Denitrification Ehancement In A Bioaugmentation Reactor Using Aerobic Denitrifier Pseudomonas Sp. T13

With the development of urbanization and industrialization in China,the discharge of domestic sewage and industrial wastewater is increasing.Nitrogen contaminant aggravates the aquatic eutrophication."13th Five-Year" plan improve the standard of wastewater discharge,while it put forward new requirements for the control of total nitrogen emissions.Thus,the efficient nitrogen removal technology has become a research hotspot.The biological nitrogen removal technology using microorganisms to convert nitrogen in water into nitrogen gas could enhance denitrification process,no second pollution and so on.Aerobic denitrifying bacteria having the characteristics such as fast growth,the ratio of carbon and nitrogen tolerance range,water quality and environmental adaptability characteristics can utilize nitrate or nitrite to realize the simultaneous nitrification and denitrification process in the reactor,which makes the connection and transformation of the existing aerobic process easier.Aiming at lack of aerobic denitrifying bacterial resources and flora competition,a stain of high efficient aerobic denitrifying bacteria was observed from the wastewater treatment system.The biological strengthening process with the the combination of aerobic denitrifying bacteria and immobilized carrier was established,treating the low nitrogen domestic sewage and high nitrogen industrial wastewater,respectively.In this process,the succession of changes of the target strains was discussed using molecular biology techniques,the bacterial diversity and its main function was analyzed in the enhanced biological denitrification process,which provided the experimental basis and technical guidance for the transformation of aerobic denitrification technology to the application.The study on screening and identification of aerobic denitrifying bacteria and their physiological and biochemical functions indicated that a high efficiency aerobic denitrification strain of Pseudomonas T13 could achieved 90% of nitrate removal rate under the conditions of 30 oC,pH=7,C/N=7:1 and DO=2.5 mg/L.Whole genome sequencing of Pseudomonas sp.T13 showed that T13 had high nitrate reduction function gene,detection of nitrate reductase found that nitrate reductase accounted for over 30% of the denitrification enzyme gene.The growth kinetics model and denitrification kinetic model of strain T13 was established using the Logistic equation and the double Monod model,describing the growth kinetics process and the relationship between the substrate and denitrifying microorganisms,fully revealing the dynamics of denitrifying bacteria in aerobic environment,providing the important support to the aerobic denitrification strengthening technology with T13.The study on Pseudomonas sp.T13 biological fluidized bed reactor with activated carbon and polyurethane filler showed that the removal rate of total nitrogen(TN)was 89 ± 4% with T13 pretreating membrane reactor,which was 8% higher than that without T13.The removal rate of nitrate was up to 93±7% in the T13 pretreating membrane reactor,while it was 88±7% in control reactors.The ammonia nitrogen concentration in domestic wastewater was lower,and the removal rate of ammonia nitrogen was up to 93±1% and 97±1%,respectively,the nitrite concentration of the effluent were up to 1.1 mg/L and 0.7 mg/L,respectively.Analysis of T13 and other biological filler attached sewage found that Brucella and Brevundimonas were enriched simultaneously,leading a lower nitrite removal rate,the nitrate was accumulated.Brevundimonas was similar to the metabolic process of Pseudomonas stutzeri,and the accumulation of nitrite was formed under the condition of high dissolved oxygen,so it was easier to reduce the total nitrogen removal rate when COD was insufficient.An aerobic denitrification system,bioaugmented initially by the isolated Pseudomonas strain,was operated to treat coal-based ethylene glycol industry wastewater.Toxicity evaluation showed that lower toxicity of effluent was achieved when industry wastewater was treated by stuffing biofilm communities than suspended communities.A relatively high TN removal(50%)and COD removal(>65%)were obtained when influent concentration was controlled below 50% of the raw industry wastewater.However,a further increased concentration led to a 20-30% decrease on nitrate and nitrite removal.The microbial network showed that a reduction of Pseudomonas was induced during the succession of the microbial community.The napA gene analysis indicated that a 20-30% decrease on nitrate and nitrite removal was resulted by a <10% abundance of Pseudomonas in the stuffing biofilm.It was pointed that the aerobic-anaerobic or anaerobic-aerobic transition phases lead to cessation of synthesis of nitrate and nitrite reductases.Therefore,a relatively low level of dissolved oxygen need to be controlled for total nitrogen removal.Porous stuffing materials can provide a gradient change of DO from outside to inner spaces,which would provide an insufficient DO zone for nitrite reduction.Biological stuffing can provide a relatively large volume of reaction,which could supply long residence time to retain amounts of organisms in the reactors.It was disclosed that the gradient concentration of dissolved oxygen in the inner spaces of the supporting stuffing would provide an effective area for nitrite reduction during aerobic denitrification.Thus,the mass transfer that effects nitrate reduction inside the supporting material will be a concerned issue to improve or regulate functional community assembly in bioreactors in future.