Quality of individual domestic greywater streams and its implication for on-site treatment and reuse possibilities.

A sampling campaign was conducted in order to characterise the quality and quantity of individual domestic greywater streams. Based on the results, various scenarios of inclusion and / or exclusion of different greywater streams were explored, and their implication for on-site greywater treatment and reuse options are discussed. Domestic greywater was found to contribute as much as 55-70% of the specific daily load of TSS and BOD, in municipal sewage. The kitchen sink was signalled out as a major contributor of VSS, CODt, and BODt with 58%, 42% and 48%, of their total daily load respectively. The washing machine was established as a significant contributor of sodium, phosphate and CODt (40%, 37% and 22% of the total load). The dishwasher, although contributing only 5% of the flow, was found to be a significant contributor of phosphate and boron. The wash basin was found to be the least polluting appliance. As "demand" for greywater within the urban environment is lower than its "production", it is logical to recycle only the less polluted greywater streams. In order to explore the consequences of the above concept on discharge volume, pollutants loads and concentrations, 18 scenarios were studied, in each at least one stream was excluded from the combined greywater stream. Exclusion of the joined stream of the kitchen sink plus the highly polluted streams of the washing machine (wash + 1st rinse) and dishwasher (pre-rinse + wash) significantly improved greywater quality, with the advantage of leaving enough greywater to be reused (65-70 l/c/d).