A Study Of Ferric-carbon Micro-electrolysis Process To Enhance Nitrogen And Phosphorus Removal Efficiency In Constructed Wetlands

As the development of the urbanization and economy,domestic sewage and industrial effluents led the increasing of nitrate and phosphorus concentration in aquatic ecosystems.Nitrate and phosphorus are the main reasons of eutrophication.Constructed wetlands(CWs)are engineered systems that have been designed and constructed to utilized the natural processes involving wetland vegetation,soils and their associated microbial assemblages to assist in treating wastewater.Constructed wetlands have become popular for the treatment of domestic sewage as a promising technology owing to the low cost,plain maintenance requirements and simple operation.It has been demonstrated that the substrates are important in removing nitrogen and phosphorus.Thus the modification of substrates has become a focus for enhancement of nitrogen and phosphorus removal in constructed wetlands.To cure the above problems,the study has applied ferric-carbon micro-electrolysis process in subsurface flow constructed wetlands(SSFCWs)to enhance the removal efficiencies of nitrogen and phosphorus in domestic sewage and explored the feasibility to combine micro-electrolysis with constructed wetlands.The study also evaluated the performance of nitrogen and phosphorus removal in F/C-M/E SSFCWs and the effect on plants growth and microbial communities in the system,and illuminated the mechanism of nitrogen and phosphorus removal.On the disadvantages presented in F/C-M/E SSFCWs,aeration has been introduced to optimize the system and to evaluated the feasibility in improving its performance.Besides,the study has evaluated the microbial communities.The main results are as follows:1.In this study,the application of ferric-carbon micro-electrolysis substrate in SSFCWs significantly enhanced the removal performance in simulated domestic sewage water treatment.The NO3--N,TN and TP removal efficiencies of F/C-M/E SSFCWs was 99.52±0.80%-99.54±0.80%,77.31±1.58%-81.45±1.27%and 88.10±5.99%-93.63 ±5.30%,which was much higher than original subsurface flow constructed wetlands.2.Ferric-carbon micro-electrolysis substrate accelerated the plant growth.Furthermore,a significant microbial diversity in the biofilm of F/C-M/E SSFCWs was also observed.The nitrification and denitrification bacteria communities and PAOs were significantly increased.The Ferric-carbon micro-electrolysis substrate observably changed the proportion of nitrogen and phosphorus removed by different pathways.The proportion of nitrogen removal through substrate adsorption and other pathways was 69.7%-74.8%,and the proportion of phosphorus removal through substrate adsorption and other pathways was 82.1%-87.2%.By the way,F/C-M/E SSFCWs reduced the release of nitrous oxide compared with original subsurface flow constructed wetlands.3.As the modification of F/C-M/E SSFCWs,aeration significantly improved NH4+-N removal efficiency.Aeration supplied aerobic environment which is beneficial to nitrification.Compared with the traditional constructed wetlands,the TN removal efficiencies of F/C-M/E SSFCWs increased by 22.98±8.34%and 21.49±7.98%,TP removal efficiency improved to 88.08±7.50%and 70.07±7.06%.F/C-M/E substrates provide plenty of electron suppliers for denitrification and the aeration make the dissolved oxygen enough for nitrification,which improved TN removal efficiency immensely.