PERFORMANCE EVALUATION OF ROTATING DRUM BIOFILTERS FOR VOC REMOVAL: EFFECTS OF GAS CONTACT TIME AND VOC PROPERTIES

Pilot-scale rotating drum biofilters (RDBs) were used to investigate the effects of gas empty bed contact time (EBCT) and inlet VOC concentrations on RDB performances for VOC removal from waste gas streams. Three types of RDBs, a single-layer biofilter, a multi-layer biofilter, and a hybrid biofilter, were used in this study. Spongy media were mounted in a cylindrical drum to support the growth of biofilms in the RDBs. Diethyl ether, toluene, and hexane were selected as the model VOC, and were evaluated separately at various gas EBCTs at a constant VOC loading rate for each the RDB. When diethyl ether or toluene was used as the model VOC, VOC removal efficiencies in the three RDBs remained constant when EBCT values were high, and decreased when the EBCT values decreased. The single-layer and hybrid RDBs both exhibited a decrease in VOC removal efficiency at the highest and lowest EBCT level, respectively. At an organic loading rate of 2.0 kg COD/m3/d, the hybrid biofilter reached VOC removal efficiency exceeding 99% for EBCTs of 15 and 30 s when fed either diethyl ether or toluene. The multi-layer biofilter achieved an average VOC removal efficiency greater than 99% at an EBCT of 30 s for the removal of both diethyl ether and toluene. The single-layer biofilter reached VOC removal efficiencies of 98% and 99% only at an EBCT of 90 s when fed either ether or toluene. When hexane was used as the model VOC, its removal efficiency in both the multi-layer and hybrid RBDs decreased and was below 57% at an organic loading rate of 0.25 kg COD/m3/d and an EBCT of 120 s. The three types of RDBs could efficiently remove and biodegrade diethyl ether and toluene separately from waste gas streams at low EBCT values, and the single-layer, multilayer, and hybrid RDBs exhibited the lowest, middle, and highest removal efficiencies, respectively under similar operating conditions. Hexane removal efficiency was low under the conditions investigated in this study. The VOC removal efficiency decreases with decreasing EBCT for all the three VOCs. The VOC removal efficiency was found to be very sensitive to EBCT for shorter values of the contact time. Process selection and design of RDBs should consider these factors.