Autotrophic denitrification via a novel membrane-attached biofilm reactor

AIMS: A laboratory-scale autotrophic membrane-attached biofilm reactor was developed to remove nitrate from drinking water. METHODS AND RESULTS: Hydrogen and carbon dioxide flowed together into the lumem side of a gas-permeable silicone tube. The gases diffused through the membrane wall to feed Alcaligenes eutrophus that formed a biofilm on the surface of the silicone tube for autotrophic denitrification. Hydrogen provided the energy source, and carbon dioxide, besides serving as the carbon source, was employed to neutralize the alkalinity from denitrification. The optimal carbon dioxide concentration in the silicone tube was between 20% and 50%. CONCLUSION: This study has demonstrated that a gas-permeable silicone tube is a convenient and efficient method to feed A. eutrophus for autotrophic denitrification. Supplying a suitable amount of carbon dioxide together with hydrogen into the silicone tube solved the problem that alkalinity formation caused during denitrification. The pH of the bioreactor was maintained at about 7 to avoid nitrite accumulation, and then the nitrogen removal rate was increased. A high specific nitrogen removal rate (1.6-5.4 g Nm(2)d(-1-1) of surface area of silicone tube) was achieved. SIGNIFICANCE AND IMPACT OF THE STUDY: In addition to combining the advantages of the hydrogenotrophic denitrification process and a membrane feeding substrate bioreactor (MFSB), this bioreactor achieved a high nitrogen removal rate and is simple to operate. It therefore is highly promising in drinking-water treatment.     

厌氧氨氧化工艺的应用现状和问题

厌氧氨氧化(Anaerobic ammonium oxidation,ANAMMOX)工艺因其高效低耗的优势,在废水生物脱氮领域具有广阔的应用前景。在过去的20年中,许多基于ANAMMOX反应的工艺得以不断研究和应用。预计到2014年末,全球范围内的ANAMMOX工程将会超过100座。综述了各种形式的ANAMMOX工艺,包括短程硝化-厌氧氨氧化、全程自养脱氮、限氧自养硝化反硝化、反硝化氨氧化、好氧反氨化、同步短程硝化-厌氧氨氧化-反硝化耦合、单级厌氧氨氧化短程硝化脱氮工艺。对一体式和分体式工艺运行条件进行了比较,结合ANAMMOX工艺工程(主要包括移动床生物膜,颗粒污泥和序批式反应器系统)应用现状,总结了工程化应用过程中遇到的问题及其解决对策,在此基础上对今后的研究和应用方向进行了展望。今后的研究重点应集中于运行条件的优化和水质障碍因子的解决,尤其是工艺自动化控制系统的开发和特殊废水对工艺性能影响的研究。     

Effect of sludge age on simultaneous nitrification and denitrification in membrane bioreactor

This study evaluated the effect of sludge age on simultaneous nitrification and denitrification in a membrane bioreactor treating black water. A membrane bioreactor with no separate anoxic volume was operated at a sludge age of 20 days under low dissolved oxygen concentration of 0.1-0.2 mg/L. Its performance was compared with the period when the sludge age was adjusted to 60 days. Floc size distribution, apparent viscosity, and nitrogen removal differed significantly, together with different biomass concentrations: nitrification was reduced to 40% while denitrification was almost complete. Modelling indicated that both nitrification and denitrification kinetics varied as a function of the sludge age. Calibrated values of half saturation coefficients were reduced when the sludge age was lowered to 20 days. Model simulation confirmed the validity of variable process kinetics for nitrogen removal, specifically set by the selected sludge age.     

Effect of low dissolved oxygen on simultaneous nitrification and denitrification in a membrane bioreactor treating black water

Effect of low dissolved oxygen on simultaneous nitrification and denitrification was evaluated in a membrane bioreactor treating black water. A fully aerobic membrane bioreactor was operated at a sludge age of 60 days under three low dissolved oxygen (DO) levels below 0.5mg/L. It sustained effective simultaneous nitrification/denitrification for the entire observation period. Nitrification was incomplete due to adverse effects of a number of factors such as low DO level, SMPs inhibition, alkalinity limitation, etc. DO impact was more significant on denitrification: Nitrate was fully removed at low DO level but the removal was gradually reduced as DO was increased to 0.5mg/L. Nitrogen removal remained optimal within the DO range of 0.15-0.35 mg/L. Experimental results were calibrated and simulated by model evaluation with the same model coefficients. The model defined improved mass transfer with lower affinity coefficients for oxygen and nitrate as compared to conventional activated sludge.     

好氧反硝化生物脱氮技术的研究进展

好氧反硝化生物脱氮技术自提出以来,凭借能实现同步硝化反硝化、节省基建投资及运行费用等诸多优点,受到国内外环境领域学者的广泛关注。本文首先总结了近年来好氧反硝化菌种的筛选分离情况,以及环境因子对好氧反硝化菌脱氮效能的影响,包括溶解氧(dissolved oxygen,DO)、碳氮比(C/N)、温度等。然后深入探讨了好氧反硝化生物脱氮技术的原理,好氧反硝化过程中的关键功能基因及酶,同时介绍了分子生物技术在好氧反硝化研究过程中的应用,以及好氧反硝化生物脱氮技术在实际应用方面的研究现状。最后,基于目前的研究瓶颈问题,对未来好氧反硝化生物脱氮技术的研究方向提出了科学展望。     

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.     

An investigation of a process for partial nitrification and autotrophic denitrification combined desulfurization in a single biofilm reactor

In this study, a vertical submerged biofilm reactor was applied to investigate autotrophic partial nitrification/denitrification and simultaneous sulfide removal by using synthetic wastewater. The appropriate influent ratios of ammonia and sulfide needed to achieve partial autotrophic nitrification and denitrification were evaluated with influent ammonium nitrogen ranging from 54.6 to 129.8 mg L^?1 and sulfide concentrations ranging from 52.7 to 412.4 mg S L^?1. The results demonstrated that the working parameter was more stable when the sulfur/nitrogen ratio was set at 3:2, which yielded the maximum sulfur conversion. Batch experiments with different phosphate concentrations proved that a suitable phosphate buffer solution to control pH values could improve synchronous desulfurization denitrification process performance.     

A novel double-membrane system for simultaneous nitrification and denitrification in a single tank

A novel biological treatment system, which contains two types of membrane modules in a single tank, was developed for simultaneous nitrification and denitrification. Both of the modules were fed with the substrates on the tube side of the silicone tubes by diffusing them to the biofilms which form on the surface of the tubes. One module was fed with methanol for denitrification and the other one was fed with pure oxygen for nitrification. As a result, the interference of organic carbon on nitrification, and that of oxygen on denitrification, were both hindered by the diffusion barriers (biofilms), thereby allowing two different niches for nitrifiers and denitrifiers to coexist in a single tank. Besides saving space and the amount of alkalinity required for nitrification, this system also produced low residual chemical oxygen demand (COD) and high nitrogen removal rates (2.9-3.4 gN m-2 d-1 of surface area of membrane).     

Removal of ammonium via simultaneous nitrification-denitrification nitrite-shortcut in a single packed-bed batch reactor

A polyurethane packed-bed-biofilm sequential batch reactor was fed with synthetic substrate simulating the composition of UASB reactor effluents. Two distinct ammonia nitrogen concentrations (125 and 250 mg l(-1)) were supplied during two sequential long-term experiments of 160 days each (320 total). Cycles of 24h under intermittent aeration for periods of 1h were applied, and ethanol was added as a carbon source at the beginning of each anoxic period. Nitrite was the main oxidized nitrogen compound which accumulated only during the aerated phases of the batch cycle. A consistent decrease of nitrite concentration started always immediately after the interruption of oxygen supply and addition of the electron donor. Removal to below detection limits of all nitrogen soluble forms was always observed at the end of the 24h cycles for both initial concentrations. Polyurethane packed-bed matrices and ethanol amendments conferred high process stability. Microbial investigation by cloning suggested that nitrification was carried out by Nitrosomonas-like species whereas denitrification was mediated by unclassified species commonly observed in denitrifying environments. The packed-bed batch bioreactor favored the simultaneous colonization of distinct microbial groups within the immobilized microbial biomass. The biofilm was capable of actively oxidizing ammonium and denitrification at high ratios in intermittent intervals within 24h cycles.     

Biofilm stratification during simultaneous nitrification and denitrification (SND) at a biocathode

The aeration of the cathode compartment of bioelectrochemical systems (BESs) was recently shown to promote simultaneous nitrification and denitrification (SND). This study investigates the cathodic metabolism under different operating conditions as well as the structural organization of the cathodic biofilm during SND. Results show that a maximal nitrogen removal efficiency of 86.9 ± 0.5%, and a removal rate of 3.39 ± 0.08 mg N L⁻¹ h⁻¹ could be achieved at a dissolved oxygen (DO) level of 5.73 ± 0.03 mg L⁻¹ in the catholyte. The DO levels used in this study are higher than the thresholds previously reported as detrimental for denitrification. Analysis of the cathodic half-cell potential during batch tests suggested the existence of an oxygen gradient within the biofilm while performing SND. FISH analysis corroborated this finding revealing that the structure of the biofilm included an outer layer occupied by putative nitrifying organisms, and an inner layer where putative denitrifying organisms were most dominant. To our best knowledge this is the first time that nitrifying and denitrifying microorganisms are simultaneously observed in a cathodic biofilm.     

限氧自养硝化-反硝化生物脱氮新技术

限氧自养硝化—反硝化是部分硝化与厌氧氨氧化相耦联的生物脱氮反应过程,通过严格控制溶解氧在0．1～0．3mg·L^-1,实现硝化反应控制在亚硝酸阶段,然后以硝化阶段剩余的NH4^+作为电子供体,在厌氧条件下实现反硝化,该反应过程是完全的自养硝化—反硝化过程,具有能耗低、脱氮效率高、反应系统占地面积小等优点,适用于处理COD／NH4^+—N低的废水,是一种非常有应用前景的生物脱氮技术,文中详细介绍了限氧自养硝化—反硝化生物脱氮反应过程的研究进展,讨论了其微生物学机理及应用前景。     

Enhanced nutrient removal in three types of step feeding process from municipal wastewater

An anoxic/oxic step feeding process was improved to enhance nutrient removal by reconfiguring the process into (1) anaerobic/anoxic/oxic step feeding process or (2) modified University of Capetown (UCT) step feeding process. Enhanced nitrogen and phosphorus removal and optimized organics utilization were obtained simultaneously in the modified UCT type with both internal and sludge recycle ratios of 75% as well as anaerobic/anoxic/oxic volume ratio of 1:3:6. Specifically, the UCT configuration and optimized operational conditions lead to the enrichment of denitrifying phosphorus removal microorganisms and achieved improved anaerobic P-release and anoxic P-uptake activities, which were beneficial to the denitrifying phosphorus removal activities and removal efficiencies. Due to high mixed liquor suspended solid and uneven distributed dissolved oxygen, 35% of total nitrogen was eliminated through simultaneous nitrification and denitrification process in aerobic zones. Moreover, 62 ± 6% of influent chemical oxygen demands was involved in the denitrification or phosphorus release processes.     

海洋环境异养硝化-好氧反硝化菌的研究进展

异养硝化-好氧反硝化（heterotrophic nitrifying-aerobic denitrification,HN-AD）菌的发现打破了传统的脱氮理论,可以在有氧条件下同时进行硝化和反硝化,成为近年来的研究热点。HN-AD细菌在海洋氮循环中发挥着重要作用。本文对海洋环境中HN-AD菌的多样性和部分已知氮代谢途径及相关酶系进行了介绍,分析了盐度、碳氮比、溶解氧、pH等环境因素对HN-AD菌脱氮效果的影响,对其工艺和技术应用、前景和发展方向进行了综述和展望。     

Modeling nitrogen removal in water hyacinth ponds receiving effluent from waste stabilization ponds

We developed a dynamic model to predict nitrogen removal in water hyacinth ponds (WHPs) receiving effluent from waste stabilization ponds (WSPs). The model is based on the biofilm reaction on the root surface of plant and pond walls. The model consists of mass balances of six main substrates including: particulate organic nitrogen (PON), dissolved organic nitrogen (DON), ammonium (NH₄⁺), nitrite and nitrate (NOx), soluble chemical oxygen demand (SCOD), and particulate chemical oxygen demand (PCOD). The model, incorporating major nitrogen transformation mechanisms such as hydrolysis, mineralization, and nitrification–denitrification, accounts also for carbon consumption and plant uptake. The model's application to a pilot plant showed good agreement between measured and predicted values. According to the modeling results, in the WHPs, nitrification and denitrification were the predominant nitrogen removal processes occurring simultaneously. Temperature and hydraulic retention time (HRT) had a profound effect on the performance of nitrogen removal while an algae biomass (PCOD) accumulated in the WHPs, was a useful carbon source for denitrification.     

Treatment of effluents polluted by nitrogen with new biological technologies based on autotrophic nitrification-denitrification processes

In recent years, various technologies have been developed for the removal of nitrogen from wastewater that is rich in nitrogen but poor in organic carbon, such as the effluents from anaerobic digesters and from certain industries. These technologies have resulted in several patents. The core of these technologies is some of the processes and patents described in this paper: Aerobic denitrification, Sharon, Anammox, OLAND, CANON, NOx process, DEMON. More specifically, one of the first innovative options described for removing nitrogen include partial nitrification under aerobic conditions (partial Sharon process) followed by autotrophic anaerobic oxidation (Anammox process). The partial Sharon-Anammox process can be performed under alternating oxic and anoxic conditions in the same bioreactor or in two steps in two separate bioreactors. This overview focuses on the technical and biological aspects of these new types of treatment system, and compares them to other technologies. Given the fact that nitrification is a sensitive process, special attention is paid to conditions such as temperature, dissolved oxygen, hydraulic retention time, free ammonia, nitrous acid concentration, and pH. A discussion of the pros and cons of such treatment systems is also included since autotrophic nitrogen removal has advantages as well as drawbacks. The paper concludes with a discussion of future research that could improve these systems by enhancing performance and reducing costs.     

Novel mathematical modeling on pilot-scale of plug-flow aerated submerged biofilm reactor for dissolved organic matter and nitrogen removal

The investigation aimed to present mathematical models for describing the dynamic behavior of the dissolved organic matter removal and nitrification in the Aerated Submerged Bio-Film (ASBF) for a plug-flow reactor. Based on the experimental data from the batch system of the ASBF pilot plant, mathematical models for the plug-flow reactor were developed to predict dissolved organic matter and ammonia nitrogen removal rates as a function of heterotrophic and autotrophic bacteria populations, dissolved organic matter concentrations, ammonia nitrogen concentrations, dissolved oxygen concentrations, and temperature. The mathematical models for dissolved organic matter and ammonia nitrogen removal in ASBF include two differential equations reflecting heterotrophic and autotrophic bacteria populations, and a number of kinetic parameters. Consequently, the results present a better insight into the dynamics behavior of heterotrophic and autotrophic biofilm growth and their practical application to wastewater for dissolved organic matter and ammonia nitrogen removal process. The mathematical model for ammonia nitrogen and dissolved organic matter removals present good results for the plug-flow reactor.     

Simultaneous nitrification,denitrification, and phosphorus removal in a lab-scale sequencing batch reactor

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic-enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the energy and COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen (DO) concentration (0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification, and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHAs), accompanied by phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to <0.5 mg/L by the end of the cycle. Ammonia was also oxidized during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis showed that the final denitrification product was mainly nitrous oxide (N(2)O), not N(2). Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms (DGAOs), rather than denitrifying polyphosphate-accumulating organisms (DPAOs), were responsible for the denitrification activity.     

Simultaneous nitrification and denitrification by controlling vertical and horizontal microenvironment in a membrane-aerated biofilm reactor

Nitrogen and carbon components in domestic modified wastewater were completely removed by simultaneous nitrification and denitrification using a membrane-aerated biofilm reactor where biofilm was fixed on a hollow-fiber membrane. To measure the spatial distribution of pH, ammonium and nitrate ions and to observe microbes inside the biofilm fixed on the membrane, microelectrodes and the fluorescence in situ hybridization (FISH) method were applied. Due to plug flow in the vertical direction (from the bottom to the top of the reactor), ammonium nitrogen was gradually removed and negligible nitrate nitrogen was detected throughout the reactor. FISH revealed that ammonia-oxidizing bacteria were mainly distributed inside the biofilm and other bacteria, which included denitrifying bacteria, were mainly distributed outside the biofilm and over the suspended sludge. In order to characterize bacterial activity in the vertical direction of the reactor, nitrification rates at lower, central and upper points were calculated using microelectrode data. The nitrification rate at the lower point was 7 and 125 times higher than those at the central and upper points, respectively. These results show that the removal of carbon and nitrogen compounds was accomplished efficiently by using various kinds of bacteria distributed vertically and horizontally in a single reactor.     

Nitrogen removal from wastewater using a double-biofilm reactor with a continuous-flow method

Wastewater microorganisms of nitrification and denitrification were cultivated to compose two biofilm modules, termed the permeable support bioreactor (PSB) and the membrane feeding substrate bioreactor (MFSB). PSB and MFSB were combined in a single tank to develop a double-biofilm reactor, which was used to treat nitrogen contaminants in wastewater. With a membrane supplement of substrates (O(2) and CH(3)OH), the D.O. and COD levels were at a low value in the bulk solution thus inhibitive effects between nitrification and denitrification were minimized. Simultaneous nitrification/denitrification was conducted in the reactor and the double-biofilm reactor achieved high nitrification and denitrification efficiency, of 96.5% and 82%, respectively.     

湖泊氮素氧化及脱氮过程研究进展

自然界中氮的生物地球化学循环主要由微生物驱动,由固氮作用、硝化作用、反硝化作用和氨化作用来完成。过去数十年间,随着异养硝化、厌氧氨氧化和古菌氨氧化作用的发现,人们对环境中氮素循环认识逐步深入,提出了多种脱氮途径新假说。对湖泊生态系统中氮素的输入、输出及其在水体、沉积物和水土界面的迁移转化过程进行了概括,对湖泊生态系统中反硝化和厌氧氨氧化脱氮机理及脱氮效率的最新研究进展进行了探讨,并对以后的氮素循环研究进行了展望。