Study On The Removal Of Nitrogen In Saline Wastewater By Salt-tolerant Microorganism Intensified Constructed Wetlands

In recent decades,with the rapid development of aquaculture industry in coastal areas of China,a large amount of coastal aquaculture wastewater has been discharged,which brought about various negative impacts on the environment.The coastal aquaculture wastewater usually contains both inorganic salts and many contaminants including nitrogen.Furthermore,with the rapid development of industrialization,a large number of saline wastewater sources,e.g.,pickled wastewater,textile wastewater and oily wastewater,etc.,have been produced in various industrial processes.Most saline industrial wastewaters also contain a lot of nitrogen pollutants.The increasing discharge of untreated saline wastewater from aquaculture and industry has threatened the aquatic,terrestrial and wetland ecosystems.Therefore,the removal of nitrogen pollutants from saline wastewater has become an urgent problem.As a lower cost,high efficiency and energy saving water remediation technology with no production of secondary pollutants,constructed wetlands?CWs?have been widely applied in treatment of nitrogen pollutants in wastewater.However,the nitrogen removal capacity of CWs decreased significantly under saline conditions.In this study,through the isolation of strains with high efficiency of salt-tolerance and denitrification,the application of microbial augmentation technology for saline wastewater treatment in CWs was studied,the growth and nitrogen accumulation of plants were investigated,and the changes of microbial community structure in CWs were analyzed.This study will provide a new solution for the treatment of saline wastewater in CWs.A salt-tolerant denitrifying bacterium strain F2 was isolated by the dilute soil suspension and spread plate techniques from seawall muddy water in Dalian City,Liaoning Province,China.By morphological observations,physiological and biochemical characteristics and 16S rDNA identification,strain F2 was identified as Alishewanella sp.,named Alishewanella sp.F2?GenBank accession no.MN396708?.Strain Alishewanella sp.F2 can tolerate the NaCl concentration up to 70 g/L.At the salinity of 0-30 g/L NaCl,most efficient denitrification capacity of strain Alishwanella sp.F2 was observed,and the removal percentages for both nitrite nitrogen?NO₂^--N?and nitrate nitrogen?NO₃^--N?were approximately 99%.When the pH was 8-10,the NaNO₂ initial concentration was 0.4-0.8 g/L and the inoculation size was 5-7%,strain Alishewanella sp.F2 had an efficient denitrification capacity at the salinity of 30 g/L NaCl.The salt-tolerant microbial inoculum was prepared by strain Alishewanella sp.F2,and it was directly added into CW microcosms to treat the saline wastewater at different salinity levels.At salt stress,the addition of the salt-tolerant microbial inoculum can enhance the denitrification capacity of CWs,and had efficient removal capacities of ammonia nitrogen?NH₄⁺-N?,NO₃^--N and total nitrogen?TN?.At an EC of 15 mS/cm,the removal percentages of NH₄⁺-N,NO₃^--N and TN in bioaugmented CW?Bio-CW?microcosms on Day 5 were 95.7%95.0%and 99.4%,respectively.Especially,the removal percentages of NH₄⁺-N and TN in Bio-CW microcosms were significantly higher?p<0.05?than that in unbioaugmented CW?un-Bio-CW?microcosms,respectively.Furthermore,both growth and TN accumulation of plants in Bio-CW microcosms were promoted compared with the un-Bio-CW microcosms.Although the strain Alishewanella sp.F2,which was used to prepare the salt-tolerant microbial inoculum,did not become one of the dominant bacteria,it had been existed in Bio-CW microcosms from the beginning to the end of this experiment.This shows that strain Alishewanella sp.F2 had a symbiotic relationship with the indigenous microorganisms in Bio-CW microcosms,and together played a role in the process of nitrogen removal.The results of high-throughput sequencing showed that the addition of salt-tolerant microbial inoculum changed the microbial community structure,and increased the survival quantity of some functional bacteria?e.g.,Thauera,Arthrobacter and Pseudomonas,etc.?in Bio-CW microcosms.Microbial augmentation technology with salt-tolerant bacteria can enhance the nitrogen removal efficiency of CWs under saline condition.