ABSTRACT
Domestic wastewater flows are commonly determined from domestic water consumption: https://www.w3.org/1998/Math/MathML"> Q w w = 10 − 3 k q P https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781849771023/0aa6a831-bb0d-4822-a2f5-f60c0c20562c/content/math74_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> where Q ww is the wastewater flow, m3/day; q is the water consumption, l/person day; P is the population connected to the sewerage system; and k is the ‘return factor’, the fraction of the water consumed that becomes wastewater. The value of k is usually 0.8–0.9. It is lower in rich areas where water is used for car washing and garden watering. Equation 7.1 gives the domestic wastewater ‘dry weather flow’ (DWF) – a term used principally from the time when ‘combined’ sewers (ie sewers receiving both sanitary and stormwater flows) were common. (Combined sewers do exist in developing countries, especially in city centres, but the current preference is to separate sanitary and stormwater flows.) Dry weather flow is the average wastewater flow per day over seven consecutive days without any rain which follow seven days with no more than 0.25 mm of rain on any one day. The mean daily flow is often taken as 1.3 × DWF.
