Domestic sewage treatment in a pilot system composed of UASB and SBR reactors

The results obtained from the operation of a treatment system composed of a n anaerobic (up-flow sludge blanket - UASB) reactor followed by an aerobic (sequencing batch - SBR) reactor treating domestic sewage are presented and discussed. The pilot plant was monitored during 6 months, aiming to obtain performance data on organic matter, nitrogen and phosphate removal under d ifferent operating conditions. The UASB reactor was operated at a constant hydraulic detention time (theta ) of 6 h while the SBR V performance was monitored in four different durati on cycles (24, 12, 6 and 4 h) corresponding to aeration 4- j times (AT) of 22, 10, 4 and 2 h, respectively. COD and TSS overall removal efficiencies (Eo) up to 91 % and 84%, respectiv ely, were achieved independently on the aeration time applied to the SBR. I n respect to nitrification and phosphate removal, AT was found to be a dete rminating operating parameter. TKN removal of approximately 90% was achieve d for AT equal to or higher than 10 h; complete nitrification occurred for AT higher than 4 h; significant phosphate removal (72 %) occurred only at t he AT of 2 h. It was not possible to achieve simultaneous efficient removal of nitrogen and phosphate, under the operating conditions imposed on the t reatment system.