| Reduced sulfur compounds (RSCs) and Volatile organic compounds (VOCs) are twomajor groups of pollutants generally released from a wide variety of industrious processes.Both RSCs and VOCs are very harmful to human health and ecosystem. In addition, VOCshave been shown to play an important role in the atmospheric chemistry. Environmentallegislation related to waste air emissions has been becoming strict in china in recent years. Inodor to abide by the regulations of governments on the protection of the environment and airquality, industrial plants need to efficiently removal RSCs or VOCs from gaseous effluentprior to their release into the atmosphere. Biofiltration has proven to be a cost effective andenvironmental friend aternative in removing RSCs and VOCs from waste air stream, andtherefore has emerged as a promising control technology of air pollution. In this study, aseries of pilot scale experiments were carried out in various pollution sources. Bench scaleexperiment had been carried out to evaluate the performance of the biotrickling filter, whichwas inoculated with pre acclimated microbial consortiums, in removing BTEX mixture.PCR DGGE (Denaturing gradient gel electrophoresis),16S rDNA clone library and454pyrosequence techniques were employed to analysis the relationship between theoperating parameters and bacterial communities. Specific conclusions were described asfollows:1. The concentration of odor compounds varied depends on the wastewater treatmentunit. Hydrogen sulfide was a key pollutant of waste gases released from wastewater treatmentplant. Its concentration is gradually dropping along the wastewater treatment processes. Inaddition, the concentrations of all pollutants were closely related with climate conditions,especially with the temperature. Many kinds of organic compounds were also released fromthe wastewater treatment plant. Main odor causing organic compounds produced in gritchamber, settler and sludge thickener were toluene and monochlorodifluoromethane. RSCs,such as Dimethyl sulfide and Ethyl mercaptan, were another kind of odorous compoundsin the sludge dewatering workshop. Biofilters were successfully applied to control theodor pollution of wastewater treatment plant and waste compacting station. Ideal removalefficiency was obtained for biofilters, therefore, exhibiting advantages of biofiltration inpurifying odorous gases with large flow rate and low concentration even at the very shortEBRTs(Empty bed retention times).2. Two pilot field scale BTFs(Biotrickling filters), which packed with ceramic and volcanic stone, respectively, were successfully used to treat waste gases containing H2S at anaverage concentration of2.84±1.76mg/m3. The results showed that volcanic BTF was morerobust than ceramic BTF under acidic conditions. At empty bed residence times (EBRTs) of20and15s, the removal efficiency of ceramic BTF was close to100%. At EBRTs of10and5s, the removal efficiency of ceramic BTF slightly decreased. The removal efficiencies ofceramic BTF decreased by different degrees at the end of each stage, dropping to94%,81%,60%, and71%, respectively. However, the H2S removal efficiency in volcanic BTFconsistently reached99%throughout the experiment. Pyrosequencing analyses indicated thatmembers of Thiomonas dominated in both BTFs, but the relative abundance ofAcidithiobacillus was higher in volcanic BTF than in ceramic BTF.3. The performance of a field scale biotrickling filter (BTF) in the removal of wastegases containing low concentrations of mixed volatile organic compounds was evaluated.Results showed that acetone and methyl ethyl ketone (MEK) were more easily removed thantoluene and styrene. The removal efficiency for acetone and MEK reached over99%on days28and25of the operation, whereas those for toluene and styrene were80%and63%on day38. The maximum individual elimination capacities for styrene, toluene, acetone, and MEKwere10.2,2.7,4.7, and8.4g/m3.h, respectively. These values were achieved at inlet loadingrates of13.9,3.3,4.8, and8.5g/m3, respectively, at an empty bed retention time of14s. theremoval efficiency for styrene and toluene rapidly increased from67%and83%to86%andover99%, respectively, when the concentration of ammonia nitrogen (N NH+4) andphosphates (P) in the nutrients increased from350to840mg/l and76to186mg/l. When theBTF was restarted after a four day shutdown, the removal efficiency for toluene was restoredto over99%within a week. However, that for styrene was not restored to its previous levelbefore the shutdown. No noticeable adverse effect on acetone and MEK removal wasobserved. DGGE results for the bacterial community in the BTF during VOC removal showedthat proteobacterial phylum was dominant microorganisms, and the changes of nutrientconcentration and shutdown periods may have played a role in the community structuredifferences.4. Three microbial consortiums were enriched and obtained from Petroleumcontaminated soil. Clone library method were employed to analysis in detail the bacterialcommunities of these consortiums. Results showed that proteobacterial phylum was thedominant microorganisms in three consortiums. The bacterial community tends to simple afterlong time of acclimation. There were only two dominant bacterial genus existed in eachconsortium, and the proportion of dominant bacterial genus were42.4%,62.3%and68.3%, respectively. Three pure strains were isolated from above the consortiums; these strains couldrapidly degraded toluene, m xylene, p xylene and styrene.5. Two microbial consortiums were used as start inoculums of a bench scale biotricklingfilter, and the performance of the biotrickling filter on the removal of BTEX mixture wereevaluated. Results showed that BTFs that inoculated with the pre acclimated consortiumscould successfully start in very short time, and obtained ideal removal efficiency. Biomassrapidly accumulated in the BTF, but the press drop across the filter bed was kept very low(10mm H2O) during the experiments. This result can be attributed to the packing materials,which have large porosity. In spite that BTF that simultaneously inoculated with consortiumsand activated sludge need less time than that BTF only inoculated with consortiums to reachthe steady state, there were no significant difference of removal capacity between both BTFs.Removal capacity of BTF were significantly enhanced by the absorb column that packed withactivated carbon, the value increased from176g/m3.h to263g/m3.h.. However, removalcapacity of BTF without absorb column only increased from176g/m3.h to191g/m3.h, butremoval efficiency dropped from99%to91%. Fingerprint of DGGE for two biotricklingfilters indicates that the dominant microorganisms in the pre acclimated bacterial consortiumcould steadly reside in the two biotrickling filters. Bacterial communities of top and bottom ofpacking materials in two biotrickling filters were very silimler despit of various BTEX inletloading. |
PDF Full Text Request