Study On The Characteristics Of Pure Culture And Mixed Culture Of DNRA Process

In recent years,nitrate pollution in water and NOx pollution in the atmosphere are becoming more and more serious,which not only harm the environment,but also seriously affect human health.The process of dissimilatory nitrate reduction to ammonium（DNRA）is to transform nitrogen pollutants such as nitrate into ammonia which can be used as resources.It is of great significance to the nitrogen cycle in nature and the recovery of nitrate in wastewater and nitrogen oxides in exhaust gas.For the reduction of Fe（Ⅱ）EDTA-NO produced in chemical absorption-biological reduction（CABR）flue gas denitrification process,the ammonia production characteristics of Fe（Ⅱ）EDTA-NO were investigated by Shewanella sp.RQS-106under pure culture condition.The effects of electron donor,C/N ratio,Fe（Ⅱ）EDTA-NO concentration,p H and temperature on ammonia production by Fe（Ⅱ）EDTA-NO were investigated.For the process of nitrate reduction to ammonia in wastewater,the performance and influencing factors of DNRA in heterotrophic and sulfur autotrophic environments were studied by anaerobic moving bed biofilm reactor.The main research results are as follows.After passing NO into Fe（Ⅱ）EDTA solution to produce Fe（Ⅱ）EDTA-NO,it can be reduced to produce ammonia by using Shewanella sp.RQs-106.Experimental results show,strain RQs-106 could not use sodium citrate and sodium acetate to reduce Fe（Ⅱ）EDTA-NO to produce ammonia.Sodium formate and sodium lactate could be used to reduce Fe（Ⅱ）EDTA-NO and sodium lactate was the most suitable electron donor for strain RQs-106.When the C/N range was 5-25,strain RQs-106 could almost completely degrade 1 mmol/L Fe（Ⅱ）EDTA-NO and the optimal C/N ratio was 20.High concentration of complex NO inhibited the activity of strain RQs-106.The concentration of Fe（Ⅱ）EDTA-NO should be controlled as 1 mmol/L under this experimental condition.When the initial p H was 5.0-6.0,the strain RQs-106 could not reduce Fe（Ⅱ）EDTA-NO.The optimum p H was 8.0 for strain RQs-106.The strain RQs-106 could re-duce Fe（Ⅱ）EDTA-NO and produce ammonia in the range of 20-35℃,and the optimum tem-perature was 30℃.In the heterotrophic anaerobic MBBR,the removal rate of nitrate remained at a high level for 270 days,and the effluent was free of nitrate nitrogen and nitrite nitrogen after the seventh stage.The improvement of C/N mass ratio,reaction temperature and hydraulic retention time were beneficial to DNRA.Increasing p H was not favorable to ammonia production,while changing the type of carbon source had little effect on ammonia production.The maximum concentration of ammonia nitrogen in the effluent of the reactor was 87.42 mg/L and the max-imum conversion rate of ammonia nitrogen produced by NO₃^--N reduction was 29.4%.The functional bacteria of DNRA in the sixth stage of reactor operation mainly included Thauera,Rhizobium and unclassified-Rhodocyclaceae,while the proportion of Ornatilinea was rela-tively small.The proportion of nitrite reductase for ammonia increased during the reactor op-eration,indicating that the DNRA functional bacteria in the reactor had been enriched in large quantities in the sixth stage.In the anaerobic MBBR under sulfur autotrophic condition,the nitrate removal rate reached 100%after the third stage of reactor operation.The increase of S/N mass ratio,tem-perature and dihydrogen phosphate concentration were all favorable to the process of nitrate reduction to produce ammonia.When the reactor was operated for 86 days,the maximum con-centration of ammonia nitrogen was 17.54 mg/L and the maximum conversion rate of ammonia nitrogen was 46.90%.Pseudomonas and unclassified＿Rhodocyclaceae may contribute to the increase of ammonia nitrogen in the effluent during the third stage of reactor operation.How-ever,the existing species unclassified＿anaerolineaceae,Pirellula and Singulisphaera can con-sume ammonia nitrogen through the process of Anammox.The increase of sulfide concentra-tion in the sixth stage of reactor operation inhibited the activity of anammox bacteria,and many sulfur oxidizing bacteria appeared,which have the function of nitrate reduction to ammonium.From the inoculation of sludge to the sixth stage of ammonia production,the proportion of nitrite reductase continues to increase,indicating that the competitiveness of nitrate reducing ammonia-producing bacteria in the reactor is continuously increasing.