Physical, chemical and biological characteristics of stored greywater from unsewered suburban Dakar in Senegal

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There is a lack of data on the characteristics of greywater (GW) from developing countries. Published data on GW quality in Senegal were not found in the literature. The lack of data has probably led to the public perception that GW is innocuous and, as such, to the careless handling of it. A physical, chemical and microbiological characterization of mixed household GW was undertaken at Apecsy, in unsewered north suburban Dakar, with the view of determining the extent of health hazards related to the hand carrying disposal of GW effluents. Samples were collected from a GW holding tank every 2 hours over a 24-h period and analysed for temperature, pH, electrical conductivity (EC), faecal coliforms (FC), E. coli, dissolved oxygen (DO), BOD5, COD, TOC, TS, SS, VTS, TN, NH4 – N, NO3 – N, TP and PO4 – P. Results were then compared with raw combined domestic wastewater (CDW) data from Dakar and reported data on GW and CDW from both industrial and developing countries. FC and E. coli densities were lower in GW than in CDW but remained significantly high in spite of the absence of urine and faeces. The organic matter was five times higher in GW and its chemical nature quite different from that of organic matter in CDW. GW was three times higher in solids than CDW but the chemical characteristics and size distributions of solids were found to be quite similar in two samples. GW was slightly lower in nitrogen and phosphorus than CDW. The high GW strength seems to be due to the much lower flow associated with the presence of large amounts of food particles and the storage of effluents. Results have shown that GW generated from unsewered suburban Dakar may be equally or more polluted than CDW and, as such, deserves much more attention from both public authorities and populations themselves.