When water is desired to sustain and support life, it is required in adequate quantity and desirable quality. You should have learnt about the desirable quality parameters in the previous units.
One of the main reasons why water is often not in desired quality is due to contamination from various sources, especially wastes. Wastes generally could be in solid, liquid or gaseous form. Our concern here is the liquid form otherwise known as wastewaters. Please enjoy your study.
What isWaste water?
Wastewater is water containing dissolved and suspended solids from municipal or industrial sources. All the water used in the home that goes down the drains or into the sewage collection system is wastewater. This includes water from baths, showers, sinks, dishwashers, washing machines, and toilets.
Small businesses and industries often contribute large amounts of wastewater to sewage collection systems; others operate their own wastewater treatment systems. In combined municipal sewage systems, water from storm drains is also added to the municipal wastewater stream.
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Wastewater is about 99 percent water by weight and is generally referred to as influent as it enters the wastewater treatment facility.
Wastewaters come from homes (domestic wastewaters), institutions, commercial outfits, industries, farms (agricultural) and from urban areas after rain (storm runoff). The term ‘wastewater’ is more or less a replacement of the older, more restrictive term ‘sewage’. These sources are described briefly in the next section.
Sources of Wastewaters
Ogedengbe (1998) grouped the different sources of wastewaters into the following:
Domestic Wastewaters: These come from homes (residences) and consist of wastes from kitchens, toilets, bathrooms, etc. As they are derived from food wastes and fecal matter, they are highly decomposable, consisting of carbohydrates, proteins and fats in varying stages of digestion.
The strengths of such wastes are measured in terms of BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), suspended solids concentration, dissolved solids, ammonia concentrations, etc.
The BOD of typical domestic wastewaters is not much different from the BOD of wastewaters elsewhere and may range from about 200 to 500mg/l. Ammonia concentration ranges from 10 to 50mg/l and suspended solids concentration should also be about 200 to 500mg/l.
Institutional Wastewaters: These come from institutions such as schools, prisons, clinics/hospitals, etc. as can be expected, these wastewaters should be similar to domestic ones except that hospital wastes may contain in addition, clinical wastes (e.g. germs, human blood, x-ray wastes, etc).
A study by Ademoroti (1989) showed that the wastewaters from the University College Hospital community in Ibadan arises from the residences of the medical students, staff and student nurses, house officers, resident doctors, domestic servants and also from the hospital laboratories, wards and clinics.
Raw wastewaters from the institution at a time was characterised by 26 – 280C as temperature, 6.9 – 7.4 as pH and 106 – 222mg/l, 206 – 385 mg/l and (3.5 – 3.9) x 107, respectively as suspended solids, BOD and Total coliforms per 100ml sample.
Commercial Wastewaters: These come from hotels, restaurants, cafeteria, “bukataria,” markets, cottage industries and similar places. The wastes are also, by and large, domestic in character. Levels of BOD, COD, and suspended solids may be higher than those of domestic wastewater due to special inputs from the handling of milk, ice cream, sweets, etc.
A study on a medium sized market in Ile-Ife showed that the wastewaters from the market is characterized by 30.90C, 5.7, 9.4mg/l and 340.2mg/l, respectively as temperature, pH, BOD and Dissolved Solids (Eludoyin, etal.,2008).
Industrial Wastewaters: These come from industries. Common wastewater generating industries include breweries, beverages, bottling, textiles, pulp and paper, pharmaceutics, meat packing, dairies, paint, metal finishing, etc.
These wastewaters may be direct by-products of wet processes or may arise from equipment and floor washings. Thermal power plants (e.g. Egbin Thermal station) discharge hot water which on its own is a potent wastewater.
Industrial wastewaters, as a class of wastewater, are by far more complex than domestic wastewaters. This is because, in addition to having, possibly, the characteristics of domestic wastewaters as earlier described, they may contain other complex organic matter, toxic chemicals, and heavy metals, depending on the type of industries.
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Table 3 for example, shows the groups of industries in Nigeria, such that their by-products could be envisaged. It could easily be deduced that groups 1, 2, 3, 4 would be particularly involved in wastewater generation.
Agricultural Wastewaters: Apart from the domestic wastewaters generated on agricultural lands, runoffs from farmlands may be laden with dissolved agrochemicals (fertilizers, herbicides, and pesticides), animal dung, sand and silt which as non-point sources pollute aquatic environments.
Storm Runoff: Runoff from rain in urban areas may be laden with organic and inorganic dirt (depending on how dirty the community is) and may contain also sand, silt, etc.
Table 3: The Groups of Industries in Nigeria as Classified by the Manufacturers Association of Nigeria (MAN)
|1||Food, Beverages and Tobacco||Beer, starch, flavouring, soft drinks and carbonated water, flour and grain milling, meat/poultry/ fish, tea/coffee, dairy products, fruit juices, tobacco, biscuits and bakery products, animal feeds, sugar distillery and blending of spirit, cocoa/chocolate, confectionery.|
|2||Chemicals and Pharmaceuticals||Paints/vanishes, industrial/medical/special gases, soap/detergent, agro-chemicals, pharmaceuticals, foam manufacturers, safety matches, domestic insecticide aerosol, dry cell battery, petroleum refineries, gramophone/musical tape manufacturers, candle manufacturers, printing ink manufacturers, toiletries/cosmetics, basic industrial chemicals, automotive battery.|
|3||Domestic and Industrial Plastic and Rubber||Rubber products, domestic/industrial plastics|
|4||Basic Metal, Iron and Steel and Fabricated Metal Products||Steel Pipe Manufacturers Association, metal packaging manufacturers, foundry, metal manufacturers and fabricators, aluminum products, enamel wares/welding electrode manufacturers, galvanized iron sheets manufacturers, nail and wire manufacturers group, steel manufacturers.|
|5||Pulp, paper and paper products, Printing and Publishing||Chemical /stationery manufacturers, printing and publishing, pulp and paper products|
|6.||Electrical and Electronics||Electronics, refrigerators and air conditioning/ domestic appliances, electric bulbs/lamps/accessories/fittings, electric power control/distribution equipment, cable/wire|
|7||Textile, Wearing Apparel and Leather||Textile/wearing apparel manufacturers, leather products/carpets and rug/footwear manufacturers, cordage / rope/twine manufacturers|
|8.||Wood and wood products including furniture||Wood products and furniture (excluding metal furniture), plywood and particle board manufacturers|
|9.||Non-metallic mineral products||Glass/ceramics/asbestos manufacturers, school chalk and crayon, cement manufacturers|
|10||Motor vehicle and miscellaneous assembly||Boat/ship building, automotive components manufacturers, electric generator assemblers, miscellaneous, horological, motor vehicle assemblers.|
Source: Ogedengbe, 1998