好氧反硝化菌脱氮特性研究进展

好氧反硝化菌的发现,是对传统反硝化理论的丰富与突破. 由于其在脱氮方面的独特优势,已成为目前废水生物脱氮领域研究的热点. 好氧反硝化菌能够在有氧条件下,利用有机碳源生长的同时将含氮化合物反硝化生成N2等气态氮化物,多数还能同时进行异养硝化作用,将铵态氮直接转化为含氮气体. 本文从电子理论、反硝化酶系等方面对目前已分离出的一些好氧反硝化菌的脱氮特性及其脱氮机理进行探讨,分析了溶解氧、碳源类型及C/N等环境条件对其脱氮作用的影响,介绍了好氧反硝化菌的筛选方法及应用现状,对其应用前景和发展方向进行了展望.     

Improved simultaneous nitrification and denitrification in a single reactor by using two different immobilization carriers with specific oxygen transfer characteristics

To maximize nitrogen utilization rates during nitrification and denitrification in a simultaneous reaction for direct nitrogen removal from ammonia–nitrogen in a single reactor, two different carriers were applied that immobilized nitrifiers and denitrifiers separately. With the optimized DO concentration and mixing ratio of immobilization carriers, ammonium–nitrogen was successfully removed as designed until the middle phase of treatment where nitrogen removal rate was higher than 83% of the theoretical value, although an imbalance between nitrification and denitrification occurred at a later phase of treatment where residual nitrate–nitrogen concentration was less than 2 mg/l. The new approach using two different carriers to immobilize nitrifiers and denitrifiers separately was proved useful for controlling both nitrification and denitrification rates, enabling the utilization of maximum treatment ability of both nitrifiers and denitrifiers in a single reactor for direct nitrogen removal from ammonium–nitrogen.     

Simultaneous Nitrification and Denitrification in Aerobic Chemostat Cultures of Thiosphaera pantotropha

Thiosphaera pantotropha is capable of simultaneous heterotrophic nitrification and aerobic denitrification. Consequently, its nitrification potential could not be judged from nitrite accumulation, but was estimated from complete nitrogen balances. The maximum rate of nitrification obtained during these experiments was 93.9 nmol min⁻¹ mg of protein⁻¹. The nitrification rate could be reduced by the provision of nitrate, nitrite, or thiosulfate to the culture medium. Both nitrification and denitrification increased as the dissolved oxygen concentration fell, until a critical level was reached at approximately 25% of air saturation. At this point, the rate of (aerobic) denitrification was equivalent to the anaerobic rate. At this dissolved oxygen concentration, the combined nitrification and denitrification was such that cultures receiving ammonium as their sole source of nitrogen appeared to become oxygen limited and the nitrification rate fell. It appeared that, under carbon-and energy-limited conditions, a high nitrification rate was correlated with a reduced biomass yield. To facilitate experimental design, a working hypothesis for the mechanism behind nitrification and denitrification by T. pantotropha was formulated. This involved the basic assumption that this species has a “bottleneck” in its cytochrome chain to oxygen and that denitrification and nitrification are used to overcome this. The nitrification potential of other heterotrophic nitrifiers has been reconsidered. Several species considered to be “poor” nitrifiers also simultaneously nitrify and denitrify, thus giving a falsely low nitrification potential.     

Abundance and Diversity of Bacterial Nitrifiers and Denitrifiers and Their Functional Genes in Tannery Wastewater Treatment Plants Revealed by High-Throughput Sequencing

Biological nitrification/denitrification is frequently used to remove nitrogen from tannery wastewater containing high concentrations of ammonia. However, information is limited about the bacterial nitrifiers and denitrifiers and their functional genes in tannery wastewater treatment plants (WWTPs) due to the low-throughput of the previously used methods. In this study, 454 pyrosequencing and Illumina high-throughput sequencing, combined with molecular methods, were used to comprehensively characterize structures and functions of nitrification and denitrification bacterial communities in aerobic and anaerobic sludge of two full-scale tannery WWTPs. Pyrosequencing of 16S rRNA genes showed that Proteobacteria and Synergistetes dominated in the aerobic and anaerobic sludge, respectively. Ammonia-oxidizing bacteria (AOB) amoA gene cloning revealed that Nitrosomonas europaea dominated the ammonia-oxidizing community in the WWTPs. Metagenomic analysis showed that the denitrifiers mainly included the genera of Thauera, Paracoccus, Hyphomicrobium, Comamonas and Azoarcus, which may greatly contribute to the nitrogen removal in the two WWTPs. It is interesting that AOB and ammonia-oxidizing archaea had low abundance although both WWTPs demonstrated high ammonium removal efficiency. Good correlation between the qPCR and metagenomic analysis is observed for the quantification of functional genes amoA, nirK, nirS and nosZ, indicating that the metagenomic approach may be a promising method used to comprehensively investigate the abundance of functional genes of nitrifiers and denitrifiers in the environment.     

New pathways for ammonia conversion in soil and aquatic systems

Ammonia conversion processes are essential for most soil and aquatic systems. Under natural conditions, the many possible reactions are difficult to analyze. For example, nitrification and denitrification have long been regarded as separate phenomena performed by different groups of bacteria in segregated areas of soils, sediments or aquatic systems sequentially in time. It has now been established that strict segregation in place and time of the two processes is not necessary and that both denitrifiers and nitrifiers have versatile metabolisms. However, the rates described for aerobic denitrifiers are very low compared to the rates observed under anoxic conditions. Also the rates of nitrifier denitrification are quite low, indicating that these conversions may not play an important role under natural conditions. In addition, these processes often result in the emission of quite large amounts of undesirable products, NO and N₂O. Heterotrophic nitrification might be of relevance for systems, that contain a high carbon to nitrogen ratio. Recently, a novel process (Anammox) has been discovered in which ammonium serves as the electron donor for denitrification of nitrite into dinitrogen gas. ¹⁵N labeling studies showed that hydrazine and hydroxylamine were important intermediates in this process. Enrichment cultures on ammonium, nitrite and bicarbonate resulted in the dominance of one morphotypical microorganism. The growth rate of the cultures is extremely low (doubling time 11 days), but the affinity for ammonium and nitrite and the conversion rates (9.2 10^–4 mol kg^–1 s^–1) are quite high. Some of the reported high nitrogen losses in soil and aquatic systems might be attributed to anaerobic ammonium oxidation. In addition, this conversion offers new opportunities for nitrogen removal, when it is combined with recently developed processes for partial nitrification.     

Feasibility of nitrification/denitrification in a sequencing batch biofilm reactor with liquid circulation applied to post-treatment

An investigation was performed on the biological removal of ammonium nitrogen from synthetic wastewater by the simultaneous nitrification/denitrification (SND) process, using a sequencing batch biofilm reactor (SBBR). System behavior was analyzed as to the effects of sludge type used as inoculum (autotrophic/heterotrophic), wastewater feed strategy (batch/fed-batch) and aeration strategy (continuous/intermittent). The presence of an autotrophic aerobic sludge showed to be essential for nitrification startup, despite publications stating the existence of heterotrophic organisms capable of nitrifying organic and inorganic nitrogen compounds at low dissolved oxygen concentrations. As to feed strategy, batch operation (synthetic wastewater containing 100 mg COD/L and 50 mg N-NH(4)(+)/L) followed by fed-batch (synthetic wastewater with 100 mg COD/L) during a whole cycle seemed to be the most adequate, mainly during the denitrification phase. Regarding aeration strategy, an intermittent mode, with dissolved oxygen concentration of 2.0mg/L in the aeration phase, showed the best results. Under these optimal conditions, 97% of influent ammonium nitrogen (80% of total nitrogen) was removed at a rate of 86.5 mg N-NH(4)(+)/Ld. In the treated effluent only 0.2 mg N-NO(2)(-)/L,4.6 mg N-NO(3)(-)/L and 1.0 mg N-NH(4)(+)/L remained, demonstrating the potential viability of this process in post-treatment of wastewaters containing ammonium nitrogen.     

Relative Rates of Nitric Oxide and Nitrous Oxide Production by Nitrifiers, Denitrifiers, and Nitrate Respirers

Biogenic emissions of nitric and nitrous oxides have important impacts on the photochemistry and chemistry of the atmosphere. Although biogenic production appears to be the overwhelming source of N₂O, the magnitude of the biogenic emission of NO is very uncertain. In soils, possible sources of NO and N₂O include nitrification by autotrophic and heterotrophic nitrifiers, denitrification by nitrifiers and denitrifiers, nitrate respiration by fermenters, and chemodenitrification. The availability of oxygen determines to a large extent the relative activities of these various groups of organisms. To better understand this influence, we investigated the effect of the partial pressure of oxygen (pO₂) on the production of NO and N₂O by a wide variety of common soil nitrifying, denitrifying, and nitrate-respiring bacteria under laboratory conditions. The production of NO per cell was highest by autotrophic nitrifiers and was independent of pO₂ in the range tested (0.5 to 10%), whereas N₂O production was inversely proportional to pO₂. Nitrous oxide production was highest in the denitrifier Pseudomonas fluorescens, but only under anaerobic conditions. The molar ratio of NO/N₂O produced was usually greater than unity for nitrifiers and much less than unity for denitrifiers. Chemodenitrification was the major source of both the NO and N₂O produced by the nitrate respirer Serratia marcescens. Chemodenitrification was also a possible source of NO and N₂O in nitrifier cultures but only when high concentrations of nitrite had accumulated or were added to the medium. Although most of the denitrifiers produced NO and N₂O only under anaerobic conditions, chemostat cultures of Alcaligenes faecalis continued to emit these gases even when the cultures were sparged with air. Based upon these results, we predict that aerobic soils are primary sources of NO and that N₂O is produced only when there is sufficient soil moisture to provide the anaerobic microsites necessary for denitrification by either denitrifiers or nitrifiers.     

好氧反硝化菌的研究进展

综述了好氧反硝化菌的种类和特性、好氧反硝化菌的反硝化作用机制和影响因素.好氧反硝化菌主要包括假单胞菌属(Pseudomonas)、产碱杆菌属(Alcaligenes)、副球菌属(Para-coccus)和芽孢杆菌属(Bacillus)等,属好氧或兼性好氧异养微生物.好氧反硝化菌能在好氧条件下进行反硝化,其主要产物是N2O,并可将铵态氮直接转化成气态产物.催化好氧反硝化菌反硝化作用的硝酸盐还原酶是周质酶而不是膜结合酶.溶解氧和C/N往往是影响好氧反硝化菌反硝化作用的主要因素.介绍了间歇曝气法、选择性培养基法等好氧反硝化菌的主要分离筛选方法.概述了好氧反硝化菌在水产养殖、废水生物处理、降解有机污染物以及对土壤氮素损失的影响方面的研究进展.     

Simultaneous nitrogen and carbon removal in a packed A/O reactor: effect of C/N ratio on microbial community structure

In this research, a novel packed anoxic/oxic moving bed biofilm reactor (MBBR) was established to achieve high-organic matter removal rates, despite the carbon/nitrogen (C/N) ratio of 2.7–5.1 in the influent. Simultaneous nitrification–denitrification (SND) was investigated under a long sludge retention time of 104 days. The system exhibited excellent performance in pollutant removal, with chemical oxygen demand and total nitrogen (TN) enhanced to 93.6–97.4% and 34.4–60%, respectively. Under low C/N conditions, the nitrogen removal process of A/O MBBR system was mainly achieved by anaerobic denitrification. The increase of C/N ratio enhanced SND rate of the aerobic section, where dissolved oxygen was maintained at the range of 4–6 mg/L, and resulted in higher TN removal efficiency. The microbial composition and structures were analyzed utilizing the MiSeq Illumina sequencing technique. High-throughput pyrosequencing results indicated that the dominant microorganisms were Proteobacteria and Bacteroidetes at the phylum level, which contributes to the removal of organics matters. In the aerobic section, abundances of Nitrospirae (1.12–29.33%), Burkholderiales (2.15–21.38%), and Sphingobacteriales (2.92–11.67%) rose with increasing C/N ratio in the influent, this proved that SND did occur in the aerobic zone. As the C/N ratio of influent increased, the SND phenomenon in the aerobic zone of the system is the main mechanism for greatly improving the removal rate of TN in the aerobic section. The C/N ratio in the aerobic zone is not required to be high to exhibit good TN removal performance. When C/NH₄⁺ and C/TN in the aerobic zone were higher than 2.29 and 1.77, respectively, TN removal efficiency was higher than 60%, which means that carbon sources added to the reactor could be saved. This study would be vital for a better understanding of microbial structures within a packed A/O MBBR and the development of cost-efficient strategies for the treatment of low C/N wastewater.

     

Microbial nitrogen removal of ammonia wastewater in poly (butylenes succinate)-based constructed wetland: effect of dissolved oxygen

Constructed wetland (CW) is popular in wastewater treatment for its prominent advantage of low construction and operation cost. However, the nitrogen removal in conventional CW is usually limited by the low dissolved oxygen (DO) and insufficient electron donor. This paper investigated the nitrogen removal performance and mechanisms in the poly (butylenes succinate)-based CW (PBS-CW) while treating ammonia wastewater under different DO levels. The average DO contents in limited-aeration and full-aeration phases were 1.68 mg L⁻¹ and 5.71 mg L⁻¹, respectively. Results indicated that, with the ammonia nitrogen loading rate of 25 g N m⁻³ day⁻¹, total nitrogen removal ratios in the PBS-CW under the limited-aeration and full-aeration phases were 72% and 99%, respectively. Combined analyses revealed that simultaneous nitrification and denitrification (SND) via nitrite/nitrate were the main microbial nitrogen removal pathways in the aeration phase of the PBS-CW (> 89%). The microbial carrier of biodegradable material was believed to play a significant role in prompting SND performance while dealing with low C/N wastewater. Due to the coexistence of micro-anaerobic zone and carbon supply inside the coated biofilm, the high DO level in the PBS-CW increased the abundance of the nitrifying bacteria (amoA and nxrA), denitrifying bacteria (narG, nirK, nirS, and nosZ), and even anammox bacteria (anammox 16s rRNA). These features are beneficial to many microbial processes which require the simultaneous aerobic, anoxic, and anaerobic environment.

     

Simultaneous nitrification–denitrification and microbial community profile in an oxygen-limiting intermittent aeration SBBR with biodegradable carriers

To enhance the startup and efficient simultaneous nitrification and denitrification for sewage treatment, sequencing batch biofilm reactors (SBBRs) partially coupled with rice husk were established and operated under various intermittent micro-aeration cycles (IMCs) and COD/N ratios under oxygen-limiting intermittent aeration conditions. Experimental results showed that the increase of IMCs with non-aeration/micro-aeration mode of (8 h/4 h)₁ to (2 h/1 h)₄ in a 12 h-cycle accelerated the startup performance and improved NH₄⁺–N and COD removal. NH₄⁺–N, TN and COD removal efficiencies were 98.7?±?0.9, 89.2?±?5.2 and 82.9?±?6.7% at COD/N ratio of 7.6 with the highest IMCs in SBBR, respectively. Higher TN removal efficiencies of 87.2?±?4.0 and 58.1?±?3.5% were also achieved at lower COD/N ratio of 5.6 and 2.8, respectively. In SBBRs with various IMCs, facultative denitrifier like genus Acinetobacter and solid-phase denitrifier belonging to Comamonadaceae family were enriched. However, aerobic denitrifiers with function of heterotrophic nitrification like Paracoccus were favored to enrich under higher IMCs condition, and more anoxic denitrifiers like sulfur-based autotrophic denitrifier Thiothrix and heterotrophic denitrifiers like Pseudomonas and Methyloversatilis were observed at lower IMCs condition. Autotrophic nitrifier (Nitrosomonas and Nitrosipra) and heterotrophic nitrifiers both contributed to the efficient nitrification.     

Role of heterotrophic aerobic denitrifying bacteria in nitrate removal from wastewater

With the increase in industrial and agricultural activities, a large amount of nitrogenous compounds are released into the environment, leading to nitrate pollution. The perilous effects of nitrate present in the environment pose a major threat to human and animal health. Bioremediation provides a cost-effective and environmental friendly method to deal with this problem. The process of aerobic denitrification can reduce nitrate compounds to harmless dinitrogen gas. This review provides a brief view of the exhaustive role played by aerobic denitrifiers for tackling nitrate pollution under different ecological niches and their dependency on various environmental parameters. It also provides an understanding of the enzymes involved in aerobic denitrification. The role of aerobic denitrification to solve the issues faced by the conventional method (aerobic nitrification–anaerobic denitrification) in treating nitrogen-polluted wastewaters is elaborated.     

Production of nitrogen oxide and dinitrogen oxide by autotrophic nitrifiers

Autotrophic nitrifiers have been shown to produce nitrogen oxide and dinitrogen oxide under oxic conditions. Dinitrogen oxide is produced mainly during nitrite reduction (i.e. aerobic denitrification) whereas nitrogen oxide is produced during both aerobic denitrification and as a result of chemodenitrification. Oxygen is the single most influential environmental factor affecting the production of nitrogen and dinitrogen oxides; a decrease in oxygen can result in a several-fold increase in nitrogen oxide and dinitrogen oxide production. Emission of nitrogen oxide and dinitrogen oxide from wastewater treatment plants and fertilized soils is well documented; however, only recently have the contributions from such environments to the global nitrogen and dinitrogen oxide budget been considered.     

Aerobic denitrification by novel isolated strain using NO-₂-N as nitrogen source

Biological denitrification reaction can be achieved under aerobic environment. Few aerobic denitrifiers using nitrite as sole nitrogen source were identified. Using nitrite as the sole nitrogen source, this work assessed the denitrification activity of yy7, an aerobic heterotrophic denitrifier identified as Pseudomonas sp. (94% similarity) by 16S rRNA sequencing analysis. The logistic equation describes the cell growth curve, yielding a generation time of 2.9h at an initial 18 mg l(-1)NO(-)?-N. Reduction of NO(-)?-N was primarily achieved during its logarithmic growth phase, and was accompanied by an increase in suspension pH and near complete consumption of dissolved oxygen. Three genes relating to nirK, norB, and nosZ were noted to involve in isolate strain. Isolate yy7 can survive and remove up to 40 mg l(-1)NO(-)?-N and, hence, can be applied as an effective aerobic denitrifier during simultaneous nitrification and denitrification via nitrite processes.     

异养硝化细菌脱氮特性及研究进展

异养硝化细菌能够在利用有机碳源生长的同时将含氮化合物硝化生成羟胺、亚硝酸盐、硝酸盐等产物, 多数还能同时进行好氧反硝化作用, 直接将硝化产物转化为含氮气体。因此, 这类细菌已成为废水处理中生物脱氮新工艺的重要研究对象。本文综述了目前所分离出的一些异养硝化菌的脱氮特性, 分析了各种环境条件如温度、pH、溶解氧、碳源类型、C/N以及抑制剂等对异养硝化菌的影响, 并介绍了异养硝化菌的应用现状及前景。     

Effects of temperature on simultaneous nitrification and denitrification via nitrite in a sequencing batch biofilm reactor

A laboratory scale experiment was described in this paper to enhance biological nitrogen removal by simultaneous nitrification and denitrification (SND) via nitrite with a sequencing batch biofilm reactor (SBBR). Under conditions of total nitrogen (TN) about 30 mg/L and pH ranged 7.15–7.62, synthetic wastewater was cyclically operated within the reactor for 110 days. Optimal operation conditions were established to obtain consistently high TN removal rate and nitrite accumulation ratio, which included an optimal temperature of 31 °C and an aeration time of 5 h under the air flow of 50 L/h. Stable nitrite accumulation could be realized under different temperatures and the nitrite accumulation ratio increased with an increase of temperature from 15 to 35 °C. The highest TN removal rate (91.9%) was at 31 °C with DO ranged 3–4 mg/L. Process control could be achieved by observing changes in DO and pH to judge the end-point of oxidation of ammonia and SND.     

Characterization of microbial community in an aerobic moving bed biofilm reactor applied for simultaneous nitrification and denitrification

A continuous-flow moving bed biofilm reactor (MBBR) under aerobic conditions was established for simultaneous nitrification and denitrification (SND), and microbial communities were investigated by a combination of denaturing gel gradient electrophoresis (DGGE) and fluorescence in situ hybridization (FISH). DGGE analysis has revealed more similar microbial community structures formed in the biofilms with more similar carbon nitrogen (C/N) ratios. FISH analysis shows that the dominance of both Betaproteobacteria ammonia-oxidizing bacteria and Nitrospira-like nitrite-oxidizing bacteria were negatively correlated to C/N ratios. Sequence analysis of DGGE bands has indicated the presence of anoxic denitrifying bacteria Agrobacterium tumefaciens and Rhizobium sp., suggesting that the oxygen gradient inside the biofilm may be responsible for the mechanism of SND in aerobic MBBRs. The study confirms that appropriate control of microbial community structure resulting from optimal C/N ratio is beneficial in improving SND, thus optimizing nitrogen removal in aerobic MBBR. The established SND-based MBBR can save operation space and time in comparison to the traditional nitrogen removal process, and might be very attractive for future practical applications.     

Ammonia removal from a waste air stream using a biotrickling filter packed with polyurethane foam through the SND process

This paper presents the results of a bench-scale biotrickling filter (BTF) on the removal of ammonia gas from a waste stream using a simultaneous nitrification/denitrification (SND) process. It was found that the developed BTF could completely remove 100 ppm ammonia from a waste stream, with an empty bed retention time of 60 s and 98.4% nitrogen removal through the SND process under the tested conditions. It was elucidated that both autotrophic and heterotrophic bacteria were involved in the nitrogen removal trough the SND process in the BTF. Additionally, the elimination capacity of total nitrogen by the BTF increased from 3.5 to 18.4 g N/m³ h with an inlet load of 20.6 g N/m³ h (73.6%). The findings of this study suggest that the BTF can be operated to attain complete ammonia removal through the SND process, thereby making the treatment of ammonia-laden gas streams both short and cost-effective.     

Simultaneous nitrification and denitrification using stored substrate (PHB) as the electron donor in an SBR

The potential for PHB (poly-beta-hydroxybutyrate) to serve as the electron donor for effective simultaneous nitrification and denitrification (SND) was investigated in a 2-L sequencing batch reactor (SBR) using a mixed culture and acetate as the organic substrate. During the feast period (i.e., acetate present), heterotrophic respiration activity was high and nitrification was prevented due to the inability of nitrifying bacteria to compete with heterotrophs for oxygen. Once acetate was depleted the oxidation rate of PHB was up to 6 times slower than that of soluble acetate and nitrification could proceed due to the decreased competition for oxygen. The slow nature of PHB degradation meant that it was an effective substrate for SND, as it was oxidised at a similar rate to ammonium and was therefore available for SND throughout the entire aerobic period. The percentage of nitrogen removed via SND increased at lower DO concentrations during the famine period, with up to 78% SND achieved at a DO concentration of 0.5 mg L(-1). However, the increased percentage of SND at a low DO concentration was compromised by a 2-times slower rate of nitrogen removal. A moderate DO concentration of 1 mg L(-1) was optimal for both SND efficiency (61%) and rate (4.4 mmol N x Cmol x(-1) x h(-1)). Electron flux analysis showed that the period of highest SND activity occurred during the first hour of the aerobic famine period, when the specific oxygen uptake rate (SOUR) was highest. It is postulated that a high SOUR due to NH(4) (+) and PHB oxidation decreases oxygen penetration into the floc, creating larger zones for anoxic denitrification. The accumulation of nitrate towards the end of the SND period showed that SND was finally limited by the rate of denitrification. As PHB degradation was found to follow first-order kinetics (df(PHB)/dt = -0.19 x f(PHB)), higher PHB concentrations would be expected to drive SND faster by increasing the availability rate of reducing power and reducing penetration of oxygen into the floc, due to the corresponding increased SOUR. Process control techniques to accumulate higher internal PHB concentrations to improve PHB-driven SND are discussed.     

异养硝化-好氧反硝化的研究进展

近年来,异养硝化-好氧反硝化菌的发现打破了传统硝化反硝化理论,其在去除氮素和有机污染物的同时,能够实现同时硝化反硝化(SND),因此受到广泛关注。文章介绍了异养硝化-好氧反硝化菌的影响因素和一些已筛选菌的最佳脱氮效果,及其与传统硝化反硝化菌作用酶系的不同,列出了一些已筛选菌的氮代谢途径,并对中间产物NO2--N积累和复合菌方面的研究进展进行了综述,最后提出了异养硝化-好氧反硝化在生物强化应用中的研究现状和面临的挑战。