title: Variation of dissolved oxygen and redox potential and their correlation with microbial population along a novel horizontal subsurface flow wetland.
abstract: OBJECTIVE
  This study was conducted to evaluate the performance of a novel horizontal subsurface flow wetland (HSFW) in naturally improving the dissolved oxygen (DO) and the impact on redox condition, microbial activity and the nitrogen removal in the HSFW bed.
  
  
  METHODS
  The HSFW, equipped with cascaded natural aeration ditches (NADs), was the second stage of a hybrid constructed wetland (CW) after vertical-baffled flow wetland beds. The performances of the HSFW for organics and nitrogen removal in a full-scale hybrid CW system treating municipal wastewater for more than three years have been analysed. The spatial distributions of the oxidation-reduction potential (ORP), DO, microbial population density and specific oxygen uptake rate were determined, and their correlations were analysed in one selected section of the HSFW bed.
  
  
  RESULTS
  A 7-m-long shallow NAD increased the DO concentration from 0.28 mg O2 L(-1) to 3.80 mg O2 L(-1) and the ORP from +37.3 mV to +247.7 mV, creating an aerobic zone with a hydraulic retention time (HRT) of 0.5 h and an anoxic zone of another 0.5 h in series in the subsequent wetland bed. For the whole HSFW with three NADs, the macro aerobic and anoxic environment with a total HRT of 3 h can be created.
  
  
  CONCLUSIONS
  The unique DO distribution in HSFW may contribute to an optimum environment for partial nitrification and anammox, and obtain a high performance for nitrogen removal. Correlation analysis showed that the microbial activity in the HSFW relied obviously on the redox condition.
authors.affiliation: Chongqing University, Chongqing, P.R. China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhai
authors.forename: Jinsong
authors.initials: J
authors.lastname: Zou
authors.forename: Qiang
authors.initials: Q
authors.lastname: He
authors.forename: Kejia
authors.initials: K
authors.lastname: Ning
authors.forename: Haiwen
authors.initials: H
authors.lastname: Xiao
mesh_terms: D059013:Microbial Consortia; D009584:Nitrogen / Q000302:isolation & purification*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis*; D018508:Water Purification; D053833:Wetlands
chemical_list: D009584:Nitrogen; D010100:Oxygen