Total nitrogen removal in a hybrid, membrane-aerated activated sludge process

The hybrid (suspended and attached growth) membrane biofilm process (HMBP) is a novel method to achieve total nitrogen removal from wastewater. Air-filled hollow-fiber membranes are incorporated into an activated sludge tank, and a nitrifying biofilm develops on the membranes, producing nitrite and nitrate. By suppressing bulk aeration, the bulk liquid becomes anoxic, and the nitrate/nitrite can be reduced with influent BOD. The key feature that distinguishes the HMBP from other membrane-aerated processes is that it is hybrid; heterotrophic bacteria are kept mainly in suspension by maintaining low bulk liquid BOD concentrations. We investigated the HMBP's performance under a variety of BOD and ammonium loadings, and determined the dominant mechanisms of nitrogen removal. Suspended solids increased with the BOD loadings, maintaining low bulk liquid BOD concentrations. As a result, nitrification rates were insensitive to the BOD loadings, remaining at 1gNm(-2)day(-1) for BOD loadings ranging from 4 to 17gBODm(-2)day(-1). Nitrification rates decreased during short-term spikes in bulk liquid BOD concentrations. Shortcut nitrogen removal was confirmed using microsensor measurements, showing that nitrite was the dominant form of oxidized nitrogen produced by the biofilm. Fluorescence in situ hybridization (FISH) showed that ammonia oxidizing bacteria (AOB) were dominant throughout the biofilm, while nitrite oxidizing bacteria (NOB) were only present in the deeper regions of the biofilm, where the oxygen concentration was above 2mg/L. Denitrification occurred mainly in the suspended phase, instead of in the biofilm, decreasing the potential for biofouling. When influent BOD concentrations were sufficiently high, full denitrification occurred, with total nitrogen (TN) removal approaching 100%. These results suggest that the process is well-suited for achieving concurrent BOD and TN removal in activated sludge.     

低温条件下生物转盘处理低浓度污染地表水

为实现低温条件下(冬季水温为8~15℃)快速启动生物转盘处理低浓度污染地表水,采用自然挂膜法G1、活性污泥挂膜法G2和硝化菌挂膜法G3这3种方式进行生物转盘挂膜,并对出水指标与生物膜表观形貌、群落组成进行对比研究。结果表明,从启动速率与抗冲击负荷能力来看,G3>G2>G1;25 d后接种硝化菌的生物转盘对氨氮的去除率即可达到88.78%。稳定运行后,3种挂膜方式的生物转盘对低浓度污染地表水的处理效果相近,对NH4+-N和COD的去除率均可稳定在90%和20%。3种挂膜方式的微生物丰度与种类相似,与硝化反应有关的细菌主要有Nitrosospira、Candidatus nitrotoga、Nitrosomonas,在3种挂膜方式中分别占比15.85%、12.04%、12.47%;与COD降解有关的细菌主要有Reyranella、Thermomonas、Polymorphobacter、Sphingomonas与Arenimonas,在3种挂膜方式中分别占比10.69%、12.39%、15.02%。微生物多样性和均匀度呈现出后端生物转盘盘片大于前端的趋势,说明微生物种类和均匀度与污染物种类和浓度有关。     

通过控制泥龄实现亚硝酸盐型同步硝化反硝化

采用序批式活性污泥法处理人工配制的城市生活污水，通过控制泥龄成功地实现了亚硝酸盐型同步硝化反硝化，曝气过程中NO2^-N／NOx^-N值始终保持在84．48％以上，曝气结束时大约有80．39％的氨氮通过同步硝化反硝化途径被去除。在适宜的曝气量下，利用排泥的方法控制反应器内适宜的泥龄，可以实现稳定的亚硝酸盐型同步硝化反硝化。     

Mechanisms of N2O production in biological wastewater treatment under nitrifying and denitrifying conditions

Nitrous oxide (N₂O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N₂O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions.Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N₂O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N₂O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N₂O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N₂O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N₂O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO₂/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment.Under anoxic conditions, nitrate reducing experiments confirmed that N₂O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N₂O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations.     

Nitrous oxide emissions from secondary activated sludge in nitrifying conditions of urban wastewater treatment plants: effect of oxygenation level

In order to better understand the mechanisms of N(2)O emissions from nitrifying activated sludge of urban WWTPs, sludge from the Valenton plant (Paris conurbation) are subjected to lab-scale batch experiments under various conditions of oxygenation. The results show that the highest N(2)O emissions (7.1 microgN-N(2)OgSS(-1) h(-1) in average) occur at a dissolved oxygen (DO) concentration of around 1mgO(2)L(-1). These high emissions at low oxygenation (from 0.1 to 2 mg O(2)L(-1)) are due to two processes: autotrophic nitrifier denitrification and heterotrophic denitrification. Nitrifier denitrification always dominates, representing from 58% to 83% of the N(2)O production. This N(2)O production originating from nitrifying activated sludge becomes 8 times higher when nitrite is added at a DO of 1 mg O(2)L(-1); a decrease is observed both at higher and lower oxygenation. Heterotrophic denitrification represents less than 50% of the N(2)O production, decreasing from 42% to 17% when oxygenation increases from 0.1 to 2 mg O(2) L(-1). We show that ammonium oxidizing bacteria (AOB) can shift to nitrifier denitrification when oxygen is depleted in the environments including in the WWTPs, nitrite then plays the role of oxygen as the final electron acceptor. As opposed to what happens in nitrification, the end products of nitrifier denitrification are gaseous forms of nitrogen, where N(2)O is not negligible compared to N(2). Overall, N(2)O emissions represent 0.1-0.4% of oxidized NH(4)(+), depending on the oxygenation level. N(2)O emissions would range from 0.11 to 0.42 TN-N(2)O day(-1) for a tertiary treatment of the Paris wastewater effluents, consisting exclusively of activated sludge nitrification.     

Treatment of anaerobically pre-treated domestic sewage by a rotating biological contactor.

The performance of a rotating biological contactor (RBC) for the post-treatment of the effluent of an up-flow anaerobic sludge blanket (UASB) was the subject of this study. Different hydraulic and organic loading rates have been investigated. The removal efficiencies of COD(total), COD(suspended), COD(colloidal) and COD(soluble) increased at a higher hydraulic retention time (HRT) and a lower influent organic loading rate. The results obtained indicated that a two-stage RBC reactor at an HRT of 10 h and an organic loading rate of 6.4g COD m(-2) d(-1) represents an effective post-treatment process. Most COD(suspended) and COD(colloidal) were removed in the first stage while nitrification proceeded in the second stage. The overall nitrification efficiency was 92% at an ammonia loading rate of 1.1 gm(-2) d(-1). Total E. coli removal at HRTs of 10, 5 and 2.5h were 99.5%, 99.0% and 89.0%. respectively. The major part of suspended E. coli ( >4.4 microm) was removed by sedimentation or by adsorption in the biofilm of the first stage of RBC (99.66%). However, E. coli in the colloidal fraction (<4.4 to >0.45 microm) was eliminated in the second stage of RBC (99.78%). A comparison of the performance of a one-stage versus two-stage RBC system, operated at the same total loading rate, revealed an improvement in the effluent quality of the two-stage effluent as compared to the one-stage effluent. The two stages RBC were used to examine the effect of hydraulic shock loads on reactor performance in terms of COD, nitrification and E. coli removal.     

Suspended biofilm carrier and activated sludge removal of acidic pharmaceuticals

Removal of seven active pharmaceutical substances (ibuprofen, ketoprofen, naproxen, diclofenac, clofibric acid, mefenamic acid, and gemfibrozil) was assessed by batch experiments, with suspended biofilm carriers and activated sludge from several full-scale wastewater treatment plants. A distinct difference between nitrifying activated sludge and suspended biofilm carrier removal of several pharmaceuticals was demonstrated. Biofilm carriers from full-scale nitrifying wastewater treatment plants, demonstrated considerably higher removal rates per unit biomass (i.e. suspended solids for the sludges and attached solids for the carriers) of diclofenac, ketoprofen, gemfibrozil, clofibric acid and mefenamic acid compared to the sludges. Among the target pharmaceuticals, only ibuprofen and naproxen showed similar removal rates per unit biomass for the sludges and biofilm carriers. In contrast to the pharmaceutical removal, the nitrification capacity per unit biomass was lower for the carriers than the sludges, which suggests that neither the nitrite nor the ammonia oxidizing bacteria are primarily responsible for the observed differences in pharmaceutical removal. The low ability of ammonia oxidizing bacteria to degrade or transform the target pharmaceuticals was further demonstrated by the limited pharmaceutical removal in an experiment with continuous nitritation and biofilm carriers from a partial nitritation/anammox sludge liquor treatment process.     

Application of calorimetric measurements for biokinetic characterisation of nitrifying population in activated sludge

A preliminary investigation is described on the application of calorimetry as a sensitive technique to evaluate nitrifying activity in activated sludge. Calorimetric profiles (thermograms) related to heat dissipation due to biological nitrification reactions (ammonia or nitrite consumption) have been interpreted. Correlations between calorimetric data and the main process variables, i.e. ammonia and nitrite concentration and oxygen uptake, have been verified, and confirm the potential of calorimetry to investigate, monitor and control even weakly exothermic biological processes like autotrophic nitrification. Heat yields (Y(Q/i)) for ammonia, nitrite, and oxygen, defined as the heat released per unit amount of converted reactant, have been separately evaluated. Moreover, calorimetric experiments on activated sludge from a full-scale nitrogen removal wastewater treatment plant have been carried out and kinetic parameters for both ammonia and nitrite oxidising bacteria have been estimated.     

Process optimization by decoupled control of key microbial populations: distribution of activity and abundance of polyphosphate-accumulating organisms and nitrifying populations in a full-scale IFAS-EBPR plant

This study investigated the abundance and distribution of key functional microbial populations and their activities in a full-scale integrated fixed film activated sludge-enhanced biological phosphorus removal (IFAS-EBPR) process. Polyphosphate accumulating organisms (PAOs) including Accumulibacter and EBPR activities were predominately associated with the mixed liquor (>90%) whereas nitrifying populations and nitrification activity resided mostly (>70%) on the carrier media. Ammonia oxidizer bacteria (AOB) were members of the Nitrosomonas europaea/eutropha/halophila and the Nitrosomonas oligotropha lineages, while nitrite oxidizer bacteria (NOB) belonged to the Nitrospira genus. Addition of the carrier media in the hybrid activated sludge system increased the nitrification capacity and stability; this effect was much greater in the first IFAS stage than in the second one where the residual ammonia concentration becomes limiting. Our results show that IFAS-EBPR systems enable decoupling of solid residence time (SRT) control for nitrifiers and PAOs that require or prefer conflicting SRT values (e.g. >15 days required for nitrifiers and <5 days preferred for PAOs). Allowing the slow-growing nitrifiers to attach to the carrier media and the faster-growing phosphorus (P)-removing organisms (and other heterotrophs, e.g. denitrifiers) to be in the suspended mixed liquor (ML), the EBPR-IFAS system facilitates separate SRT controls and overall optimization for both N and P removal processes.     

异养硝化菌的分离及其强化活性污泥脱氮效果

为提高水处理过程中的脱氮率，实现好氧条件下对总氮的去除。通过试验分离出一株异养硝化菌，该菌株为白色革兰氏阴性球状菌。将该菌扩大培养后接种于活性污泥系统并进行了处理模拟废水的试验。结果表明：该菌能在好氧条件下分别代谢氨氮、亚硝酸盐氮、硝酸盐氮，并通过好氧反硝化实现对总氮的去除。用该菌株强化的活性污泥系统对以氨氮、亚硝酸盐氮、硝酸盐氮为惟一氮源的模拟废水进行处理，4h的总氮去除率分别为85％、60％、70％。     

Development of a 2-sludge, 3-stage system for nitrogen and phosphorous removal from nutrient-rich wastewater using granular sludge and biofilms

A novel 2-sludge 3-stage process using a combination of granular sludge and biofilm was developed to achieve biological removal of nitrogen and phosphorus from nutrient-rich wastewater. The system consists of a granular sequencing batch reactor (SBR) working under alternating anaerobic/anoxic conditions supplemented with a short aerobic phase and an aerobic biofilm SBR. The wastewater is first fed to the granular SBR reactor, where easily biodegradable carbon sources are taken up primarily by polyphosphate accumulating organisms (PAOs). The supernatant resulting from quick settling of the granular sludge is then fed to the biofilm SBR for nitrification, which produces oxidized nitrogen that is returned to the granular reactor for simultaneous denitrification and phosphorus removal. While maximizing the utilization of organic substrates and reducing operational costs, as do other 2-sludge processes previously reported in literature, the proposed system solves the bottleneck problem of traditional 2-sludge systems, namely high effluent ammonia concentration, due to its high-volume exchange ratios. An ammonia oxidation rate of 32 mg N/Lh was achieved in the biofilm SBR, which produced nitrite as the final product. This nitrite stream was found to cause major inhibition on the anoxic P uptake and also to result in the accumulation of N(2)O. These problems were solved by feeding the nitrite-containing stream continuously to the granular reactor in the anoxic phase. With a nitrogen and phosphorus removal efficiency of 81% and 94%, respectively, the system produces an effluent that is suitable for land irrigation from a wastewater stream containing 270 mg N/L of total nitrogen and 40 mg P/L of total phosphorus.     

Influence of detachment on substrate removal and microbial ecology in a heterotrophic/autotrophic biofilm

Competition between heterotrophic bacteria oxidizing organic substrate and autotrophic nitrifying bacteria in a biofilm was evaluated. The biofilm was grown in a tubular reactor under different shear and organic substrate loading conditions. The reactor was initially operated without organic substrate in the influent until stable ammonia oxidation rates of 2.1 g N/(m² d) were achieved. A rapid increase of fluid shear in the tubular reactor on day 156 resulted in biofilm sloughing, reducing the biofilm thickness from 330 to 190 μm. This sloughing event did not have a significant effect on ammonia oxidation rates. The addition of acetate to the influent of the reactor resulted in decreased ammonia oxidation rates (1.8 g N/(m² d)) for low influent acetate concentrations (17 mg COD/L) and the breakdown of nitrification at high influent acetate concentrations (55 mg COD/L). Rapidly increasing fluid shear triggered biofilm sloughing in some cases—but maintaining constant shear did not prevent sloughing events from occurring. With the addition of acetate to the influent of the reactor, the biofilm thickness increased up to 1350 μm and individual sloughing events removed up to 50% of the biofilm. Biofilm sloughing had no significant influence on organic substrate removal or ammonia oxidation. During 325 days of reactor operation, ammonia was oxidized only to nitrite; no nitrate production was observed. This lack of nitrite oxidation was confirmed by fluorescent in situ hybridization (FISH) analysis, which detected betaproteobacterial ammonia oxidizers but not nitrite oxidizers. Mathematical modeling correctly predicted breakdown of nitrification at high influent acetate concentrations. Model predictions deviated systematically from experimental results, however, for the case of low influent acetate concentrations.     

Evaluating operating conditions for outcompeting nitrite oxidizers and maintaining partial nitrification in biofilm systems using biofilm modeling and Monte Carlo filtering

In practice, partial nitrification to nitrite in biofilms has been achieved with a range of different operating conditions, but mechanisms resulting in reliable partial nitrification in biofilms are not well understood. In this study, mathematical biofilm modeling combined with Monte Carlo filtering was used to evaluate operating conditions that (1) lead to outcompetition of nitrite oxidizers from the biofilm, and (2) allow to maintain partial nitrification during long-term operation. Competition for oxygen was found to be the main mechanism for displacing nitrite oxidizers from the biofilm, and preventing re-growth of nitrite oxidizers in the long-term. To maintain partial nitrification in the model, a larger oxygen affinity (i.e., smaller half saturation constant) for ammonium oxidizers compared to nitrite oxidizers was required, while the difference in maximum growth rate was not important for competition under steady state conditions. Thus, mechanisms for washout of nitrite oxidizing bacteria from biofilms are different from suspended cultures where the difference in maximum growth rate is a key mechanism. Inhibition of nitrite oxidizers by free ammonia was not required to outcompete nitrite oxidizers from the biofilm, and to maintain partial nitrification to nitrite. But inhibition by free ammonia resulted in faster washout of nitrite oxidizers.     

Nitrification of ammonia-nitrogen in refinery wastewater

Wastewater from integrated petroleum refineries normally contains 20–80 mg/l ammonia-nitrogen which is harmful to the fishes in the receiving water bodies. To remove ammonia-nitrogen completely in the biotreatment system of refinery wastewater, various enrichment and cultivation methods of nitrifying bacteria were tried.

Results indicated that by supplementing glucose nutrient, over 90% ammonia-nitrogen in the refinery wastewater could be converted into nitrite within 7–14 days in either an activated sludge or rotating biological contactor system. Trace nitrate was detected. Further addition of yeast powder to the treatment systems stimulated the growth of Nitrobacter which accelerated the oxidation of nitrite to nitrate. Complete oxidation of the influent ammonia-nitrogen was observed 7 days later after adding 5 mg/l yeast powder to the influent wastewater. It also showed that neither glucose nor yeast powder were required for sustaining ammonia nitrification after the augmentation of Nitrobacter was achieved.     

生物沸石滤池去除微污染水源水中氨氮的挂膜启动

对沸石滤料生物滤池处理微污染水源水中低浓度氨氮的挂膜启动性能进行了研究。试验结果表明,挂膜过程可以根据氨氮、亚硝酸盐氮、硝酸盐氮浓度的变化分为三个阶段：初期沸石发挥本身对铵离子的吸附交换性能,氨氮去除率达88％以上;中期开始出现生物硝化作用,亚硝酸盐积累明显,硝酸盐出水浓度不稳定,氨氮去除率稳定,但下降至65％左右;后期硝化反应稳定进行,亚硝酸盐迅速转化为硝酸盐,氨氮去除率稳定在60％以上。生物沸石滤池挂膜同时应考察亚硝酸盐氮、硝酸盐氮浓度变化,在出水亚硝酸氮明显积累后又稳定降低,且硝酸盐氮稳定积累时方可认为挂膜成功。进出水pH值的变化可以指示硝化反应的进行程度和生物膜形成阶段。     

城市污水短程硝化的实现途径

探讨了影响废水中亚硝酸盐积累的三大主要因素：溶解氧、温度和pH。针对常温低氨氮城市污水,从理论上分析了以活性污泥法和生物膜法的形式进行亚硝化的启动方法和运行策略,为短程硝化／厌氧氨氧化工艺在城市污水处理中的应用提供了可借鉴的研究基础。     

Kinetic considerations on the performance of activated sludge reactors and rotating biological contactors

This study compares the performance characteristics of laboratory-scale activated sludge and rotating biological contactor (RBC) units treating an industrial effluent. It is found that, within the range of hydraulic detention time examined (0.3–1.7 days), the two plants show very similar BOD₅ removal kinetics. These results indicate that an RBC unit with a geometrical area of the discs of 1340 cm²1⁻¹ of aeration reactor is equivalent to an activated sludge plant with an MLVSS concentration of about 2000 mg 1⁻¹. Experimental data from the two units are also analyzed by two steady-state kinetic models. It is proved that the kinetic constants of suspended microbial growths may be used successfully for fixed biological films. At the same time, a simplified design equation for RBC systems is verified and an estimation procedure for the effective surface area of the biofilm developed.     

Influence of operational parameters on nitrogen removal efficiency and microbial communities in a full-scale activated sludge process

To improve the efficiency of total nitrogen (TN) removal, solid retention time (SRT) and internal recycling ratio controls were selected as operating parameters in a full-scale activated sludge process treating high strength industrial wastewater. Increased biomass concentration via SRT control enhanced TN removal. Also, decreasing the internal recycling ratio restored the nitrification process, which had been inhibited by phenol shock loading. Therefore, physiological alteration of the bacterial populations by application of specific operational strategies may stabilize the activated sludge process. Additionally, two dominant ammonia oxidizing bacteria (AOB) populations, Nitrosomonas europaea and Nitrosomonas nitrosa, were observed in all samples with no change in the community composition of AOB. In a nitrification tank, it was observed that the Nitrobacter populations consistently exceeded those of the Nitrospira within the nitrite oxidizing bacteria (NOB) community. Through using quantitative real-time PCR (qPCR), nirS, the nitrite reducing functional gene, was observed to predominate in the activated sludge of an anoxic tank, whereas there was the least amount of the narG gene, the nitrate reducing functional gene.     

Identification and quantification of nitrogen removal in a rotating biological contactor by 15N tracer techniques

High autotrophic nitrogen removal rates of 858mg NL(-1) day(-1) or 1.55g Nm(-2) day(-1) were obtained in a lab-scale rotating biological contactor treating an ammonium rich influent. It was postulated that ammonium was removed as dinitrogen gas by a sequence of aerobic ammonium oxidation to nitrite taking place in the outer biofilm layer and anaerobic ammonium oxidation with nitrite as electron acceptor occuring in the deeper biofilm layer. Chemical evidence for anaerobic ammonium oxidation within intact biofilm sludge from a lab-scale rotating biological contactor could be provided, without direct identification of responsible organisms catalysing this reaction. 15N tracer techniques were used for identification and quantification of nitrogen transformations. In batch tests with biofilm sludge at dissolved oxygen concentrations lower than 0.1mgL(-1), ammonium and nitrite did react in a stoichiometric ratio of 1:1.43 thereby forming dinitrogen. 15N isotope dilution calculations revealed that anaerobic ammonium oxidation was the major nitrogen transformation leading to concomitant ammonium and nitrite removal. Isotopic analysis of the produced biogas showed that both ammonium-N and nitrite-N were incorporated in N(2).     

Nitrification with high nitrite accumulation for the treatment of wastewater with high ammonia concentration

The objective of this paper was to determine the best conditions for partial nitrification with nitrite accumulation of simulated industrial wastewater with high ammonia concentration, lowering the total oxygen needed in the nitrification step, which may mean great saving in aeration. Dissolved oxygen (DO) concentration and pH were selected as operational parameters to study the possibility of nitrite accumulation not affecting overall ammonia removal. A 2.5L activated sludge reactor was operated in nitrification mode, feeding a synthetic wastewater simulating an industrial wastewater with high ammonia concentration. During the start-up a pH of 7.85 and a DO of 5.5mg/L were used. The reactor was operated until stable operation was achieved at final nitrogen loading rate (NLR) of 3.3kgN- NH(4)(+)/m(3)d with an influent ammonia concentration of 610mg N-NH(4)(+)/L.The influence of pH was studied in continuous operation in the range of 6.15-9.05, changing the reactor pH in steps until ammonia accumulation (complete nitrification inhibition) took place. The influence of DO was studied in the same mode, changing the DO in steps from 5.5 to 0.5mg/L.The pH was not a useful operational parameter in order to accumulate nitrite, because in the range of pH 6.45-8.95 complete nitrification to nitrate occurs. At pH lower than 6.45 and higher than 8.95 complete inhibition of nitrification takes place. Setting DO concentration in the reactor at 0.7mg/L, it was possible to accumulate more than 65% of the loaded ammonia nitrogen as nitrite with a 98% ammonia conversion. Below 0.5mg/L of DO ammonia was accumulated and over a DO of 1.7mg/L complete nitrification to nitrate was achieved.In conclusion, it is possible under the conditions of this study, to treat high ammonia synthetic wastewater achieving an accumulation of at least 65% of the loaded nitrogen as nitrite, operating at a DO around 0.7mg/L. This represents a reduction close to 20% in the oxygen necessary, and therefore a considerable saving in aeration.