| In recent years, pig breeding industry has been developing rapidly in China, the biggest pig breeding country. Half of the pigs in the world are bred in China. Available data show that the environmental due to pig farming is quite serious. Its discharged waste contains highly concentrated organic matter, excessive suspended solids, large content of ammonia nitrogen and phosphorus. All of its water quality indices exceed the national discharge standards several times or even dozens of times, becoming one of the major sources of water pollution. According to statistics, the annual COD discharge of the swine wastewater is far more than the total amount of national industrial wastewater and domestic sewage. The incomplete treated pollutants discharged into lakes, rivers or other water bodies, cause serious pollution of lakes and rivers. UASB is the typical anaerobic treatment technology of swine wastewater. Previous work on swine wastewater anaerobic treatment with UASB mainly focused on technical aspects such as start-up method, rector design, and processing parameters and few efforts have been made to understand mechanisms of organic pollutant degradation and the relationship between the structure and the function of the microbial community in the reactors.The objective of this study is to investigate the anaerobic biodegradation mechanism of organic pollutants in swine wastewater using microbial molecular ecology methods in combination with traditional microbial methods. The results can be summarized as follows:Microbial community structure, dynamics and diversity analysis Two UASB reactors inoculated with different inocula sources were started up in 36 days. These two reactors operated steadily for another two months with the COD removal rate of 84-88 % and 90-95 %. The methane production of 5.5-10.5 and 9.0-14.0 L day-1 respectively as the influent COD was between 3000-6000 mg L-1. The start-up rate, COD removal rates and methane production, microbial activity characterized by VSS and VSS/TSS of reactor A were slightly lower than those of the reactor B in the same operation time. The VFAs level of the both reactors was appropriate for microorganism activities. According to the results of DGGE and ARDRA, the bacterial communities were diversified after a long time of acclimation and were similar to each other in the two reactors inoculated with different sources but changed insignificantly during the steadily operation time. This community structure shift of the reactors was in accordance with their functions. 55 operational taxonomic units (OTUs) were identified from 346 positive clones. The microbial population percentages distributions were 33 % (Firmicutes), 23 % (Acidobacteria), 19 % (Proteobacteria), 11 % (Bacteroidetes), 8 % (Nitrospira), 4 % (Chloroflexi) and 2 % (others). The analysis of 16S rRNA clone library showed that the bacterial community was quite different from those related with swine waste treatment by other technologies such as biofilter and pig slurry anaerobic storage in previous studies.Typical reluctant organic compounds biodegradation mechanism analysis One bacterial strain named LPC24 was isolated from the activated sludge from the USAB reactor for swine wastewater treatment by direct spreading plate method. This bacterial strain was finally identified as Psedomonas putida based on its phenotype and genotype characteristics. This isolate could utilize indole or 3-MI as the sole source of carbon source. 3.0 mM indole and 2.0 mM 3-MI could be degraded in 18 days and 30 days respectively by this bacterium. Additionally, this strain could oxidize ammonia and deoxidize nitrate effectively without nitrite accumulation. According to the results of HPLC and GC-MS, the metabolic pathways of indole by strain LPC24 was oxindole /isatin /anthranilic acid which was similar to that proposed previously. The degrading pathway of 3-MI by strain LPC24 was identified as 3-methyloxindole /formylaminoacetophenone /2-aminoacetophenone which was different from the pathways proposed so far in other studies. 26 strains were isolated from piggery sludge and manure from one big pig farm, and ten of them with larger halos were selected to further study. A composite microbial system was constructed by five bacteria named as LCB03, LCB12, LCB52, LCD12 and LCD51 with higher cellulases activities from the ten isolates. About 0.36 gram of rice straw and 0.10 gram filter paper were degraded by the composite microbial system within 1 -week individually. These five bacteria were identified as Pseudomonas citronellolis. Stenotrophomonas maltophilia, Pseudomonas aeruginosa, Pseudomonas aeruginosa and Flavobacterium mizutaii respectively according to the results of phenotype and genotype. To our best knowledge, little work has been done before on cellulose degradation using bacteria S. maltophilia and F. mizutaii.Bio-augmentation of recalcitrant pollutants degradation and microbial community dynamics analysis Six isolates with strong capability of degrading indole and skatole or cellulose were inoculated into an UASB reactor to strengthen the degradation capability of these recalcitrant pollutants. The results showed that the capability of degrading the recalcitrant pollutants including indole, skatole and cellulose was enhanced to different degrees in the whole process of bio-augmentation. COD removal performance was improved 2-7 %, the cellulose degrading capability of was increased more than 20 %, and the removal rates of indole and skatole increased 15-20 %. The bacteria activity characterized as the VSS and VSS/TSS was also improved; the microbial community structure analyzed by means of molecular tools PCR-DGGE was changed apparently. The inoculated bacteria Flavobacterium mizutaii and Pseudomonas dominated, and the strain Stenotrophomonas maltophilia failed to dominate in the microbial community in the bio-augmentation system. With the effect of bio-augmentation, some new bacterial community identified as Clostridia, Acidobacteria and Nitrospira appeared in the bioaugmented system. Additionally, the bacterial structure and diversity under low temperature incubation were detected. The bacterial community structure was changed dramatically. The density of all of the dominant groups of Chloroflexi and Acidobacteria, and three Bacteroidetes, one Proteobacteria and one Firmicutes group substantially decreased or even disappeared from the bacterial system incubated under the temperature of 30-35℃. Some bacterial groups which could dominant in the community under low temperature were found. These bacterial groups are of ecological significance to lower energy requirement in anaerobic digestion in cold climates which might serve as an alternative strategy for practical swine wastewater treatment.
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