Feasibility study of a pilot-scale sewage treatment system combining an up-flow anaerobic sludge blanket (UASB) and an aerated fixed bed (AFB) reactor at ambient temperature

A feasibility test of a 17 m³-pilot-scale sewage treatment system was carried out by continuous feeding of raw municipal sewage under ambient temperature conditions. The system consisted of a UASB and an aerated fixed bed reactor. Some of the effluent from the fixed bed reactor was returned to the UASB influent in order to provide a sulfate source. The total BOD of 148-162 mg l^-1 in the influent was reduced to a more desirable 11-25 mg l^-1 in the final effluent. The levels of methane-producing activity from acetate and H₂/CO₂ gas at 10 °C were only 2% and 0% of those at 35 °C, respectively. On the other hand, the sulfate-reducing activity levels of the UASB sludge were relatively high at 10 °C, for example, 18% for acetate and 9% for H₂/CO₂ gas, compared to the activity levels at 35 °C. Therefore, BOD oxidization by sulfate reduction in the UASB was greater than that by methane production under low temperature conditions. This sulfate-reducing activity tended to be proportional to the copy number of adenosine-5′-phosphosulfate (APS) reductase genes in DNA extracted from the sludge.