Screening And Optimization Of Microbials For Nitrogen Removal

To decrease the concentration of nitrogen element is one of key issues in wastewater treatment and prevention of eutrophication of water body. Taking advantage of the good biocompatibility and high effectiveness of nitrogen removal with microbes, microbiological methods with nitrifying and denitrifying bacteria are becoming more and more widely used.Our work was devoted to screen nitrifying bacterium and aerobic denitrifying bacterium which can perform high nitrogen removal rate, investigate some influence factors on nitrogen removal efficiency and make its nitrogen removal efficiency maximization, study the nitrogen removal capability of the strain WSH 1001 in actual wastewater, then improve the cell concentration by high density culture for preparations. The concrete research and results are as follows.(1) In this research, an aerobic nitrifying-denitrifying bacterium was successfully screened from activated sludge by choosing medium, which can perform the nitrifying-denitrifying capability of removing ammonium, nitrate and nitrite nitrogen. The strain was identified as Pseudomonas sp. (CCTCC No M2010209) according to its 16S rDNA sequence and named as Pseudomonas sp. WSH 1001. The ammonia- and nitrate-nitrogen removal rate of Pseudomonas sp. WSH 1001 was stable in preservation which demonstrated that Pseudomonas sp. WSH 1001 was favorable to practical application. (2) The influence factors on nitrogen removal rate by Pseudomonas sp. WSH 1001 and its application in actual wastewater have been studied in this research. The results indicated that ammonia- and nitrate-nitrogen removal rate was higher when glucose or sodium citrate was used as carbon sources in the pre-cultured process of Pseudomonas sp. WSH 1001. The type of carbon source and carbon-nitrogen ratio in synthetic wastewater greatly influenced the removal efficiency of NH4+-N and NO3--N. The temperature had no effect on ammonia- and nitrate-nitrogen removal efficiency when the treatment temperature was set between 20 oC and 35 oC. The dissolved oxygen level in shaking flask greatly influenced ammonia- and nitrate-nitrogen removal efficiency. Metal ions such as Cu2+, Co2+ and Zn2+ greatly restricted the capability of ammonia- and nitrate-nitrogen removal efficiency. The strain WSH 1001 had competitive ability to survive in open environment, which demonstrated that Pseudomonas sp. WSH 1001 was favorable to practical application. The total nitrogen removal rate and removal efficiency were greatly influenced by inoculum size. When the initial concentration of NH4+-N and NO3--N in synthetic wastewater were less than 70 and 40 mg·L^-1, the nitrogen removal rate reached 94% and 99% in 9 h, respectively. When initial ammonia nitrogen concentration was 70 mg L^-1 in synthetic wastewater, the removal efficiency of ammonia nitrogen and total nitrogen was 99.6% and 94.9% in 6 h, respectively, and with no nitrate- and nitrite nitrogen accumulated in the whole process of nitrogen removal. When nitrate nitrogen was used as sole nitrogen source (50 mg L^-1), nitrate nitrogen removal efficiency was 87.7% in 8 h with no nitrite nitrogen accumulated. Preliminary comparisons of nitrogen removal capacity between this microbe and other commercially available microbial preparations in the treatment of synthetic wastewater revealed its promising potential to be used in the actual wastewater treatment plant for nitrogen removal. When Pseudomonas sp. WSH 1001 was used as microbial preparations in the treatment of actual wastewater (the initial concentration of ammonia nitrogen and COD was 44 and 113 mg L^-1, respectively) and 3 g L^-1 sodium succinate was added as external carbon source, ammonia nitrogen removal efficiency was 99.2% and the capability was higher than other commercial available microbial preparations. The removal efficiency of ammonia nitrogen and COD were greatly improved when the strain WSH 1001 was added into the simulated wastewater reactor.(3) In high cell density culture, firstly, we studied the initial pH value, the type and concentration of carbon and nitrogen source in shake flask on cell growth and subsequent nitrogen removal capability; secondly, in the 3 L fermenter, we took the strategies of combination of pH control and substrate-feeding to further improve cell concentration and study the nitrogen removal capacity of high concentration of bacteria. The study found that the strain WSH 1001 grow well as initial pH set between 6⁷; when sodium citrate and ammonium sulfate used as carbon and nitrogen source and the concentration maintained at 9.7 and 1.3 g L^-1, respectively, the cell dry weight of the strain WSH 1001 obtained its maximum, and the ability of nitrogen removal kept constant. And in the process of high cell density fermentation, cell dry weight reached 10.5 g L^-1 and increased 5 times compared to shake flask culture by adjusting pH 7.0 and feeding cultured, however, the nitrogen removal capability of the strain WSH 1001 with high cell concentration decreased to 55 mg L^-1 when the initial ammonia nitrogen concentration was 70 mg L^-1 and kept constant in the process of nitrate nitrogen removal.