| Constructed wetlands have developed rapidly in the world currently.Besides the nitrogen removal effect,people also have paid attention to its negative environment effects of N20 emission.The carbon source is the limiting factor of denitrification,as well as important for N2O emissions in constructed wetlands.Therefore,it was very valuable to analyze the relationships among carbon source,denitrification and N2O emissions.A set of constructed wetlands were built under greenhouse,two different carbon source were selected:glucose(CWs)and sodium acetate(YWs)with the influent COD:N 20:1,10:1,7:1 and 4:1.A comparison group(CK)with COD:N 0:1 was set in the research,too.In this paper,the carbon source effects on denitrification,the emission of N2O and the microbial community structure in constructed wetlands were studied.The main contents and results were as following:(1)DO decreased rapidly within 1h in all constructed wetlands,and there was no significant difference in different carbon sources and COD:N(p>0.05).The effluent pH was higher in YWs than in CWs,while pH decreased slowly by time in CK.The changing of ORP indicated that constructed wetlands with carbon source would quickly change from the oxidation state to the reduced state.(2)The COD removal rates were over 80%in all carbon source wetlands,and the degradation rate of sodium acetate were slower than glucose;The removal rate of NH4+-N in CK could reach 83.53%,significantly higher than other constructed wetlands(p<0.05).The NH4+-N removal rates of CW1 and YW1 were just below CK;NO3--N could be completely removed in CWs and YWs,but the removal rate of NO3--N in YWs were significantly faster than that of CWs,while NO3--N accumulated in CK;NO2--N had already gone through a short accumulating period in carbon source wetlands,and the NO2--N accumulation amount of CW4 was significantly higher than other wetlands(p<0.05);The removal rates of TN were above 70%in all carbon source wetlands,and CW1 achieved the highest removal rate of 88±5.6%,while the TN removal in CK was only about 20%.(3)Carbon source and COD:N influenced greatly on emissions of N2O in constructed wetlands.The average fluxes of N2O in CWs and YWs were between 0.40±0.05～1.94± 0.85mg·(m2·h)-1 and 0.09 ± 0.02～0.29± 0.01mg·(m2·h)-1,while the accumulation of N2O were between 5.93 ± 3.13～64.81 ± 16.45mg·m-2 and 2.56±0.79～6.76±0.63mg·m-2,respectively.The average fluxes and accumulation of N2O in YWs were generally lower than that in CWs.The accumulation of N20 and the cumulative N2O-N emission of total removal TN in CW4 were significantly higher than other wetlands(p<0.05),which were 64.81 ±16.45 mg·m-2 and 1.07±0.25%,respectively.And no N2O emission could be detected in CK;There was significant correlation between N2O emission and NO2--N(p<0.05)in CWs.(4)Adding external carbon source was beneficial to the increasing of sludge and total PLFAs in constructed wetlands,especially in CWs.The species of identified PLFAs groups and special microbes content of PLFAs were both increasing with the rising of COD:N. |
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