| In recent years, urban rivers in China were heavily polluted, thus malodorous were seasonal or year-round occurred commonly. With a large number of nitrogen and phosphorus flowing into rivers and lakes, eutrophication, a phenomenon badly influencing the aquatic ecology, had been aggravated,. It is urgent to solve the crucial problems of removing nutrient elements such as nitrogen and phosphorus effectively for eutrophication control and aquatic ecological system restoration. This project is based on the National Key Technology R&D Program——"Research and demonstration of urban malodorous river exogenous blocking, engineering repair and in-situ multilevel ecological purification key technology"(2009ZX07317-006). This research aimed to investigate the effect and its microorganism functionalmechanism of nutrients removal in hydroponic plant purification tanks treating the urban malodorous river in Shanghai by changing exogenous conditions such as season, aeration intensity and plantspecies.The results showed that:(1) Based on the plant root biofilm from plant purification tank, this research had optimized PCR-DGGE fromDNA extract method, PCR experiment and DGGE drawing condition successfully, which enable a faster and better analysis of microbial community and functional groups. DNA extract method was TENP buffer/PBS buffer-Bead beating OMEGA kit combination methods, PCR primer was R518and F357-GC, reaction system(50μL) is HS PCR Master Mix(2×),3μL primer each,2.5ng DNA template, distilled water up to50μL. PCR amplified condition is94℃pre-denaturation3min,94℃denaturation30sec,57℃annealing45℃,72℃extension40sec, after35cycles,72℃extension7min. Electrophoresis was at200V for240min.(2) Different aeration conditions had certain effects on nutrient removal and microbial mechanisms of plant purifying-tank. For plant purifying-tank without aeration, the DO concentrationand nutrients removal rate in early winter was higher than those in midsummer and late summer. While at the aeration tank, the system obtained the maximum removal efficiency of nutrients at the end of summer. TN, TP and NH3-N showed different removal trends under different aeration conditions.2#purifying-tank with the minimum aeration intensity of15L/min had the optimal TN removal efficiency, whereas3#purifying-tank with moderate aeration intensity (30L/min) reached the highest NH3-N and TP removal rate. This result suggested that the increase of aeration intensity might inhibit the plant growth and excessive aeration was not beneficial to the TN removal. Therefore, the plant growth and the balance of aerobic and anaerobic condition in the system should be taken into consideration for choosing a proper aeration intensity.Obvious differences in both the number and brightness of the sequencing results of PCR-DGGE bands from different aeration intensity indicated that the structure successionof the microbial community is closely related with the aeration condition changing. The result of sequence blastingalso showed that the major microbial communities in the purification tanks had high similarity with α-proteobacterium, Cyanobacterium, Methylocystis sp., Acetobacteraceae bacterium, Epsilon proteobacterium, Lactococcus sp. and so on. There existed denitrification δ-proteobacterium and nitrification sporacetigenium sp. in2#purification tank at the end of summer. The DGGE bands from3#purification tank were high covered and brightest among all the purification tanks in the same season. The DGGE analysis showed that3#tank had a Shannon index of about3.36which indicated that the microbial community diversity was higher, and it was mainly consisted by nitrification Acetobacteraceae bacterium and Methylocystis sp..In conclusion, a certain aeration intensity could increase the microbial functional community species and its amount in plant purification tanks and also improve the microcosm of microbe.and purification effect on malodorous river water. Treatment effect was best when aeration intensity was30L/min in this study.(3) Different plants species had certain effects on nutrient removal and microbial metabolism mechanisms of plant purifying-tank.Nymphaea alba and Nelumbo nucifera had well nutrients removal effects on malodorous river. The removal rates of TN, NH3-N, TP and PO43--P by Nymphaea alba and Nelumbo nucifera were47.71%and67.88%,40.75%and75.30%,16.77%and51.61%,9.34%and87.53%, respectively.The sequencing results of PCR-DGGE bands showed that the major microbial communities in the purification tanks had high similarity with Actinobacterium、 Methylomicrobium alcaliphilum and so on. The Shannon index of Nelumbo nucifera purification tanks was higher than Nymphaea alba, indicated the microbial community diversified and the nitrification Actinobacterium is predominant species.To sum up, Nelumbo nucifera had better nutrients removal effects on malodorous river than Nymphaea alba. Based on their well removal efficiency of nitrogen and phosphorus and its landscape value, the two plants are recommended as species of aquatic vegetation in phytoremediation of urban malodorous river.Finally, the thesis briefly discussed some further research including increasing sampling frequency, optimizing aeration and reinforcing the study of microbial molecular level from the root system. |
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