Treatment Of Agricultural Drainage Water In Horizontal Subsurface Flow Constructed Wetlands Using Corn Straw As A Sustained-release Carbon Source

When using constructed wetlands to treat agricultural drainage water,the characteristics of low C/N of agricultural drainage water affect its removal effect on nitrogen.Therefore,it is necessary to find a low-cost,renewable,environmentally friendly external solid sustained-release carbon source to improve the removal of nitrogen from constructed wetlands.In this paper,the effects of different pretreatment methods(pretreatment,acid treatment,alkali treatment and comminution)on carbon release from maize straw were studied.On this basis,corn straw was used as a solid sustained-release carbon source in constructed wetland to treat low C/N agricultural drainage water.The treatment effect was studied and compared with that of sodium acetate as additional carbon.The following results were obtained.:1.The concentration of chemical oxygen demand(COD),total nitrogen(TN)and total phosphorus(TP)in different corn straw treatments showed a relatively fast dissolution in the early stage,and then a stable trend.The C/N of final untreated,acid treated,alkali treated and crushed treatments were 9.4,13.2,24.3 and 4.2(p<0.05)respectively.The alkali treated corn straw has the highest C/N and can provide more carbon sources.The hydraulic retention time(HRT)of W2,W4 and W5 were 2,3 and 1 d,respectively.The removal rates of TN were 71.9%,87.9% and 52.3%,respectively,significant different(p<0.05).The removal rates of TP were 49.7%,65.4% and 33.4%,significant different(p<0.05).When HRT was 3 d,the treatment effect of agricultural drainage water is the best.3.The advantages and disadvantages of corn straw and sodium acetate as additional carbon sources were analyzed and compared from the aspects of treatment effect,operation cost,complexity and safety of follow-up management.The average removal rates of TN were 71.9% and 67.9% respectively when corn straw and sodium acetate were added as additional carbon sources.Compared with the blank constructed wetland device W1(HRT=2d),the removal efficiency of TN by W2 and W3 increased 21.1% and17.1% respectively.Compared with sodium acetate,corn straw has characteristics of low material cost,accessibility,long-term release.It has great advantages in treatment effect and cost,and achieves the goal of using waste to treat waste.