Page 20 - Energy from Toxic Organic Waste for Heat and Power Generation

Toxic Waste From Municipality 9

But it has major environmental impacts like leachate formation, gas for-
mation, and infections leading to health problems. Leachate is a liquid that
contains all sorts of components that existed in the waste, which is very
toxic and will affect the ground water. The wastes in the landfilling leads
to decompose and other activities which produce gases like methane and
carbon dioxide. Methane is highly flammable which is to be handled prop-
erly. Carbon dioxide is a greenhouse gas which is another major drawback.
The landfilling is open to the environment, which in turn will cause infec-
tious diseases for the people in and around those landfillings.

2.2 METHODS OF ENERGY RECOVERY FROM WASTES

The other way of waste utilization is to recover energy they contain with
them. The most used energy recovery methods are thermal conversions (in-
cineration, fast and slow pyrolysis, gasification, production of refuse derived
fuel (RDF)), biochemical (composting, vermicomposting, anaerobic diges-
tion/biomethanation), and chemical conversions (trans-esterification and
other processes to convert plant and vegetable oils to biodiesel). Choice of
conversion process depends on the type, property and quantity of biomass
feedstock, the desired form of the energy, end use requirements, environ-
mental standards, economic conditions, and project-specific factors.
2.2.1 Thermal Conversions

Combustion, gasification, and pyrolysis are the thermal conversion processes
available for the thermal treatment of solid wastes. As shown in Fig. 2.1,
different by-products are produced from the application of these processes
and different energy and matter recovery systems can be used to treat these
products.

2.2.1.1 Incineration
Incineration is a general technique for management of waste, as it reduces
waste by around 70% in mass and 90% in volume. This also recovers en-
ergy by utilizing the heat content in converting water into steam to run
a steam power plant. Fig. 2.2 shows the layout of an incinerator [2]. This
system comprises of a lined furnace, fire grate, and air blowers and ranges in
capacities from 50 kg to 20 tons per hour. Incineration process takes places
between 750°C and 1000°C and it is coupled with steam and electricity
generation process. Mass incineration without pretreatment of the munic-
ipal solid waste with electricity generation is regarded as the most reliable