Specific Nitrification Research Articles

Long-term operation of membrane biofilm reactors for nitrogen removal with autotrophic bacteria

Efficient gas delivery and biofilm development on membrane fibers in a membrane biofilm reactor (MBfR) would be well suited to autotrophic nitrification and denitrification using hydrogen. Total nitrogen removal in a two-step MBfR system incorporating sequential nitrification and hydrogen-driven autotrophic denitrification was investigated in order to achieve nitrogen removal by autotrophic bacteria alone. This study also aimed at the long-term stable operation, which proved difficult in previous studies due to excessive biofilm accumulation in autotrophic denitrification systems. Consecutive operation of nitrification and autotrophic denitrification lasted 230 days. Average specific nitrification rate of 1.87 g N/m(2) d was achieved and the performance was very stable throughout the experimental periods. Nitrification performance from this study showed comparable rates to previous studies although this work was conducted at slightly lower temperature. Batch tests confirmed the presence of nitrifiers from the effluent of the nitrification reactor, which reattached to the biofilm in the denitrification reactor leading to further nitrification. Performance of autotrophic denitrification was maintained stably throughout the experimental periods, however biofilm control by nitrogen sparging was required for process stability. Average specific denitrification rate of 1.41 g N/m(2) d and a maximum specific denitrification rate of 2.04 g N/m(2) d was maintained. This study showed that, with an appropriate biofilm control plan, stable long-term operation of a fully autotrophic MBfR system for total nitrogen removal was possible without major membrane cleaning procedures.

Influence of a prolonged solid retention time environment on nitrification/denitrification and sludge production in a submerged membrane bioreactor

A three-stage submerged MBR was operated under a prolonged SRT condition—more than 800 days—to treat high strength industrial wastewater. Throughout the entire experiment, chemical and biological effects on sludge production and nitrification/denitrification were investigated. The trend of MLSS growth was found to be divided into four phases. An initial growth phase followed by a pseudo stable phase which the biomass growth stabilised in the region of 13,000 mg.L −1 and then a transformation phase which caused the biomass concentration to increase again before finally stabilising at 18,000 mg.L −1 in a final stable phase. Total COD and TN removal in the three-stage submerged MBR were maintained consistently at 98% and 97%, respectively. Specific nitrification rate in the pseudo-growth phase stabilised in the region of 1.42 mgN.gMLVSS −1.h −1, after which it started to increase to 1.71 mgN.gMLVSS −1.h −1 when the system enter the final stable phase. Specific denitrification rate follows a “flatout” trend and stabilised in the region of 2.11 mg N.g MLVSS −1.h −1. Low sludge yield (0.22 gVSS.gCOD −1) and endogenous decay coefficient (0.05 day −1) were achieved in 300 days SRT MBR compared to CAS process. The experimental results revealed that both MBRs with SRT of 10 days and 300 days have an identical ratio of dead to live cells (three dead cells:seven live cells). Nevertheless, 300 days SRT MBR had large cell population (3.93×10 6 cell.ml −1) compared to 10 days SRT MBR (3.56×10 5 cell.ml −1). The high viability of microbial population in 300 days SRT MBR explained the high COD removal efficiency (97%) under a prolonged SRT condition. Additionally, the results revealed that the occurrence of protozoa in 300 days SRT MBR may also be responsible for the low sludge production.

Effect of loading rate and oxygen supply on nitrification in a non-porous membrane biofilm reactor

A nitrifying membrane biofilm reactor (MBfR) was operated over 170 days, to assess the effect of ammonia loading rate under O 2-excess conditions, and the effect of dissolved oxygen under O 2-limiting conditions on nitrification efficiency. The MBfR was fed pure oxygen by diffusion through a non-porous membrane. Five different loading rates, ranging from 1.92 to 5.53 g N/m 2 d, were tested, yielding specific nitrification rates (SNR) ranging from 1.54 to 2.60 g N/m 2 d. SNR increased linearly with specific loading rate, up to the load of 3.5 g N/m 2 d, which indicated that mass transfer was linearly related to the bulk ammonia concentration. Beyond that load, substrate diffusion limitation inhibited further increase of SNR. When operating the system under limited oxygen supply conditions, 100% oxygen utilization was achievable. Maintenance of higher oxygen supply allowed a slightly higher SNR due to the growth of nitrifiers at the outer side of the biofilm (away from the membrane surface). Nitrification batch tests confirmed that the fraction of nitrifiers in the solids detached from the surface of the biofilm (and washed out with the effluent), was twice as high during oxygen-excess conditions when compared to oxygen-limiting conditions.

Improvement of N fertilization by using the nitrification inhibitor DMPP [3,4-dimethylpirazole phosphate] in drip-irrigated citrus trees

Nitrogen management in orchards should tend to improve the fertilizer N use efficiency for a sustainable agriculture where productivity, fruit quality and environment are reconciled. The use of specific nitrification inhibitors could increase the N fertilizer uptake and decrease the potential groundwater pollution by nitrate leaching. The aim of this experiment was to assess the effect of application frequency of the ammonium sulphate (AS) and the nitrification inhibitor (NI), 3,4-dimethylpirazole phosphate (DMPP) supply on: nitrate-N and ammonium-N seasonal changes in soil; N and Fe concentrations in the spring-flush leaves; and yield and fruit quality. The experiment was carried out with clementine cv. Nules (Citrus clementine Hort. Tanaka x Citrus reticulate Blanco) mandarins grafted on Troyer citrange (Citrus sinensis x Poncirus trifoliata) rootstock under field conditions during three consecutive years. The trees were fertilized with 324 Kg N/ha from which 192 Kg N/ha were applied as AS (21% NH4+ -N) either with or without NI, and the remainder N came from irrigation water. The AS and AS+NI were split into 1, 2 or 4 applications per month by drip irrigation. The NH4+ -N concentration in the 0-20 and 20-40 cm soil layers was significantly higher in the AS+NI treatment. By contrast, the NO3- -N concentration was significantly higher in the soil treated only with AS. Moreover, the addition of NI to AS originated a significantly higher N and Fe concentrations in the spring-flush leaves. The yield was higher and some fruit quality parameters improved in trees fertilized with AS+NI compared to those fertilized only with AS.

Nitrification and inorganic nitrogen distribution in a large perturbed river/estuarine system: the Pearl River Estuary, China

Abstract. We investigated the spatial distribution and seasonal variation of dissolved inorganic nitrogen in a large perturbed estuary, the Pearl River Estuary, based on three cruises conducted in winter (January 2005), summer (August 2005) and spring (March 2006). On-site incubation was also carried out for determining ammonium and nitrite oxidation rates (nitrification rates). We observed a year-round pattern of dramatic decrease in NH4+, increase in NO3−, but insignificant change in NO2− in the upper estuary at salinity ~0–5. However, species and concentrations of inorganic nitrogen at upper estuary significantly changed with season. In winter, with low runoff, the most upper reach of the Pearl River Estuary showed relatively low rates of ammonia oxidation (0–5.4 μmol N L−1 d−1) and nitrite oxidation (0–5.2 μmol N L−1 d−1), accompanied by extremely high concentrations of ammonia (up to >800 μmol L−1) and nitrate (up to >300 μmol L−1). In summer, the upper estuary showed higher nitrification rates (ammonia oxidation rate ~1.5–33.1 μmol N L−1 d−1, nitrite oxidation rate ~0.6–32.0 μmol N L−1 d−1) with lower concentrations of ammonia (<350 μmol L−1) and nitrate (<120 μmol L−1). The Most Probable Number test showed relatively lower nitrifier abundance in summer at most sampling stations, indicating a greater specific nitrification rate per cell in the warm season. Temperature appeared to control nitrification rates to a large degree in different seasons. Spatial variability of nitrification rates appeared to be controlled by a combination of many other factors such as nutrient concentrations, nitrifier abundance and dissolved oxygen (DO) concentrations. In addition to aerobic respiration, nitrification contributed significantly to the consumption of DO and production of free CO2 at upper estuary. Nitrification-induced consumption accounted for up to approximately one third of the total water column community DO consumption in the upper estuary during the surveyed periods, boosting environmental stress on this large estuarine ecosystem.

Automatic set-point titration for monitoring nitrification in SBRs

Nitrification is usually the bottleneck of biological nitrogen removal processes. In SBRs systems, it is not often enough to monitor dissolved oxygen, pH and ORP to spot problems which may occur in nitrification processes. Therefore, automated supervision systems should be designed to include the possibility of monitoring the activity of nitrifying populations. Though the applicability of set-point titration for monitoring biological processes has been widely demonstrated in the literature, the possibility of an automated procedure is still at its early stage of industrial development. In this work, the use of an at-line automated titrator named TITAAN (TITrimetric Automated ANalyser) is presented. The completely automated sensor enables us to track nitrification rate trend with time in an SBR, detecting the causes leading to slower specific nitrification rates. It was also possible to perform early detection of toxic compounds in the influent by assessing their effect on the nitrifying biomass. Nitrifications rates were determined with average errors+/-10% (on 26 tests), never exceeding 20% as compared with UV-spectrophotometric determinations.

Application of Moving Bed Biofilm Process for Biological Organics and Nutrients from Municipal Wastewater

In this study, experiments have been conducted to evaluate the organics and nutrients removal from synthetic wastewater by a laboratory scale moving bed biofilm process. For nutrients removal, moving bed biofilm process has been applied in series with anaerobic, anoxic and aerobic units in four separate reactors. Moving bed biofilm reactors were operated continuously at different loading rates of nitrogen and Phosphorus. During optimum conditions, close to complete nitrification with average ammonium removal efficiency of 99.72% occurred in the aerobic reactor. In the aerobic reactor, the average specific nitrification rate was 1.8 g NOx-N kg VSS −1 h −1 . The results of the average effluent soluble COD concentration from each reactor showed that denitrification process in the second anoxic reactor consumed most of the biodegradable organic matter. As seen from the results, denitrification rate has increased with increasing NOx-N loading in the second anoxic reactor. The aerobic phosphate removal rate showed a good correlation to the anaerobic phosphate release rate. Moreover, phosphate removal rate showed a strong correlation to the phosphate loading rate in the aerobic reactor. In optimum conditions, the average SCOD, total nitrogen and phosphorus removal efficiencies were 96.9, 84.6 and 95.8%, respectively. This study showed that the moving bed biofilm process could be used as an ideal and efficient option for the total nutrient removal from municipal wastewater.

Population size and specific nitrification potential of soil ammonia-oxidizing bacteria under long-term fertilizer management

Population size of soil ammonia-oxidizing bacteria (AOB) was quantified by real-time PCR in a long-term (16 years) field experiment under different fertilizer managements. AOB population sizes in mineral nitrogen-fertilized soils and organic manure-fertilized soil were 10.3 and 3.1 times, respectively, that of the control, while phosphorus and potassium fertilization had no significant effect. On the other hand, the AOB specific nitrification potential (soil nitrification potential per AOB cell) was significantly higher ( P < 0.05) in organic manure-fertilized soil than in mineral-fertilized soils and the control, indicating that AOB was likely more metabolically active in organic manure-fertilized soils than in mineral nitrogen-fertilized soils after long-term application.

Estimation of Autotrophic Maximum Specific Growth Rate Constant—Experience from the Long‐Term Operation of a Laboratory‐Scale Sequencing Batch Reactor System

The autotrophic maximum specific growth rate constant, muA,max, is the critical parameter for design and performance of nitrifying activated sludge systems. In literature reviews (i.e., Henze et al., 1987; Metcalf and Eddy, 1991), a wide range of muA,max values have been reported (0.25 to 3.0 days(-1)); however, recent data from several wastewater treatment plants across North America revealed that the estimated muA,max values remained in the narrow range 0.85 to 1.05 days(-1). In this study, long-term operation of a laboratory-scale sequencing batch reactor system was investigated for estimating this coefficient according to the low food-to-microorganism ratio bioassay and simulation methods, as recommended in the Water Environment Research Foundation (Alexandria, Virginia) report (Melcer et al., 2003). The estimated muA,max values using steady-state model calculations for four operating periods ranged from 0.83 to 0.99 day(-1). The International Water Association (London, United Kingdom) Activated Sludge Model No. 1 (ASM1) dynamic model simulations revealed that a single value of muA,max (1.2 days(-1)) could be used, despite variations in the measured specific nitrification rates. However, the average muA,max was gradually decreasing during the activated sludge chlorination tests, until it reached the value of 0.48 day(-1) at the dose of 5 mg chlorine/(g mixed liquor suspended solids x d). Significant discrepancies between the predicted XA/YA ratios were observed. In some cases, the ASM1 predictions were approximately two times higher than the steady-state model predictions. This implies that estimating this ratio from a complex activated sludge model and using it in simple steady-state model calculations should be accepted with great caution and requires further investigation.

Process evaluation of HASP with IMET system through SNR and SDNR for the efficient management of Sewage Treatment Plant

Hybrid Activated Sludge Process (HASP) with IMET was developed and applied to an activated sludge process for the advanced nutrient treatment in Korea. The characteristics of nitrogen removal from the HASP were investigated through a kinetic study by batch-type experiment. Online DB analysis produced from the IMET was conducted for the nutrient removal performance in the field demonstration plant treating 10,000 m3/day in G city of Korea. In this paper, we aimed to determine the effect of increasing NHM4+-N load on the specific nitrification rate (SNR) and the specific denitrification rate (SDNR) through a batch-type experiment, and to estimate the net reaction time for the phase-transfer rate using online DB analysis in the HASP operation. Experimental results include: (1) both the nitrification and denitrification followed first-order kinetics; (2) the maximum SNR and SDNR were 4.0301 mgN/gVSS·hr and 2.785 mgN/gVSS·hr, respectively; (3) comparison of reaction rates between nitrification and denitrification from the non-linear regression analysis found that nitrification rate was higher than denitrification.

Simultaneous Nitrification and Denitrification of Municipal Wastewater in Aerobic Membrane Bioreactors

Simultaneous nitrification-denitrification (SND) of municipal wastewater was investigated in a laboratory-scale membrane bioreactor (MBR) operated at two different hydraulic retention times (HRTs), 0.5 and 1 day, dissolved oxygen 3.0 to 0.5 mg/L, and solids retention time (SRT) between 28 and 120 days. The organic loading rate (OLR) (0.11 to 0.64 kg chemical oxygen demand [COD]/m3/d) and influent soluble COD (SCOD)/ total Kjeldahl nitrogen (TKN) ratio (5 to 19) were varied by the addition of glucose. The ammonia-nitrogen and TKN removals were over 97%, and total nitrogen removal was approximately 89% in the MBR. The maximum specific nitrification rates (98 mg N/d/g VSS) and specific denitrification rates (81 mg N/d/g VSS) occurred at an SCOD/TKN ratio of 9.1. The optimum conditions for maximum total nitrogen removal by SND in a single reactor MBR have been found to be low dissolved oxygen (< 0.6 mg/L) and high OLR (approximately 0.64 kg COD/m3/d) at an HRT of 0.5 day and SRT of approximately 85 days.

Nitrification in sequencing batch reactors with and without glucose addition at 11 °C

Nitrification was investigated in two laboratory-scale sequencing batch reactors (SBRs) at 11 °C, one with glucose addition (G-Reactor) and the other without (N-Reactor). The characteristics of nitrification and the distribution of ammonia oxidizing bacteria (AOB) within activated sludge flocs in the two reactors were examined. A high specific nitrification rate existed in the N-Reactor, while a high volumetric nitrification rate existed in the G-Reactor. The proportion of AOB enriched in the N-Reactor was about three times that in the G-Reactor. The activated sludge flocs in the N-Reactor had a larger floc size and a higher biomass density than in the G-Reactor. AOB were mainly in a form of clusters in the activated sludge flocs in the N-Reactor, but were well dispersed throughout the flocs in the G-Reactor.

Biological nutrient removal with volatile fatty acids from food wastes in sequencing batch reactor

Volatile fatty acids (VFAs) derived from food waste were used as an alternative carbon source in biological nutrient removal. The pH Profiles were monitored during the nutrient removal in an Na-acetate fed sequencing batch reactor (SBR) (C source). Effluent N, P and SCOD concentrations of 0.5 and 0.1 mg/L were achieved with 5.5 hour of HRT (hydraulic retention time) when influent concentrations of NH 4 + -N, PO 4 3− and SCOD were 42.5, 5.92 and 180 mg/L. Then the SBR was fed with four solutions of VFAs produced under different acidogenesis conditions of food wastes. VFAs-added SBR showed similar specific nitrification rates (3.0 to 3.9 mg-N/g MLSS · h) to that of acetate, but specific denitrification rates (3.2 to 4.2 mg NO 3 − N/g MLSS·h) were slightly lower than with acetate of 4.67 mg NO 3 − -N/g MLSS·h. VFAs-introduced SBR efficiently removed phosphorus except when the SBR was fed with a VFA-solution containing high amounts of valerate and caproate.

Empirical model of the pH dependence of the maximum specific nitrification rate

A bell-shaped empirical model was proposed to describe the pH-dependent behavior of the maximum specific substrate utilization rates (MSSUR, q ˆ pH ) of ammonium and nitrite oxidations. The model was developed using a cosine function. The model satisfactorily captured the bell-shape decrease of the MSSUR as the pH deviated from the optima. Analysis of 7 experimental data sets gave that the optimum pH (pH opt) lied in the range of 8.2 ± 0.3 for ammonium oxidizing bacteria (AOB) and 7.9 ± 0.4 for nitrite oxidizing bacteria (NOB). The pH range ( w ) within which the MSSUR maintained above a half of the greatest MSSUR ( q ˆ max ) was 3.1 ± 0.4 for AOB and 2.2 ± 0.4 for NOB, which means that NOB is more sensitive to pH changes. Since the pH opt and the pH range ( w ) for NOB were smaller than those for AOB, it was inferred that a selective enrichment of AOB and consequent nitrite accumulation could be possible at an alkaline pH near or greater than the pH opt of AOB.

Effect of Cold‐Temperature Shock on Nitrification

Nitrification is known as the most temperature-sensitive step among the biological processes in wastewater treatment. The purpose of this study was to investigate the effect of temperature on nitrification, in the case of a sharp decrease of temperature, and to compare this effect with that of a gradual temperature decrease. It was found that a sudden temperature decrease affected nitrification much more than predicted. The immediate decrease of temperature by 10 degrees C led to a 20% larger decrease of specific nitrification rate than predicted by the temperature correction factor of 1.072. The change of nitrification rate resulting from a gradual temperature decrease was modeled correctly with the current default temperature correction factor of 1.072. It was concluded that the correction factor actually can be applied to a gradual temperature-change situation; however, in the case of a sudden temperature decrease, measures need to be taken to avoid nitrifier washout.

Effects of environmental conditions on the nitrifying population dynamics in a pilot wastewater treatment plant

The effect of environmental conditions, especially ammonium concentration, on community composition and nitrification activity of nitrifying bacterial biofilms in a pilot wastewater treatment plant was examined. A decreasing ammonium gradient was created when four aerated tanks with suspended carrier material were serially fed with wastewater. Community composition was analysed using fluorescence in situ hybridization (FISH) probes as well as partial 16S rRNA and amoA gene analysis using polymerase chain reaction-denaturating gradient gel electrophoresis (PCR-DGGE) and sequencing. Fluorescence in situ hybridization probes identified at least five ammonia-oxidizing bacterial (AOB) and two nitrite-oxidizing bacterial (NOB) populations. A change in nitrifying community was detected in the tanks, indicating that ammonium was an important structuring factor. Further, we found support for different autoecology within the Nitrosomonas oligotropha lineage, as at least one population within this lineage increased in relative abundance with ammonium concentration while another population decreased. Absolute numbers of AOB and NOB growing in biofilms on the carriers were determined and the cell specific nitrification rates calculated seemed strongly correlated to ammonium concentration. Oxygen could also be limiting in the biofilms of the first tank with high ammonium concentrations. The response of the nitrifying community to increased ammonium concentrations differed between the tanks, indicating that activity correlates with community structure.

Effects of operational parameters on aeration on/off time in an intermittent aeration membrane bioreactor

This study was performed to evaluate the operational parameters on aeration on/off time in an intermittent aeration membrane bioreactor for wastewater treatment. The membrane bioreactor has 5.5 L of effective working volume including a microfiber membrane. The influent wastewater contained 133mg/L of BOD, 195 mg/L COD, 98 mg/L SS, 30 mg/L total nitrogen, and 3.8 mg/L total phosphorous. Operational conditions related to aeration on/off time were 8.8 h HRT, 10 LMH flux, 10 L/min air flow, and 6300 mg/L MLSS. For 2 h/cycle, aeration on/off time was operated for 12 cycles in three variations: 60/60 min, 50/70 min (I), and 40/80 min. Suction on/off time was 10/2 min, 8/2 min, and 8/2 min, respectively, but also 50/70 min (II) when aeration on/off time was operated at 8300 mg/L MLSS. The BOD removal efficiency rate of this process was higher than 97% regardless of the aeration on/off time distribution. To get higher than 82% total nitrogen removal efficiency rate, aeration off time in the reactor needs to be more than 70 min. The specific denitrification rate was 2.68 mgNO 3-N/gMv/h at 40/80 min on/off aeration times, which was 2.6 times more than at 60/60 min, and 1.4 times more than at 50/70 min (I) for 6300 mg/L MLSS. The specific nitrification rate was 1.96 mgNH 4-N/gMv/h at on/off aeration times of 50/70 min, 1.4 times less than at 40/80 min, but was ineffective for nitrification. Microbial activity was affected only a little by variation in aeration on/off time, though oxygen demand was reduced by aeration off time and allowed microbial concentration to increased. EPS (extracellular polymeric substance) per unit of microorganisms increased with aeration off time.

Effects of irrigation sources on ammonia-oxidizing bacterial communities in a managed turf-covered aridisol

Ammonia-oxidizing bacteria (AOB) perform the rate-limiting step of nitrification, a key process in the global nitrogen cycle. In this study, chemical factors controlling AOB activity, diversity, and composition in a turfgrass-covered aridisol irrigated with groundwater, Colorado River water, or reclaimed wastewater were examined. Activity of AOB contributed an average of 96% of potential nitrification activity in four soils examined, and this activity correlated positively with ammonium concentration and negatively with salinity of the irrigation water. AOB abundance, as determined by quantitative polymerase chain reaction, also correlated positively with ammonium concentration in the irrigation water but negatively with soil salinity. Characterization of AOB communities by denaturing gradient gel electrophoresis showed the presence in every soil of AOB taxa, most commonly found in high-ammonia environments. The soil with the fewest years of management had the least diverse AOB population, compared to the other three soils, and much lower specific nitrification activity. This soil was irrigated with highly saline Colorado River water, which likely exerted acute negative effects on the activity of AOB. In summary, this study revealed that, although AOB activity and growth responded positively to ammonium availability in irrigation water, the salinity of the water and soil had strong negative effects on these aspects of the AOB community.

Analysis of the Activated Sludge Process in an MBR under Starvation Conditions

An aerobic membrane bioreactor (MBR) at complete biomass retention was studied over a period of time under starvation conditions. Kinetic parameters were determined in a no-feed batch test. The decay rate of activated sludge, kd = 0.05 d-1, was determined by tracking the decrease of MLSS. The ratio of MLVSS/MLSS was in the range 0.76– 0.85. The pH values were between 7.02 and 8.23. As a function of different initial concentrations of MLSS, specific nitrification rates, qN, decreased from 4.23 to 0.02 mg-N/(g MLVSS d) and specific biodegradation rates, qb, increased from 0.23 to 1.90 mg COD/(g MLVSS d). From experimental data the kinetic constants for respiration, which followed Monod kinetics, were determined as qO2max = 9.8 mg O2/(g MLVSS h), Kx = 2.9 g/dm3. Additionally, a linear correlation between MLSS and mean floc size was found to exist during the biodegradation process.

A technique to determine nitrogen removal rates in systems performing simultaneous nitrification and denitrification

This paper reports on a possible technique to determine specific nitrification and denitrification rates (SNR and SDNR) in an oxidation-reduction potential (ORP) controlled, intermittent aeration (IA) tank, in which simultaneous nitrification and denitrification (SND) occurred. In addition, SNRs in a three-stage Bardenpho aerobic zone and SDNRs in its anoxic zone were determined. This research was done at bench scale. The technique involves a steady-state run and two additional transient-state tests (created by either ammonia or nitrate shock loading). The rates obtained, using this technique, are the maximum rates possible in a continuous process under certain, improvised conditions. The technique is extremely flexible and generates data relating the rate to substrate concentration in one steady-state run. Data analysis was performed using the integral method; an excellent agreement between predicted and experimental data was found. Zero-order kinetics could describe nitrification in an ammonia concentration range of 1–30 mg/L and denitrification in a nitrate concentration range of 10–30 mg/L. The SNRs in the intermittently aerated, complete-mix (IACM) tank (0.39–1.69 mg g–1 h–1) were considerably lower than those in the 3-stage Bardenpho aerobic zone (3.4–3.81 mg g–1 h–1) due mainly to imposed dissolved oxygen limitations. The SDNRs in the IACM tank were in a range of 0.16–1.26 mg g–1 h–1, which were also considerably lower than that in the 3-stage Bardenpho anoxic zone (2.0–2.5 mg g–1 h–1). Key words: acetate, denitrification, intermittent aeration, kinetics, methanol, nitrification, ORP control, simultaneous nitrification and denitrification.