title: Nitrate-rich agricultural runoff treatment by Vallisneria-sulfur based mixotrophic denitrification process.
abstract: Vallisneria-sulfur based mixotrophic denitrification (VSMD) process was put forward for the treatment of nitrate-rich agricultural runoff with low COD/TN (C/N) ratio in free water surface constructed wetland mesocosms, whose feasibility and mechanism were thoroughly studied through 273-day operation. The results showed that the average NO3--N removal efficiency and denitrification rate of VSMD mesocosms were 97.7% and 1.5gNO3--Nm-3d-1under 5.0 or higher C/N ratio conditions in phase II (7-117d), which were similar with those of Vallisneria packed heterotrophic denitrification (VHD) mesocosms. However, VSMD mesocosms with 2.0 average C/N ratio in phase III (118-273d) were more stable and efficient than VHD mesocosms. More than 49.4mg NO3--N was reduced by VSMD mesocosms than that by VHD mesocosms throughout the operation. NO2--N accumulation in phase I (0-6d) had no influence on denitrification performance of VSMD mesocosms. In phase II and III, effluent COD, NH4+-N and NO2--N could meet the Class II standard of Environmental quality for surface water (GB3838-2002) if the experiment was carried out in batch mode. pH in VSMD mesocosms fluctuated between 7.0 and 8.9 throughout the operation without any pH buffer. The abundance of three denitrifying genes coding for nitrate (narG), nitrite (nirS), and nitrous oxide (nosZ) reductases in bottom soil and mixture from litter bags was quantified. VSMD could supply more favorable circumstances for the growth of denitrificans containing narG (3.1×108±7.9×107copiesg-1mixture-1) and nirS (2.1×108±2.0×106copiesg-1mixture-1) in litter bags than VHD, i.e., 8.7×107±1.4×107and 1.4×108±1.5×107copiesg-1mixture-1for narG and nirS respectively. Sulfur addition in VSMD mesocosms might increase the abundance of denitrificans containing narG and nirS, thus led to better denitrification performance.
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China; Research Center for Water Pollution Control Technology, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China.
authors.forename: Qianyu
authors.initials: Q
authors.lastname: Hang
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China; Research Center for Water Pollution Control Technology, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China. Electronic address: wanghy@craes.org.cn.
authors.forename: Haiyan
authors.initials: H
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China; Research Center of Lake Eco-Environments, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China. Electronic address: chuzs@craes.org.cn.
authors.forename: Zhaosheng
authors.initials: Z
authors.lastname: Chu
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China; Research Center of Lake Eco-Environments, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China.
authors.forename: Zeying
authors.initials: Z
authors.lastname: Hou
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China; Research Center for Water Pollution Control Technology, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China.
authors.forename: Yuexi
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, No. 8 Da Yang Fang, Anwai, Chaoyang District, Beijing 100012, PR China; Lanzhou University, Lanzhou 730000, PR China.
authors.forename: Chunmei
authors.initials: C
authors.lastname: Li
keywords: Agricultural runoff; Mixotrophic denitrification; Sulfur; Vallisneria decomposition