Removal of a Volatile Organic Compound in a Hybrid Rotating Drum Biofilter

A hybrid bioreactor, combining an activated sludge process (ASP) and a rotating drum biofilter (RDB), was developed and evaluated for the treatment of volatile organic compounds (VOCs) in waste gas streams. The effects of the influent VOC concentration and the organic loading rate on the VOC removal efficiency and on the pattern of biomass accumulation were investigated. Toluene was used as the model VOC, the flow rate of the waste gas stream was 0.59 L/s, and the empty-bed retention time (EBRT) in the ASP portion was 46 s with an actual retention time of about 2 s. The EBRT in the RDB portion was 38 s based on the drum volume. When the VOC feed concentration increased from 221 to 884 mg toluene/m3 (from 57.2 to 229 ppm), correspondingly the organic loading rate of the hybrid bioreactor increased from 1.58 to 6.32 kg chemical oxygen demand/m3/day (from 0.505 to 2.02kg?toluene/m3/day) based on the drum volume, both the ASP and RDB decreased, and the overall toluene removal efficiency declined from 99.8 to 74.1%. Biomass accumulation at different medium depths became more even when the organic loading rate was increased. Part of the applied VOC was biodegraded by the ASP, which suggests that this hybrid bioreactor could achieve longer runs between medium cleanings and higher VOC removal efficiencies than a single RDB bioreactor without an ASP portion at the same organic loading rate.