| The census bulletin of Chinese environment proposed that rural non-point source pollution has been the biggest source of pullution, it caused serious impact on the quality of rural water environment. Constructed wetland as a popular rural sewage treatment system is used at present, however, it is one of the potential source of methane emission. Considered that methane as the greenhouse gases has potential effective and its effect on the global climate change, it is very significant to control the methane emission from constructed wetlands.In this study, three vertical-flow constructed wetlands at Buddhist Temple Base of Sichuan Agriculture University were built to degrade the sewage from rural non-point sewage pollution. The size of every constructed wetland was 3600mm×1200mm×1200mm, with planting the Cyperus alternifolius L. and the substrates of every constructed wetland were three different sizes of gravel from 10mm to 40mm. From top to down in every constructed wetland, the first layer of gravel substrate was 400 mm depth and 10mm-20mm diameters, the second layer of gravel substrate was 400 mm depth and 20mm-40mm diameters, and the third layer of gravel substrate was 250 mm depth and 30mm-40mm diameters. Besed on the orthogonal experimental design, the research objects of methane emission control during sewage degradation from Dujiangyan rural non-point source pollution by vertical-flow constructed wetlands was analyzed by different operation condition, that included different water tables, aeration intensity, aeration duration and aeration interval time. The methane flux and corresponding water quality parameters under different operation conditions in these constructed wetlands treatment system were measured and analyzed, in order that the main influence factors and maximum control measurements for methane emission in constructed wetlands were investigated for the atmosphere and water quality requirements and the basis of greenhouse gas emission reduction.Main results are as follows:(1) The average of methane flux in the vertical constructed wetlands was 1.34 mol/m2/day, which is a relatively high-level of methane emsssion and a typical methane emission source, compare with other research results.(2) The aeration volumes was the key impact factor for methane emission in constructed wetland system among different orthogonal experiments operation conditons. The bigger or less aeration volumes caused the unexpected control results of methane emission. The results shows that the lowest methane emission control conditions in these vertical constructed wetlands were the aeration volumes of 6.5m3/6h, water level of 110 cm, aeration duration of 20 minutes, interval aeration time of 340 minutes, the aeration intensity of 3.9 m3/h and aeration period of 6 hours, with the variety of methane emission flux was 0-0.97mol/m2/day, the average minimum methane emission flux of 0.355mol/m2/day.(3)The variety of methane emission flux was 0.76-2,41mol/m2/day in blank experiment and the average minimum methane emission flux of 1.42mol/m2/day. When the constructed wetlands were aerated, the variety of methane emission flux was 0.11-1.40mol/m2/day in blank experiment and the average minimum methane emission flux of 0.66mol/m2/day. The methane flux was reduced by 53.21% when the intensity of aeration, time of aeration, interval of aeration and the water table were optimally controlled.(4)Microporous aeration technology can increase the transfer efficiency in this study, average increased oxyen value of DO was 54.34%. It was found that the most important influence control factors to aeration efficiency in CWs were the water table and the horizontal locations of installed aerators. The highest mean oxyen transfer efficiency was 21.25%. Energy consumption in the pipelines during aeration was sharp, which the losses of energy was 25.86 Pa in every aerator in CWs.(5) The results of methane emission impacted by water quality was the order of water temperature>TOC>TN>TN>DO>pH>Eh>TC>TP>Conductivity, respectively. |
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