Analysis Of Denitrification Characteristic And Microbial Community Changes Of Symbiotic System Consisting Of Aquatic Worms And Microorganism

Recently, the problem of sewage sludge treatment incused by wastewater treatment plants (WWTPs) is becoming severely, this has led to an increased interest in techniques that economic and effective to reduce sludge. With advantages such as low cost and no secondary pollution, this technology which using aquatic worms'predation to reduce excess sludge has recently received increasing attention by some researchers. However, the effect of biological wastewater treatment may be influenced by aquatic worms, the relationship between aquatic worms and waste treatment is therefore needed to be investigated.Thus, in this study, the effect of bio-nitrification and bio-denitrification was systematical invested by incoluating aquatic worms that widely used in sludge reduction researches. Then, FISH (fluorescence in situ hybridization) and PCR-DGGE (Polymerase Chain Reaetion-denaturing gradient gel electrophoresis) were used to indagate microbial community of sludge samples extracted from nitrifying system and denitrification system, aimed to find out the influencing mechanism of aqutic worms on bio-nitrification and bio-denitrification, which can provid reliable rationale and useful scientific instruction in further The principal conclutions were obtained as follows.(1) The effect of different NH4+-N concentrations on the growth and sludge reduction of aquatic worms was investigated by cultivating with fresh activated sludge in batch test. Result showed that aquatic worms could grow from juvenile to adult normally at low NH4+-N concentrations, and the growth trend in accordance to Guass curve, however, the growth of aquatic worms was restricted at high NH4+-N concentrations. The application of sludge reduction by aquatic worms was suitable for low NH4+-N concentrations.(2) Sequencing batch reactors (SBRs) seeded with activity sludge were started up to enrich nitrifiers and their nitrifying efficiencies,microbial community were studied by adding aquatic worms. Results showed that the presence of aquatic worms caused a16.65%decrease in nitrification rates and a24%decrease in NO2--N oxidation rates compared to the test groups (not added aquatic worms). When investigated the variation rule of N concentration in single-cycle, there was a significant accumulation of NO2--N in the test groups and the phenomenon could be eliminated by extending the nitrifying time. The oxygen uptake rates (OURs) of nitrifiers were also implied that the activities of nitrifiers could be inhibited by the aquatic worms. What'more, deeper research find that aquatic worms may decrease the population diversity of microorganism by FISH and PCR-DGGE technologies, at the same time, some nitrifiers may be induced enrichment by aquatic worms, sequence results of different DGGE bands indicated that1/4microorganism was Uncultured bacterium, and the dominate microbial was Uncultured Nilrosospira, which was a typical nitrifiers. Moreover, the microorganisms in SBRs also including Uncultured Proteobacteria, Uncultured Bacteroidetes, Uncultured Fimicules, Epistylis urceolata and Uncultured Chloroflexi bacterium.(3) Sequencing batch reactors (SBRs) seeded with activity sludge were started up to enrich denitrifiers under anerobic condition and their nitrifying efficiencies, microbial community were studied by adding aquatic worms. Results showed that aquatic worms could help promote TN removal and COD removal, improving the stability of the denitrifying system. In addition, aquatic worms could also enhance the population diversity of microorganism by analysing of DGGE profile, results of different DGGE bands showed that most microorganisms was Uncultured bacterium.