Impact of plant carbon addition on water quality purification and greenhouse gas emissions in constructed wetlands
Constructed wetlands have the problem of severely limiting denitrification by the lack of carbon sources when treating low C/N wastewater.To supplement the carbon source for denitrification,dilute alkaline-heated corncobs(hereinafter referred to as precorn)and common corncobs were selected as the additional carbon sources of the constructed wetlands.Two stages of experiments such as plant carbon sources pretreatment and the different amounts of carbon sources added(C/N=6,5,and 4)were conducted to study their effect of water purification and greenhouse gas emissions from constructed wetlands.The results of the first stage experiments showed that the constructed wetlands with plant carbon sources dosing decreased the removal rates of COD and NH4+-N.The COD of the effluent from the constructed wetlands with precorn and corncobs dosing were 19.25～25.97 mg·L-1 and 22.22～23.56 mg·L-1,and the average COD removal rates were in the range of 82.61％～87.12％and 84.22％～85.13％,respectively.The average removal rates of NH4+-N were 82.44％～92.53％and 78.27％～92.86％,respectively,while those of the control groups were above 90％.After adding carbon sources,the average removal rates of NO3--N in the system were all above 99％.The addition of plant carbon sources did not significantly increase the emission flux of CH4 flux,but it significantly increased the N2O flux(P＜0.05).The results of the second stage of the experiment showed that the effluent COD increased gradually with the increase of C/N.The average COD removal rates were 86.38％,88.76％,and 92.38％when C/N ratios were 6,5,and 4,respectively.The effluent NH4+-N concentrations at C/N ratio of 6,5,and 4 were all extremely low,and their removal rates were higher than 99％,the effluent TN was mainly dominated by NO3--N.The average removal rates of NO3--N were 62.75％,58.41％,and 47.70％at C/N ratio of 6,5,and 4,respectively.The N2O flux from the constructed wetlands increased with increasing C/N.The CH4 flux was lower compared to that at the first stage,and constructed wetlands was weak sources of CH4 at C/N ratios of 6,5,and 4.In summary,the addition of plant carbon sources improved N removal by constructed wetlands,and the increase of C/N enhanced N removal rate.However,the addition of plant carbon sources increased the N2O emission,which was the main contributor to the integrated GWP,accounting for more than 90％.
万方数据
维普
