The Impact Of Volatile Organic Compound On Micro Fauna(Protozoa/Metazoa) Predation Of Biofilms Bacteria

Formation of biofilm and biomass accumulation as a natural phenomenon is widely investigated, but researches on the constructed biofilm employed for contaminants removal from waste gases are still very limited. Uneven biomass distribution and excess biomass accumulation are the existing most difficult problems in gas phase biofilters for a long period of operation, which would lead some serious problems including the clogging of filter bed, great pressure drop and flow channeling following the deterioration of the biofilter performance. Characteristics, mechanisms and patterns of and process modeling on biomass accumulation in gas biofiltration were summarized. Existing strategies for biomass control in gas biofiltration can be categorized into physical techniques, chemical methods, biological predation, biofilter improvement and operation mode, each of which was restricted by its own limitations. A successful method for biomass control in gas biofiltration should well manage the constructed ecosystem to less biomass accumulation and even biomass distribution in the filter bed.The bacterium used in this study was identified as Pseudomonas sp. in view of its morphology, cultural characteristics and physiological and biochemical properties. A stock culture was stored at4℃with mineral oil. The ciliates and nematodes were identified as Chilodonella and Caenorhabditis sp., respectively, in view of their morphology. They were all isolated from tubular gas-phase biofilters using toluene as the sole source of carbon and energy in our laboratory at Changsha. Caenorhabditis and Chilodonella were cultured and maintained on nematode growth medium (NGM) agar plates with Pseudomonas sp. at room temperature and transferred at least once every month.The influence of toluene concentration on the predation of toluene-degrading bacteria (Pseudomonas sp.) by ciliate (Chilodonella) and nematode (Caenorhabditis sp.) was investigated in suspended batch cultures continuously aerated with toluene-contaminated air. At gas phase concentrations of80to150mg m-3of toluene, the activities of Chilodonella and Caenorhabditis were not affected significantly, and the final concentration of Pseudomonas was found to be less than the initial concentration. As the toluene concentration was increased to300-600mg m-3, growth of Caenorhabditis was inhibited. Bacterial cell concentration showed a remarkable decline at the exponential growth phase of Pseudomonas in the mixed culture. At900 mg m-3, growth of Chilodonella was completely inhibited. In the comparison tests, specific growth rates of Pseudomonas in cultures inoculated respectively with Chilodonella, Caenorhabditis and the control group were0.033,0.042, and0.058h-1Overall, the results presented herein demonstrate that Chilodonella prey on Pseudomonas in the early stages of the experiments, thereby reducing the specific growth rates of Pseudomonas. Due to their motility, burrowing and predation, Caenorhabditis are also helpful for the control of the specific growth rate of Pseudomonas and the removal of dispersed Pseudomonas through grazing.