Studies on the Influence of Different Metabolic Uncouplers on the Biodegradation of Toluene in a Differential Biofilter Reactor

One of the biggest challenges in a traditional biofilter is to overcome the low volumetric degradation rate, which often makes the footprint excessive. The volumetric degradation rate or elimination capacity (EC) is directly influenced by the specific biodegradation rate of the microorganism involved in degrading the pollutants. Application of metabolic uncouplers in biofiltration could improve the biodegradation rate of microorganisms, which in turn could increase the EC. The addition of metabolic uncouplers to the growth system decreases the biomass growth whereas in energy-excess, non-growth systems like biofiltration, it is expected to increase the specific substrate uptake rate since the substrate requirement for maintenance energy should increase, which in turn should increase the EC. Seven potential metabolic uncouplers were screened in batch serum bottles and subsequently tested in a continuous biofilter reactor with soil as the biofilter medium. The metabolic uncouplers tested were benzoic acid, carbonylcyanide p-trifluoromethoxy phenylhydrazone (FCCP), carbonylcyanide m-chloromethoxy phenylhydrazone (CCCP), pentachlorophenol (PCP), malonic acid, 2, 4, 6-trichlorophenol (TCP) and m-chlorophenol (mCP). Only PCP and 2, 4, 6-TCP increased the toluene degradation rate significantly. PCP increased the toluene degradation rate by 35% at 140 μM, whereas 4051 μM TCP increased the rate by 18%. FCCP did not significantly affect the degradation rate and the other metabolic uncouplers decreased the degradation rate. Five toluene degraders were isolated from soil subjected to toluene and were identified using 16s rDNA/18s rDNA analysis. Out of five, two potential toluene degraders, Stenotrophomonas maltophilia and Pseudomonas putida were used to develop a biofilm reactor. PCP, TCP and CCCP were tested in the biofilm reactors and found that PCP increased the surface elimination capacity (SEC) by 85% at 140 µM in S. maltophilia biofilm reactor and CCCP increased the SEC by 27% at 1 µM in P. putida biofilm reactor.