| Constructed wetlands(CWs)have been considered as one of sources being methane emission to atomshpere in the world,although CWs are one effective degradation method of rural deomestic wastewater treatment system.Methane(CH4)being an important greenhouse gases(GHG)makes a significant contribution to the global climate change,which methane ranks the second following the carbon dioxide’s contribution.Therefore,it is significant to explore controlling methane emissions from CWs.Based on the previous research results from our research team,methane emissions from integrated vertical-flow constructed wetland(IVCW)were furtherly conducted to control during agricultural non-point soure sewage pollution treatment.With same sizes(3600 mm length×1200 mm width×1200 mm depth),these IVCWs composed of an influent tank and an effluent tank with the wall depth of 10 mm thickness,consists of different substrates filling three layers from tank top to tank bottom and wetland plant using Cyperus alternifolius L..A hybrid power system coupled with wind enengy and solar energy was installed to provide energy to intermittent aeration in IVCW for the mitigation CH4 emission,under the conditons of aeration parameters coming from previous investigation results from our team.Meantime,the potassium peroxymonosulfate(PMS),as the Eh regulator,was added into IVCW with dosage of 31.25g,62.5g,125g,250g and 500g,respectively,for the mitigation CH4 emission from IVCW compared with the intermittent aeration experiment.After synchronously measuring CH4 fluxes and parameters of water quality,the better control of CH4 emission from IVCW in study can be determined to the conduct of saving energy and reducing CHG emission.Results from this study are as follows:(1)The average CH4 flux from IVCW2 was 0.342、0.989、1.411、0.824 and 1.214mol/m2/day,respectively,when PMS dosage of 31.25g,62.5g,125g,250g and 500g was respectively added for the control of CH4 emission.For the same sampling time for IVCW 1,the corresponding CH4 flux was 0.150,0.518,1.311,0.845 and 0.874mol/m2/day,respectively,when using intermittent aeration by a hybrid power system coupled with wind energy and solar energy for the reduce of CH4 emissions.Reslut from IVCWs shows that the average CH4 emissions(0.956 mol/m2/day)after adding five dosage of PMS was 1.29 times more than that by intermittent aeration(0.74mol/m2/day).It was found that CH4 emissions from in IVCW 2 were significantly influenced by adding PMS.When the mass of PMS increased from 62.5g to 250g,the CH4 emission was reduced by 1.2 times.When the mass of PMS increased from 125g to 500g,the CH4 emission was reduced by 0.86 times.Meantime,Result of the regression between the reduction of CH4 and the increase of PMS mass in IVCW 2 presents a nonlinear relationship,which the equation was yCH4 decrease=-9E-05x2PMS-increase+0.03xPMS-increase-1.6(R2 = 0.90).The intermittent aeration time has been influenced by local sunlight and wind when using a hybrid power sytem for the control of CH4 emission.With the increase of electric energy,the CH4 emission decreased gradually.When the electric energy was increased by 6 times(from 1728 kJ to 10368 kJ),the CH4 emission was reduced by 8.74 times.Important result in this study is that CH4 emission by intermittent aeration coupled with wind and solar energy had reduced by 0.216 mol/m2/day from IVCW,compared with the control of CH4 emission by the addition of Eh regulator(PMS).(2)When adding five dosage of PMS into IVCW 2 for the control of CH4 emissions,the average CH4 flux in IVCW 2 from the root-water subsystem of Cyperus alternifolius L.was 0.439 mol/m2/day,but CH4 flux in IVCW 2 from the stem-leaf subsystem of Cyperus alternifolius L.was 0.517 mol/m2/day.The similar results of CH4 emission from IVCW 1 were also found when using intermittent aeration.Correspondingly,the average CH4 flux in IVCW 1 from the root-water subsystem of Cyperus alternifolius L.was 0.296 mol/m2/day,but CH4 flux in IVCW 1 from the stem-leaf subsystem of Cyperus alternifolius L.was 0.444 mol/m2/day when the control of CH4 emissions was used by intermittent aeration providing local wind and solar energy.The average value of CH4 flux from the stem-leaf subsystem of Cyperus alternifolius L.in IVCWs was significantly higher than from root-water subsystem of Cyperus alternifolius L.in IVCWs,when using both CH4 control methods of PMS and intermittent aeration.Additionally,the average CH4 emissions(0.481 mol/m2/day)of the stem-leaf subsystem of Cyperus alternifolius L.was 1.3 times than that in the root-water subsystem of Cyperus alternifolius L.(0.368mol/m2/day)during using both PMS and intermittent aeration.(3)By intermittent aeration control of CH4 emission in IVCW 1,the average removal rate of COD,TN,TP,TC and TOC was 63.09%,59.69%,66.65%,39.82%and 50.01%,respectively,while the corresponding removal rate was 62.47%,62.11%,64.33%,40.07%,and 57.15%,respectively,by PMS control of CH4 emission in IVCW 2.The average removal rate of COD and TP promoted by 0.62%and 2.32%by intermittent aeration control of CH4 emission,compared with PMS control of CH4 emission.However,the average removal rate of TN by PMS control of CH4 emission increased by 2.42%compared with intermittent aeration control of CH4 emission.(4)The regression equations of Eh among electric energy,temperature,dissolve oxygen(DO),and sampling time by intermittent aeration control of CH4 emission in IVCW 1 was following significantly correlation:yEh=45.63xElectric energy-2.32xTemp+13.28xDO-0.07t-73.14(R2=0.99).When PMS control of CH4 emission in IVCW 2,the regression equations of Eh among PMS,temperature,DO,and sampling time was following significantly correlation:yEh=-0.44xPMS+6.82xTemp+16.08xDO+0.38t-264.1(R2=0.99).It’s evident that the DO content in IVCWs was promoted by using both PMS and intermittent aeration.DO content by using PMS and intermittent aerationin IVCW was promoted by 15.57%and 12.19%respectively,and correspondingly Eh promoted by 33.55%and 29.51%,respectively.It indicats that the effect of improvement of DO and Eh from IVCWs by intermittent aeration control of CH4 emission was better than by PMS control of CH4 emission.(5)It’s found that the water quality has siginificantly influence of CH4 emissions in IVCWs in this study.CH4 emissions from IVCWs were significantly correlated with COD(p<0.01),and significantly correlated with TN(p<0.05).The methane emission influenced by parameters of water quality from IVCWs has the order of COD>TN>Eh>TC>pH>DO>TP>temperature>conductivity>TOC.In general,it’s found in this study that the average CH4 emissions from IVCW by intermittent aeration control of CH4 emission coupled with wind and solar engergy was siginificantly less than by PMS control of CH4 emission.Moreover,the intermittent aeration control of CH4 emission coupled with wind and solar engergy can make full use of local natural resources and can improve the water quality.Therefore,the control methods of CH4 emission from IVCWs in this study can be applied and be scaling-up with the combination of different geographical areas,when treating rural non-point wastewater for both considerations of climate change and water quality. |
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