Toluene removal in membrane bioreactors under recirculating and non-recirculating liquid conditions

A single-, dual- and multiple-tube dense phase silicone rubber membrane bioreactor were investigated for control of toluene-contaminated air under circulating and non-recirculating liquid conditions. A mathematical model was developed to describe the system. The reactors were seeded with a mixed bacterial consortium isolated from activated sludge and capable of aromatic biodegradation. After operating with recirculating liquid nutrient solution, the reactors were operated with no recirculation of the liquid, for 50 days or more in each instance. Average toluene removal measured in the single-tube reactor was 93 ppm with recirculating liquid and 102 ppm without recirculation of the liquid. Average removal measured in the dual-tube reactor was 396 ppm with recirculating liquid and 319 ppm without recirculation of the liquid. Operation under stagnant liquid conditions had no significant detrimental impact on bioreactor performance. Biokinetic parameters were measured for both the suspension and biofilm with values of the maximum specific utilization rate values (k) ranging from 0.01 to 0.42 h−1 and half saturation constant values (K S) ranging from 1.5 to 14.3 mg L−1. Results suggest that membrane bioreactors might be operated under non-recirculating liquid conditions without performance detriment, reducing or eliminating the energy requirements and costs associated with pump operation.