Denitrification Performance Of Strain LV2 In High-salt Wastewater And Its Strengthen The Application

With the development of chemical industry,pharmaceutical industry and aquaculture in coastal areas,a large number of high salt and nitrogen containing wastewater are produced.In recent years,with the acquisition of heterotrophic nitrification aerobic denitrification strains,it is possible to achieve simultaneous nitrogen and carbon removal economically and efficiently,and it has also become one of the main research directions of scholars.When the salinity is high,the number,species and activity of microorganisms in the system will be inhibited to a certain extent,resulting in the reduction of nitrogen removal efficiency.At present,researchers have found that salt tolerant heterotrophic nitrification aerobic denitrification bacteria can grow in higher salinity wastewater and remove nitrogen efficiently compared with ordinary heterotrophic nitrification aerobic denitrification bacteria.Therefore,it is an economic,efficient and feasible method to treat high salinity wastewater with salt tolerant heterotrophic nitrification aerobic denitrification bacteria.This paper studies the performance and denitrification mode of salt tolerant heterotrophic nitrification aerobic denitrification bacteria in the treatment of high salt and nitrogen containing wastewater,explores the salt tolerant mechanism of salt tolerant bacteria and the enhancement of high salt and nitrogen containing wastewater in laboratory scale reactor,so as to provide certain theoretical guidance for the treatment of high salt and nitrogen containing wastewater by salt tolerant bacteria in the future.The main research content of this paper is to screen a salt tolerant heterotrophic nitrification aerobic denitrification strain,preliminarily explore the salt tolerance and salt tolerance mechanism of the strain,systematically explore the influencing factors of its heterotrophic nitrification performance,and speculate the denitrification path of the strain through its utilization ability of different nitrogen sources,nitrogen balance experiment and enzyme activity test.Then,the strain was inoculated in sequencing batch biofilm reactor(SBBR)as an enhanced strain to compare the degradation effect of biological enhanced system and ordinary biological system in the treatment of high salt and nitrogen-containing wastewater,and further explain the reason of biological enhancement by studying the changes of microbial activity and extracellular polymer in the two systems.The results will provide theoretical guidance for the practical application of the strain.The main conclusions are as follows:(1)A salt tolerant heterotrophic nitrification aerobic denitrification strain was isolated and screened.The 16S r DNA sequence showed that the strain was Pseudomonas sp.,named LV2.(2)LV2 has a certain salt tolerance,and the best removal performance of ammonia nitrogen is when no salinity is added.With the increase of salinity,the average removal rate of ammonia nitrogen decreases.The soluble sugar increased with the increase of salinity,which provided energy for the growth of the strain;The decrease of intracellular protein content with salinity may be due to the resistance of strains to higher salinity consumption or blocked amino acids of synthetic protein.(3)The results of single factor experiments showed that the optimal conditions for the heterotrophic nitrification and growth of strain LV2 in wastewater with salinity of 2%were as follows:sodium pyruvate as carbon source,C/N ratio of 12,initial p H of 5.0?8.0 and temperature of 30?40?.Under the optimal conditions,strain LV2 could remove more than95%of ammonia nitrogen in high salt wastewater.(4)At 2% salinity,strain LV2 had excellent heterotrophic nitrification performance,which could remove 97.34%of ammonia nitrogen at 18 h,leaving only 2.75 mg/L;The results of denitrification experiment showed that strain LV2 could use nitrate nitrogen and nitrite nitrogen as the only nitrogen source in high salt environment,and the NO₃^-–N and NO₂^-–N concentrations reached the lowest at 26.26 mg/L and 11.96 mg/L after 24 h and 48h,respectively,with removal rates of 76.35%and 88.33%respectively;When mixed nitrogen(NH₄⁺–N and NO₃^-–N or NH₄⁺–N and NO₂^-–N)was used as nitrogen source,the results showed that strain LV2 used ammonia nitrogen preferentially,and the removal rates of NH₄⁺–N and NO₃^-–N were 95.76%and 90.97%respectively,and the removal rates of NH₄⁺–N and NO₂^-–N were 95.08%and 88.76%respectively.At 2%salinity,strain LV2detected the production of N₂in the gas products when using ammonia nitrogen as substrate.The nitrogen balance experiment showed that 61.49%of the initial nitrogen was transformed into intracellular nitrogen and 21.56%into N₂.It was speculated that strain LV2 had denitrification and produced N₂.The activities of Hao,NR and NIR were detected in the process of ammonia nitrogen degradation by strain LV2.By analyzing the utilization of different nitrogen sources,nitrogen balance,gas production experiment and enzyme activity determination,it was inferred that the nitrogen removal path of strain LV2 might be:NH₄⁺?NH₂OH?NO₂^-?NO₃^-?NO₂^-?NO?N₂O?N₂.(5)Comparing the performance of enhanced system and common microorganism system adding salt resistant strain LV2 to degrade high salt nitrogen wastewater,it is found that the removal rate of ammonia nitrogen and COD in the effluent of the biological strengthening system is higher than that of the ordinary microorganism system when salinity is more than 2%,which is due to the high microbial activity in the biological strengthening system,and the protein and polysaccharide content in extracellular polymer is higher than that of the ordinary microorganism system,This will help to resist the harsh environment caused by high salt.