寒冷地区多级垂直流人工湿地系统设计及氮磷去除效率

为了解决北方寒冷地区人工湿地冬季效率低、运行不稳定的问题,设计建设了两个多级垂直流人工湿地系统(multistage vertical-flow constructed wetlands,MVCWs),处理北京房山区居民生活污水,通过工程设计以及添加碳源强化系统脱氮效果,增加磷吸附基质等措施,提高系统稳定性和污染物的去除效率。研究结果表明,湿地系统Ⅰ化学需氧量(chemical oxygen demand,COD)的平均去除率为87.3%;总磷(total phosphorus,TP)的平均去除率为91.9%;总氮(total nitrogen,TN)的平均去除率为68.9%,能够全年稳定运行。湿地系统Ⅱ采取半间歇式运行方式,在0.5 m3/(m2·d)的水力负荷条件下,对COD、TN、TP的平均去除率分别为92.5%、53.8%、77.2%。湿地系统Ⅱ厌氧单元添加62 kg木块后,COD/TN从0.93上升到1.85,比添加31 kg木块单元对TN的去除率提高15.6%。木块作为厌氧阶段的外加碳源,有效促进了垂直流人工湿地系统对氮的去除。通过垂直流人工湿地多级合理的单元设计,在厌氧阶段添加碳源有利于反硝化脱氮以及添加吸附磷的基质,提高冬季没有植物参与时高效除氮、磷,有效地保证对各种污染物的去除效率。使该研究中的人工湿地系统能够全年稳定运行,该研究结果可为人工湿地在中国北方的推广应用提供参考。

Multistage vertical-flow constructed wetlands and removal efficiency of nitrogen and phosphorus in cold area

In order to solve the problems of low efficiency and unstable operation of constructed wetland in winter, 2 multistage vertical-flow constructed wetlands (MVCWs) systems were designed and constructed for treating the sewage of the residents in Fangshan District, Beijing City. Through the engineering design, adding extra carbon (C) source for denitrification effect, and increasing phosphorus (P) adsorption matrix, the system stability and the removal efficiency of pollutants were improved. MVCWs I was designed for the hydraulic loading of 70 m3/d at Houshiyang Village sewage treatment station in Fangshan District; MVCWs II was designed for the adjustable hydraulic loading, and the equipment was the controllable connection of 6 units with the same size for treating the pollutants under different hydraulic loading, different extra C source amount added, and different operation mode. Results showed that in MVCWsⅠ, the removal rate of chemical oxygen demand (COD) was 77.0%-93.7%, and the average removal rate was 87.3%; the removal rate of total phosphorus (TP) was 75.8%-97.0%, and the average removal rate was 91.9%; the total nitrogen (TN) removal rate was 26.4%-97.2%, and the average removal rate was 68.9% in the full year operation. MVCWsⅠhad a stable operation throughout the year, although the removal rate of organic pollutants was decreased in winter. MVCWsⅡ was added with the wood chips as the extra C source in the third-stage unit, and added with the aluminum ball to enhance the adsorption of P in the fourth-stage unit, which operated from July to November in 2015. With the semi-batch operation mode and the hydraulic load of 0.5 m3/(m2·d), the average removal rate of COD, TN and TP for MVCWsⅡ were 92.5%, 53.8% and 77.2%, respectively. After adding 62 kg wood chips, in MVCWsⅡ, the COD/TN increased from 0.93 to 1.85, and the TN removal rate increased by 15.6% compared with adding the 31 kg wood chips in the anaerobic stage. By adding extra C source and the design conducive to nitrogen removal, the efficient removal of N in winter without plants could be improved. Although wood chips supplement to MVCWsⅡ could improve microbe conditions and intensify nitrogen removal function, the effluent COD concentration was increased in the unit added with C source. Excessively adding extra C source would cause the COD in the sewage to increase by remaining C, and the C could not be fully used in denitrification, so the extra C source should be added with right amount. In this research, the COD of the water at the outlet increased with the increase of the wood chip added in the unit. However, the average removal rate of the COD in system was not significantly different under different C source adding amount. It was proved that the fourth-stage aerobic unit played an important role in the degradation of the remaining C, and also reflected the necessity of the fourth-stage unit. The vertical-flow constructed wetland multistage reasonable unit design can effectively guarantee the various pollutants’ removal efficiency, and improve the efficiency in N removal in the winter without plants. In the MVCWs system design, adding C source for denitrification in the anaerobic stage makes the artificial wetland system run stably for a full year. The study results can provide the reference for the application of constructed wetland in northern China.