Screening Of Halotolerant Aerobic Denitrification Bacteria And Its Treatment Of Mariculture Wastewater

With the rapid development of mariculture in China,a large amount of mariculture wastewater has been produced.It is very easy to cause marine eutrophication and endanger the sustainable development of marine ecological environment if the mariculture wastewater is directly discharged into the ocean.Rapid and efficient removal of inorganic nitrogen from mariculture wastewater has become an urgent problem to be solved in mariculture wastewater treatment.In recent years,heterotrophic nitrification aerobic denitrification（HN-AD）bacteria have attracted much attention because of their ability of simultaneous nitrification and denitrification.However,the high salinity of mariculture wastewater greatly limits the application of HN-AD bacteria in mariculture wastewater treatment.Therefore,in this paper,halotolerant HN-AD bacteria were domesticated and screened,and the study on the treatment of mariculture wastewater by halotolerant HN-AD bacteria was carried out.Firstly,the common HN-AD bacteria were acclimated by salinity gradient,and four salt tolerant aerobic denitrifying bacteria were isolated and screened.After the preliminary identification of nitrification and denitrification ability,a strain with the best nitrification and denitrification capacity was selected.Combined with the colony characteristics,individual morphological characteristics,physiological and biochemical characteristics and 16S r RNA sequencing analysis of the strain,it was identified as Vibrio sp.,and named Vibrio sp.LY1024.Secondly,the nitrogen removal characteristics of Vibrio sp.LY1024 were measured,and the nitrogen removal pathway of Vibrio sp.LY1024 was deduced.The results of heterotrophic nitrification showed that Vibrio sp.LY1024 could remove both ammonia nitrogen and COD effectively.After 36 h of inoculation,the removal rates of NH₄⁺-N and COD were 98.8%and 90.2%,respectively.Some NO₃^--N and trace NO₂^--N accumulated in the reaction process.The results of aerobic denitrification showed that NO₃^--N and NO₂^--N were almost completely removed after 24 h of inoculation,and the removal rate of COD reached more than 90%.In addition,Vibrio sp.LY1024 had good simultaneous heterotrophic nitrification and aerobic denitrification ability.NH₄⁺-N,NO₃^--N and NO₂^--N were rapidly degraded simultaneously after Vibrio sp.LY1024 was inoculated in mixed nitrogen source medium.After 36 h,the NH₄⁺-N removal rate reached 98.16%,NO₃^--N was 100%removed after 27 h,and NO₂^--N was 100%removed after 21 h.The denitrification path of Vibrio sp.LY1024 was speculated as NH₄⁺-N→NH₂OH→NO₃^--N→N₂O→N₂.Then,the suitable environmental conditions for nitrogen removal by Vibrio sp.LY1024 were explored.The results showed that strain LY1024 had excellent nitrogen removal efficiencies in the initial total nitrogen concentration range of 20–200 mg/L,so it could treat wastewater with a wide range of nitrogen content;C/N>15,neutral or slightly alkaline environment was favorable for the growth and nitrogen removal of strain LY1024;The temperature of 20–30℃was favorable for the growth and denitrification of strain LY1024,but as low as 15℃,the removal rate of NH₄⁺-N and NO₃^--N were still 97.3%and 76.4%,respectively;Strain LY1024 could grow well and has strong nitrogen removal ability in the wide salinity range（0–8.5%）.In other words,strain LY1024 has good nitrogen removal performance under the conditions of high nitrogen content,low temperature and high salinity.Finally,a simulated biofilm reactor was prepared to treat mariculture wastewater with natural shells as the carrier and Vibrio sp.LY1024 as the main microorganism.The results showed that the biofilm reactor had good nitrogen and carbon removal ability.After 24 h,the removal rates of COD,NO₃^--N,NH₄⁺-N and TN were 88.5%,97.1%,99.0%and96.9%,respectively.Both inorganic nitrogen and total nitrogen in effluent met the first level standards of Discharge Requirements for Mariculture Water（SC/T 9103-2007）and Discharge Standard for Pollutants in Aquaculture Tail Water（DB43/1952-2020）.In conclusion,Vibrio sp.LY1024 has excellent heterotrophic nitrification-aerobic denitrification capacity and strong salt tolerance.It has great application potential in the field of mariculture wastewater treatment.