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Highlights • AnMBR needs further research to optimize process efficiency. • Modelling can provide insight into the factors playing a key role in AnMBR. • Process models still face a long path to adaptation in practice. • Better understanding of fouling mechanisms in AnMBRs is required. • Control strategies can be further optimized from mechanistic knowledge of fouling. Abstract The use of anaerobic membrane bioreactor technology (AnMBR) is rapidly expanding. However, depending on the application, AnMBR design and operation is not fully mature, and needs further research to optimize process efficiency and enhance applicability. This paper reviews state-of-the-art of AnMBR focusing on modelling and control aspects. Quantitative environmental and economic evaluation has demonstrated substantial advantages in application of AnMBR to domestic wastewater treatment, but detailed modelling is less mature. While anaerobic process modelling is generally mature, more work is needed on integrated models which include coupling between membrane performance (including fouling) and the biological process. This should include microbial factors, which are important to generation of specific foulants such as soluble and particulate inert organics. Mature and well-established control tools, including better feedback control strategies are also required for both the process, and for fouling control. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Created a nitritation-denitritation/denitrification-nitrification. • Spontaneous recovery of permeability can be achieved. • The aerobic granular sludge (AGS) was cultivated successfully. • The deploying of AOB and NOB was reached by the two-stage system. Abstract A novel pilot gravity-driven anoxic/oxic fed-batch membrane bioreactor (AFMBR) was developed to treat real domestic wastewater. In this process, the anoxic and oxic stages created favorable conditions for stable and continuous nitritation-denitritation/denitrification-nitrification links without adding external carbon source. Excellent removals of organic carbon/nitrogen (NH 4 +-N: 71–97%, COD: 78–96%, UV 254 : 70–95%, TN: 20–60%) and spontaneous permeability recovery were achieved simultaneously. It was assessed at micro levels by characterizing sludge particle morphologies, microbiota functional evolutions, fouling layer properties and energy consumptions. It was demonstrated that the aerobic granular sludge (AGS) was cultivated successfully. Notable differences of microbial diversity were observed in different regions of AFMBR. The SEM and AFM spectra suggested the loose cake layers can shed automatically due to low pressure and continue flushing. The energy consumption in AFMBR was around 0.042 kWh/m3, far lower than that of conventional MBR. Overall, the AFMBR has a potential on improvement of domestic wastewater treatment. [ABSTRACT FROM AUTHOR]

Aerobic granular sludge technology has been extensively studied over the past 20 years and is regarded as the upcoming new standard for biological treatment of domestic and industrial wastewaters. Aerobic granules (AG) are dense, compact, self-immobilized microbial aggregates that allow better sludge-water separation and thereby higher biomass concentrations in the bioreactor than conventional activated sludge aggregates. This brings potential practical advantages in terms of investment cost, energy consumption and footprint. Yet, despite the relevant advances regarding the process of AG formation, instability of AG during long-term operation is still seen as a major barrier for a broad practical application of this technology. This paper presents an up-to-date review of the literature focusing on AG stability, aiming to contribute to the identification of key factors for promoting long-term stability of AG and to a better understanding of the underlying mechanisms. Operational conditions leading to AG disintegration are described, including high organic loads, particulate substrates in the influent, toxic feed components, aerobic feeding and too short famine periods. These operational and influent wastewater composition conditions were shown to influence the micro-environment of AG, consequently affecting their stability. Granule stability is generally favored by the presence of a dense core, with microbial growth throughout the AG depth being a crucial intrinsic factor determining its structural integrity. Accordingly, possible practical solutions to improve granule long-term stability are described, namely through the promotion of minimal substrate concentration gradients and control of microbial growth rates within AG, including anaerobic, plug-flow feeding and specific sludge removal strategies. [ABSTRACT FROM AUTHOR]

Objective of the present study was to simultaneously biodegrade synthetic petroleum refinery wastewater containing phenol (750 mg/L), sulphide (750 mg/L), hydrocarbon (as emulsified diesel of 300 mg/L), ammonia-nitrogen (350 mg/L) at pH >9 in anoxic–aerobic sequential moving bed reactors. The optimum mixing speed of anoxic reactor was observed at 20 rpm and beyond that, removal rate remained constant. In anoxic reactor the minimum hydraulic retention time was observed to be 2 days for complete removal of sulphide, 40–50% removal of phenol and total hydrocarbons and 52% of sulphur recovery. The optimum HRT of aerobic moving bed reactor was observed as 16 h (total HRT of 64 h for anoxic and aerobic reactors) for complete removals of phenol, total hydrocarbons, COD (chemical oxygen demand) and ammonia-nitrogen with nitrification. [ABSTRACT FROM PUBLISHER]

Influence of aeration rate and COD:N:P (C:N:P) ratio on the performance of an upflow partially aerated submerged fixed film (UP/ASFF) bioreactor for simultaneous carbon and nutrient removal from highstrength nitrogen wastewater was investigated during 6 months. Airflow rates at three levels of 1.5, 3, and 4.5 L/min and C:N:P ratios at four levels of 450:300:10, 450:150:10, 450:100:10, and 450:75:10 were selected as the two main input factors. All experiments were performed at constant chemical oxygen demand (COD), phosphorus (P) and hydraulic residence time of 450 mg COD/L, 10 mg PO3-/4 P/L and 7.3 h, respectively. The results showed when the airflow rate increased from 1.5 to 4.5 L/ min, complete COD removal was achieved. At an airflow rate of 4.5 L/min, total nitrogen removal reached a maximum value of 75% for the C:N:P ratio of 450:75:10. A maximum value of 54% for total phosphorus removal, however, was obtained at an airflow rate of 3 L/min for the C:N:P ratio of 450:75:10. Analysis of variance for the obtained data revealed that aeration rate and nitrogen concentration had more impact on phosphorus removal than COD and nitrogen removal. The study demonstrated that the UP/ASFF system has considerable potential for use in simultaneous removal of carbon and nutrients for high-strength nitrogen wastewater. [ABSTRACT FROM AUTHOR]

The amount of nanoparticles released from industrial and consumer products has increased rapidly in the last decade. These products may enter landfills directly or indirectly after the end of their useful life. In order to determine the impact of TiO[sub 2] and Ag nanoparticles on aerobic landfilling processes, municipal solid waste was loaded to three pilot-scale aerobic landfill bioreactors (80 cm diameter and 350 cm height) and exposed to TiO[sub 2] (AT) and Ag (AA) nanoparticles at total concentrations of 100 mg kg[sup -1] of solid waste. Aerobic landfill bioreactors were operated under the conditions about 0.03 L min[sup -1] kg[sup -1] aeration rate for 250 days, during which the leachate, solid waste, and gas characteristics were measured. The results indicate that there was no significant difference in the leachate characteristics, gas constituents, solid quality parameters, and temperature variations, which are the most important indicators of landfill operations, and overall aerobic degradation performance between the reactors containing TiO[sub 2] and Ag nanoparticles, and control (AC) reactor. The data also indicate that the pH levels, ionic strength, and the complex formation capacity of nanoparticles with Clions can reduce the toxicity effects of nanoparticles on aerobic degradation processes. The results suggest that TiO[sub 2] and Ag nanoparticles at concentrations of 100 mg kg[sup -1] of solid waste do not have significant impacts on aerobic biological processes and waste management systems. [ABSTRACT FROM AUTHOR]

The effect of air flow rate (AFR), pretreatment time, and temperature on a microaerobic pretreatment were determined, including its effect on CH 4 generation. For this, four AFR (0.1, 0.3, 0.5 and 1 vvm), three temperatures (20, 25 and 35 °C) and three aeration times (24, 48 and 60 h) were evaluated in 1-L and 5-L bioreactors. The effect on CH 4 production was evaluated in 280-mL bioreactors, using previously aerated sewage sludge. It was found that the micro-aerobic pretreatment improves the hydrolytic process, with an increase of proteins, total sugars, soluble chemical oxygen demand (COD), and a greater removal of volatile suspended solids (VSS) compared to a system without aeration. It was determined that an AFR = 0.3 vvm, 48 h of aeration time, and a temperature of 35 °C were the best operational conditions for increasing hydrolysis rate. VSS removal under the aerobic pretreatment follows first order kinetics. Finally, the aeration pretreatment allows a 211% increase of methane generation compared to a process without pretreatment, improving also total COD and VSS removal. [ABSTRACT FROM AUTHOR]

Effective domestic wastewater treatment is among our primary defenses against the dissemination of infectious waterborne disease. However, reducing the amount of energy used in treatment processes has become essential for the future. One low-energy treatment option is anaerobic-aerobic sequence (AAS) bioreactors, which use an anaerobic pretreatment step (e.g., anaerobic hybrid reactors) to reduce carbon levels, followed by some form of aerobic treatment. Although AAS is common in warm climates, it is not known how its compares to other treatment options relative to disease transmission, including its influence on antibiotic resistance (AR) in treated effluents. Here, we used metagenomic approaches to contrast the fate of antibiotic-resistant genes (ARG) in anaerobic, aerobic, and AAS bioreactors treating domestic wastewater. Five reactor configurations were monitored for 6 months, and treatment performance, energy use, and ARG abundance and diversity were compared in influents and effluents. AAS and aerobic reactors were superior to anaerobic units in reducing ARG-like sequence abundances, with effluent ARG levels of 29, 34, and 74 ppm (198 ppm influent), respectively. AAS and aerobic systems especially reduced aminoglycoside, tetracycline, and β-lactam ARG levels relative to anaerobic units, although 63 persistent ARG subtypes were detected in effluents from all systems (of 234 assessed). Sulfonamide and chloramphenicol ARG levels were largely unaffected by treatment, whereas a broad shift from target-specific ARGs to ARGs associated with multi-drug resistance was seen across influents and effluents. AAS reactors show promise for future applications because they can reduce more ARGs for less energy (32% less energy here), but all three treatment options have limitations and need further study. [ABSTRACT FROM AUTHOR]

The paper concerns an aerobic microbiological process occurring in a bubble tank bioreactor. If the process is inhibited by a carbonaceous substrate, then the steady states characteristics obtained using models without biofilm indicates a danger of irreversible washout of the biomass. It was shown that taking into account the biofilm immobilized on bioreactor's walls and proper design of the bioreactor can lead to disappearance of the region of the multiple steady-states, i.e. to disappearance of the turning point at the steady state branches. Therefore, the operation of the bioreactor is safe in a wide range of feed flow rates, even those leading to the washout of the biomass from the liquid phase. This property was called apparent elimination of inhibition phenomenon. [ABSTRACT FROM AUTHOR]

Abstract: Aerobic operation of an immersed hollow fibre membrane bioreactor, treating municipal wastewater supplemented with molasses solution, has been studied across mixed liquor suspended solids (MLSS) concentrations between 8 and 32 g L−1, the higher concentrations being normally associated with thickening operations. Only a marginal loss in membrane permeability was noted between 8 and 18 g L−1 when operation was conducted without clogging. The sustainable operational flux attainable above 18 g L−1 was highly dependent upon both the MLSS concentration and the state of the membrane. A temperature-corrected flux of 28 L m−2 h−1 (LMH) was sustained for 18 h at an MLSS of 8 g L−1 using membranes close to initial their virgin-state permeability. This value decreased to around 14 LMH at 20 g L−1 and 5 LMH at 32 g L−1 MLSS for an aged membrane whose permeability had been recovered following clogging. Below the threshold flux operation without significant clogging was possible, such that the membrane permeability could be recovered with a chemically enhanced backflush (CEB). Above this flux clogging took place at a rate of around 7–14 g solids per m2 membrane per m3 permeate volume passed irrespective of the MLSS concentration. The permeability of the unclogged membrane was depressed and could not be recovered using a standard CEB, indicative of irrecoverable pore clogging. The outcomes corroborated previously reported observations concerning the deleterious long-term impacts of clogging, and confirmed the critical importance of operation at a sustainable flux value. [Copyright &y& Elsevier]

Highlights: [•] Aerobic fibrous-bed bioreactor using bagasse as immobilized carrier was designed. [•] The time of immobilization fermentation is 48h while free-cell 72h. [•] PGA yield of 71.21g/L was achieved by repeated fed-batch fermentation in APFB. [•] We evaluated the stability of the APFB system. [•] The changes in the cells of free and immobilized cell fermentation were compared. [ABSTRACT FROM AUTHOR]

Abstract: A granular sludge sequencing batch reactor (SBR) was operated for 340 days for treating a synthetic wastewater containing fluoroquinolones (FQs), namely ofloxacin, norfloxacin and ciprofloxacin. The SBR was intermittently fed with FQs, at concentrations of 9 and 32 μM. No evidence of FQ biodegradation was observed but the pharmaceutical compounds adsorbed to the aerobic granular sludge, being gradually released into the medium in successive cycles after stopping the FQ feeding. Overall COD removal was not affected during the shock loadings. Activity of ammonia oxidizing bacteria and nitrite oxidizing bacteria did not seem to be inhibited by the presence of FQs (maximum of 0.03 and 0.01 mM for ammonium and nitrite in the effluent, respectively). However, during the FQs feeding, nitrate accumulation up to 1.7 mM was observed at the effluent suggesting that denitrification was inhibited. The activity of phosphate accumulating organisms was affected, as indicated by the decrease of P removal capacity during the aerobic phase. Exposure to the FQs also promoted disintegration of the granules leading to an increase of the effluent solid content, nevertheless the solid content at the bioreactor effluent returned to normal levels within ca. 1 month after removing the FQs in the feed allowing recovery of the bedvolume. Denaturing gradient gel electrophoresis revealed a dynamic bacterial community with gradual changes due to FQs exposure. Bacterial isolates retrieved from the granules predominantly belonged to α- and γ-branch of the Proteobacteria phylum. The capacity of the system to return to its initial conditions after withdrawal of the FQ compounds in the inlet stream, reinforced its robustness to deal with wastewaters containing organic pollutants. [Copyright &y& Elsevier]

An anaerobic membrane bioreactor and aerobic granulation technologies were tested at laboratory scale to treat winery wastewater, which is characterised by a high and variable biodegradable organic load. Both technologies have already been tested for alcohol fermentation wastewaters, but there is a lack of data relating to their application to winery wastewater treatment. The anaerobic membrane bioreactor, with an external microfiltration module, was started up for 230 days, achieving a biogas production of up to 0.35 L CH4 L-1 d-1 when 1.5 kg COD m-3 d-1 was applied. Average flux was 10.5 L m-2 h-1 (LMH), obtaining a treated effluent free of suspended solids and a chemical oxygen demand (COD) concentration lower than 100 mg COD L-1. In contrast, the aerobic granular sequencing batch reactor coped with 15 kg COD m-3 d-1, but effluent quality was slightly worse. Aerobic granulation was identified as a suitable technique to treat this kind of wastewater due to excellent settleability, high biomass retention and a good ability to handle high organic loads and seasonal fluctuations. However, energy generation from anaerobic digestion plays an important role, favouring anaerobic membrane bioreactor application, although it was observed to be sensitive to sudden load fluctuations, which led to a thorough pH control and alkali addition. [ABSTRACT FROM AUTHOR]

Terephthalic acid (TA) and ethylene glycol (EG) are the main pollutants in polyester fabric alkalipeeling process wastewater (PAP-wastewater). The biodegradability of TA is crucial to the deep treatment of PAP-wastewater. Batch and continuous experiments were adopted to study the biodegradation of TA in synthetic wastewater. In anoxic batch experiments TA began to degrade gradually after EG was depleted completely. However, in aerobic batch experiments the biodegradation curves of TA in the presence of EG were almost identical to those of TA in the absence of EG. The combined process of anoxic hydrolysis-acidification bioreactor (HABR) and aerobic hybrid membrane bioreactor (HMBR) was employed to treat synthetic PAP-wastewater in continuous experiments. When TA was fed as sole substrate, about 6.1% was removed in the anoxic HABR and 92.1% was biodegraded in the aerobic HMBR. When TA and EG were fed as substrate, only 1.9% of TA was biodegraded in the anoxic HABR and 96.6% of TA was removed in the aerobic HMBR. By contrast, most EG was removed in the anoxic HABR. The experimental results revealed that the combined process of anoxic HABR and aerobic HMBR was an attractive alternative for the treatment of PAP-wastewater and other similar wastewater. [ABSTRACT FROM AUTHOR]

Bisphenol-A (BPA) biodegradation was studied in a membrane bioreactor under aerobic conditions. The effects of the initial BPA concentration and initial chemical oxygen demand (COD) concentration on BPA biodegradation were investigated. The degradation process followed a first-order kinetic (more than 98% of BPA was removed) with a kinetic rate constant of 1.134 h-1 using an initial BPA concentration of 1.0 mg L-1. The kinetic rate constant decreased to 0.611 h-1 when the initial BPA concentration increased to 5.0 mg L-1. The initial COD concentration (400 and 2,000 mg L-1) did not affect the biodegradation kinetic of BPA. [ABSTRACT FROM AUTHOR]

Abstract: Aerobic biological treatment was conducted for the treatment of high strength olive oil mill wastewater (OMW). Two different approaches were used for kinetic modeling of OMW biodegradation. TOC removal and CO2–C evolution were monitored in an open and a closed bioreactor systems, respectively. Gompertz, Refractory organics plus first-order (RFO) and Chen–Hashimoto equations were applied to estimate the kinetic parameters by using the data from bioreactors. Furthermore, change in oxidation stage of carbon was monitored and temperature dependency of OMW biodegradation was investigated based on activation energy. At room temperature, 64% of TOC was removed in the open bioreactor while cumulative CO2–C evolution was 6.32 g L−1 in closed the bioreactor. Higher biodegradation efficiency and kinetic parameters were obtained at 25 °C rather than 10 °C. Gompertz and RFO equations provided better fitting with CO2–C and TOC data, respectively. Experimental and kinetic estimations indicated that OMW constituted of approximately 30% refractory organics. The comparison of two different modeling approaches showed that kinetic modeling based on CO2–C provided better correlation with the experimental data. Temperature coefficient indicated that biological degradation of OMW is slightly dependent on temperature. [Copyright &y& Elsevier]

Highlights: [•] Aerobic granular sludge technology has the potential in biological wastewater treatment. [•] High 4-ClA shock could cause the disintegration of aerobic granular sludge. [•] The granular stability is affected by the sludge EPS component and microbial community. [•] The decrease of specific protein contents in the sludge EPS is not good for granular stability. [ABSTRACT FROM AUTHOR]

Abstract: The selective sludge discharge mode was studied in the aerobic granular sludge reactor for improving the long-term stability of aerobic granular sludge process. Results showed that the nitrogen removal performance was obviously improved with the preliminary granulation of the bioreactor at sludge settling time of 1min after 15days. After the formation of fine granular sludge, 5–10% volume of the total granular sludge was discharged for the sludge retention time (SRT) controlling, and the removal efficiencies of and TN reached 95.9±2.0% and 75.3±3.0% at the SRTTotal of 5.3±0.4days, SRTGranules of 9.9±0.9days and SRTFlocs of 2.7±0.5days, respectively. The granular rate and average granular diameter of the bioreactor were stabilized at 80±5.0% and 2.3±0.3mm, respectively. The results demonstrated that a long SRT of granular sludge leads easily into the deterioration of aerobic granule, and an appropriate selective sludge discharge mode favors the stability of aerobic granular sludge process via the discharge of proportional aging granular sludge and retention of enough new-born flocs. [Copyright &y& Elsevier]

Abstract: Interest in increasing the sustainability of water management is leading to a reevaluation of domestic wastewater (DWW) treatment practices. A central goal is to reduce energy demands and environmental impacts while recovering resources. Anaerobic membrane bioreactors (AnMBRs) have the ability to produce a similar quality effluent to aerobic treatment, while generating useful energy and producing substantially less residuals. This review focuses on operational considerations that require further research to allow implementation of AnMBR DWW treatment. Specific topics include membrane fouling, the lower limits of hydraulic retention time and temperature allowing for adequate treatment, complications with methane recovery, and nutrient removal options. Based on the current literature, future research efforts should focus on increasing the likelihood of net energy recovery through advancements in fouling control and development of efficient methods for dissolved methane recovery. Furthermore, assessing the sustainability of AnMBR treatment requires establishment of a quantitative environmental and economic evaluation framework. [Copyright &y& Elsevier]

Abstract: This paper describes the results of laboratory experiments using a thermophilic aerobic MBR (TMBR) at 50°C. An innovative use of submerged flat-sheet MBR modules to treat circuit wastewater from the paper industry was studied. Two experiments were conducted with a flux of 8–13L/m2/h without chemical membrane cleaning. COD and BOD5 elimination rates were 83% and 99%, respectively. Calcium was reduced from 110 to 180mg/L in the inflow to 35–60mg/L in the permeate. However, only negligible membrane scaling occurred. The observed sludge yield was very low and amounted to 0.07–0.29gMLSS/g CODeliminated. Consequently, the nutrient supply of ammonia and phosphate can be lower compared to a mesophilic process. Molecular-biological FISH analysis revealed a likewise high diversity of microorganisms in the TMBR compared to the mesophilic sludge used for start-up. Furthermore, ammonia-oxidising bacteria were detected at thermophilic operation. [Copyright &y& Elsevier]

Abstract: A two-stage UASB and 2-stage BAF series bioreactor was used for treating the microcrystalline cellulose (MCC) wastewater. The treating efficiency, dominant microbes, eubacterial and archaebacterial composition and cel5A, cel6B and bglC gene expression levels were examined using combined PCR-DGGE and real-time PCR technology. The results showed that under three MCC loads (1000, 2000 and 3000mgL−1), the total MCC degradation efficiency of the UASB-BAF system was 82.0%, 83.5% and 70.5%, respectively. In different MCC load cases, the first stage UASB and BAF formed an approximate full-value cellulase system where cellulolytic microorganisms were the dominant flora, while the second stage UASB and BAF formed a low-value cellulase system where non-cellulolytic microorganisms were the dominant flora. Eubacteria were dominant in every UASB-BAF unit. The rate-limiting enzyme gene for MCC degradation in every unit was cel6B. These results will support the development of high efficiency bio-reactors for the degradation of MCC. [Copyright &y& Elsevier]

Aerobic thermophilic treatment (ATT) of cattle slurry and industrial food waste (whey and jam) was conducted semi-continuously, with the aim of developing the ATT process. We could improve the final products in terms of hygiene, environmental effects and heat production. In addition we tried to solve the foaming problem mechanically. The trial was done by using a farm-scale bioreactor with a total volume of 12 m3 and a theoretical retention time of some 15 days. Temperature increased to 55 °C at the end of the trial. The process could be an efficient method for the control of foam. Using the waste food (whey and jam) improved the process. [ABSTRACT FROM AUTHOR]

Aerobic biological treatment of digested sludge was studied in a continuously operated laboratory set-up. An aerated reactor was filled with thermophilically digested sludge from the Moscow wastewater treatment plant and inoculated with special activated sludge. It was then operated at the chemostat mode at different flow rates. Processes of nitrification and denitrification, as well as dephosphatation, occurred simultaneously during biological aerobic treatment of thermophilically digested sludge. Under optimal conditions, organic matter degradation was 9.6%, the concentrations of ammonium nitrogen and phosphate decreased by 89 and 83%, respectively, while COD decreased by 12%. Dewaterability of digested sludge improved significantly. The processes were found to depend on hydraulic retention time, oxygen regime, and temperature. The optimal conditions were as follows: hydraulic retention time 3-4 days, temperature 30-35 °C, dissolved oxygen levels 0.2- 0.5 mg/L at continuous aeration or 0.7-1 mg/L at intermittent aeration. Based on these findings, we propose a new combined technology of wastewater sludge treatment. The technology combines two stages: anaerobic digestion followed by aerobic biological treatment of digested sludge. The proposed technology makes it possible to degrade the sludge with conversion of ∼45% volatile suspended solids to biogas, to improve nitrogen and phosphorus removal in reject water from sludge treatment units, and to achieve removal of malodorous substances after 8-9 days of anaerobic- aerobic sludge treatment. [ABSTRACT FROM AUTHOR]

Abstract: N-Nitrosodimethylamine (NDMA) is a suspected human carcinogen that has recently been detected in wastewater, groundwater and drinking water. Treatment of this compound to low part-per-trillion (ng/L) concentrations is required to mitigate cancer risk. Current treatment generally entails UV irradiation, which while effective, is also expensive. The objective of this research was to explore potential bioremediation strategies as alternatives for treating NDMA to ng/L concentrations. Batch studies revealed that the propanotroph Rhodococcus ruber ENV425 was capable of metabolizing NDMA from 8 μg/L to <2 ng/L after growth on propane, and that the strain produced metabolites that do not pose a significant risk at the concentrations generated (). A laboratory-scale membrane bioreactor (MBR) was subsequently constructed to evaluate the potential for long-term ex situ treatment of NDMA. The MBR was seeded with ENV425 and received propane as the primary growth substrate and oxygen as an electron acceptor. At an average influent NDMA concentration of 7.4 μg/L and a 28.5 h hydraulic residence time, the reactor effluent concentration was 3.0 ± 2.3 ng/L (>99.95% removal) over more than 70 days of operation. The addition of trichloroethene (TCE) to the reactor resulted in a significant increase in effluent NDMA concentrations, most likely due to cell toxicity from TCE-epoxide produced during its cometabolic oxidation by ENV425. The data suggest that an MBR system can be a viable treatment option for NDMA in groundwater provided that high concentrations of TCE are not present. [ABSTRACT FROM AUTHOR]

Abstract: The study on the integrated COD and nitrogen removal from domestic wastewater was carried out in a micro-aerobic granular sludge reactor. The influences of oxygen flux, hydraulic retention time (HRT), biomass concentration and sludge loading were investigated. The reactor showed stable and effective COD removal all through the experiment. Nevertheless, nitrogen removal much depended on the operation mode. Under the optimal condition, i.e. oxygen influx, HRT, MLSS and sludge loading rate (SLR) were 0.20g/L·d, 8h, 11∼16g/L and below 0.10kgCOD/kgMLSS·d, respectively, total nitrogen (TN) removal efficiency achieved 82%, and the concentration of NH4+-N and TN in effluent were 5.5mg/L and 8.2mg/L, respectively. Besides, deteriorated sludge settling and filamentous granules were found as SLR increased to 0.18kgCOD/kgMLSS·d. [Copyright &y& Elsevier]

With the current need for more efficient and reliable processes for municipal and industrial wastewaters treatment, membrane bioreactor (MBR) technology has received considerable attention. After just a couple of decades of existence, MBR can now be considered as an established wastewater treatment system, competing directly with conventional processes like activated sludge treatment plant. However, MBR processes still suffer from major drawbacks, including high operational costs due to the use of anti-fouling strategies applied to the system to maintain sustainable filtration conditions. Moreover, this specific use of membranes has not reached full maturity yet, as MBR suppliers and users still lack experience regarding the long-term performances of the system. Still, major improvements of the MBR design and operation have been witnessed over the recent years, making MBR an option of choice for wastewater treatment and reuse. This mini-review reports recent developments and current research trends in the field. [ABSTRACT FROM AUTHOR]

Abstract: Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently treat high-strength and toxic wastewaters. The aerobic granules cultivated with low ammonium and phosphates lost structural stability within 3days in continuous-flow reactors. Conversely, stable aerobic granules were cultivated in substrate with high levels of ammonium salts that could stably exist for 216days in continuous-flow reactors with or without submerged membrane. The scanning electron microscopy, energy dispersive spectroscopy microanalysis and the confocal laser scanning microscopy imaging detected large amounts of calcium and iron precipitates in granule interiors. The Visual MINTEQ version 2.61 calculation showed that the phosphates and hydroxides were the main species in the precipitate. [Copyright &y& Elsevier]

Abstract: Impact of long solids residence times (SRTs) on nutrient removal was investigated using a submerged plate-frame membrane bioreactor with anaerobic and anoxic tanks. The system was operated at 10, 25, 50 and 75 days SRTs with hydraulic retention times (HRTs) of 2 h each for the anaerobic and anoxic tanks and 8 h for the oxic tank. Recirculation of oxic tank mixed liquor into the anaerobic tank and permeate into the anoxic tank were fixed at 100% each of the influent flow. For all SRTs, percent removals of soluble chemical oxygen demand were more than 93% and nitrification was more than 98.5% but total nitrogen percent removal seemed to peak at 81% at 50 days SRT while total phosphorus (TP) percent removal showed a deterioration from approximately 80% at 50 days SRT to 60% at 75 days SRT. Before calibrating the Biowin® model to the experimental data, a sensitivity analysis of the model was conducted which indicated that heterotrophic anoxic yield, anaerobic hydrolysis factors of heterotrophs, heterotrophic hydrolysis, oxic endogenous decay rate for heterotrophs and oxic endogenous decay rate of PAOs had the most impact on predicted effluent TP concentration. The final values of kinetic parameters obtained in the calibration seemed to imply that nitrogen and phosphorus removal increased with SRT due to an increase in anoxic and anaerobic hydrolysis factors up to 50 days SRT but beyond that removal of phosphorus deteriorated due to high oxic endogenous decay rates. This indirectly imply that the decrease in phosphorus removal at 75 days SRT may be due to an increase in lysis of microbial cells at high SRTs along with the low food/microorganisms ratio as a result of high suspended solids in the oxic tank. Several polynomial correlations relating the various calibrated kinetic parameters with SRTs were derived. The Biowin® model and the kinetic parameters predicted by the polynomial correlations were verified and found to predict well the effluent water quality of the MBR at 35 days SRT. [Copyright &y& Elsevier]

Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently treat high-strength and toxic wastewaters. Aerobic granules disintegrate under high organic loading rates (OLR). This study cultivated aerobic granules using acetate as the sole carbon and energy source in three identical sequencing batch reactors operated under OLR of 9–21.3 kg chemical oxygen demand (COD) m−3 day−1. The cultivated granules removed 94–96% of fed COD at OLR up to 9–19.5 kg COD m−3 day−1, and disintegrated at OLR of 21.3 kg COD m−3 day−1. Most tested isolates did not grow in the medium at >3,000 mg COD l−1; additionally, these strains lost capability for auto-aggregation and protein or polysaccharide productivity. This critical COD regime correlates strongly with the OLR range in which granules started disintegrating. Reduced protein quantity secreted by isolates was associated with the noted poor granule integrity under high OLR. This work identified a potential cause of biological nature for aerobic granules breakdown. [ABSTRACT FROM AUTHOR]

Abstract: Aerobic sludge granulation is an attractive new technology for biological wastewater treatment. However, the instability of aerobic granules caused by fungal growth is still one of the main problems encountered in granular bioreactors. In this study, laboratory experiments were conducted to investigate the fate and transformation of aerobic granules under different organic loading conditions. Bacterial granules (2–3mm) in a poor condition with fungi-like black filamentous growth were seeded into two 1L batch reactors. After more than 100d of cultivation, the small seed granules in the two reactors had grown into two different types of large granules (>20mm) with different and unique morphological features. In reactor R1 with a high organic loading rate of 2.0g COD L−1 d−1, the black filaments mostly disappeared from the granules, and the dominance of rod-shaped bacteria was recovered. In contrast, at a low loading of 0.5g COD L−1 d−1 in reactor R2, the filaments eventually became dominant in the black fungal granules. The bacteria in R1 granules had a unique web-like structure with large pores of a few hundred μm in size, which would allow for effective substrate and oxygen transport into the interior of the granules. DNA-based molecular analysis indicated the evolution of the bacterial population in R1 and that of the eukaryal community in R2. The experimental results suggest that a high loading rate can be an effective means of helping to control fungal bloom, recover bacterial domination and restore the stability of aerobic granules that suffer from fungal contamination. [Copyright &y& Elsevier]

Abstract: The feasibility of a new flowchart describing simultaneous hydrogen sulfide removal from biogas and nitrogen removal from wastewater was investigated. It took 30days for the reactor inoculated with aerobic sludge to attain a removal rate of 60% for H2S and NO x –N simultaneously. It took 34 and 48days to attain the same removal rate for the reactor without inoculated sludge and the reactor inoculated with anaerobic sludge respectively. The reactor without inoculated sludge still operated successfully, despite requiring a slightly longer startup time. The packing material was capable of enhancing the removal efficiency of reactors. Based on the concentration of NO x –N and H2S in the effluent, the loading rate and the ability of the system to resist shock loading, the performance of the reactor filled with hollow plastic balls was greater than that of the reactor filled with elastic packing and the reactor filled with Pall rings. [Copyright &y& Elsevier]

Abstract: The effects of phenol, 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and 1,2,4-trichlorobenzene (1,2,4-TCB) on the biodegradation kinetics of the conventional activated sludge system (CASS) and the selector activated sludge system (SASS) were investigated. Experiments were carried out using a respirometric method on unacclimated biomass from two lab-scale systems that were operated with the sludge age of 8days. Toxicity of the test compounds for both reactors were arranged according to EC50 (effective concentration) values in order as: 1,2,4-TCB>2,4-DCP>2-CP>phenol. All selected test compounds induced higher inhibition effect in the CASS. The SASS appeared to reduce inhibition effect in comparison to the CASS, by 21.36%, 66.95%, 64.37% and 33.33% for phenol, 2-CP, 2,4-DCP and 1,2,4-TCB, respectively. Consequently, the SASS may be recommended as a promising configuration alternative for the waste streams containing toxic compounds. [Copyright &y& Elsevier]

Abstract: Anaerobic–aerobic systems have been remarkably employed in industrial and municipal wastewater treatment for many years. While previously most treatment of wastewaters have been carried out in conventional anaerobic–aerobic treatment plants, in recent years, high rate anaerobic–aerobic bioreactors have been increasingly employed for wastewaters with high chemical oxygen demand (COD). This paper provides a review of the various types of high rate anaerobic–aerobic water treatment techniques currently available including high rate bioreactors and integrated anaerobic–aerobic bioreactors. The integrated bioreactors are classified into four types, which are (i) integrated bioreactors with physical separation of anaerobic–aerobic zone, (ii) integrated bioreactors without physical separation of anaerobic–aerobic zone, (iii) anaerobic–aerobic Sequencing Batch Reactors (SBR), and (iv) combined anaerobic–aerobic culture system. The integration of aerobic and anaerobic degradation pathways in a single bioreactor is capable of enhancing the overall degradation efficiency. The merits of different integrated anaerobic–aerobic bioreactors are highlighted and comparison made to identify possible future areas of research to fully utilize these methods of wastewater treatment. The comparison demonstrates that using an integrated bioreactor with stacked configuration in treating high strength industrial wastewaters is advantageous due to minimal space requirements, low capital cost and excellent COD removal efficiencies (in excess of 83%). [Copyright &y& Elsevier]

The aerobic granular sludge process and the membrane bioreactor process are promising, novel environmental bioprocesses for the reclamation of industrial and municipal wastewaters. They are practical and have attracted much research interest. The combination of these two processes in the aerobic granular membrane bioreactor (AGMBR), yields reclaimed water of high quality in a compact reactor. Information on the microbial community in an AGMBR operated at a high organic loading rate is lacking. This study elucidates the microbial dynamics in acetate-fed AGMBR operated in sequencing batch reactor mode. The structure of the microbial community revealed by denaturing gradient gel electrophoresis, demonstrates the dominance of the denitrifying microbial community, which is affiliated with members of the families Comamonadaceae and Alcaligenaceae, of the class Betaproteobacteria. The role of the predominant strains in the AGMBR is discussed. [ABSTRACT FROM AUTHOR]

The main purpose of this work was to conduct a kinetic study on cell growth and hexavalent chromium [Cr(VI)] removal by Candida sp. FGSFEP in a concentric draft-tube airlift bioreactor. The yeast was batch-cultivated in a 5.2-l airlift bioreactor containing culture medium with an initial Cr(VI) concentration of 1.5 mM. The maximum specific growth rate of Candida sp. FGSFEP in the airlift bioreactor was 0.0244 h−1, which was 71.83% higher than that obtained in flasks. The yeast strain was capable of reducing 1.5 mM Cr(VI) completely and exhibited a high volumetric rate [1.64 mg Cr(VI) l−1 h−1], specific rate [0.95 mg Cr(VI) g−1 biomass h−1] and capacity [44.38 mg Cr(VI) g−1 biomass] of Cr(VI) reduction in the airlift bioreactor, with values higher than those obtained in flasks. Therefore, culture of Candida sp. FGSFEP in a concentric draft-tube airlift bioreactor could be a promising technological alternative for the aerobic treatment of Cr(VI)-contaminated industrial effluents. [ABSTRACT FROM AUTHOR]

Abstract: This work proposes a mathematical model for the acclimatization process of a bioreactor treating toxic wastewater. Experimental data was used to identify the changing kinetic parameters of the model as acclimatization progresses. It was found that only one key parameter, the specific biomass growth rate function, changed during the acclimatization process. Therefore, an acclimatization model was proposed to explain the changes of this parameter. [Copyright &y& Elsevier]

An intermittently aerated membrane bioreactor (IAMBR) system has been developed to improve the efficiency of nutrient removal, and for the stable treatment of organic matter which is contained as suspended solid (SS) in the influent. The important operating factors of an intermittently aerated bioreactor (IABR) are sludge retention times (SRTs) and carbon/nitrogen (C/N) ratios. Because research on IAMBR is young, this paper explores the effect of SRTs and C/N ratios on these systems. For SRTs of 20, 25, 30, and 40 days, there was little difference in the removal of COD, T–N, and T–P. In comparing C/N ratios of 4.5, 7, and 10, the COD concentration in permeate with a C/N ratio of 10 was most stable, although the concentration of organic matter in the influent was high. The removal efficiencies of T–N and T–P in permeate with a C/N ratio of 10 were the highest at 92.9% and 88.9%, respectively. This implies that a C/N ratio above 10 should be maintained for a nutrient removal efficiency of approximately 90%. [Copyright &y& Elsevier]

Two landfill bioreactors were operated under aerobic and anaerobic conditions in a thermo-insulated room at a constant temperature of 32°C. Reactors were filled with 19.5kg of shredded synthetic solid waste prepared according to the average municipal solid waste compositions determined in Istanbul and operated under wet-tomb management strategy by using leachate recirculation. Aerobic conditions in the reactor were developed by using an air compressor. The results of experiments indicated that aerobic reactor had higher organic, nitrogen, phosphorus and alkali metal removal efficiencies than the anaerobic one. Furthermore, stabilization time considerably decreased when using aerobic processes with leachate recirculation compared to the anaerobic system with the same recirculation scheme. [Copyright &y& Elsevier]

This study aimed to produce polyhydroxyalkanoates (PHAs) from organic wastes by mixed bacterial cultures using anaerobic-aerobic fermentation systems. Palm oil mill effluent (POME) was used as an organic source, which was cultivated in a two-step-process of acidogenesis and acid polymerization. POME was operated in a continuous flow anaerobic reactor to access volatile fatty acids (VFAs) for PHAs production. During fermentation, VFA concentration was produced in the range of 5 to 8 g/L and the COD concentration reduced up to 80% from 65 g/L. The VFA from anaerobic fermentation was then utilised for PHA production using a mixed culture in availability of aerobic bioreactor. Production of PHAs was recorded high when using a high volume of substrates because of the higher VFA concentration. Even though the maximum PHA content was observed at only 40% of the cell dried weight (CDW), their production and performance are significant in mixed microbial culture. [ABSTRACT FROM AUTHOR]

Abstract: The aerobic treatment of hydrocarbon polluted groundwater was performed experimentally in a three phase fluidized-bed bioreactor (FBBR) using mixed culture of living cells immobilized on PVC particles. The characteristic of the living cells immobilized in FBBR were identified and the kinetic parameters of the biochemical reaction were evaluated. A steady-state biofilm model was developed based on porous pellet model which considers the diffusion and reaction of hydrocarbons within biofilm, axial dispersion coefficient in bioreactor and external mass transfer resistance between biofilm and completely mixed liquid phase. The developed model assumes a first-order biochemical reaction within biofilm. Experimental results were used to test the validity of the proposed model. A reasonable agreement between the experimental and theoretical results was found. [Copyright &y& Elsevier]

The performance of an anaerobic mesophilic packed bed reactor, with a mixture of GAC and tezontle, followed by an aerobic suspended growth system was studied for the treatment of organic chemical wastewater with a high COD concentration (22-29 g/L). The testing of the anaerobic-aerobic system was conducted in an experimental set-up for almost 2.5 years. Different operational conditions were evaluated. The anaerobic reactor showed performance stability and COD removals higher than 80% were obtained with loads up to 16.6 kg.m-3.d-1. The acclimation of the aerobic biomass to the substrate in the anaerobic effluent was very quick and COD removals higher than 94% were obtained even at high organic loads. The combined anaerobic-aerobic system allowed total COD removals higher than 99.5% and the accomplishment of the discharge requirements of 200 mgCOD/L when the anaerobic reactor was operated with loads of 8-11 kg.m-3.d-1 and the aerobic reactor with 0.33 kg.kg-1.d-1, being the total HRT of 4.4. The average TKN removal in the anaerobic-aerobic system was 97%, the average for the anaerobic reactor being 52% and that one for the aerobic system being 94%. [ABSTRACT FROM AUTHOR]

An investigation into aerobic biological wastewater treatment was conducted over the temperature range 25–75°C in a semi-batch bioreactor using waste metalworking fluids (MWFs) generated from Liverpool John Moores University's engineering workshop. The best treatment performance in terms of chemical oxygen demand (COD) removal occurred at 50°C (97.27%), with an operational time of 77.5 h. Cell viability was observed throughout the operation and it was found that higher temperature did not directly correlate to low viability. Effluent turbidity reduced considerably from 35 to 50°C and increased thereafter. Even when the system encountered alkaline shock, the overall performance was not affected, thus indicating how stable the system was. The results of this study indicate that an existing industrial-activated sludge plant could be used to treat waste MWFs under thermophilic conditions. The COD reduction was significant but further investigation into biodegradation of recalcitrant compounds is needed to achieve optimum performance. [ABSTRACT FROM AUTHOR]

The production of small amounts of well-stabilized biological sludge is one of the main advantages of upflow anaerobic sludge bed (UASB) reactors over aerobic wastewater treatment systems. In this work, sludge produced in three pilot-scale UASB reactors used to treat sewage under subtropical conditions was assessed for both stability and specific methanogenic activity. Stability of primary sludge from settling tanks and digested sludge from conventional sludge digesters was also measured for comparison purposes. Kinetic parameters like the hydrolysis rate constant and the decay rate constant were calculated. High stability was observed in sludge from UASB reactors. Methanogenic activity in anaerobic sludges was relatively low, probably due to the low organic matter concentration in influent sewage. Knowledge on sludge growth rate, stability, and activity might be very useful to optimize sludge management activities in full-scale UASB reactors. [ABSTRACT FROM AUTHOR]

Wastewater originating from chemical industries may contain com- pounds that could adversely affect the treatment processes, mainly the biological process, by either toxic or inhibition effects. The objectives of this study were to evaluate practical possibilities to upgrade existing wastewater treatment facilities by operating aerobic treatment based on membrane bioreactor (MBR) technology. Three different industries were included in this study: a paper mill that operates raw solid separators followed by anaerobic treatment; a food production plant that operates oil and grease separators, chemical flocculation, and dissolved air flotation; and port fuel facilities that include gravity oil separators. In all the above cases the biological treatment was exposed to different problems, which included: (a) the possible presence of deflocculating materials such as starch and biocides, in the case of the paper mill; (b) residual hydrophobic compounds that may affect diffusion through biosolids surfaces in the food plant; and (c) organic matter characterized by low biodegradability (hydrocarbons), in the case of the fuel port facilities. The experimental work in this study indicated that biological treatment of industrial wastewater containing contaminants characterized by hydrophobicity and/or by low biodegradability could be successfully performed by MBR configuration, obtaining effluent of high quality. However, these particular types of industrial wastewater would require the adaptation of the MBR operation conditions, by lowering cell residence time and mixed liquor volatile suspended solids (MLVSS) in the bioreacttor and by increasing the amounts of excess biosolids accordingly. [ABSTRACT FROM AUTHOR]

Membrane bioreactor (MBR) is a promising alternative to conventional wastewater treatment methods. However this process is still under-used due to its high running costs. Its main power requirement comes from aeration, which is used to supply dissolved oxygen to the micro-organisms and to maintain the solids in suspension. In addition, in submerged MBRs, aeration is used for membrane cleaning. A complex matrix links the biomass characteristics, the aeration and the oxygen transfer. These parameters can impact on each other and/or delete one another effect. In order to understand the phenomena occurring in MBRs, similar aerobic biological processes, such as fermentation, mineral industry and slurry, were investigated. This review discusses the interrelations of the biomass characteristics (solids concentration, particle size and viscosity), the aeration intensity and the oxygen transfer in MBRs. [ABSTRACT FROM AUTHOR]