Characterising the quantity and quality of domestic wastewater inflows

A major source of inflow into sewer networks derives from domestic (sanitary) wastewater. The wastewater is made up of contributions from the various household appliances, influencing both flow quantity and quality. The results from two appliance usage surveys are presented to give detailed insight into the sub-daily variations of flow (quantity) and the relative importance of each appliance throughout the day. The most significant wastewater generating appliance is shown to be the WC, with the least contribution coming from the wash-basin. To establish at-source quality and its variation, limited published information was analysed in conjunction with the survey data. The contribution of each appliance to a wastewater pollutant concentration is a combination of both the appliance flow rate and pollutant load, the proportions of which vary throughout the day. Pollutagraphs were produced for BOD, ortho-phosphate, ammonia and nitrate. The WC was found to be a major contributor to all four pollutants and in particular to ammonia. The washing machine was a significant contributor to ortho-phosphate and nitrate and the wash-basin to ortho-phosphate. Inflow pollutant concentrations were of comparable magnitude to published treatment plant data, although BOD values were found to be higher than expected.