| Water pollution is one of the global environmental problems and restricts the development of economy. Constructed wetland has been used for water treatment and has high removing efficiency of N and P with low construction cost. Easy operation of the system makes it to be an attractive way for water treatment.This paper is studies on optimum technics of coupled vertical and horizontal subsurface flow constructed wetland for the nitrogen removal of the high concentration nitrogenous, which is based on the small sale plots (SSP). Factors infecting nitrogen removal of coupled systems are concerned as follows: HRT, dissolved oxygen (DO), TN loading of influent, carbon source, temperature, pH value.Transform rule and regulations of NH4+-N in VF system, different forms nitrogen removal mechanism, and hydraulic conduction condition were studied. The study results showed that: (1) It is necessary to distribute waste water intermittently and keep constructed wetland no waste water in VF system for avoiding jam in system. (2) DO fluctuation along the direction of waste water flow is propitious to transformation from NH4+-N to NO3--N and removal of TN. (3) Insolate VF system from the bottom of equipment, make sure DO in the system not below 1.5 mg/L, TN concentration of influent is about 60 mg/L, NH4+-N concentration of influent is about 50 mg/L, HRT is 2d, TN removal efficiency is up to 51.9%. NH4+-N that was not removed has been transformed into NO3--N, at this time, NO3--N concentration of effluent is 96.5% in proportion of TN concentration.(4) When DO is above 1.5 mg/L, the high removal efficiency from NH4+-N to NO3--N can be obtained. But DO value is improved unceasingly, increase of transform efficiency of NH4+-N is not obvious. When DO value is below 1.2mg/L, transform efficiency of NH4+-N is below 30%.(5) When TN concentration of influent is 80mg/L, removal efficiency of TN is low, transform efficiency from NH4+-N to NO3--N is still high, when TN concentration of influent is high than 80mg/L, transform efficiency from NH4+-N to NO3--N decreased rapidly.A series of successional tests are carried out with HF system. Factors infecting denitrification in HF system concerned are TN loading, DO, carbon source, HRT, temperature, pH value. The study results showed that: (1) Append carbon source into effluent of VF system, the mixture is immitted into HF system. DO value in HF system will reduce to below 0.5mg/L, which leads to a propitious condition for denitrification in HF system. (2) TN concentration of influent is between 20mg/L to 120mg/L, that has been appended carbon source. The result shows that carbon source is enough when TOC/TN is above 2.5, and removal efficiency of TN can be up to above 94%. (3) High TN removal efficiency can be obtained when TN concentration of influent is 60 mg/L, HRT is 1.5d, TOC/TN is 3. (4) When TOC/TN is 3, HRT is 1.5d, TN concentration of influent is between 20mg/L to 120mg/L, a series of tests are carried out. Results show that TN removal efficiency is above 94.1% when TN concentration of influent is below 60mg/L. TN removal efficiency is obviously infected by gradually increased TN concentration of influent.A series of tests based on coupled systems are carried out. The results show that high TN removal efficiency can be obtained at proper condition if the high concentration nitrogenous waste water flows across VF-HF coupled constructed wetlands, TN removal efficiency can be up to above 90% with coupled system. The optimal condition lists as follows: TN concentration of influent is between 20mg/L-80mg/L (NH4+-N accounts for more than 80%), circumstance tempreture is around 20℃, pH value of influent is between 6.3-7.5, HRT of VF system is 2 days, DO value in VF systems is not below 1.5mg/L, HRT of HF system is 1.5 days, TOC/TN of influent of HF system is 3. According to contamination discharge standard of town sewage treatment plants (GB18918-2002), water quality of effluent of coupled system is arranged at first grade A scale.
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