Long-term Performance And Microbial Mechanism In Intertidal Wetland Sediment Introduced Constructed Wetlands Treating Saline Wastewter

This study explored intertidal wetland sediment（IWS）as an inoculation source for long-term operation in batch flow constructed wetlands（CWs）.Through the microbial enhancement technology to improve the performance of CWs for saline wastewater.Here,two types of CWs were set up,CWs with IWS introduced into the substrate（IWS-introduced CWs）and control CWs.The microcosms were fed with synthesized saline wastewater（150 mg/L Na Cl）over three years.The chemical oxygen demand（COD）,total phosphorus（TP）,and ammonia nitrogen（NH₄⁺–N）removal rates in CWs were investigated to identify the effect of IWS addition to the performance of CWs.The bacteria in substrate and rhizosphere of CWs was identified during the operation,to elaborate the inter-annual variation in microbial community diversity.Finally,the functional microorganisms in the CWs was studied,to identify the role and influence of IWS in nutrient removal from the microbial aspect.Results showed that:（1）The average TP removal rate in saline IWS-enhanced CWs was 86.48%±7.08%,which was significantly higher than that in control CWs（79.80%±6.47%,p<0.05）.After three years,TP removal rates in the IWS-enhanced CWs was in a stable value（>90%）,while that in the control CWs dropped significantly（<70%,p<0.05）.This showed that the introduction of IWS could significantly improve the TP removal capacity of the CWs during the long-term operation.（2）The removal rate of NH₄⁺–N in all groups was more than 90%,showed that NH₄⁺–N in saline wastewater was all removed thoroughly in this experiment.Although there is no significant difference（p>0.05）,the NH₄⁺–N removal rate in IWS-enhanced CWs（94.50%±1.33%）was significantly higher than that in control CWs.In the third year,the NH₄⁺–N removal rate in the control CWs showed a downward trend（<93%）,while that in the IWS-enhanced CWs was still above 96%.The introduction of IWS could improve the degradation of NH₄⁺-N,thereby achieving higher NH₄⁺-N removal efficiency.（3）The COD removal rate in IWS-enhanced CWs was significantly higher than that in the control CWs（56.94%±6.74%）.In the third year,the COD removal rate of the two groups gradually tended to be stable,but the IWS-enhanced CWs still had obvious advantages（p<0.05）.This proved that the IWS microbial-enhanced technology could effectively improve the degradability and stability of the CWs in COD removal.（4）Lots of halophilic bacteria（Proteobacteria and Chloroflexi）was observed in the substrate and rhizosphere of the IWS-enhanced CWs,which was more than 30%of the total bacterial biomass.During the three years,the relative abundance of Proteobacteria and Chloroflexi in IWS-enhanced CWs was at the highest value（>20%）.This indicated that IWS introduced halophilic bacteria that were more suitable for high salty environments.（5）The dominant substrate bacterial in IWS-enhanced CWs were mostly denitrifying bacteria（Anaerolineaceae）,heterotrophic anaerobes（Actinobacteria and Gammaproteobacteria）,and denitrifying phosphorus accumulating bacteria（Pseudomonadaceae）.During the three-year,the relative abundance of these functional microorganisms in the IWS-enhanced CWs had a significant advantage compared with the control CWs（p<0.05）.These dominant microorganisms could effectively remove the NH₄⁺-N,COD and TP indicators in wastewater through the denitrification,anaerobic respiration,and anaerobic phosphorus accumulation process.（6）Photosynthetic bacteria（Chloroplast）,aerobic phosphorus accumulating bacteria（Alphaproteobacteria）,nitrifying bacteria（Anaerolineaceae）and plant symbiotic bacteria（Rhodobacteraceae and Rhizobiaceae）were found in the rhizosphere of the IWS-enhanced CWs.After three years,the relative abundance of these bacterial in IWS-enhanced CWs increased yearly,while that in the control CWs decreased significantly（p<0.05）.These bacteria could increase the O₂content,the organic matter removal rates,and the tolerance to salt stress of plants through photosynthetic,aerobic phosphorus accumulation,nitrification and plant hormone regulation under aerobic conditions.（7）The functional bacteria in IWS-enhanced CWs were mainly Candidatus,Nitrospira,Psedomonas,Bryobacter and Arthrobacter at the genus level.These functional genera had excellent performance in nitrogen removal,phosphorus removal and COD removal.By increasing the number of functional microorganisms,IWS enhanced the performance and tolerance of CWs in long-term saline wastewater treatment.