The Experimental Investigation On The Treatment Of Rural Domestic Sewage By Subsurface Flow Constructed Wetland

In order to respond positively to the call of"Poyang Lake Ecological Economic Zone"proposed by our country, the features of the rural domestic sewage and its influence on environment were introduced in this paper. Apply constructed wetland to the treatment of sewage in rural areas was proposed. Through reading and analysis of literature, the main factors to impact the removal efficiency of nitrogen and phosphorus in constructed wetland were determined. Then through the Orthogonal tests, the influence on removal effects of hydraulic loadings, pH, ratio of carbon to nitrogen and plants under their three revels were analyzed by SPSS13.0. Then, The impact of the pollutants removal efficiency by the hydraulic loadings under different levels, seasons, plant harvest were also analyzed. On this basis, the hydraulic test were done. A more comprehensive analysis of the hydraulic load, hydraulic residence time about the removal efficiency displine of organic matter, nitrogen and phosphorus in the rural sewage was finished. And the first-order kinetics equation between the Organic Compounds, nitrogen and phosphorus pollutants in rural domestic sewage and HRT was established.Finally, Comparison test and analysis was made withdifferent factors,for example,summer and winter seasons, different treatment plants.The study conclusions can be summarized as follows:(1) Orthogonal experiment Analysis of variance showed that: pH,hydraulic loading, ratio of carbon to nitrogen and plant all had very significant effect on the removal rate of TN and TP in rural domestic wastewater(p<0.01). pH,hydraulic loading and plant all had very significant effect on the removal rate of COD_Cr in rural domestic wastewater(p<0.01), while ratio of carbon to nitrogen had significant effect on it(0.01<p<0.5). PH,hydraulic loading and ratio of carbon to nitrogen all had very significant effect on the removal rate of COD_Cr in rural domestic wastewater(p<0.01), while plant had significant effect on it(0.01<p<0.5). Single Factor Analysis results shows that:while pH was 7.5, hydraulic loading was 33mm/d, ratio of carbon to nitrogen was 15, the removal efficiency of COD_Cr, TN, NH₃-N could reach their maximum value;the most effective plant of the three were respectively Rush, Donax Linn,Vetiver grass. while pH was 9.5, hydraulic loading was 33mm/d, ratio of carbon to nitrogen was 3, the plant was Vetiver grass, the removal efficiency of TP could reach its maximum value.(2) Hydraulic load test Hydraulic loading was closely related with the treatment effect. The removal efficiency of various pollutants by the four wetland beds decreased with the increase of lower hydraulic loading.When the hydraulic loading was 48mm/d (HRT was about 3.5d), the Effluent quality as COD_Cr, TN, TP of Each wetland bed were lower than the first class A criteria specified in"Municipal Wastewater Treatment Plant Pollutant Emission Standards (GB 18918-2002)"( Hereinafter referred to as"emissions standards") , and the Effluent quality as NH₃-N of Each wetland bed were lower than the first class B criteria specified in emissions standards. Under various hydraulic loadings in the experiment, the removal rate of COD_Cr by four wetland beds was 77.92%⁹3.25%; the number of TN was 41.52%⁷9.9%;the number of NH₃-N was 43.04%⁸4.77%; the number of TP was78.85%⁹7.12%.(3) Season test of treatment effect The removal efficiency of COD_Cr, TN, NH₃-N, TP in the bed of horizontal subsurface flow constructed wetland system were affected by the seasons. Treatment effect in summer was better than in winter, but it still could get good treatment in JiangXi Province.In this experiment, the Effluent quality as COD_Cr, TN, TP of four plant wetland beds in summer were lower than the first class A criteria specified in emissions standards, and NH₃-N were lower than the first class B criteria specified in emissions standards.While in winter, the Effluent quality as COD_Cr of Vetiver grass, Amur silvergrass, Rush bed were lower than the first class B criteria specified in emissions standards(60mg/L), but the Effluent quality as COD_Cr of Donax Linn wetland bed in summer were lower than the first class A criteria specified in emissions standards(50mg/L).The Effluent quality as TN of Donax Linn, amur silvergrass bed were lower than the first class B criteria specified in emissions standards(20mg/L), but the Effluent quality as TN of Vetiver grass, Rush wetland bed in summer were lower than the first class A criteria specified in emissions standards(15mg/L).The Effluent quality as NH₃-N of Each wetland bed in summer were both lower than the first class B criteria specified in emissions standards.(in winter the water temperature below 12℃reference standard to take 15mg / L). The effluent quality as TP of Each wetland bed in summer were lower than the first class A criteria specified in emissions standards (0.5mg/L) . Thus, the different seasons and different indicators of wetland beds had different influence on the removal effiency: Seasons had more significant effect as COD_Cr on Donax Linn, Amur silvergrass, and rush than Vetiver grass; Seasons had more significant effect as TN on Donax Linn, Amur silvergrass than Vetiver grass, rush; Seasons had limit effect as NH₃-N , TP on each wetland bed.(5) Analysis of a kinetic model First order kinetic equation could well simulate the removal discipline of COD_Cr, TN, NH₃-N and TP in rural domestic sewage by subsurface flow constructed wetlands in JiangXi Province, and the correlation coefficient established R2 were higher than 0.9(except the coefficient of ammonia nitrogen by Donax Linn).The removal rate of various pollutants by four plant beds varied a lot.The order of COD_Cr is Amur silvergrass >Donax Linn >Rush> Vetiver grass;The order of TN is Rush> Vetiver grass >Donax Linn > Amur silvergrass;The order of NH₃-N is Donax Linn >Amur silvergrass > Vetiver grass> Rush;The order of TP is Donax Linn >Amur silvergrass >Rush>Vetiver grass.