some mechanism, usually earth-moving equipment is used to compress the garbage, which now forms a cell. Thus, everyday, garbage is dumped and becomes a cell.
After the landfill is full, the final layer is covered by soil of about one meter to prevent rodents from burring into the refuse and scattering and the site can thereafter be developed as a parking lot or a park.
Landfills have many problems as all types of waste are dumped in landfills and when water seeps through them it gets contaminated and in turn pollutes the surrounding area. This contamination of groundwater and soil through landfills is known as leaching.
5. Sanitary Landfills:
Sanitary land filling involves the disposal of municipal wastes on or in the upper layers of the earth’s mantle especially in degraded area in the need of restoration. An alternative to landfills which will solve the problem of leaching to some extent is a sanitary landfill which is more hygienic and built in a methodical manner.
These are lined with materials that are impermeable such as plastics and clay, and are also built over impermeable soil. The advantages of a sanitary landfill, as opposed to an open dump are:
1. The public health problems are minimized because flies, rats and other pests are unable to breed in the covered refuse.
2. There is no air pollution from burning.
3. Fire hazards are minimal.
Constructing sanitary landfills is very costly and they are having their own problems. Some authorities claim that often the plastic liner develops cracks as it reacts with various chemical solvents present in the waste.
The rate of decomposition in sanitary landfills is also extremely variable. This can be due to the fact that less oxygen is available as the garbage is compressed very tightly. It has also been observed that some biodegradable materials do not decompose in a landfill.
Another major problem is the development of methane gas, which occurs when little oxygen is present, i.e., during anaerobic decomposition. In some countries, the methane being produced from sanitary landfills is tapped and sold as fuel.
6. Incineration Plants:
The process of burning waste in large furnaces is known as incineration. In these plants, the recyclable material is segregated and the highly combustible wastes like plastics, cardboard, paper, rubber and combustible wastes like cartons, wood scrap, floor sweepings, food wastes etc. are subjected to burn at very high temperatures in presence of oxygen.
At the end of the process all that is left behind is ash. During the process some of the ash floats out with the hot air. This is called fly ash. Both the fly ash and bottom ash (that is left in the furnace after burning) have high concentrations of dangerous toxins such as dioxins and heavy metals. Disposing of this bottom ash is a problem. The ash that is buried at the landfills leaches the area and cause severe contamination.
Burning garbage is not a clean process as it produces tones of toxic ash and pollutes the air and water. A large amount of the waste that is burnt here can be recovered and recycled. In fact, at present, incineration is kept as the last resort and is used mainly for treating the infectious waste.
The advantages of incineration include wide range ability for handling varying loads and small space requirement for ultimate disposal. However, the method requires fairly high level of maintenance and the operation of sanitary landfill.
Organic matter constitutes 35% – 40% of the municipal solid waste generated in India. This waste can be recycled by the method of composting, one of the oldest forms of disposal. It is the natural process of decomposition of organic waste that yields manure or compost, which is very rich in nutrients.
Composting is a biological process in which micro-organisms, mainly fungi and bacteria, convert degradable organic waste into humus like substance. This finished product, which looks like soil, is high in carbon and nitrogen and is an excellent medium for growing plants. It recycles the nutrients and returns them to the soil as nutrients.
Apart from being clean, cheap, and safe, composting can significantly reduce the amount of disposable garbage. The organic fertiliser can be used instead of chemical fertilizers and is better specially when used for vegetables. It increases the soil’s ability to hold water and makes the soil easier to cultivate. It helped the soil to retain more of the plant nutrients.
Composting: Some Benefits:
1. Compost allows the soil to retain more plant nutrients over a longer period.
2. It supplies part of the 16 essential elements needed by the plants.
3. It helps reduce the adverse effects of excessive alkalinity, acidity, or the excessive use of chemical fertilizer.
4. It makes soil easier to cultivate.
5. It helps keep the soil cool in summer and warm in winter.
6. It aids in preventing soil erosion by keeping the soil covered.
7. It helps in controlling the growth of weeds in the garden.
8. Pyrolsis or Destructive Distillation:
In this disposal method, the solid wastes are heated under anerobic conditions, i.e., burning without oxygen. The organic components of the solid wastes split up into gaseous liquid and gaseous fractions (CO, CO2, CH4, tar, charred carbon). Unlike the highly exothermic process of combustion, pyrolysis is a highly endothermic process and that is why it is also called destructive distillation.
9. Land Farming:
The organic wastes are either applied on top of the land or injected below the soil surface with suitable equipment, where they undergo bacterial and chemical decomposition. At frequent intervals, the land farming sites can be reused without any adverse effects provided the land farming site is properly managed.
10. Waste Utilization:
A developing country cannot afford wastage. By proper utilization of solid waste a developing counter like India can avail of many advantages. Many solid wastes generated by industries can be utilized directly.
Fly ash and bottom ash from power plants can be used commercially, largely as cement substitute. New uses are developed for fly ash, e.g., to make bricks, to dewater industrial wastewater sludge, as a land cover etc.
Recycling involves the collection of used and discarded materials processing these materials and making them into new products. It reduces the amount of waste that is thrown into the community dustbins thereby making the environment cleaner and the air fresher to breathe.