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The Study of Sewage Purification Capacity about Two Kinds of Constructed Wetlands

Author: ZhangYongJing
Tutor: MaJianMin
School: Henan Normal
Course: Ecology
Keywords: integrated vertical flow constructed wetland horizontal subsurface flow constructed wetland hydraulic retention time parameters seasonal effect sewage purification aeration
CLC: X703
Type: Master's thesis
Year: 2010
Downloads: 92
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Abstract

In this paper, there are two kinds of constructed wetlands to be of the research objects, which are integrated vertical flow constructed wetland and horizontal subsurface flow constructed wetland, to be carried out the following studies, respectively.The main research contents include: studied the better parameter of seasonal hydraulic retention time and the sewage purification effect of the two kinds of constructed wetlands when they were working in the four seasons of a year, by monitoring the water samples from the import and export of the two kinds of constructed wetlands respectively; researched the purifying effect of pollutants in the different substrate layers in the two kinds of artificial wetlands in the different months and the effects of aeration on sewage purification in two kinds of constructed wetlands, by monitoring the effluent sampled from the side different heights and the inflow of the two kinds of artificial wetlands respectively. In the paper, the water quality indicators monitored: temperature (T), dissolved oxygen (DO), potential of hydrogen (pH), total nitrogen (TN), total phosphorus (TP), chemical oxygen demand(COD), ammonium nitrogen (NH4+-N), nitrate (NO3--N). The main conclusions of this thesis are as follows:(1) The optimum parameter of seasonal hydraulic retention time of the two kinds of artificial wetlands are as follows:The optimum parameter of seasonal hydraulic retention time of integrated vertical flow constructed wetland are in between eight and ten hours in spring and autumn, six hours in summer, twelve hours in winter.The optimum parameter of seasonal hydraulic retention time of horizontal subsurface flow constructed wetland are in between ten and twelve hours in spring and autumn, in between six and eight hours in summer, in between twenty-four and thirty-six hours in winter.It can clearly be seen that the optimum parameter of seasonal hydraulic retention time of integrated vertical flow constructed wetland are less than the horizontal subsurface flow constructed wetland.(2) The two kinds of constructed wetlands has a similar purification effect to the domestic sewage which contain thetotal nitrogen concentration between 0.50 and 16.0 milligrams per liter, the total phosphorus concentration between 0.10 and 4.00 milligrams per liter and the organic compound concentration between 100 and 300 milligrams per liter. There exists an obvious seasonal variations about the different pollutants removal in the two kinds of constructed wetlands.The chemical oxygen demand removal in different seasons is no significant differences between the two kinds of constructed wetlands; The total nitrogen average removal in each of the different seasons is higher in integrated vertical flow constructed wetland than in horizontal subsurface flow constructed wetland. The ratio of ammonium nitrogen content in the proportion of total nitrogen affects the nitrogen removal efficiency in the two kinds of constructed wetlands. The greater the ratio is, the lower the nitrogen removal efficiency is.The total phosphorus removal in the two kinds of constructed wetlands shows a poor regularity because of the seasonal effects of phosphorus load, hydraulic retention time parameter and the temperature change. About the removal efficiency of ammonium nitrogen, only in winter is better, the other seasons are lower. (3) The seasonal variations of water temperature in the two kinds of constructed wetlands is significantly correlated with the removal change of total nitrogen, and is not significant with the removal change of total phosphorus. The N, P removal affected by water temperature in integrated vertical flow constructed wetland was significantly more than in horizontal subsurface flow constructed wetland. (4) There is no significant difference about the COD removal in the different substrate layers of the two kinds of constructed wetlands.The TN average removal in the fill material surface of two kinds of constructed wetlands is high and stable; in the different months the TN removal efficiency have a greater volatility in the middle and bottom substrate layers of the two kinds of constructed wetlands, which can be seen filling the TN removal rate changes for the whole wetland TN removal.In integrated vertical flow constructed wetland, the ammonium nitrogen removal occurred mainly in the bottom of filler, in its surface and middle filler layers the ammonium nitrogen removal efficiency is slightly worse than the bottom filler; in the surface substrate layer of the two kinds of constructed wetlands there exist the ammonium nitrogen removal wider fluctuation margin phenomenon.In horizontal subsurface flow constructed wetland, the ammonium nitrogen removal occurred mainly in the surface and bottom filler, and in the middle substrate layer it is worst. (5) In integrated vertical flow constructed wetland, the surface and middle filler have stable phosphorus removal; removal; in different months the phosphorus removal of surface layer there are significant differences. In horizontal subsurface flow constructed wetland, the phosphorus removal occurre mainly in the bottom of filler; because of the combined effect of the temperature, HRT, phosphorus pollution load there exists a serious phenomenon of phosphorus releasing from the matrix in horizontal subsurface flow constructed wetland.(6) In integrated vertical flow constructed wetland there is significant impact on the removal of TN, NH4+-N and TP with the change of water environment temperature within constructed wetland; while the removal impact of various pollutants in horizontal subsurface flow constructed wetland is not significant. DO concentration in the interstitial water, has a significant positive correlation with the removal of TN, TP and COD of integrated vertical flow constructed wetland; with the NH4+-N removal of horizontal subsurface flow constructed wetland.(7) The results show that using the gas-water ratio of 2 to do aeration experiment in integrated vertical flow constructed wetland can get the best effects of sewage purification. The average removal rate of chemical oxygen demand、total nitrogen、ammonia nitrogen and nitrate nitrogen of the effluence of upstream pond respectively increase 16.47%, 5.15%, 13.84% and 96.91% than non-aerated experiment. The results indicate that the effect of removal COD at the gas-water ratio of 6 is better than 2, In dealing with domestic higher load can use this gas-water ratio to aerate.(8) In horizontal subsurface flow constructed wetland, aeration can make the treating effect of COD improve more obviously than non-aerated experiment, especially when gas-water ratio is 6 the increase can be up to 30%; the average removal rate of TN and NH4+-N is not obvious change when the gas-water ratio is 2, and there is a substantial increase in the removal rate of NO3--N; when gas-water ratio continues to increase, nitrogen removal have varying degrees of reduction. In the two kinds of constructed wetlands, the removal rate of total phosphorus is no significant change in the two conditions of aeration and non-aeration.

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