Sewage and solid waste disposal Social Pharmacy Notes, PDF, Books
Solid wastes are unwanted, discarded material from domestic, commercial, industrial and agricultural operations. It is also called refuse or litter. It comprises dust, ash, vegetables, fruits, paper and packaging of all types, rags and other fabrics, combustible, non-combustible debris.
Solid waste is disposed of by using the following methods.
- Dumping: Dry refuse is mainly dumped in low lying areas which help not only in disposal but also in reclamation of land. By the action of bacteria, the volume of the refuse decreases considerably in volume and is converted gradually into humus. It is not an ideal method. It causes public nuisance , attracts insects and animals . It causes air and water pollution .
- Controlled tipping or Sanitary landfill: This is the most satisfactory method of refuse disposal. In this method a trench is dug. The refuse is compactly dumped in these pits and at the end of each working day is covered with earth, when the trench is full; again it is covered with earth and is compacted. In this method the chemical and bacteriological processes decompose the refuse into simple substances with generation of heat. The refuse is fully decomposed at the end of six months and can be used as manure.
- Incineration or Burning: Refuse can be disposed off hygienically by burning. It requires special equipment called an incinerator. It is a hollow cylinder made of metal, the refuse is put on the land and covered with an incinerator . Hospital refuse which is particularly dangerous is best disposed of by burning.
- Composting: It is a method of combined disposal of refuse and night soil. The basic principle is, when the refuse and night soil (excreta) are dumped in a pit and covered with earth there is anaerobic decomposition. The heat produced during decomposition kills the organisms and ultimately we get compost, which is used as manure. In a big trench , layers of 15 cm refuse alternating with 5 cm layer of excreta are placed on one another till it is full.
- Burial : A small trench is dug and refuse is put in it and covered with earth every day and when full , it is covered with earth and another trench is used . it is useful as short term method
It is a watertight masonry tank ( bricklayer) into which household sewage is admitted for treatment.
Eg: Excreta and liquid waste from individual houses, groups of houses or institutions can be laid down to it.
It is a tank in which the household waste and excreta can be disposed of. It is a suitable method for a small group of houses and institutions. Septic tank is usually rectangular in shape with a length of 1.5 to 2 times the breadth and the depth is 1.5 to 2 meters. A septic tank should have a minimum capacity of 200,000 litres. There is an inlet and outlet pipe above the water level. A cover of cement concrete is provided at the top with a manhole in the centre and the manhole is covered with another lid.
The mechanism in the working of septic tanks is anaerobic digestion of the contents. It takes place inside the septic tank. The heavy solid settles down and decomposes by anaerobic bacteria which cause a reduction in its volume and is made harmless. The solid at the bottom is sludge. The fast rise to the surface and is passed out.
It occurs outside the septic tank. The supernatant liquid contains microorganisms and is allowed to be collected in trenches. It spreads in soil and organic matter gets oxidized and gets converted to nitrates, carbon dioxide and water. This is aerobic decomposition.
- Use of soap water and disinfectant should be avoided. They are injurious to bacteria in the septic tank.
- The contents of the septic tank should be bailed out every year.
- Newly built septic tank should be seeded with ripe sludge drawn from an old tank. This will provide the bacteria which is required for the decomposition process.
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