Terms Of Nitrogen Removal Research Articles

Coupling Iron Sludge Addition and Intermittent Aeration for Achieving Simultaneous Methanogenesis, Feammox, and Denitrification in a Single Reactor Treating Fish Sludge.

An integrated anaerobic digestion system for the simultaneous removal of carbon and nitrogen from fish sludge was developed by coupling iron sludge supplementation with intermittent aeration. In terms of nitrogen removal, Fe(III) in iron sludge could trigger Feammox reactions and intermittent aeration could drive the Fe(II)/Fe(III) cycle to sustain continuous ammonia removal. Mass balance analysis suggested that nitrate was the main product of Feammox, which was subsequently removed through heterotrophic denitrification. In terms of carbon removal, the Fe(III)-induced dissimilatory iron reduction (DIR) process significantly promoted fish sludge hydrolysis and provided more simple organics for methanogens and denitrifiers, but aeration showed a negative impact on methanogenesis. To promote nitrogen removal and avoid serious methanogenesis inhibition, different aeration intensities were studied. Results showed that compared with the control without aeration or iron sludge addition, aeration for 5 min every 3 days (150 mL/min) contributed to a 29.0% lower NH4+-N concentration and a 12.1% lower total chemical oxygen demand level on day 28, and the decline in methane yield was acceptable (only 13.5% lower). Simultaneous methanogenesis, Feammox, and denitrification in a single reactor treating fish sludge were achieved, which provides a simple and low-cost strategy for the treatment of organic wastewater.

Seasonal purification efficiency, greenhouse gas emissions and microbial community characteristics of a field-scale surface-flow constructed wetland treating agricultural runoff

Controlling nonpoint source pollution (NPSP) is very important for protecting the water environment, and surface-flow constructed wetlands (SFCWs) have been widely established to mitigate NPSP loads. In this study, the pollutant removal efficiencies, greenhouse gas (GHG) emissions, and chemical and microbial community properties of the sediment in a large-scale SFCW established beside a plateau lake (Qilu Lake) in southwestern China to treat agricultural runoff were evaluated over a year. The SFCW performed best in terms of nitrogen removal in autumn (average efficiency of 63.5% at influent concentrations of 9.3–35.4 mg L−1) and demonstrated comparable efficiency in other seasons (23.7–40.0%). The removal rates of total phosphorus (TP) and chemical oxygen demand (COD) were limited (18.6% and 12.4% at influent concentrations of 1.1 and 45.5 mg L−1 on average, respectively). The SFCW was a hotspot of CH4 emissions, with an average flux of 31.6 mg m−2·h−1; moreover, CH4 emissions contributed the most to the global warming potential (GWP) of the SFCW. Higher CH4 and N2O fluxes were detected in winter and in the front-end section of the SFCW with high pollutant concentrations, and plant presence increased CH4 emissions. Significant positive relationships between nutrient and heavy metal contents in the SFCW sediment were detected. The microbial community compositions were similar in autumn and winter, with Thiobacillus, Lysobacter, Acinetobacter and Pseudomonas dominating, and this distribution pattern was clearly distinct from those in spring and summer, with high proportions of Spirochaeta_2 and Denitratisoma. The microbial co-occurrence network in spring was more complex with stronger positive correlations than those in winter and autumn, while it was more stable in autumn with more keystone taxa. Optimization of the construction, operation and management of SFCWs treating NPSP in lake watersheds is necessary to promote their environmental benefits.

The role of magnetite (Fe3O4) particles for enhancing the performance and granulation of anammox

In this study, two lab-scale sequencing batch reactors each with an effective volume of 2.3 L were operated as C-AMX (no carrier addition) and M-AMX (magnetite carrier added) for 147 days with synthetic wastewater at an NLR range of 0.19–0.47 kgN/m3/d. The long-term effect of magnetite on the granulation and performance of anammox bacteria in terms of nitrogen removal and other essential parameters were confirmed. In phase I (1–24 days), M-AMX took approximately 12 days to obtain a nitrogen removal rate (NRR) above 80 % of the initial input nitrogen. Although free nitrous acid inhibited the reactor at a high concentration at the onset of phase III, the NRR of M-AMX recovered about 3.7 times faster than that of C-AMX. In addition, it was confirmed that the M-AMX granules had a dense and compact structure compared to C-AMX, and the presence of the carrier promoted the development of these resilient granules. While the measured microbial stress gradually increased in C-AMX reactor, a vice versa was observed in the M-AMX reactor as granulation proceeded. Compared to other alternative iron-based carrier particles, the stable crystal structure of magnetite as a carrier created a mechanism where filamentous bacteria groups were repelled from the granulation hence the microbial stress in the M-AMX in the final phase was 61.54 % lower than that in the C-AMX. The iron rich environment created by the magnetite addition led to Ignavibacteria, (a Feammox bacteria) increasing significantly in the M-AMX bioreactor.

Unraveling the capability of graphene nanosheets and γ-Fe2O3 nanoparticles to stimulate anammox granular sludge

In this study, we investigated the potentials of nanomaterials to enhance anaerobic ammonium oxidation (anammox) process, in terms of nitrogen removal, microbial enrichment, and activity of key enzymes. Graphene nanosheets (GNs) and γ-Fe2O3 nanoparticles (NPs) were selected due to their catalytic functions as conductive material and electron shuttles, respectively. The obtained results revealed that the optimum dosage of GNs (10 mg/L) boosted the nitrogen removal rate (NRR) by 46 ± 3.1% compared to the control, with maximum NH4+-N and NO2−-N removal of 86.5 ± 2.7% and 97.1 ± 0.5%, respectively. Moreover, hydrazine dehydrogenase (HDH) enzyme activity was augmented by 1.1-fold when using 10 mg/L GNs. The presence of GNs promoted the anammox granulation via enhancement of hydrophobic interaction of extracellular polymeric substances (EPS). Regarding the use of γ-Fe2O3 NPs, 100 mg/L dose increased NRR by 55 ± 3.8%; however, no contribution to HDH enzyme activity and a decrease in EPS compositions were observed. Given that the abiotic use of γ-Fe2O3 NPs further resulted in high adsorption efficiency (~92%), we conclude that the observed promotion due to γ-Fe2O3 NPs was mainly abiotic. Moreover, the 16S rRNA analysis revealed that the relative abundance of genus C. Jettenia (anammox related bacteria) increased from 11.9% to 12.3% when using 10 mg/L GNs, while declined to 8.3% at 100 mg/L γ-Fe2O3 NPs. Eventually, nanomaterials could stimulate the efficiency of anammox process, and this promotion and associated mechanism depend on their dose and composition.

Kinetic characteristics and N2O production of a heterotrophic nitrifying bacterium Pseudomonas putida YH capable of tolerating adverse environmental conditions

AbstractBACKGROUNDHeterotrophic nitrifying bacteria (HNB) have rapid growth rate, high activity and strong anti‐shock ability. These attributes are advantageous in engineering applications, yet the use of HNB is restricted by lack of clarity about the kinetics and metabolic mechanisms involved. Thus, nitrogen conversion characteristics, kinetics and N2O production of the HNB Pseudomonas putida YH were evaluated.RESULTSStrain YH exhibited superior heterotrophic nitrification‐aerobic denitrification (HNAD) ability in treating nitrogenous wastewater, with maximum removal rates of 10.07, 8.86 and 8.78 mg L−1 h−1 for NH4+–N, NO3−–N and NO2−–N, respectively. Mass balance analysis demonstrated that the removed TN was mainly due to bacterial assimilation (53–55%) and conversion into gaseous N2 (34–39%), instead of nitrification intermediate accumulation and N2O emission. In addition, the kinetics of nitrogen degradation and cellular growth of strain YH exactly conformed to the modified Gompertz equation and the Logistic equation, respectively. Moreover, strain YH showed excellent adaptability to variations of temperature, pH, C:N ratio and initial NH4+–N concentration in terms of nitrogen removal and N2O emission. The highest NH4+–N removal rate was obtained at pH 7.0, temperature 30 °C and C:N ratio of 15. Furthermore, the heterotrophic nitrification ability was just partially deteriorated after the addition of inhibitors, which further proved the multiple metabolic pathways of heterotrophic nitrification by strain YH.CONCLUSIONThe results demonstrated that strain YH exhibited excellent abilities of HNAD, N2O emission control and tolerance to adverse conditions, indicating that strain YH can be an effective candidate for treating nitrogenous wastewater without secondary pollution. © 2019 Society of Chemical Industry

Two-stage granular sludge partial nitritation/anammox process for the treatment of digestate from the anaerobic digestion of the organic fraction of municipal solid waste

The increasing amount of source separated organic fraction of municipal solid wastes (OFMSW) treated by anaerobic digestion for energy recovery requires the implementation of cost-efficient processes for the treatment of the produced digestate, especially in terms of nitrogen removal. The autotrophic nitrogen removal process, based on the coupling of two biological processes, partial nitritation (PN) and anammox (A), appears as a suitable solution due to important savings in operational costs compared to conventional treatment processes. However, its application could be hampered by the high salinity and inhibitory potential of this kind of digestate. In this contribution, two lab-scale granular sludge reactors performing the PN and anammox processes, respectively, were used to treat (opportunely diluted) real OFMSW digestate originating from full-scale biogas plants with the aim of assessing their treatment feasibility in a two-stage PN/A configuration. The PN process was implemented in an air-lift granular sludge reactor and was able to treat a nitrogen loading rate of about 1 g N L−1 d−1 at 30 ± 0.5 °C; moreover, its effluent was suitable for the subsequent anammox treatment, with an appropriate effluent NO2−/NH4+ ratio and marginal inhibiting effects. In the anammox granular sludge reactor, the anammox activity was affected by high salinity levels, nonetheless a stable reactor performance at a nitrogen removing rate of 0.83 ± 0.20 and 0.31 ± 0.04 g N L−1 d−1 at 35 ± 0.5 °C, were achieved when treating 50% and 30% diluted real wastewaters at a conductivity in the reactor of 9.1 and 11.2 mS cm−1, respectively.

Comparison of operational strategies for nitrogen removal in aerobic granule sludge sequential batch reactor (AGS-SBR): A model-based evaluation

The nitrogen removal in the aerobic granule sludge sequential batch reactor (AGS-SBR) could be operated as two modes: the simultaneous nitrification and denitrification (SND) mode and the denitrification-nitrification reaction in serials mode. It is not clear which mode deliver better nitrogen removal performance. In this study, the performance of the two operation modes and their control strategies were evaluated in three operation scenarios (A, B and C) based on mathematical model simulation. The control strategy for the SND in AGS-SBR involved the dissolved oxygen (DO) concentration control, in which the DO was manipulated to optimize nitrogen removal (scenario A). The denitrification-nitrification AGS-SBR was achieved by pre-denitrification, high DO nitrification and low DO SND configuration. In the operation scenario B, the duration of high DO nitrification was manipulated to produce optimized nitrogen removal. The duration for pre-denitrification, high DO nitrification and low DO SND were fixed for the operation scenario C, without using control strategies. The results indicated that operation scenario B and C produced better performance than scenario A in terms of nitrogen removal. The average TN removal rate was 84.4%, 95% and 92% for the scenario A, B and C respectively. The DO control strategy used in scenario A could not cope with the dynamic influent feeding condition. The pre-denitrification, high DO nitrification and low DO SND operation scenarios demonstrated satisfactory nitrogen removal even without using control strategies.

Formation and removal of dissolved organic nitrogen (DON) in membrane bioreactor and conventional activated sludge processes.

Dissolved organic nitrogen (DON) has become a growing concern due to its contribution to eutrophication and nitrogenous disinfection byproducts (N-DBPs) formation. However, information of DON in membrane bioreactors (MBRs) is very limited. In this study, occurrence, transformation and fate of DON in an MBR system were systematically investigated. MBR sludge showed a larger hydrolysis rate of particle organic nitrogen (PON) and also a higher transformation rate of DON to nitrate compared to conventional activated sludge (CAS). For long-term experiments, MBR achieved higher DON removal efficiency at low temperature than CAS; however, at high temperature, the effluent DON concentrations were almost the same in both systems. Batch tests on DON biodegradability showed that DON concentration increased and large molecular weight DON accumulated after 3-h aeration at low temperature, while DON concentration continuously decreased with the increase of aeration time at high temperature. The obtained results provide insights in DON removal in MBRs for meeting increasingly stringent regulations in terms of nitrogen removal.

Increased nitrogen removal in existing volumes at Sundet wastewater treatment plant, Växjö

Many wastewater treatment plants need to improve their nitrogen removal due to stricter requirements and increasing loads. This often means larger bioreactor volumes, which can be very expensive and is sometimes impossible if space is limited. Therefore, there is a need for compact hybrid solutions that can increase capacity within existing volumes. Two full-scale demonstration projects using moving bed biofilm reactor (MBBR) technology has proven to be an efficient way to treat nitrogen in existing volumes at Sundet wastewater treatment plant in Växjö. Increased nitrification and denitrification capacity in parts of the main stream were demonstrated through the Hybas™ process, a combination of MBBR and activated sludge using the integrated fixed-film activated sludge technology. The ANITA™ Mox process, using autotrophic N-removal through anaerobic ammonium oxidation (anammox), provided high nitrogen removal for the sludge liquor. Data collected on-site for over a year are analyzed and compared with the performance of conventional treatment systems. These two full-scale demonstration projects have been a successful learning experience in identifying and correcting both process and operational issues, which may not have arisen at pilot scale. The set objectives in terms of nitrogen removal were met for both processes and design modifications have been identified that will improve future operation at Sundet WWTP.

Improving total nitrogen removal in aeration basin retrofitted with entrapped biomass

This study presented a method to upgrade existing aeration tanks to remove total nitrogen (TN). Bioplates carrying entrapped biomass were installed in an aeration basin to create anoxic/anaerobic zones where denitrification can proceed. In a reactor that coupled bioplates containing entrapped biomass (equivalent to as high as 7,500 mg/L of biomass) and an activated sludge suspension (at mixed liquor suspended solids of 1,300-2,400 mg/L), nitrification efficiency exceeded 95% for an influent wastewater containing 21-54 mg/L of NH3-N. In all cases amended with alkalinity and with or without added methanol as an electron source, TN removal was between 60 and 70%. The results demonstrated anoxic/oxic or anaerobic/anoxic/oxic processes could be incorporated in a conventional aeration basin, requiring no substantial modifications of the vessel and operation, and thus providing improved treatment in terms of nitrogen removal in the conventional suspended-growth process.

Enhanced nitrogen removal in trickling filter plants

The Beaudesert Sewage Treatment Plant (STP), originally built in 1966 and augmented in 1977, is a typical biological trickling filter (TF) STP comprising primary sedimentation tanks (PSTs), TFs and humus tanks. The plant, despite not originally being designed for nitrogen removal, has been consistently achieving over 60% total nitrogen reduction and low effluent ammonium concentration of less than 5 mg NH3-N/L. Through the return of a NO3(-)-rich stream from the humus tanks to the PSTs and maintaining an adequate sludge age within the PSTs, the current plant is achieving a substantial degree of denitrification. Further enhanced denitrification has been achieved by raising the recycle flows and maintaining an adequate solids retention time (SRT) within the PSTs. This paper describes the approach to operating a TF plant to achieve a high degree of nitrification and denitrification. The effectiveness of this approach is demonstrated through the pilot plant trial. The results from the pilot trial demonstrate a significant improvement in nitrogen removal performance whilst maximising the asset life of the existing infrastructure. This shows great potential as a retrofit option for small and rural communities with pre-existing TFs that require improvements in terms of nitrogen removal.

Influence of temperature and pH on nitrogen removal in a series of maturation ponds treating anaerobic effluent

This paper presents an evaluation of the influence of pH and temperature on nitrogen removal in a series of three shallow maturation ponds serving as post-treatment of upflow anaerobic sludge blanket (UASB) reactor effluent (approximately 200 population equivalent). Monitoring was from January 2007 to May 2009. Throughout this period, the ponds maintained relatively stable operational conditions in terms of depth and hydraulic retention time, thus enabling the evaluation of the influence of variations in temperature and pH on the performance in terms of nitrogen removal. In general, as expected, the removal of nitrogen was more effective when the temperature and pH of the ponds were higher, implying that these variables are relevant in the removal of nitrogen. Due to the fact that these parameters are included in the prediction equations for effluent ammonia and total nitrogen found in traditional models from the literature, fitting of the models to the experimental data was investigated. The models gave acceptable fittings in the estimation of effluent concentrations of ammonia and total nitrogen from maturation ponds treating UASB reactor effluent.

Shall we upgrade one-dimensional secondary settler models used in WWTP simulators? – An assessment of model structure uncertainty and its propagation

In WWTP models, the accurate assessment of solids inventory in bioreactors equipped with solid-liquid separators, mostly described using one-dimensional (1-D) secondary settling tank (SST) models, is the most fundamental requirement of any calibration procedure. Scientific knowledge on characterising particulate organics in wastewater and on bacteria growth is well-established, whereas 1-D SST models and their impact on biomass concentration predictions are still poorly understood. A rigorous assessment of two 1-DSST models is thus presented: one based on hyperbolic (the widely used Takács-model) and one based on parabolic (the more recently presented Plósz-model) partial differential equations. The former model, using numerical approximation to yield realistic behaviour, is currently the most widely used by wastewater treatment process modellers. The latter is a convection-dispersion model that is solved in a numerically sound way. First, the explicit dispersion in the convection-dispersion model and the numerical dispersion for both SST models are calculated. Second, simulation results of effluent suspended solids concentration (XTSS,Eff), sludge recirculation stream (XTSS,RAS) and sludge blanket height (SBH) are used to demonstrate the distinct behaviour of the models. A thorough scenario analysis is carried out using SST feed flow rate, solids concentration, and overflow rate as degrees of freedom, spanning a broad loading spectrum. A comparison between the measurements and the simulation results demonstrates a considerably improved 1-D model realism using the convection-dispersion model in terms of SBH, XTSS,RAS and XTSS,Eff. Third, to assess the propagation of uncertainty derived from settler model structure to the biokinetic model, the impact of the SST model as sub-model in a plant-wide model on the general model performance is evaluated. A long-term simulation of a bulking event is conducted that spans temperature evolution throughout a summer/winter sequence. The model prediction in terms of nitrogen removal, solids inventory in the bioreactors and solids retention time as a function of the solids settling behaviour is investigated. It is found that the settler behaviour, simulated by the hyperbolic model, can introduce significant errors into the approximation of the solids retention time and thus solids inventory of the system. We demonstrate that these impacts can potentially cause deterioration of the predictive power of the biokinetic model, evidenced by an evaluation of the system's nitrogen removal efficiency. The convection-dispersion model exhibits superior behaviour, and the use of this type of model thus is highly recommended, especially bearing in mind future challenges, e.g., the explicit representation of uncertainty in WWTP models.

Effect of biomass concentration on the performance and modeling of nitrogen removal for membrane bioreactors

The study investigated the effect of biomass concentration on nitrogen removal in a membrane bioreactor by model evaluation of system performance. The steady state operation of a pilot membrane bioreactor fed with domestic sewage at a sludge age of 74 days and an average biomass concentration of 27,000 mg/L was monitored. The results were evaluated by calibration of a suspended growth model designed for this purpose and compared with those of an earlier experiment on the same system operated at a sludge age of 34 days, with a markedly lower biomass concentration. The membrane bioreactor always sustained a dissolved oxygen concentration of around 2 mgO2/L which could be explained by diffusion limitation of dissoved oxygen from the bulk liquid into the floc. Nitrogen removal was controlled and limited by nitrification which occurred only partially throughout the study. The oxidized nitrogen was always fully removed by means of simultaneous nitrification denitrification reducing the level of nitrate to a very low level so that the anoxic tank in front of the membrane bioreactor was totally useless in terms of nitrogen removal. Comparison of the results of the two experimental runs indicated that increasing the biomass concentration drastically changed the system behavior from denitrification limitation to nitrification limitation due to increased constraints on the mass transfer of dissolved oxygen. The selected model could be successfully calibrated for the model parameters by means of substantially higher oxygen half saturation constants for heterotrophs (KOH) and autotrophs (KOA) determined as 2.0 mgO2/L and 2.25 mgO2/L, respectively.

Full-Scale Application of the Alternating Oxic/Anoxic Process: An Overview

This article describes the results obtained in terms of nitrogen removal, energy savings, and waste sludge production upon application of an alternate cycle process and a remote control system in r...

SFGP 2007 - Two-Step Process of Thermo-Chemical Conversion of Wood Waste Contaminated by Aminoplast Resins

The aim of this study is to develop a two-steps process of thermal valorisation of wood waste containing urea-formaldehyde and melamine-formaldehyde resins such as wood board or laminated flooring. The first step of the process known as "refinement" is a low temperature pyrolysis between 250°C and 300°C which aims to remove nitrogen thermally. This step is studied by IRTF spectrometry. Ultimate analysis enables the assessment of the efficiency of the process in terms of nitrogen removal. It is shown that around 68 wt% of nitrogen can be removed during this first stage and that a 250°C treatment gives the best results in terms of energy recovery. The second step is a fast pyrolysis of the residue of the first step which aims to produce combustible gas. Three temperatures of pyrolysis are studied (800°C, 900°C and 1000°C) by GC-TCD analysis. It is shown that the temperature of the pyrolysis has an influence on the volume of gas produced and on its Low Heating Value. The best results are obtained with the 1000°C pyrolysis which produces a higher volume of gas and gives the best energetic efficiency. The residual char after fast pyrolysis step still contains energy and nitrogen. Its combustion would improve the energetic efficiency of the process but a conversion into an activated char has to be considered to improve the economic efficiency of such a type of waste disposal process.

Thermal removal of nitrogen species from wood waste containing urea formaldehyde and melamine formaldehyde resins

The removal of nitrogen from wood board waste through a low temperature pyrolysis (523–573 K) is investigated with two analytical methods. The kinetic study of the thermal behaviour of wood board and of its components (wood, UF and MF resins) shows the feasibility of removing thermally nitrogen from wood board waste. Indeed, the range of temperatures associated with the degradation of wood is different from the one obtained for the degradation of UF and MF resin. Isothermal conditions enable the determination of a kinetic model for degradation of wood board and of its components and demonstrate that the thermal behaviour of wood board is not the reflection of the sum of its components’ behaviour. FTIR analysis of gas products confirms the feasibility removing nitrogen thermally and enables the evaluation of the optimum treatment conditions (temperature/duration). Elementary analysis of the treated samples and study of their low heating value (LHV) enable to quantify the efficiency of the thermal treatment in terms of nitrogen removal and of energy recovery. Results show that around 70% of the initial nitrogen can be removed from the waste, and that the temperature of treatment (between 523 K and 573 K) does not influence the efficiency in terms of nitrogen removal. Nevertheless, the ratio Residual energy/Initial energy (between 76% and 90%) is improved with the lowest temperature of treatment.

Cotton-supported heterotrophic denitrification of nitrate-rich drinking water with a sand filtration post-treatment

The biological denitrification (BD) process represents an interesting solution to remove nitrate from water and as well as to close the natural nitrogen cycle. Potential applications are related to both groundwater denitrification and treatment of nitraterich effluents from reverse osmosis and ion-exchange processes. This paper presents the results obtained from a pilot-scale cotton-supported heterotrophic denitrification reactor (HDR) where cotton acts as both organic carbon source and supporting material for the growth of a denitrifier biofilm. A trickling sand filter (TSF) was inserted as post-treatment to remove TOC released by the HDR and to re-oxygenate the treated water. The system is evaluated for drinking water treatment. Nitrate removal efficiency of the HDR was over 90% for 85 mg/ℓ of inlet nitrate concentration which is a mean groundwater value in many EU countries. The process maintained its high performance up to 358 mg of daily nitrate inlet with a maximum specific volumetric ratio of 24.5 gN/m3·d. A first-order kinetic value was shown for sequential nitrate-nitrite and nitrite-nitrogen gas transformations. For that, the kinetic constants of 2.6 ℓ/d (K1) and 15.9 ℓ/d (K2) were assumed. The TSF provided additional nitrification-aerobic denitrification at a rate of 20.7gN/m3·d. Although both reactors showed high performances in terms of nitrogen removal, this plant configuration cannot assure an adequate TOC outlet concentration (>3 mg/ℓ).. Water SA Vol. 31 (2) 2005: pp.229-236

Sludge wash-out as strategy for Anammox process start-up

In this study sludge wash-out was evaluated as a strategy to start-up the Anammox process in order to establish it in a shorter period of time. Sludge from a domestic wastewater treatment plant (WTP) was used to seed two (RI and RII) anaerobic sequencing batch reactors (ASBR). During the start-up period RI was operated as a continuous stirred tank reactor (CSTR) using a dilution rate of 0.2 d −1, which promoted the sludge wash-out. After this period, the remaining sludge was retained in the reactor. The reactor RII was operated as an ASBR throughout the study period with a high cell retention. The performance of the two reactors in terms of nitrogen removal was compared over a period of 380 days. During the last RI operation phase the specific nitrogen removal rate increased exponentially, attaining values of 85 mg N/g TSS d. However, a rate of 190 mg N/g TSS d in the batch test under optimal conditions was achieved. The specific nitrogen removal rate remained almost constant for RII with a mean value of 6 mg N/g TSS d being observed during the operation period. The rate for the RII batch test was 20 mg N/g TSS d. These results confirm that the higher total suspended solids (TSS) in RII (reactor with high cell retention) was not effective in terms of N removal improvement. Anammox-like bacteria were found using fluorescence in situ hybridization (FISH) in reactor RI after 225 days and a new Anammox species was identified.

Baffled membrane bioreactor (BMBR) for efficient nutrient removal from municipal wastewater

Submerged membrane bioreactors (MBRs) are now widely used for various types of wastewater treatment. One drawback of submerged MBRs is the difficulty in removing nitrogen because intensive aeration is usually carried out in the tank and the MBRs must therefore be operated under aerobic conditions. In this study, the feasibility of treating municipal wastewater by a baffled membrane bioreactor (BMBR), particularly in terms of nitrogen removal, was examined. Simultaneous nitrification/denitrification in a single and small reaction tank was possible by inserting baffles into a normal submerged MBR as long as wastewater was fed in the appropriate way. To examine the applicability of the BMBR, pilot-scale experiments were carried out using real municipal wastewater. Although neither external carbon addition nor mixed liquor circulation was carried out in the operation of the BMBR, average removal rates of total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) reached 85%, 97% and 77%, respectively, with the hydraulic retention time (HRT) of 4.7 h. Permeability of the membrane could be maintained at a high level throughout the operation. It was found that denitrification was the limiting step in removal of nitrogen in the BMBR in this study. Various types of monitoring carried out in the BMBR also demonstrated the possibility of further improvements in its performance.