Hybrid constructed wetlands for highly polluted river water treatment and comparison of surface-and subsurface-flow cells

A series of large pilot constructed wetland （CW） systems were constructed near the confluence of an urban stream to a larger fiver in Xi＇an, a northwestern megacity in China, for treating polluted stream water before it entered the receiving water body. Each CW system is a combination of surface- and subsurface-flow cells with local gravel, sand or slag as substrates and Phragmites australis and Typha orientalis as plants. During a one-year operation with an average surface loading of 0.053 m3/（m2.day）, the overall COD, BOD, NH3-N, total nitrogen （TN） and total phosphorus （TP） removals were 72.7% ~ 4.5%, 93.4% ＋ 2.1%, 54.0% ＋ 6.3%, 53.9% ~ 6.0% and 69.4% ：t： 4.6%, respectively, which brought about an effective improvement of the fiver water quality. Surface-flow cells showed better NH3-N removal than their TN removal while subsurface-flow cells showed better TN removal than their NH3-N removal. Using local slag as the substrate, the organic and phosphorus removal could be much improved. Seasonal variation was also found in the removal of all the pollutants and autumn seemed to be the best season for pollutant removal due to the moderate water temperature and well grown plants in the CWs.

Analysis of pollutant removal effect usinginnovative ridge-shaped constructed wetland

In this paper,a new type of ridge-shaped constructed wetland which combines surface flow and horizontal subsurface flow was proposed.The proposed wetland had simple structure,low construction and operating cost,less human interference and good pollution removal effect.The combination of surface flow and subsurface flow provided an aerobic and anaerobic alternating environment for the entire wetland.The performance of the proposed wetland was compared with a traditional horizontal subsurface flow wetland.The comparison results showed that the removal rates of BOD(biochemical oxygen demand),TN(total nitrogen),and TP(total phosphorus)in the ridge-shaped wetland increased up to 20.3%,17.0%,and 9.1%,respectively.The proposed wetland structure could be widely applied for treatment of rural and urban domestic sewage pollution or agricultural point and nonpoint source water pollution.

REDUCTION OF NON-POINT SOURCE POLLUTION IN THE YONG'AN RIVER BY CONSTRUCTED WETLAND BASED ON 9 YEARS OF MONITORING

The agricultural and livestock activities surrounding the rivers flowing into the lakes have caused non-point source pollution, leading to excessive amounts of nutrient salts in downstream rivers. Introducing river water into constructed wetlands along river course has proven to be an effective solution for decreasing nitrogen(N) and phosphorus(P) loads. This paper reports 9 years of monitoring the Yong’an River and its surrounding constructed wetlands in the upper reaches of Erhai Lake, located in Yunnan Province, China. This study analyzed the main types of pollutants in the river, and evaluated the removal efficiency of pollutants by the constructed wetlands. The findings indicate that total nitrogen(TN) and nitrate nitrogen(NO_(3)^(–)-N) are the primary pollutants in the Yong’an River, which exhibit variation throughout the year corresponding to the alternating wet and dry seasons. Although constructed wetlands are effective in removing NO_(3)^(-)-N and P, their efficacy in removing ammonium nitrogen(NH_(4)^(+)-N)and organic pollutants is limited. This limitation can be attributed to the lack of timely disposal of aquatic plant residues. This research contributes to the understanding of the potential issues that may arise during the extended use of constructed wetlands and provides solutions to address them.