Page 30 - Energy from Toxic Organic Waste for Heat and Power Generation

18 Energy from Toxic Organic Waste for Heat and Power Generation

does not vary significantly as the final product must have a consistent quality
[5]. Numerous efforts have been made to utilize the biodegradable fraction
of food processing waste (FPW) to produce useful products.
Food waste valorization to useful products not only offers economic
benefits, but also provides a solution to nuisances created by food waste
degradation in the environment and landfills. FPW may be produced in
solid, liquid, or semisolid form. Liquid wastes are generated as a result of
use of large amounts of water for many applications, including temperature
control, cleaning, process water, sanitation, transportation, cooking, and as
auxiliary water [6]. The effluent consists of suspended solids, organic matter
and nitrogen in several forms, fats and oils, and other inorganic materials [7].
Common liquid effluents include whey from cheese and yogurt produc-
tion, whey from tofu production, bakery effluent from equipment washing,
brewery effluent, oil mill effluent, soda industry effluent, potato processing
wastewater, and apple pomace sludge. Some of the major solid wastes are
tomato waste, apple pomace, inedible dough, waste bread, potato waste, soy-
bean curd residue, and grape pomace from wineries. Solid food wastes are
rich in starch, lignin, cellulose, and monosaccharides, mainly fructose and
glucose, whereas the nutrients in liquid food wastes are available in diluted
form. Generation of large amounts of food waste has an adverse impact on
natural resources like water, land, and biodiversity [2, 8].

3.2 PROPERTIES OF FOOD PROCESSING WASTE

The wastewater from food processing industries can be considered non-
toxic as it contains no or very few hazardous and nonbiodegradable com-
pounds [2, 9]. As wastewater mainly contains organic materials, it can be
treated conveniently using fermentation; however, it may sometimes con-
tain low concentrations of cleaning products that could be toxic. Tofu pro-
cessing wastewater results from cooking soybeans and pressing tofu curds
into blocks that are then prepared for sale. One kilogram of soybeans used
in a typical tofu production operation generates 101 L of wastewater and
0.25 kg of solid waste known as tofu curd residue [2, 10]. Tofu wastewater is
rich in nitrogen, but low in carbon. It contains some complex polysaccha-
rides in small amounts which make pretreatment necessary before conver-
sion via fermentation.
Whey is a food processing by-product representing the strained liquid
portion after coagulation of cheese or yogurt. Both cheese and yogurt whey
are rich in lactose. Although lactose cannot be directly fermented by all