Removal mechanisms of VOCs in an activated sludge process.

This study investigated the factors in plant operating parameters effecting volatile organic compound (VOC) removal and elucidated each individual mechanism in an activated sludge process (ASP). The results suggest that stripping increase with an increase in Henry's law constant with the exception of toluene, which differed because of the effect of biodegradation competition. The emission rate can be controlled by increasing the active biomass concentration (X(b)) in the aeration basin, hydraulic retention time (HRT), and oxygen transfer efficiency (OTE). Increasing X(b) enhances total VOC removal and biodegradation, which reduces the fraction of the stripping removal. Longer HRT can reduce stripping removal significantly if other variables such as oxygen requirement and OTE are held constant. For the same volatile compound, a process with higher air-to-water ratio requires a higher active biomass concentration to reduce stripping removal. Increasing OTE decreases the air-to-water ratio requirement, which reduces the gas-phase transfer of VOCs into the atmosphere. The results show a reasonable agreement between measured and predicted stripping values.