Effect of operating conditions on long-term performance of a biofilter treating gaseous toluene: Biomass accumulation and stable-run time estimation

To achieve a stable performance during long-term operation of biofiltration process, the effect and control of excess biomass accumulation should be investigated in detail. In this study, a biofilter treating gaseous toluene was operated continuously under different operating conditions for more than 270 days. Decrease in toluene removal efficiency and increase in pressure drops of the filter bed were simultaneously observed during the operation period due to excess biomass accumulation. The distributions of toluene concentration and gas pressure suggested that more biomass would accumulate in the inlet section. By carbon balance analysis, the variation of the biomass concentration in the biofilter was calculated. The variation of the biofilter performance and the biomass concentration demonstrated that 10,000 g C m−3 might be a critical biomass concentration for the biofilter to maintain a stable operation. An evaluation equation based on biomass growth kinetics was successfully established and used to estimate the stable-run time of a biofilter under different VOCs loadings. Bed mixing was found to be able to remove approximately 4000 g VSS m−3 of excess biomass and could also recover the performance of the biofilter.