Page 208 - Advances in Eco-Fuels for a Sustainable Environment

172 Advances in Eco-Fuels for a Sustainable Environment

high starch, protein, and lipid content make microalgae an efficient substrate
material [75].

6.9.4 Kitchen waste
Anaerobic digestion (AD) has been deemed to be an energy efficient and promising
method to dispose waste produced from municipal waste plan for its high value-added
products and low operating cost. Wastes can be classified under various headings such
as food waste, plastic waste, paper waste, solid waste, etc. Food waste is the unwanted
raw or cooked food that is discarded during or after preparation of food, which is no
longer fit (or desirable) for consumption. Here we will concentrate on kitchen waste,
which is a type of food waste.
The two main sources contributing to a large amount of kitchen waste are the
wastes from household and residential areas. Statistics say that larger households that
accommodate more people tend to waste more than their smaller counterparts. What-
ever it may be, we know one thing for sure: a lot of kitchen waste is generated every
year that needs to be disposed of in order to save our environment [76].

6.10 Second-generation biofuel production from
agricultural waste

In Asia, 998million tons of agro food waste is produced every year. Particularly in
India, 350million tons of agricultural organic waste is produced. Due to prompt
growth in population and industrial development, the global energy demand is
increasing unceasingly. In the last two decades, the emissions of CO 2 ,SO 2 , and
NO x from fossil-fuel combustion are the main causes of environmental pollution.
In this scenario, renewable energy sources might be promising alternatives to meet
energy demands as well as reduce emissions. Solar, water, biomass, and geothermal
can be alternative renewable energy sources for the energy industry while the chem-
ical industry and fuel production may depend on biomass as an alternative source. Bio-
mass is renowned as an essential world alternative energy source to compensate for
decreasing fossil fuel resources. The majority of bioenergy feedstock comes from
three sources: forests, agriculture, and waste. The industrial biomass conversion
methods are pyrolysis, gasification, and anaerobic digestion. The major problem in
pyrolysis and gasification processes is that the more char and noncondensable gases
such as CO and CO 2 are formed, similarly more amount of CH 4 is produced during the
anaerobic digestion process. This increases the amount of CO, CO 2 , and CH 4 gases,
which are also harmful to the ozone layer. Bioethanol is a crucial modern supplement
to petroleum because it is produced from renewable biomass, and moreover produces
less emission than fossil fuel combustion. It generates much less CO, CO 2 , and CH 4
emissions compared to the other conversion methods [77].
The lignocellulose biomass such as rice straw, wheat straw, food wastes, etc., are
more suitable for bioethanol conversion. Ethanol (C 2 H 5 OH) formation from lignocel-
lulosic organic waste includes the subsequent key steps: hydrolysis of hemicellulose