An Environmentally Friendly Method for Controlling Biomass in Biotrickling Filters for Air Pollution Control

Biomass accumulation is a major obstacle for long-term, stable operation of biotrickling filters treating high loadings of volatile organic compounds (VOCs). Clogging reduces pollutant removal and increases the pressure drop in biotrickling filters. Several options exist to remove excess biomass or to slow down the accumulation rate, but so far none has succeeded in combining a high VOC removal rate with a low biomass net growth rate. Recently, we observed the invasion of some of our biotrickling filters by small flies. In the best cases, a rapid reduction of the biomass content was observed. The fly larvae rapidly spread throughout the reactor and biomass was rapidly removed from the packing, initially at a rate of 13.1 kg wet weight/m.day and increasing up to 70-140 kg/m.day. In that case, the wet biomass content in the reactor was reduced from 455 to 28 kg/m reactor in 16 days with 80% of the biomass reduction occurring in 2-4 days. Analysis of the recycle liquid indicated that the major mechanism of biomass removal was detachment of biofilm, although experiments are underway to determine the exact proportion of biofilm detachment and consumption by larvae. We speculate that larval activity loosened the biofilm structure, thus enhancing biofilm detachment by shear-stress from the trickling liquid. Overall, the preliminary results presented herein highlight that the use of fly or other larvae presents a tremendous potential for controlling biomass in biotrickling filters. INTRODUCTION Biotrickling filters for waste air treatment have been extensively studied in the laboratory and efficient removal of a wide variety of organic and inorganic compounds from polluted air streams has been reported. However, the industrial deployment of biotrickling filters is still limited in spite of the many promising aspects of the treatment technique. A major obstacle to implementation of biotrickling filters in industry appears to be the instability of these reactors over the long-term. Due to rapid biomass accumulation in the packed bed, the pressure drop will increase leading to higher operational costs and pollutant removal will decrease. If no remedial action is taken, the reactor will ultimately clog. In the case of a toluene-degrading biotrickling filter with an elimination capacity of 50 g toluene/(m filter bed .