Screening Of Ammonia Nitrogen Degrading Strains And Evaluation Of Their Nitrogen Removal Efficiency

In recent years,with the rapid development of aquaculture in China,the problem of nitrogen pollution caused by aquaculture is also increasing.In addition to directly harming the health of aquatic organisms and causing huge economic losses,the discharge of nitrogen-containing wastewater will also cause eutrophication of water and damage the water ecosystem.Among many denitrification treatment methods,biological denitrification is the most economical and effective treatment method for aquaculture wastewater at present,and microbial denitrification plays an important role in biological denitrification.In this paper,three strains with high nitrogen removal capacity were screened from sediment and water samples of fish ponds and sewage treatment plants,and their classification and identification were conducted,and their nitrogen removal effects were evaluated.The main research contents are as follows:(1)Enrichment,isolation,screening and identification of strains.In order to obtain strains with high nitrogen removal capacity,221 strains of ammonia nitrogen degrading bacteria were enriched and isolated from samples collected from sediment and water samples of aquaculture ponds and sewage treatment plants.Through the safety test and the determination of ammonia nitrogen removal rate of aquaculture wastewater,three strains of effective ammonia nitrogen degradation bacteria were obtained,numbered BZ-95,RZ-44 and RK-43,with the ammonia nitrogen removal rate of 55%,72%and 59%respectively.After physiological,biochemical and16s DNA identification,it was preliminarily determined that the three strains were Bacillus zanthoxyli,Rhodococcus aetherivorans and Rhizobium rosettiformans.(2)Study on the proliferation and denitrogenation characteristics of the three strains in different nitrogen source medium.In this study,the proliferation and denitrogenation characteristics of three strains in three single and mixed nitrogen source medium were compared.The results showed that the growth of the three strains in different nitrogen source medium was positively correlated with the removal of ammonia nitrogen,and most of the initial total nitrogen changed to intracellular nitrogen.The three strains all had good ammonia nitrogen removal in the medium of various nitrogen sources,among which strain BZ-95 had the best effect,with the ammonia nitrogen removal rate of 83%-89%.Under mixed nitrogen source conditions,the utilization of various nitrogen by the three strains is different:Strain BZ-95could degrade ammonia nitrogen and nitrite at the same time,and the removal rate of ammonia nitrogen and nitrite could reach more than 87%after 48 h.Strain RZ-44 preferentially degraded ammonia nitrogen,and began to use nitrite after ammonia nitrogen was used up.Strain RK-43had no ability to use nitrite,but the removal rate of ammonia nitrogen could reach more than66%.(3)The effect of different environmental factors on the proliferation of the three strains and the degradation of ammonia nitrogen.In order to evaluate the ammonia nitrogen removal effect of strains BZ-95,RZ-44 and RK-43 in different environments,the effects of environmental factors such as temperature,p H,C/N ratio,salinity and rotation speed on the proliferation of strains and the ammonia nitrogen degradation effect were analyzed.The results showed that the three strains showed good growth and ammonia nitrogen removal effects at22℃-28℃,C/N ratio 5-20,Na Cl concentration 1-30 g/L and 0-150 r/min,and the growth and ammonia nitrogen removal rates of strain RZ-44 were better than those of the other two strains.The growth and removal of ammonia nitrogen of the three strains were not satisfactory at low temperature(16℃)and acidic environment(p H=5).(4)Evaluation of the proliferation and denitrogenation effect of the three strains in water with different ammonia nitrogen concentrations.Using aquaculture wastewater with adjusted ammonia nitrogen concentration of 0.5 mg/L,2 mg/L and 10 mg/L respectively as culture medium,the proliferation and ammonia nitrogen removal effects of three strains in aquaculture water with different ammonia nitrogen concentrations were evaluated.The results showed that as the concentration of ammonia nitrogen increased,the strain concentration increased.At 10mg/L ammonia nitrogen concentration,the strains BZ-95 and RZ-44 could reach 10~7 CFU/m L,and RK-43 could reach 10~6 CFU/m L;The ammonia nitrogen removal rates of the three strains at ammonia nitrogen concentrations of 2 mg/L and 10 mg/L were significantly higher than 0.5mg/L(P<0.05).(5)Evaluation of nitrogen removal efficiency of the three strains in actual aquaculture water.By adding three strains(final concentration of 1×10~3 CFU/m L)to evaluate the application effects of the three strains in the Oreochromis niloticus aquaculture water bodies.The results showed that within 8 days of adding three strains,the contents of ammonia nitrogen,nitrite,nitrate,and total nitrogen in the water of the experimental group were significantly lower than those of the control group(P<0.05).Among them,the T1 group(adding strain BZ-95)had the best degradation effect of ammonia nitrogen and nitrite,with respectively removal rates of 63%and 73%;The ammonia nitrogen removal rates of T2(added strain RZ-44)and T3(added strain RK-43)groups were 64%and 50%,respectively,but the nitrite removal efficiency was significantly lower than that of T1 group(P<0.05).In summary,three strains of ammonia nitrogen degrading bacteria have been selected through enrichment and isolation in this article.In both laboratory and aquaculture environments,these three strains can significantly reduce the ammonia nitrogen content of water bodies,and can effectively improve the water environment;The three strains have good adaptability to various environmental factors and can be widely used in freshwater and seawater.This study provides theoretical reference and technical support for further research and development of micro-ecological agents with good nitrogen removal effect,and provides theoretical basis for the practical application of microorganisms in aquaculture water.