Heat Transfer and Toluene Removal in Bench-Scale Membrane Bioreactors

摘要

Membrane bioreactors are increasingly being examined in the laboratory for removal of low contaminant concentrations from industrial waste gases, as they offer several distinct advantages over conventional biofiltration units. A dense phase silicone rubber membrane module was investigated for control of toluene-contaminated air under elevated recirculating liquid temperatures (37.5 °C). The reactor was seeded with a mixed bacterial consortium isolated from activated sludge and capable of aromatic biodegradation. After operation at room temperature, the reactor was operated with elevated temperatures on the liquid side and showed no statistically significant improvement in performance. At the same inlet concentration (～1000 ppm), an average removal of 20 g toluene m~(-3) h~(-1) was observed for the heated reactor compared with 17 g toluene m~(-3) h~(-1) removal at ambient temperature. Biokinetic parameters were measured for both the suspension and biofilm under ambient and elevated temperature conditions. Monod-like parameters were as follows: heated biofilm K_S = 0.8 mg L~(-1), k = 0.09 hr~(-1); heated suspension K_S =1.3 mg L~(-1), k = 0.07 hr~(-1); ambient biofilm K_S = 12.0 mg L~(-1), k = 0.2 hr~(-1); ambient suspension K_S = 1.5 mg L~(-1), k = 0.01 hr~(-1). Heat transfer coefficients of lab-scale dense phase (silicone and latex rubber) and polyporous (polysulfone) hollow fiber membrane modules were measured. Heat transfer coefficients ranged from 2.9 -17.4 W m~(-2) K~(-1) and varied somewhat between reactor modules, suggesting certain membrane materials might transfer less heat from high temperature gas streams to the attached biofilm and suspension in membrane bioreactors.