Physical, chemical and microbiological characteristics of stored greywater from unsewered urban Dakar, Senegal

Abstract

Few studies have focused on the quality of greywater (GW) from urban developing countries. In the absence of urine and faeces, GW is generally considered as innocuous and as such, little attention is devoted to it. A physical, chemical and microbiological characterization of household GW from mixed sources was undertaken at Apecsy, in unsewered north suburban Dakar, with the aim of measuring the extent of health hazards related to the hand carrying system of GW. Samples were collected each two hours from a holding tank over 24 hours and analyzed for temperature, pH, EC, DO, FC and E coli, BOD5, COD, TOC, TS, SS, VTS, TN, NH4-N, NO3-N, TP and PO 4-P. Results were then compared with raw combined domestic wastewater (CDW) and GW data from Dakar and developed countries. FC and E coli were lower in Apecsy GW compared to CDW from Dakar but varied in the same range as in typical raw CDW from the USA. GW was 5 times higher in organic matter and 3 times higher in solids than CDW. The chemical characteristics of organic matter and solids and the size distribution thereof in GW and CDW were similar. The organic matter in GW was found to be roughly biodegradable in spite of a severe nutrient deficiency noted. GW was of lower nitrogen and phosphorus. The higher GW strength was attributed to the combined effects of low flow and the storage of effluents, which are dependent on the hand-carrying system. The GW from unsewered urban developing countries may be more polluted than ordinary domestic wastewaters and as such, a change of attitude towards it is needed.