Use of sulfur dioxide in pretreatment of
fruits or sodium bisulfide in processing may
cause the sulfurcontent of wastewater to be
high enough to cause pollution problems.
These pollutants exist primarily as sulfite
and sulfate ions or precipitates. Also, sulfides
require more available oxygen if present in
water. Sulfide ions combine with various
multivalent metal ions to form insoluble pre-
cipitates, which can settle out and be
removed with the sludge. Sulfate and sulfide
determinations are possible with a trained
technician and minimal equipment. Sulfides
contribute to an undesirable odor and taste
in drinking water. Thus, it is important to
test for these compounds if the wastewater is
discharged into a stream that supplies drink-
ing water.
Solid waste disposal
Solid waste residues are composed of
process discards, residues of the process of
wastewater treatment, and organic and inor-
ganic garbage. The process of biotransfor-
mation of these residues in fertilizer is an
alternative that should be evaluated, because
of the possibility of biogas generation in one
of the parts of a fermentation process.
Disposal of solid wastes is a major chal-
lenge for the food industry. In food indus-
tries such as canneries, up to 65% of the raw
materials received must be disposed of as
solid waste. The most common method for
disposal has been to truck the wastes to
municipal garbage dumps. If a dump is not
nearby and the wastes are disposed on the
plant site, odor and insect problems will be
created. Some processing firms handle solid
wastes by composting, and the finished com-
post can then be applied to the soil as fertil-
izer. A typical analysis of composted
material is 1.25% nitrogen, 0.4% phosphates,
and 0.3% potash. Some municipal waste
treatment facilities manufacture and sell
solid waste materials for agricultural appli-
cation.
If composting is used, the organic matter
in waste material must be stabilized through
microbial action. Humus, which results from
stabilization of waste material, improves fer-
tility and tillage properties. The basic com-
posting procedures has four steps:- Solid waste material should be com-
minuted (pulverized) to expose the
organic matter to microbial attack. - The comminuted waste should be
stacked in windrows approximately 2 m
high and 3 m wide. - Aeration should be provided.
- After extensive aeration, the compost
should be comminuted again.
Addition of an inoculum will accelerate
the composting process. This process is pro-
duced through those aerobic thermophilic
microorganisms present in the waste mate-
rial in 10 to 20 days, depending on tempera-
ture and waste composition.
In addition to compost, various food
product wastes can be dehydrated and
ground for feed use. An example is the press
liquors of tomato processing wastes. The
residue from alcohol manufacture can be
dried and fed to livestock. Citrus wastes,
including activated sludge from treatment,
can also be dried and used as animal feed
because they contain B vitamins and protein.
Processed whey and rendered animal by-
products are also valuable foods for animal
consumption.
Liquid waste disposal
Whenever food is handled, processed,
packaged, and stored, wastewater is gener-
ated. Quantity, pollutant strength, and
nature of constituents of processing waste-