Removal Of Inorganic Nitrogen From Synthetic Wastewater By Rhodobacter Azotoformans

Currently, aquaculture water is seriously contaminated. Nitrogen is the most important source of pollution. Nitrogen removal is essential for aquaculture wastewater treatment. Thus, removing nitrogen and restoring micro-ecological balance are the key to solve aquaculture pollution. Anoxygenic phototrophic bacteria(APB) has showed an important role in removing inorganic nitrogen, restoring the ecological balance and improving immunity of aquaculture animals. Because aquaculture water environment is complex, exploring the effect of nitrogen removal by APB has important practical applications. Currently, the study about the APB ability to remove nitrite, transformate and remove inorganic nitrogen have been rarely reported. In addition, APB is applied to aquaculture water, which can be affected by organic nitrogen, organic carbon and salinity. In this study, we chose Rhodobacter azotoformans R7 as a material. First of all we optimized culture conditions to improve biomass. Then, we explored the characteristics of transformation and removal of inorganic nitrogen by the strains. Meanwhile, we explore the impact on the strain growth and photosynthetic pigments synthesized of organic nitrogen. In order to improve the effect of the practical application of the strain, We explore the effect of complex aquaculture water factors on the strain growth and the nitrogen efficiencies. The factors include inorganic, organic nitrogen, organic carbon and salinity. The main results are as follows:In this paper, we optimized culture conditions by a single factor rotation test, and obtain a high biomass yield. Biomass yield was increased from 2.43 mg/L to 30.31 mg/L and increased by 11.47-fold. The total carotenoid amount was increased from 3.34 mg/L to 17.59 mg/L and increased by 4.27-fold. The Pigment composition analysis showed that spheroidene, spheroidenone and OH-spheroidenone were significantly increased, spheroidene and spheroidenone were dominating carotenoid components, in addition, the result shows that spheroidenone is more stable toward light irradiation.Under different light irradiation of 0lx, 500 lx, 3000 lx, the corresponding half-lives were 568.53 h, 405.56 h, 112.64 h.The study about the characteristics of removing inorganic nitrogen showed that strain R7 was capable of growing with ammonia, nitrate or nitrite, as the sole nitrogen sources. In addition, strain R7 has strong capacity of removing nitrate and nitrite. The experimental results also showed that the maximum removal of ammonia, nitrate and nitrite were 6.10 mmol/L, 21.36 mmol/L and 16.86 mmol/L, respectively; The removal efficiency of ammonia, nitrate and nitrite were 54.38%, 31.48% and 99.95%,when the synthetic wastewater contains 43.47 mmol/L ammonia, 52.17 mmol/L nitrate and 34.78 mmol/L nitrite. The study about transformation and removal of inorganic nitrogen showed that strain R7 has an accumulation of inorganic nitrogen, except for inorganic nitrogen with the medium.Then, the accumulative nitrogen were removed. These results indicate that there are many nitrogen metabolism of strain R7, which are denitrification, anaerobic nitrification and anaerobic oxidation of nitrite.The paper studied that inorganic nitrogen effect on biomass yield and bacterial photosynthetic pigment synthesis. The results showed that ammonia(concentrations ≤ 34.78 mmol/L) and nitrate(concentrations ≤ 52.17 mmol/L)have little influence on biomass yield and carotenoid amount. Ammonia(concentrations ≤ 8.70 mmol/L) and nitrate(concentrations ≤ 8.66 mmol/L)can improve biomass yield, increasing the relative content of Car; The result indicate that Ammonia and nitrate have little influence on carotenoid amount. Nitrite can significantly affect the synthesis of carotenoid.There are many factors which are organic carbon(sugars, organic acids or alcohols), organic nitrogen(yeast extract powder, peptone or urea) and salinity in aquaculture water. We study the effect of factors on removing inorganic nitrogen. The maximum removal efficiency of inorganic nitrogen is above 87% with propionate, as the organic carbon sources; The maximum removal efficiency of ammonia and nitrite is above 85% and 98% with propionate or acetate, as the organic carbon sources; The maximum removal efficiency of nitrate is above 80% with sucrose, sodium propionate or mannitol, as the organic carbon sources; When organic nitrogen of yeast concentration is less than 1.43 mmol/L, the maximum removal efficiency of ammonia, nitrate and nitrite were 97.61%、99.50% and 99.08%; When organic nitrogen of peptone concentration is less than 3.21 mmol/L, the maximum removal efficiency of ammonia, nitrate and nitrite were 90.57%、94.36% and 99.54%; When organic nitrogen of urea concentration is less than 0.71 mmol/L, the maximum removal efficiency of ammonia, nitrate and nitrite were 98.26%、50.68% and 99.69%; When NaCl concentration is less than 2 g/L, the removal efficiency of ammonia, nitrate and nitrite were above 55.03%、96.62% and 83.53%; The study about the effect of removing inorganic nitrogen with practical aquaculture wastwater showed that R7 strain can effectively remove inorganic nitrogen under micro-aerobic conditions.In summary, Improving biomass and Car amount by optimization of culture conditions, which is a solid foundation for the practical application of strain. Furthermore, R7 strain has good ability to remove high concentrations inorganic nitrogen. In addition, R7 strain have strong adaptability and removal capacity under complex aquaculture water environment. This provide a theoretical reference for development of integrated microbial ecology preparations.