Treatment of hydrophobic volatile organic compounds using two-liquid phase biofilters.

The traditional one-liquid phase biofilter (OLPB), with water as the selected liquid phase, demonstrated low performance to volatile hydrophobic organic compounds. In this study, a novel two-liquid phase biofilter (TLPB) using silicone oil and water was established to treat gaseous dichloromethane (DCM). A comprehensive investigation of removal performance, kinetic analysis, biomass accumulations, pressure drops, CO2 productions, and microbial communities of the two biofilters was compared. Results showed that TLPB presented an average removal efficiency of 85% during 200 days of operation, which was higher than that of OLPB (63%). Owing to the buffering effects caused by silicone oil, TLPB demonstrated a superior fluctuation resistance capability than OLPB. TLPB was determined at a higher actual mass distribution coefficient of 6.00 than that of the OLPB (3.99), thereby suggesting a significantly more effective mass transfer process inside TLPB compared with that in OLPB. Furthermore, a rapid biomass accumulation process was observed in TLPB. The specific growth rates of biomass in OLPB and TLPB were calculated as 0.035 and 0.026 g of dry biomass/g of dry filter per day, respectively. The carbon balances were analyzed in the two biofilters. The yield coefficients (Y) were determined at 1.449 and 1.143 g of dry biomass/g of removed VOC for OLPB and TLPB, respectively. However, the corresponding CO2 production fraction was 0.263 g and 0.316 g per 1 g of DCM for OLPB and TLPB, respectively. The variations in fraction of carbon in DCM transformation to biomass and to CO2 suggested distinct microbial transformation pathways of utilizing DCM in the two biofilters, which were mainly caused by the different microbial communities and metabolic activities.