| This paper is subject to the problems of initial rainfall runoff pollution from old town to secondary city river. Technology of multifunctional pond-terraced constructed wetlands system for initial rainfall runoff treatment was proposed and demonstration project with treatment capacity of 1000m3/d was constructed to meet the surface environmental standards. Pollutant removal efficiency of multifunctional pond was investigated and effects of hydraulic loading, mode of operation and temperature on step-CW was discussed. Microbial community structure was studied by PCR-DGGE and 16 Sr DNA technology to discuss the functional mechanism of step CW. Main conclusions of this study were as below:(1)Multifunctional pond performed well on treating particulate pollutant in initial rainfall runoff. When HRT was 150 min, average removal rate of TSS、COD、TN and TP by precipitation treatment were 71.62%、48.16%、11.41% and 44.63%, respectively.(2) Surface hydraulic loading had an significant affect on performance of terraced-constructed wetlands. When loading increased from 0.06m3/(m2?d) to 0.65m3/(m2?d), removal efficiency of pollutants by wetlands system increased firstly and then decreased. Maximum reduction quantities of COD、NH4+-N、TN and TP(19.08 kg/d, 612.0g/d, 1893.6g/d and 406.8g/d) was observed when loading was 0.45 m3/(m2?d).(3) Feeding mode, idle duration and temperature affected the removal rate of terraced-constructed wetlands. Compared with continuous operation pattern, removal rate of COD、 NH4+-N、TN and TP increased 22.54%、22.24%、39.99% and 5.01% respectively when constructed wetland was operated in sequence. When idle time were 0h, 1h and 2h, the average removal efficiency of NH4+-N were 53.4%、76.59% and 92.49%, respectively. Removal rate of COD、 NH4+-N、TN and TP improved 45.69%、25.46%、32.67% and 25.84% when temperature increased from 27-34℃ to 10-12℃.(4) When the first CW was operated under the condition of 27-34℃ with surface hydraulic load 0.45 m3/(m2·d),(0.5h continuous feeding-6h reaction-0.5h intermittent effluent-2h idle) and both second and third CWs were operated in the pattern of “intermittent influent and effluent ”, average effluent concentration of COD、NH4+-N、TN and TP were 10.5mg/L、 0.28mg/L 、1.70mg/L and 0.30mg/L,with removal efficiency of 74.65%、94.95%、64.86% and 66.47%, respectively. Concentration of effluent COD 、NH4+-N and TP could met level Ⅴof environmental quality standard for surface water.(5) PCR-DGGE results showed that, microbial community diversity in Terraced constucted wetlands system was relatively low and species richness were significantly different in different depth of the packing layer. 16 S r DNA sequencing results suggested that, on classification level of phylum, Proteobacteria took the largest proportion(34.38%) and α-Proteobacteria,β-Proteobacteria and γ-proteobacteria were top three phylum in the system. Functional bacteria for nitrification were Arthrobacter(3.60%), Rhodobacter(3.24%、), Nitrospira(1.97%)and Pseudomonas(1.08%)in the system。... |
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