Research On The Effect And Mechanism Of Plant-substrate Enhanced Composite Constructed Wetland In The Treatment Of Saline Wastewater

Water is closely related to human life and affects all aspects of people’s survival activities.Water pollution caused by human activities will reduce or lose the use value of water.All kinds of pollutants in water will poison aquatic organisms and affect drinking water sources and scenic spots.With people’s higher and higher requirements for the living environment,water pollution has been paid more and more attention.At present,with the continuous development of all kinds of industries,the salinity of waste water is gradually increasing,and the pollution of saline water is becoming more and more common.Saline wastewater will have a serious negative impact on microorganisms,plants,phytoplankton,benthos and even fish in the aquatic environment,so it is very important to seek an efficient ecological remediation technology for saline water.Constructed wetland is a rapidly developing water ecological restoration technology in recent years,but because it is vulnerable to environmental stress,there are some limitations in the treatment of saline wastewater.The previous research results show that the coupling of microbial desalination battery and wetland system can alleviate the effect of salt stress to some extent.In order to further improve the efficiency of the composite system in purifying saline water,this study takes the composite system as the research object to explore the strengthening effect of rock wool material on the composite system under different operating conditions,and determine the best operating conditions and experimental equipment.Then,on the basis of previous research,the effect of plant community on the compound system is discussed,the better device is determined,and the operation mechanism of the system is clarified.The main research contents and results are as follows:(1)The results showed that under the condition of high salt,the removal rate of pollutants(especially TN)in wastewater by the composite device strengthened by rock wool material was significantly higher than that of the control device,and the laying mode of the middle and lower layer was better than that of the middle and lower layer,and the decontamination ability of the calamus plant was better than that of canna,so the best treatment device was determined as BCM-Ac.When S=5 and C/N ratio is 7,BCMAc reaches a better state,and the purification efficiencies of TN,TP and COD are 90.42%,89.10% and 97.01% respectively,and the concentration of each pollutant is the lowest when the Hydraulic Retention Time(HRT)is 2 days.The results of SEM and microbial analysis showed that the addition of rock wool could optimize the matrix structure,improve the richness and uniformity of microbial community in the composite device,and promote the enrichment of functional bacteria such as denitrification bacteria Thauera and Dechloromonas,phosphorus accumulation bacteria Rhodocyclaceae,organic matter degrading bacteria Actinobacteria and electricity-producing bacteria Firmicutes.And the microbial metabolic pathways in the BCM-Ac device are various,and the functions are complex and diverse,which promote the stable and effective operation of the complex system.(2)The results show that the removal efficiency of TN by plant hybrid device is significantly higher than that by single device,and the collocation effect of Acorus calamus,Iris and Copper Rush is better than that of Acorus calamus,Juncus and Copper Rush.BMC-G3 is determined as the best device,and its removal rates of TN,TP and COD reach 97.00%,91.60% and 98.8% respectively,which greatly improves the working efficiency of the system.When HRT=1d,the results of enzyme activity analysis show that different plants show different physiological and ecological responses under salinity stress,but plant communities can increase the concentration of Superoxide dismutase(SOD)and Hydrogen Peroxidase(POD)in plants and reduce the content of Malondialdehyde,MDA(MDA),and the micro-current in Microbial desalination fuel cell(MDC)system can promote the growth of plants,so plant combination can promote itself to adapt to the external high-salt environment.Microbial analysis shows that the collocation of different plant communities can improve the richness and species diversity of microbial communities in the system,promote the reproduction and enrichment of functional bacteria,optimize their distribution,and enhance the cooperation between plants and microorganisms.(3)The purification effect of the composite device strengthened by rock wool materials and plant communities on saline wastewater is significantly better than that of the traditional constructed wetland.It is speculated that the micro-current and micromagnetic field effect generated during the operation of the MDC system in the composite system can stimulate the enrichment of plants and growing microorganisms in the system.In addition,the optimization of plant communities and flora structure in the system can further promote the power generation of the MDC system,and form a virtuous cycle among plants,microorganisms and MDC system,thus enhancing the wetland system.To sum up,this study constructed a wetland system with ecological function,landscape benefit and treatment efficiency,optimized the performance of the composite system,improved the stability and efficiency of the system in treating salty sewage,and provided theoretical and technical reference for the construction of constructed wetlands,subsequent expansion and application,and ecological treatment of salty sewage.