Evaluation of trickle bed air biofilter performance for BTEX removal

Biofiltration of a gaseous stream contaminated with benzene, toluene, ethylbenzene, and the three xylene (BTEX) compounds was evaluated in this study. Experimental investigations were conducted on a pilot-scale biofilter containing randomly packed 6-mm R-635 Celite pellets as biological attachment media. The main focus of the study was to expand biofiltration technology to treat high volatile organic compounds (VOC) concentrations while maintaining consistently high removal efficiencies. Operational parameters investigated were BTEX loading, empty bed residence time (EBRT), backwashing frequency and duration, recovery of biofilter removal efficiency after backwashing, development of removal rate constants, and nutrient-phosphorous (nutrient-P) limitation as a biomass control. Periodic backwashing of the biofilter with medium fluidization was necessary for removing excess biomass and attaining stable long-term high removal efficiencies. Removal efficiencies above 99% were achieved for all the BTEX components for loadings up to 1.8 kg chemical oxygen demand (COD)/m(3)/d. Stable overall removal efficiencies of 88% were achieved for a BTEX loading of 6.2 kg COD/m(3)/d and an EBRT of 0.67 min. Evaluations of pseudo-steady-state performance data, one day following backwashing, yielded first-order removal rate constants for all the BTEX components. Removal efficiencies above 99% at BTEX loading of 2.1 kg COD/m(3)/d were attained for a period of 14 d without biofilter backwashing in the absence of nutrient-P.