The process of burning municipal solid fasted in a properly designed furnace under suitable temperature (850° to 1100°C) and operating conditions is known as incineration.
The modern municipal incinerator is of continuously burning type.
The old technology of using refractory lining is replaced by water fall construction in the combustion chamber. In this system, the water is circulated through, steel made vertical boiler tubes.
The circulated water absorbs the heat of combustion of waste and is successively used for space heating, power generation and can also be re-utilised for steam generation and heating the waste.
There are however, various other types of incinerators, namely (1) rotary kiln (2) open pit incinerators (3) controlled-air incinerators.
Incineration may reduce the volume of (MSW) by 90 per cent and weight by 75 per cent. In incineration, the process involved is oxidation.
At the end of incineration, there remains bottom ash as well as solid residue and during the process there is a disposal of fly ash (ash floats out with hot air) into the atmosphere. Fly ash consists of finely divided particulate matter, mineral dust and soot.
Both, the fly ash and bottom ash have high concentrations of toxins like dioxins, as well as heavy metals.
The other types of gases exposed to air are sulphur dioxide, oxides of nitrogen, hydrochloric acid gas and many other organic acids. Disposal of ash is again a great problem. If buried, there remains the possibility of leaching, causing health hazard.
To reduce the problems associated with incinerations, first of all substances like glass and other non combustible batteries, plastics, etc., containing heavy metals which can be recycled, should be remove Equipment such as controlled-air-incinerator can be used, scrub (a device used to neutralize acid gases by spraying liquid) to prove gases to enter atmosphere, filters to absorb tiny fly ash particles and lastly, extensive air-pollution control equipment should be used. Skill labourers are required for proper maintenance.
The advantages associated with incineration thus are, utilization of energy generated through oxidation reaction and reduction of volume. But due to production of toxic materials, incineration is kept as the last resort and is used mainly to treat infectious waste such as biomedi waste.