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BIOLOGICAL TREATMENT Biological treatment is employed when chemical and mechanical treatments cannot offer the required level of purification to render the wastewater suitable for disposal. Waste water which is to be discharged into a watercourse would have to be treated to a high quality. If the waste water was going to be discharged into the sewerage system the degree of purification would not be so great and only partial treatment would be required.
Wastewater generated from agricultural and food operations has
distinctive characteristics that set it apart from common
municipal wastewater managed by public or private wastewater
treatment plants throughout the world: it is biodegradable and
nontoxic, but that has high concentrations of biochemical oxygen
demand (BOD) and suspended solids.
The constituents of food and agriculture wastewater are often
complex to predict due to the differences in BOD and pH in
effluents from vegetable, fruit, and meat products and due to
the seasonal nature of food processing and postharvesting. Animal slaughter and processing produces very strong organic waste from body fluids, such as blood, and gut contents. This wastewater is frequently contaminated by significant levels of antibiotics and growth hormones from the animals and by a variety of pesticides used to control external parasites. Insecticide residues in fleeces is a particular problem in treating waters generated in wool processing. Processing food for sale produces wastes generated from cooking which are often rich in plant organic material and may also contain salt, flavourings, colouring material and acids or alkali. Very significant quantities of oil or fats may also be present.
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