Bioremediation Of Nitrogen Pollution In Qinhuangdao Coastal Area Of Bohai Bay

At present,nitrogen pollution in coastal Bohai Bay has become a prominent problem threatening the water environment of Bohai Bay.In recent years,heterotrophic nitrifying and aerobic denitrification（HN-AD）bacteria and photosynthetic bacteria have received extensive attention in the field of water body remediation due to their excellent nitrogen removal performance and unique physiological characteristics.In this paper,salinity gradient acclimation of HN-AD bacteria was carried out,and immobilized salt-tolerant HN-AD bacteria and immobilized photosynthetic bacteria were prepared by adsorption method.Taking Qinhuangdao coastal area as a representative research area,biological remediation of nitrogen pollution in coastal Bohai Bay was carried out with total nitrogen（TN）as the treatment object.The main conclusions were as follows:Firstly,the simulation experiment results of nitrogen release from sediments showed that when nitrogen concentration of the overlying water was low,there was a process of sediment releasing nitrogen into the overlying water.With the gradual reduction of the initial nitrogen concentration of the overlying water,the nitrogen release capacity was gradually enhanced.The release rates of NH₄⁺-N and TN in the sediment were up to55.31%and 16.35%,and the maximum release amounts were 39.46 mg/kg and 102.32mg/kg.Moreover,the p H value of overlying water might further affect the sediment nitrogen release capacity,and increase its release rate and amount.Therefore,it is necessary to simultaneously remove nitrogen from the overlying water and sediment to effectively inhibit the release of nitrogen pollutants from the sediment.Secondly,common HN-AD bacteria were domesticated by salinity gradients,then isolated and screened,and a strain of salt-tolerant aerobic denitrifying bacteria was obtained,which was identified as Vibrio alginolyticus and named Vibrio alginolyticus YT-3.At the same time,photosynthetic bacteria were activated and cultured.The effects of environmental factors on the nitrogen removal performance of Vibrio alginolyticus YT-3 and photosynthetic bacteria were explored.The results showed that Vibrio alginolyticus YT-3 had efficient nitrogen removal ability under the conditions of C/N=15～20,25～30℃,neutral and weakly alkaline conditions and a wide range of salinity（0～40‰）,and the TN removal rates of Vibrio alginolyticus YT-3 from the seawater could reach 89%～96%after 24 h.Photosynthetic bacteria had good denitrification effect under different light and dissolved oxygen conditions,medium temperature,neutral and weakly alkaline conditions,the removal rates of TN from the seawater and sediments were above60%and 45%respectively after 10 days.In addition,the addition of Fe⁰ significantly enhanced the nitrogen removal of photosynthetic bacteria.When the addition ratio was 1%,the TN removal rate was 12.9%higher than that of the control group without Fe⁰.Then,Vibrio alginolyticus YT-3 and photosynthetic bacteria were immobilized with ceramsite as the carrier.The optimal immobilization conditions were as follows:the ceramsite particle size was 2～4 mm,the solid-bacteria ratio was 1:3（mass:volume,g:ml）,and immobilization time were 24 h and 96 h,respectively.Compared with free bacteria,the immobilized Vibrio alginolyticus YT-3 and photosynthetic bacteria had a wider suitable range of temperature and p H.The TN removal rates of immobilized Vibrio alginolyticus YT-3 from the seawater reached 46.85%at 4℃and remained above 83%at p H 5～9（25℃）after 24 h.The TN removal rates of immobilized photosynthetic bacteria from the seawater and sediments increased to 13.43%and 24.16%at 4℃respectively,and reached above 40%at p H 5～9（25℃）.After immobilization,Vibrio alginolyticus YT-3 and photosynthetic bacteria were more suitable for the actual water environment in coastal area.Moreover,the high-throughput sequencing results showed that the proportion of Proteobacteria at the phylum level and Rhizobiales at the order level increased significantly after immobilization,which meant that the abundance of dominant bacteria of photosynthetic bacteria increased significantly,indicating that the immobilization process could promote the enrichment of photosynthetic bacteria.Finally,a self-made simulated remediation device was used to remove nitrogen by immobilized Vibrio alginolyticus YT-3 and photosynthetic bacteria.On the 14th day,the concentrations of NH₄⁺-N,NO₃^--N and TN in the overlying water of coastal area decreased to 0 mg/L,0.04 mg/L and 0.93 mg/L respectively,the removal ratios of NH₄⁺-N,NO₃^--N and TN reached 100%,92.50%and 88.78%.The concentration of inorganic nitrogen decreased to 0.13 mg/L,which met the first class standard of Sea water quality standard（GB 3097-1997）.After 35 days,the TN content in sediments decreased by52.88%to 295.45 mg/kg,which was lower than the standard value of TN in the sediments（550 mg/kg）specified in the"Technical Regulations for the Second National Marine Pollution Baseline Survey".In conclusion,immobilized Vibrio alginolyticus YT-3 and photosynthetic bacteria have good nitrogen removal performance with a wide range of suitable temperatures and p H,which has great potential in the field of remediating nitrogen polluted coastal Bohai Bay.