Environmental Engineering Reference
In-Depth Information
5.1 Introduction
The food processing industry produces significant amounts of residual organic
wastes as well as wastewater. The residual wastes include leftover food from res-
idences and commercial establishments such as restaurants, cafeterias, etc. and
discarded waste generated from food production operations. The amount of total
leftover food waste in the US estimated for 2002 was about 43.6 million tons [1].
The total food waste in the state of California alone was estimated to be about 4
million dry metric tons [2]. About half of this was from the food processing indus-
try and the other half from municipal solid waste streams going to landfill and
composting facilities. The state of California has developed a bioenergy develop-
ment program to increase generation of electricity from renewable resources [3].
Production of energy from food waste is included in the program and has become a
part of California's renewable portfolio standard (RPS). Conversion of food waste
into biogas makes about 4.7% of the state's renewable portfolio. Similar incentives
are also expected from other states in coming years.
The wastewater volume produced by the food industry is quite large. The bio-
logical oxygen demand (BOD) of the wastewater depends on the industry and spans
a wide range [4]. The dairy industry produces wastewater with BOD ranging from
about 1000 mg/L (milk or cheese plant wastewater) to 35,000 mg/L (whey wastew-
ater). The meat industry wastewater has a BOD ranging from 400 to 11,000 mg/L.
The sea food, edible oil, confectionary food and brewery processing industries, sim-
ilarly have a wide range of BOD from few hundred to several thousand mg/L. The
fate of the wastewater depends on the location as well as the specific industry. The
wastewater streams typically enter a common municipal wastewater stream, but
in many cases, the food processors are charged a sewer surcharge, especially for
streams with high BOD [2, 4].
The food processing wastewater streams contain carbohydrates, fats, oils and
proteins, which are much easier to degrade compared to raw biomass, such as agri-
cultural plant residues, forest product residues, etc. Release of the streams into the
environment without proper treatment can result in adverse impact on the environ-
ment. The nutrients and carbon present in the wastewater can be a valuable resource
for energy production. Use of biological methods such as anaerobic digestion has
been investigated for treatment of wastes from the food industry [4, 5]. While anaer-
obic digestion is a suitable option for very high BOD liquid and solid wastes, it may
not be the best option for low BOD wastewaters. Alternative emerging technologies
such as microbial fuel cells (MFCs) offer a potential solution for such wastewater
streams [6].
Microbial fuel cells are devices which oxidize organic matter and produce
electricity [7]. Extracting useful energy from wastewaters laden with organic mat-
ter, while cleaning the water, is one of the exciting aspects of this technology.
Several wastewaters have been investigated for their potential to generate electricity.
Removal of volatile fatty acids [8, 9], lactate [10-12], glycerol [13], proteins [14], as
well as treatment of wastewaters from vegetable processing [15], swine processing
[16, 17], and other food industry wastewaters has been demonstrated [16, 18-20].
