Study On Treatment Of Rural Domestic Sewage Irrigation Tailwater By New Subsurface Flow Constructed Wetland

As a large agricultural country,China is now facing a serious shortage of irrigation water resources.The annual discharge of rural domestic sewage is huge,and most of it has not been treated,causing environmental pollution problems.The main pollution component of rural domestic sewage is nitrogen and phosphorus,which can cause water eutrophication,but it is a kind of resource for agricultural production.Therefore,the reclaimed water obtained after proper treatment of rural domestic sewage can be used as the source of agricultural irrigation water.In the practical engineering application,the integrated nitrogen and phosphorus inorganic reactor can be used to regenerate the rural domestic sewage.After being regenerated,domestic sewage reaches the standard of farmland irrigation water and can be used as irrigation water.Agricultural production is seasonal,so there is a risk that non-irrigated reclaimed water and irrigation tail water will be discharged into the environment.In this paper,for the characteristics of low organic matter content and high nitrogen and phosphorus content in irrigation tail water,a new type of subsurface flow constructed wetland,“O-A-O New Aquatic Vegetable Wetland”,has been adopted as an environmental risk control technology.This paper studies the startup,operating process characteristics and optimization measures of the system.Results are as follows.（1）The annual operating process characteristics of system were studied.The results show:During the 29-day start-up period,the average COD removal rate was 54.24%,the average TN removal rate was 40.24%,the average removal rate of NH₄⁺-N was 42.27%,and the average TP removal rate was 48.45%.The optimum hydraulic load was determined to be0.3 m³/（m²·d）.Under this hydraulic load condition,the average removal rates of COD,NH₄⁺-N,NO₃^--N,TN,and TP were 54.06%,55.43%,59.86%,and 58.86%,respectively,and the corresponding removal loads were 7.80 g·m^-2.d^-1,1.57 g.m^-2.d^-1,3.58 g.m^-2.d^-1,and 0.26g.m^-2.d^-1.The seasonal differences of the removal effects of various pollutants in the system are obvious.The removal rules are:summer>autumn>spring>winter.The O₁ unit of the wetland system is the core unit of the system,with the highest removal rates of COD,NH₄⁺-N,and TP,and the highest contribution of the A unit to the removal of TN.（2）System optimization measures were studied.The main research is on the enhancement effect of artificial aeration and dosing of carbon source extracts on the system.The results show that the average removal rate of COD in the constructed wetland increased from 54.06%to 66.78%before the artificial aeration measures were taken;the average removal rate of ammonia nitrogen increased from 58.78%to 64.68%,the average removal rate of nitrate nitrogen decreased from 84.62%to 80.36%,and the average TN removal rate increased from 60.32%to 64.47%.After adding plant carbon source extracts,the average removal rates of NO₃^--N and TN in constructed wetlands were 61.22%and 53.37%,respectively,which were 20%and 17.5%higher than those of common constructed wetlands.The removal effect of the system under winter insulation measures was studied.The results showed that the average removal rates of NH₄⁺-N,NO₃^--N,and TN in constructed wetlands were 46.11%,48.42%and 43.87%,respectively,which were 8.45%,9%and 9.82%higher than those of unconstructed wetlands.（3）The economic benefits of the system have been studied.Rural domestic sewage is used for regenerating irrigation,which effectively saves the use of fertilizers and generates indirect economic benefits of 3758 yuan per year.Irrigation tail water is abundant in nitrogen and phosphorus.Not only aquatic vegetable-type constructed wetlands can reduce nitrogen and phosphorus load,but also can produce considerable economic benefits.The yield of water spinach is 19.37kg/m²,and the yield per 667 m² is up to 15,496 yuan.The production of cress is 17.94kg/m2,and the yield per 667 m² is as high as 11,960 yuan.