Farms with large
livestock and
poultry operations, such as
factory farms, can be a major source of
point source wastewater. In the United States, these facilities are called
concentrated animal feeding operations or
confined animal feeding operations and are being subject to increasing government
regulation.
Antibiotic-resistant bacteria have been found to infiltrate the water cycle from farms. Raising animals accounts for 73% of antibiotics use globally, and wastewater treatment facilities can transfer antibiotic-resistant bacteria to humans.''''''
Animal wastes The constituents of animal wastewater typically contain • Strong organic content — much stronger than human sewage • High
solids concentration • High
nitrate and phosphorus content •
Antibiotics • Synthetic
hormones • Often high concentrations of
parasites and their eggs • Spores of
Cryptosporidium (a protozoan) resistant to drinking water treatment processes • Spores of
Giardia • Human pathogenic bacteria such as
Brucella and
Salmonella Animal wastes from cattle can be produced as solid or semisolid manure or as a liquid
slurry. The production of slurry is especially common in housed dairy cattle.
Treatment Whilst solid manure heaps outdoors can give rise to polluting wastewaters from runoff, this type of waste is usually relatively easy to treat by containment and/or covering of the heap. Animal slurries require special handling and are usually treated by containment in lagoons before disposal by spray or trickle application to grassland.
Constructed wetlands are sometimes used to facilitate treatment of animal wastes, as are
anaerobic lagoons. Excessive application or application to sodden land or insufficient land area can result in direct runoff to watercourses, with the potential for causing severe
pollution. Application of slurries to land overlying
aquifers can result in direct contamination or, more commonly, elevation of nitrogen levels as
nitrite or nitrate. The disposal of any wastewater containing animal waste upstream of a drinking water intake can pose serious health problems to those drinking the water because of the highly resistant spores present in many animals that are capable of causing disabling disease in humans. This risk exists even for very low-level seepage via shallow surface drains or from rainfall run-off. Some animal slurries are treated by mixing with straws and
composted at high temperature to produce a bacteriologically sterile and friable manure for soil improvement.
Piggery waste confinement barn or
piggery Piggery waste is comparable to other animal wastes and is processed as for general animal waste, except that many piggery wastes contain elevated levels of
copper that can be toxic in the natural environment. The liquid fraction of the waste is frequently separated off and re-used in the piggery to avoid the prohibitively expensive costs of disposing of copper-rich liquid.
Ascarid worms and their eggs are also common in piggery waste and can infect humans if
wastewater treatment is ineffective.
Silage liquor Fresh or wilted
grass or other green crops can be made into a semi-
fermented product called
silage which can be stored and used as winter forage for cattle and sheep. The production of silage often involves the use of an acid conditioner such as
sulfuric acid or
formic acid. The process of silage making frequently produces a yellow-brown strongly smelling liquid which is very rich in simple
sugars,
alcohol, short-chain organic acids and silage conditioner. This liquor is one of the most polluting organic substances known. The volume of silage liquor produced is generally in proportion to the moisture content of the ensiled material. Silage liquor is best treated through prevention by wilting crops well before silage making. Any silage liquor that is produced can be used as part of the food for pigs. The most effective treatment is by containment in a slurry lagoon and by subsequent spreading on land following substantial dilution with slurry. Containment of silage liquor on its own can cause structural problems in concrete pits because of the acidic nature of silage liquor.
Milking parlour (dairy farming) wastes Although milk is an important food product, its presence in wastewaters is highly polluting because of its organic strength, which can lead to very rapid
de-oxygenation of receiving waters.
Milking parlour wastes also contain large volumes of wash-down water, some animal waste together with cleaning and
disinfection chemicals. Milking parlour wastes are often treated in
admixture with human sewage in a local
sewage treatment plant. This ensures that disinfectants and cleaning agents are sufficiently diluted and amenable to treatment. Running milking wastewaters into a farm slurry lagoon is a possible option although this tends to consume lagoon capacity very quickly. Land spreading is also a treatment option.
Slaughtering waste Wastewater from slaughtering activities is similar to milking parlour waste (see above) although considerably stronger in its organic composition and therefore potentially much more polluting. Treatment is as for milking parlour waste.
Vegetable washing water Washing of
vegetables produces large volumes of water contaminated by soil and vegetable pieces. Low levels of pesticides used to treat the vegetables may also be present together with moderate levels of disinfectants such as
chlorine. Most vegetable washing waters are extensively recycled with the solids removed by settlement and filtration. The recovered soil can be returned to the land.
Firewater Although few farms plan for fires, fires are nevertheless more common on farms than on many other industrial premises. Stores of pesticides, herbicides, fuel oil for farm machinery and fertilizers can all help promote fire and can all be present in environmentally lethal quantities in
firewater from
fire fighting at farms. All farm environmental management plans should allow for containment of substantial quantities of firewater and for its subsequent recovery and disposal by specialist disposal companies. The concentration and mixture of contaminants in firewater make them unsuited to any treatment method available on the farm. Even land spreading has produced severe taste and odour problems for downstream water supply companies in the past. ==See also==