Study On Performances And Microbial Ecology Of Biofilters/biotrickling Filters For Odor Removal

Odor pollution is one of the seven public pollutions in the world, and it is urgent to find effective control approach for odor pollution. Biofilter/biotrickling filter is an attractive odor removal technique with the advantages of cost-effectiveness and easy operation. High efficiency of biofilter/biotrickling filter has been demonstrated in many applications. However, the lack of overall knowledge with respect to microbial ecology, process control and new effective packing materials are drawbacks. In order to eliminate these drawbacks in biofilters/biotrickling filters, bench scale studies were carried out with trimethylamine (TMA), n-butyric acid and ammonia which have odor of low threshold concentrations. The performances of different biofilters/biotrickling filters, biotransformation mechnism of odor in reactor, variations of the microbial community composition, and the relationship between performance and microbial ecology were identified. Based on the results, operation control strategy, a new-style packing materials for biotrickling filter, as well as optimal operating parameters are put forward.Biofiltration of TMA in two three-stage biofilters packed with compost (A) and sludge (B) was investigated. TMA was successfully removed by both biofilters with 100 % efficiency. The efficiency of stage 1 of biofilter A was more than 80 % and that of biofilter B was only around 60 %. The maximum elimination capacities in stage 1 of biofilters A and B were 9.31 and 9.13 g TMA m^-3 h^-1, respectively. TMA biotransformation mechanisms were different in two biofilters. NH₃ produced by biodegradation of TMA could be removed and converted to NO₃-N in biofilter A, whereas biodegradation of TMA and adsorption of ammonia found in biofilter B. Spatial and temporal shifts of bacterial community compositions in both biofilters developed differently, which were assessed by using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) followed by clone library analysis. Besides TMA-degrading bacteria, Nitrosospira multiformis, an ammonia-oxidizing bacterium was also in compost biofilter. However, only TMA-degrading bacteria existed in sludge biofilter. The absence of ammonia-oxidizing bacterium is the biological limiting factor observed in terms of biodegrading TMA in biofilter B. Subsequently, a control strategy was put forward. It is necessary for the sludge packing material to be inoculated with ammonia-oxidizing bacteria in order to initiate ammonia oxidation in bioreactor and thus a continuous operation would be feasible.Biofiltration of n-butyric acid in two biofilters packed with compost (BFC) and sludge (BFS) and two biotrickling filters packed with pall ring (BTFP) and multidimensional hollow ball (BTFM) were investigated. Results of kinetic analysis and overall evaluation showed that the sequence was BTFM>BTFP>BFOBFS. Analyse of filtrate and CO₂ indicated n-butyric acid was removed by biodegradation. The pressure drop in BTFs are higher than that in BFs. It is important to control the thickness of the biofilm to keep high removal efficiency. The results help to select optimal odor removal techniques.Five predominant bacteria named as Ax-1, Ax-2, Ax-3, Ax-4 and Ax-5 were isolated from biofilters treating n-butyric acid. Based on colonial morphology, physiology and biochemical features and phylogenetic tree derived from 16S rDNA sequence data, they were respectively closed to Bacillus cereus, Pseudomonas sp., Enterobacter sp., Moraxella lacunata. The GenBank records are EF514401, EF514402, EF514898, EF514900 and EF514899, respectively. The number of bacteria, fungi and actinomycete in the BFs and BTFs were different. Bacteria and fungi played a key role in removing n-butyric acid. Spatial and temporal shifts of bacterial community composition in BFs and BTFs developed differently assessed by PCR-DGGE. The performance is closely relatived to the microbial community diversity. A new combined packing material for biotrickling filter was developed in this study. The removal efficiency of ammonia by biotrickling filter with combined packing material was 100 %. The complete and maximum elimination capacity was 42.3 g NH₃ m^-3 h^-1 and 90.5 g NH₃ m^-3 h^-1, respectively. Results of kinetic analysis showed that V_m was 1000 g NH₃ m^-3 d^-1 and K_s was 98.9 mg m^-3. Some optimal parameters were dicided in this research. The optimal gas retention time was 45 s. When NH₃ concentration was in the range of 0-100 mg m^-3, the optimal spray amount was 50 mL min^-1. When NH₃ concentration was in the range of 100-150 mg m^-3, the optimal spray amount was 75 mL min^-1. When NH₃ concentration was larger than 150 mg m^-3, the optimal spray amount was 100 mL min^-1.