4. Energy recovery. Recovery of energy from waste incineration or the combustion of
landfill gas. Many wastes, including municipal solid waste, sewage sludge and scrap
tyres, contain an organic fraction which can be burnt in an incinerator. The energy is
recovered via a boiler to provide hot water for district heating of buildings or high-
temperature steam for electricity generation. The incinerator installation represents a
high initial capita! cost and sopbisticated emissions control measures are required to
clean-up the flue gase. Producing energy by combined heat and power (CHP) enables
the maximum recovery of energy from waste by producing both electricity and district
heating. The waste is again incinerated, but CHP systems would use a different type of
steam turbine which would generate, a lower amount of electricity, then the steam
effluent from the turbine would be at a higher temperature, enabling district heating
also to be incorporated. The production of landfill gas from the biodegradation of the
organic fraction of wastes such as domestic waste and sewage sludge in a landfill site,
produces a gas consisting mainly of methane which can be collected in a controlled,
engineered way and burnt. Again the derived energy is used for either district heating
or power generation. Additionally, there are newer technologies such as pyrolysis and
gasification which can recover energy in the form of gas or liquid fuels. These can then
be exported to power stations or used to generate energy on site.