These water bodies get polluted. If these wastes are absorbed in the soil, they can easily pollute-the groundwater. This method of dumping the waste in open areas is being replaced by the landfilling of waste.
It is now a widely used method for municipal solid waste disposal. In this method, the landfills are covered with earth, so that insects do not enter these landfills. The wastes are then left to decompose. A number of physical, chemical and biological reactions take place and a variety of toxic gases, such as carbon dioxide, methane, ammonia and hydrogen sulphide, are released.
The landfills are generally far away from residential areas. This method has the following advantages:
1. There is no pollution of air, as the landfills are covered by earth.
2. The health hazards are few, as the mosquitoes and rats do not breed.
3. It is most suitable for non-biodegradable waste, which is not suitable for composting, recycle or reuse.
4. It is free from fire hazards.
Composting is a natural biodegradation process in which the biodegradable solid wastes can be converted into nutrient-rich manure in the presence of microorganisms. Composting can be done either in the presence of atmospheric air (aerobic composting) or in the absence of atmospheric air (anaerobic composting).
The aerobic composting is more common in our country, due to the ease with which it can be practised. However, it is less economical and leads to emission of greenhouse gases. This method is more prevalent in agriculture based areas, as this method requires the decaying plants, leaves, etc. to be buried in a small pit and left to decay. It has the following advantages:
1. It enhances the soil nutrients, such as nitrogen and phosphorus.
2. It enhances the water retention capacity of the soil.
3. It increases the fertility of soil by adding humus.
4. It works as a natural waste disposal system.
Vermicomposting is another method, in which manure is obtained from biodegradable waste by adding earthworms to the compost. The earthworms help in degrading the waste and the excreta of the worms makes the compost rich in nutrients.
Drainage is a system in which water is removed from the surface or subsurface area (residential, agricultural or industrial) by artificial or natural methods. In this system channels are constructed to allow the water flow from surface or subsurface. If the channels are properly built in a planned manner, it can prevent soil erosion. It also helps in preventing excessive accumulation of soluble salts in the soil, which may be harmful to the growth of plants.