Energy recovery is one of the important aspects of solid waste management. Municipal solid waste consists of organic and inorganic matter. The organic substances usually release energy on decomposition and this can be effectively trapped and utilized in various ways. Nowadays there are various waste processing and treatment technologies which allow one to recover energy from wastes.
When different waste composition technologies are used, the total volume of wastes gets reduced from sixty to ninety percent. The landfill areas are also becoming scarce near cities and towns and so is the cost of transportation of wastes to landfill areas. Again, reduction in pollution levels is important and one of the ways to minimize wastes is to recycle and reuse different materials and opt for energy recovery from wastes wherever possible.
These are in principle some of the aims and principles of waste management.
There are some basic techniques which are used for energy recovery. The two methods which are principally followed for energy recovery are thermo chemical conversion and bio chemical conversion. Thermo chemical conversion consists of thermal decomposition of organic matter and this helps to release heat energy as well as fuel oil or gas. The bio chemical conversion process is the way in which the enzymatic decomposition of organic matter takes place. Here the microbes work on the organic matter to produce methane gas or alcohol.
While the thermo chemical conversion process is suitable for organic matter with low moisture content, the bio chemical conversion process of energy recovery is opted for when there is high level of moisture content, thus aiding microbial activity.
There are various parameters which help to determine how much of energy can be recovered from solid wastes. The quantity of waste and the physical and chemical composition of wastes help to determine how much of energy can be recovered.
The physical parameters are of importance such as the size of the constituents, the density and moisture content. The smaller the size of the particles of waste matter and the higher the density, the amount of biodegradable organic matter is usually more in a given amount of waste. When the moisture content is high, the bio chemical conversion can take place faster than compared to drier conditions. Then again, in high moisture content, the incineration or pyrolysis processes can be effective on breaking down such wastes.
Again, the chemical parameters of wastes such as the carbon content, the carbon/nitrogen ratio, the calorific value and other volatile solids contained in waste matter will help to determine which wastes can go into incineration methods and which cannot. Then again, many additives are often required to be added to make wastes more combustible than they naturally are.
In these ways, wastes are classified for the different forms of conversion processes by which the energy recovery from such solid wastes can take place.