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with human wastes. Sanitary wastewaters generated in residences are called domestic wastewaters (domestic sewages). Industrial wastewaters are wastewaters produced in the process of manufacturing. Thus, because a myriad of manufacturing processes are used, a myriad of industrial wastewaters are also produced. Sanitary wastewaters produced in industries may be called industrial sanitary wastewaters. To these wastewaters may also be added infiltration and inflow.

Wastewaters are conveyed through sewers. Various incidental flows can be mixed with them as they flow. For example, infiltration refers to the water that enters sewers through cracks and imperfect connections and through manholes. This water mostly comes from groundwater and is not intended to be entering into the sewer. Inflow is another incidental flow that enters through openings that have been purposely or inadvertently provided for its entrance. Inflow may be classified as steady, direct and delayed. Steady inflows enter the sewer system continuously. Examples of these are the discharges from cellar and foundation drains that are constantly subjected to high groundwater levels, cooling water and drains from swampy areas, and springs. Direct inflows are those inflows that result in an increase of flow in the sewer almost immediately after the beginning of rainfall. The possible sources of these are roof leaders, manhole covers, and yard drains. Delayed inflows are those portions of the rainfall that do not enter the sewer immediately but take some days to drain completely. This drainage would include that coming from pumpage from basement cellars after heavy rains and slow entries of water from ponded areas into openings of manholes. Infiltration and inflows are collectively called infiltration-inflow.

1.4 sources and quantities of wastewater

The types of wastewaters mentioned above come from various sources. Sanitary wastewaters may come from residential, commercial, institutional, and recreational areas. Infiltration-inflow, of course, comes from rainfall and groundwater, and industrial wastewaters come from manufacturing industries.

The quantities of these wastewaters as they come from various sources are varied and, sometimes, one portion of the literature would report a value for a quantity of a parameter that conflicts on information of the quantity of the same parameter reported in another portion of the literature. For example, many designers often assume that the amount of wastewater produced is equal to the amount of water consumed, including the allowance for infiltration-inflow, although one report indicates that 60 to 130% of the water consumed ends up as wastewater, and still another report indicates that 60 to 85% ends up as wastewater. For this reason, quantities provided below should not be used as absolute truths, but only as guides. For more accurate values, actual data should be used.

1.4.1 Residential

Flow rates are commonly normalized against some contributing number of units. Thus, flow rates from residences may be reported as liters per person per day (normalized against number of persons), or flow rates from a barber shop may be reported as liters per chair per day (normalized against number of chairs) and so on.

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