Decontamination Efficiency And Structural Characterization Of Microbial Communities In Vertical Flow Constructed Wetland

Highly polluted river water have high concentrations of organic pollutants、nitrogen and phosphorus, the constructed wetland can be take advantage of its high removal efficiency、low energy consumption and environmentally friendly, etc., it has been widely promoted and applied in domestic and abroad, in particularly, the treatment of high polluted river water in vertical flow constructed wetlands has been paid more attention. Currently, most of the studies focused on the analysis of treatment effect, relatively few studies on the characterization of microbial communities in vertical flow constructed wetlands, and lacking in sufficient understanding of inherent essential characteristic in wetland treatment, it’s necessary for constructed wetland in depth studing on correlation between microbial communities structural characteristics and its decontamination effect.In order to investigate removal efficiency and mechanism of the organic pollutants、nitrogen and phosphorus, and microbial decontamination mechanism in vertical flow constructed wetland for highly polluted river water treatment, the water quality indexes of inflow and outflow in wetland system were measured for a period of 11-month. And the characterization of microbial communities in substrates and rhizosphere in vertical flow constructed wetland for highly polluted river water treatment were investigated by using PCR following Denaturing Gradient Gel Electrophoresis(DGGE). The 16 S r DNA genes(V3 to V5 region) were amplified with two universal primers(BAC 338 F GC and BAC 805R). The results indicate that:(1) The organic pollutants of wastewater can be removed effectively in vertical flow constructed wetland, which removal efficiency of COD、BOD5 were 72.59% ~ 95.88% and 85.00% ~ 99.27%;COD removal efficiency in wetland system is better in the summer and autumn, and poor in the spring and winter, BOD5 removal efficiency in wetland system is stable. The SS can be remove efficiently in wetland system, and its average removal rate was 98.48%, up to 100%,the suspended organic contaminants was also be remove effectively.(2) TN and NH3-N removal efficiency in vertical flow constructed wetlands were 23.19% ~ 91.95% and 30.84% ~ 99.59%, which changed with the seasons, first increase, then stabilize, finally decreased;temperature and dissolved oxygen play the important role in affecting nitrogen removal in wetland system, which directly affected the microbes ammonification, nitrification and denitrification processes.(3) TP and PO43--P removal efficiency in vertical flow constructed wetlands were well, and its average annual phosphorus removal efficiency were 88.28% and 84.23%, respectively; phosphorus removal efficiency were stable in spring、summer and autumn, and at a high level, which was decreased slightly due to the effect of reed harvest in winter. Phosphorus removal in wetland system was less affected by temperature.(4) The microbial community diversity in substrates from the wetland system first increased and then decreased with the depth drop. And microbial community diversity in rhizosphere declined with the depth increase. Furthermore, in the same vertical depth, the microbial community diversity in rhizosphere was higher than that in substrates. A special aerobic bacteria Acinetobacter tjernbergiae have been analyzed in rhizosphere due to the oxygen secretion of the plants roots.(5) Cluster analysis of DGGE profiles show that microbial communities have highly similarity in the wetland system, which was declined with the depth increase. Sequence analysis indicate that Bacteroidetes and Proteobacteria in the wetland system have shown the highly sequence homologies in the phylogenetic tree, respectively, where the dominant species were Flavobacterium sp., Thiobacillus denitrificans and Uncultured Firmicutes bacterium.(6) The aerobic bacteria including Flavobacterium sp. and Sporocytophaga sp. were widely distributed in the top and middle layers. These desulfurization bacterium including uncultured Thiobacillus sp., Thiobacillus denitrificans and Uncultured desulfuromonas sp. appeared in large numbers in the wetland system, indicated that the wetland received the highly polluted river water which contained sulfur compounds, which would restrain from the process of nitrification, and the desulfurization bacterium appeared in large numbers in the wetland system.