[Studies on nitrogen and phosphorus enhancing removal in combined shale and steel slag subsurface constructed wetlands].

Effluent of municipal wastewater treatment plant operated under A/O process was treated by constructed wetlands for reclamation and reuse. These methods, such as phosphorus removal by adsorption of shale and steel slag, regulating C/N ratio and nitrogen oxidability in influent of wetland, were employed to study efficiency and impact factors of nitrogen and phosphorus removal in pilot-scale in combined shale and steel slag subsurface constructed wetlands. Results indicate that, When COD area load rate, TN area load rate, TP area load rate and hydraulic retention time (HRT) is 6.5-20.7 g x (m2 x d)(-1), 2.57-8.22 g x (m2 x d)(-1), 0.41 -1.32 g x (m2 x d)(-1) and 0.5- 1.6d, respectively. Removal efficiency of ammonium nitrogen, nitrite nitrogen and nitrate nitrogen is 85.8%, 56.3% and 18.6%, respectively. Removal efficiency, area load removal rate and removal kinetic constant of total nitrogen are 58.0%, 3.58 g x (m2 x d)(-1) and 0.31m x d(-1), respectively. TN area load removal rate is linearly increased with the increase of total nitrogen area load rate. Removal efficiency, area load removal rate and removal kinetic constant of total phosphorus are 90.4%, 0.89 g x (m2 x d)(-1) and 0.86 m x d(-1), respectively. TP area load removal rate is linearly increased with the increase of total phosphorus area load rate. Water temperature, HRT, COD/TN ratio and (NO2(-) -N + NO3(-) -N) /TN ratio are primary factors impacting nitrogen and phosphorus area load removal rate. Along with HRT and COD/TN ratio increase, TN area load removal rate increases according to power function. Along with water temperature and (NO2(-) -N + NO3(-) -N)/TN ratio increase, TN area load removal rate increases according to exponential function.