Technical feasibility of the treatment of domestic wastewater by a CEPS-UASB system

Raw domestic wastewater was treated continuously under laboratory condition s for 170 days by a chemically enhanced primary sedimentation (CEPS) follow ed by an upflow anaerobic sludge blanket (UASB) reactor. The CEPS was carri ed our with 70 mg FeCl(3)l(-1) from day 1 to 82 and with 24 mi l(-1) of the water extract of Moringa oleifera seeds from day 83 to 170. Compared to th e natural primary sedimentation (NPS), the CEPS increased the ratio of solu ble chemical oxygen demand to volatile suspended solids (CODs/VSS) of the s upernatant by a factor 3 and 10 respectively. Although the FeCl3 increased the CODs/VSS ratio, it caused a decrease of the soluble content of the wast ewater by a factor 1.4. This resulted in a low influent concentration suppl ied to the UASB reactor and consequently a low biogas production. However, the reactor achieved 54 % removal of total COD (CODt) at a hydraulic retent ion time (HRT) of 2 hours and a volumetric loading rate (Bv) of 1.4 g COD l (-1) d(-1). The Moringa oleifera seeds, besides the increase of CODs/VSS ra tio, also allowed to increase the CODs content of the wastewater by a facto r 2.2. As a consequence, the reactor produced a higher amount of biogas. Th e reactor achieved 71 % removal of CODt at a HRT of 2 hours and a By of 1.4 g COD l(-1) d(-1). The UASB reactor operated without the need to discharge regularly the biological excess of sludge produced. The implementation of the CEPS can decrease the volume needed by a conventional one step UASB rea ctor by a factor 0.4.