Biodegradation of MTBE in a pilot-scale biofilter

A pilot-scale biofilter was inoculated with a MTBE degrading culture. The biofilter acclimated within three weeks, and achieved greater than 95% removal of MTBE (based on inlet MTBE concentrations averaging 35 ppmv), at the end of 10 weeks. The biofilter was fed the same concentration of MTBE for about 180 days, and achieved close to 100% removal consistently. Toluene was then introduced at a concentration of about 8 ppmv initially, then 25 and 70 ppmv, over a period of 3 weeks, while the MTBE concentration was maintained the same. The biofilter acclimated quickly to toluene, achieving greater than 90% removal within the first 6 hours. The presence of toluene at 8 and 25 ppmv did not seem to influence MTBE degradation. At 70 ppmv toluene however, both MTBE and toluene removal efficiency dropped gradually to less than 70% over the period of 8 days. This drop was believed to be the result of nitrogen limitation in the biofilter. The same drop in removal efficiency was observed when the biofilter was fed a higher concentration of MTBE (70 ppmv), after the toluene feed has been cut off. An increase in the nitrogen concentration in the nutrient solution feed, resulted in almost complete recovery of the biofilter.