Experimental Study On Remediation Of Black-odorous Water By Horizontal Subsurface Flow Constructed Wetland With Aeration

Black-odorous water is a prominent water environment problem in China recently.Black-odorous water has significant odor and relatively low transparency.It maily contains pollutants of organic matters and ammonia nitrogen.Horizontal subsurface-flow constructed wetland is commonly used for treatment of black-odorous water;however,traditional horizontal subsurface-flow constructed wetlands have relatively low content of dissolved oxygen,which leads to bad effects of purification for ammonia nitrogen and odor.In order to solve the above-mentioned problem,in this research,restoration experiments on black-odorous water is carried out through the establishment of horizontal subsurface-flow constructed wetlands with enhanced aeration.Firstly,constructed wetland substrates were selected based on their characterization,then,experiments of the purifying effects on black-odorous water of constructed wetlands with different aeration method were carried out,and the quantity of functional microfloras were studied to discuss the reasons for different purifying effects,finally,the stability of purifying effects of constructed wetlands with different aeration method was studied.Main contents and conclusions of this research are as follow:(1)4 substrates(zeolite,red brick,corallite,and vermiculite)were selected for substrate screening research.According to isothermal adsorption test,the maximum theoretical adsorbing capacity of substrates in respect of ammonia nitrogen is: zeolite(2.63 mg/g)> vermiculite(2.57 mg/g)> red brick(0.24 mg/g)> corallite(0.19 mg/g);and adsorption kinetics test shows that the equilibrium absorption capacity of substrates in respect of ammonia nitrogen is: zeolite(2.16 mg/g)> vermiculite(1.52 mg/g)> red brick(0.26 mg/g)> corallite(0.20 mg/g).Therefore,zeolite was selected as the substrate of constructed wetlands.(2)In the research,constructed wetlands with different aeration method were built for research on purifying effect of black-odorous water.According to purifying effects of no aeration(NA),continuous aeration(CA),and intermittent aeration(IA),the purifying effects of CA and IA on COD,ammonia nitrogen,transparency,and odor are better than that of NA;enhanced aeration can improve the purifying effect of constructed wetlands;the purifying effects of CA,IA,and NA are 92.9%,87.6%,and 75.3% respectively on COD;98.8%,97.3%,and 89.4% respectively on ammonia nitrogen;157 cm,134 cm,and 43 cm respectively on transparency.The purifying effects(odour thresholds)on undesirable odor are 0,0,and 11 respectively.The purifying effect of IA on total nitrogen is better than CA,where the purifying effects of IA and CA on total nitrogen are 91.9% and 53.7% respectively.Therefore,intermittent aeration is the best aeration method in respect of purifying effect.(3)In the research,study on the quantity of functional microfloras in constructed wetlands was carried out.Aeration enhancement increased the quantity of total bacteria,ammonifying bacteria,and nitrite bacteria in the forepart of constructed wetlands and improved the purifying effect of constructed wetlands on COD and ammonia nitrogen.At the first sampling point on the upper layer of constructed wetlands along the water flow direction,the quantity of total bacteria,ammonifying bacteria,and nitrite bacteria of IA are respectively 1.3,2.1,and 1.8 times of those of NA,and the quantity of total bacteria,ammonifying bacteria,and nitrite bacteria of CA is 1.3,2.5,and 2.1 times of those of NA;at the first sampling point on the lower layer of constructed wetlands along the water flow direction,those of IA are 1.7,1.0,and 1.3 times of those of NA,and those of CA are 1.6,2.1,and 1.5 times of those of NA.(4)Finally,the fluctuation of black-odorous water was simulated to study the stability of purifying effects of constructed wetlands with different aeration method.The stability of purifying effects on COD and ammonia nitrogen of CA and IA is better than that of NA;compared with the condition of normal inflow,the COD purifying effects of CA,IA,and NA are reduced by 5%,8.2%,and 12.8% respectively,and the purifying effects on ammonia nitrogen are reduced by 1.2%,2.9%,and 19.8% respectively.The purifying effect of IA on total nitrogen is better than CA,where the purifying effects on total nitrogen of IA and CA are 82.8% and 57.4% respectively.Therefore,intermittent aeration is the most stable aeration method.In conclusion,intermittent aeration increased the content of DO in horizontal subsurface-flow constructed wetland and increased the quantity of total bacteria,ammonifying bacteria,and nitrite bacteria.It not only solves the "black" and "smelly" of Black-odorous Water,but also has good purification effect and stability.It is hoped to provide reference for the treatment of Black-odorous Water by constructed wetlands.