Environmental Engineering Reference
In-Depth Information
correlate with population size and consumption of protein (Environmental Protection Agency
[EPA], 2010). When compared with carbon dioxide and methane, nitrous oxide is released in
small amounts from human activity, but its 100-year global warming potential of 310 makes
it an important contributor as a greenhouse gas (Intergovernmental Panel on Climate Change
[IPCC], 2001).
HFCs emitted in food production come from stationary and mobile refrigeration equipment.
HFCs are a replacement of CFCs and HCFCs, which were found to deplete the ozone layer.
However, it has since been found that HFCs have a global warming potential much higher than
carbon dioxide. Just to illustrate, HFC-134a, one of the most used HFCs, is 1300 more
powerful than carbon dioxide as a global warming potential gas (EPA, 2008).
In a sustainable food company, emissions of greenhouse gases would be eliminated or
reduced to levels manageable by the Earth systems. At the agricultural phase, carbon dioxide
emissions would be reduced by changing agricultural practices and the use of soil as a carbon
sink for carbon sequestration. Carbon dioxide emissions during processing, transportation,
and waste treatment would be virtually taken to zero by using renewable fuels and renewable
energy.
Methane production could be reduced by changing agricultural practices and the use of
wastes to produce renewable fuel through anaerobic fermentation. The only promising
approach to reduce methane from enteric fermentation is to improve productivity and
efficiency of livestock production (EPA, 2007).
Nitrous oxide emissions from fuel combustion and nitric acid production (use for
production of fertilizers) could be addressed by technical modifications. Excess emissions of
nitrous oxide from overuse of synthetic fertilizers could be reduced by better management
practices.
Refrigeration systems using HFCs and other refrigerants with high global warming
potential could be replaced with systems that use carbon dioxide or ammonia as working
fluids. Despite its toxicity, ammonia is used in many food-processing plants these days. For
distribution centers and supermarkets, transcritical refrigeration is turning into a mature
technology and becoming a reality. Several supermarket chains in Europe are pilot testing
transcritical carbon dioxide systems in many of their grocery stores.
Biodegradable liquid and solid wastes
Liquid streams from food-processing plants are in all cases biodegradable. High contents of
dissolved solids contained by the streams, though, require mechanical energy to promote their
degradation before being discharged into water bodies. This mechanical energy comes from
electricity that is generated with nonrenewable fossil fuels.
This practice would become sustainable by either using renewable energy or using
alternative technologies to degrade organic materials. Anaerobic digestion is an alternative to
the traditional aerobic systems that would not only save mechanical energy but would also
open the possibility of harvesting biogas for energy generation. Anaerobic digestion is a
mature technology that is suitable for streams with high biochemical oxygen demand like the
ones from food-processing plants.
A second alternative for wastewater treatment without high-energy expenditures is the use
of engineered natural systems that use an assortment of plants, solids, and microorganisms to
reduce or eliminate the pollutants in water. More on “green” wastewater treatment methods is
covered in Chapter 8.
With the exception of packaging, solid wastes from food processing are biodegradable and
the amount of solid wastes and applications varies from industry to industry. The meat industry,
