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

Raw domestic wastewater was treated continuously under laboratory conditions for 170 days by a chemically enhanced primary sedimentation (CEPS) followed by an upflow anaerobic sludge blanket (UASB) reactor. The CEPS was carried 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 the natural primary sedimentation (NPS), the CEPS increased the ratio of soluble chemical oxygen demand to volatile suspended solids (CODs/VSS) of the supernatant 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 wastewater by a factor 1.4. This resulted in a low influent concentration supplied to the UASB reactor and consequently a low biogas production. However, the reactor achieved 54 % removal of total COD (CODt) at a hydraulic retention 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 ratio, also allowed to increase the CODs content of the wastewater by a factor 2.2. As a consequence, the reactor produced a higher amount of biogas. The 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 reactor by a factor 0.4.