Anaerobic treatment of domestic sewage with a rotating stationary fixed-film reactor

Abstract

An anaerobic reactor was developed for on-site and small scale wastewater treatment applications. The up-flow fixed-film reactor was packed with two different types of circular media: stationary and rotating. Experimental results showed the reactor can treat primary settled domestic wastewaters efficiently, under different operating conditions. At 29°C the mixing action did not improve the organic matter removal efficiencies (65% COD removal was obtained with an organic load of 1.7 kg COD m −3 day −1 and a 6 h space time). However, at 16°C the removal efficiency was greatly dependent on the mixing conditions: a gentle agitation (5 rpm) up-graded significantly the reactor operation, but no improvement was observed beyond 15 rpm. It appears that at low temperatures liquid biofilm mass transfer is the rate limiting step when treating sewage anaerobically. Gas production was rather limited [0.11 m 3 (STP) kg −1 COD removed] and calculations suggest that more than 50% of the total CH 4 produced is lost due to its dissolution in the effluent. Improved effluent quality, reduced sludge production (0.11 kg TSS kg −1 COD supplied), low energy requirements and low maintenance needs make this reactor a good, compact alternative to conventional household wastewater treatment processes.