Biofilm Airlift Suspension Reactor Treatment of Domestic Wastewater

Domestic wastewater with an influent COD of 160 to 327 mg L^-1 was evaluated for treatment by the Biofilm Airlift Suspension-reactor (BAS-reactor). Ceramic materials withdiameters of 0.25–0.5 mm (for reactor (1)) and 0.5–0.71 mm(for reactor (2)) were used as carriers, respectively. Theresults show that reactor (1) with smaller carriers outperformedreactor (2) with larger carriers. At steady state, the BAS-reactors showed high COD removal efficiencies. When the HRT was kept at 0.5 hr, the mean effluent CODs were 33±4 and 58±5 mg L^-1 for reactors (1) and (2), respectively, at a confidence interval of 95% (p = 95%). When HRT was extended to 1.0 hr, these values decreased to 24±2 and 30±3 mg L^-1 for reactors (1) and (2), respectively (p = 95%). Biomass concentration increased whilebiofilm thickness decreased with an increase in carrierconcentration. Biomass concentrations as high as 6.16±0.12 and 5.50±0.10 g VSS L^-1 (p = 0.95) were achieved at carrier concentrations of 100 g L^-1 forreactors (1) and (2), respectively. Biofilm thickness had a significanteffect on reactor performance: with an increase in biofilm thickness, biomass concentration increased and the critical gas velocity to maintain carrier fluidization decreased. An oxygenation model for a BAS-reactor was proposed and the effectsof gas velocity and carrier concentration on the oxygen transfercoefficient were examined. It was found that oxygen transfer coefficient increased with gas velocity while the relationship between carrier concentration and oxygen transfer coefficient wascomplicated. During a period of more than three months of steadystate operation, carrier washout with the effluent was negligible.Comparison of the parameters of the conventional activated sludgeprocess to that of the BAS-reactor shows that the BAS-reactor isa promising wastewater treatment process with high efficiency andlow operation cost.