The garbage disposal has been an age-old civic problem, and has increased with the growing population. Unlike sewage, it cannot be pumped along the drains. In the country districts the garbage is often taken outside the town or village, and then dumped at some unused land or a disused quarry. The waste paper etc. is set alight.
Sometimes the garbage is even used to fill the low-lying areas. It is spread out in even layers with the help of heavy machines, pressed down and covered with a layer of soil. This process is repeated until thick garbage and a soil sandwich has been made. It is then covered with a fine layer of soil and left to rot. Small organisms in the soil help to decompose the rubbish and make the soil fertile.
In the large towns and cities often there is not enough wasteland, so reducing the volume of the garbage done through processes known as pulverization and incineration.
The pulverization is a simple mechanical process whereby the rubbish is pounded into small particles by sheer force. It is of two types: wet and dry. A wet pulverizer consists of a typical rotating inner drum which is fitted with deflector plates, and baffles to pound down the rubbish. This inner drum is made of a grid of alloy steel bars, and once the rubbish has been ground to small bits, it passes between the bars into an outer drum. This drum also rotates and grinds the rubbish still smaller. Although the wet pulverization decreases the volume of the waste, the added water increases its weight. This raises the cost of transport. So the system is economical only when the pulverizer is sited at the rubbish tip itself. The dry pulverizers are fitted with rotating hammers to crush brittle materials and rotating steel teeth to shred the softer materials such as cardboard etc. These pulverizers can reduce glass to fine powder. They may be vast machines, capable of dealing with over 50 tonnes of rubbish an hour.
The most effective way of reducing the volume of rubbish is the incineration —high temperature burning. In this method, garbage is put into huge furnaces called incinerators, and burnt at a very high temperature. Everything is reduced to ashes, except metals which are collected and may be used again.
In some cities newspapers, rags are separated from the rest of the rubbish, plastics, glass, and metal, so that they may be used again.
One interesting recent development is the utilization of garbage to generate power. The burning of the garbage produces heat energy which is then converted into other forms of energy. The Bombay Municipal Corporation (BMC) has made a system for using its garbage for such power generation.