A review on anaerobic membrane bioreactors (AnMBRs) focused on modelling and control aspects

Integrated model of sequential anaerobic and algal membrane bioreactor (A2MBR) system for wastewater reuse and resource recovery

We developed a novel integrated model for describing the A2MBR system, treating municipal wastewater for resource recovery. The model couples an anaerobic membrane bioreactor (AnMBR) with an algal photo membrane bioreactor (APMBR). The AnMBR details organic matter fractionation and its effect on SMP and EPS, while the APMBR incorporates alga-bacteria interaction, light, temperature, and membrane separation effects. While showing good agreement between simulated and measured values, results suggest that higher sludge retention time (SRT) drives COD removal, promoting biogas production in the AnMBR (2.5-3 days HRT and 60-90 days SRT not to exceed a 25 g MLSS/l). For the APMBR, shorter HRTs and longer SRTs promote microalgae growth, and longer HRTs enhance nutrient removal (maximum nutrient removal at 3 days HRT and 10 days SRT). Long-term operational data are needed to validate the proposed model. This modeling tool is valuable for modelers describing anaerobic/algal membrane processes for multi-purpose wastewater treatment.

Modeling MBR fouling: A critical review analysis towards establishing a framework for good modeling practices

This study critically analyses filtration process modeling in membrane bioreactor (MBR) technology. More specifically, the variety of approaches and assumptions considered within a curated selection of resistance-in-series (RIS) filtration models found in the literature is critically assessed. Aimed to move towards good filtration process modeling practices, the basis for establishing a unified framework rooted in the fundamentals of membrane fouling is defined in this work, considering fouling classifications, process dynamics, and underlying processes used by different authors for elucidating membrane fouling phenomena. Systematically analyzing these factors should be considered as a basic step for efficiently comparing the performance of different models. This involves a detailed examination of the processes applied within each model and their interplay with the involved resistances and fouling types. A lack of homogeneity in RIS-based filtration modeling has been observed. To address this, basic guidelines towards good modeling practices are proposed aimed at balancing model accuracy and complexity. Specifically, seven model processes, six resistances, and three subgroups for types of fouling, further divided into four or five categories are proposed to guide the selection of processes and state variables in the model structure. Hence, this study facilitates the understanding of different approaches to be used during the modeling exercise of membrane filtration processes within the MBR field, not only to enhance the comprehensibility of available filtration models, but also to help the comparison, implementation, and adaptation of available models and the comprehensive development of new ones.

Ion exchange columns. A promising technology for nitrogen and phosphorus recovery in the main line of a wastewater treatment plant

Anaerobic membrane bioreactor (AnMBR) technology has great advantages for treating urban wastewaters, but, when irrigation cannot be applied and the effluent is discharged in a sensitive zone, a post-treatment of this effluent is needed for nitrogen and phosphorus removal. Under this scenario, ion exchange processes represent one of the most promising technologies for treating this effluent. Ion exchange technology allows to meet discharge limits and to recover these nutrients in a highly concentrated stream. In this work, the technical feasibility of using a commercial resin for phosphorus recovery and a natural zeolite (clinoptilolite) for nitrogen recovery was evaluated. Purolite FerrIX A33E resin removed phosphate from the AnMBR permeate within 500 Bed Volumes (BVs) with a maximum adsorption capacity (qmax) of 2,1 mg P-PO4/g resin. Regeneration of the resin (2% NaOH 2% NaCl) recovered over 95% of the phosphorous retained, achieving a concentration of 316,7 mg P-PO4/L in the regeneration solution. In the absence of a long-term study, the resin showed a stable adsorption capacity during 16 cycles of saturation-regeneration. Clinoptilolite removed nitrogen within 139 BVs obtaining a qmax of 3,68 mg N-NH4/g zeolite. 97 % of the retained N-NH4 was recovered in the regeneration stage (0,8% NaOH) with an average concentration of 577 mg N-NH4/L. Continuous exposure of the zeolite to alkaline solutions led to reduction of 50% of the adsorption capacity after 17 cycles.

Optimization of MBRs through integrated modelling: A state of the art

The optimization of integrated membrane bioreactors (MBRs) models is of paramount importance in view of reducing the costs, greenhouse gas emissions or enhancing the water quality. On this behalf, this paper, produced by the International Water Association (IWA) Task Group on Membrane modelling and control, reviews the current state-of-the-art regarding the control and optimization of integrated MBR models. Whether aerobic or anaerobic, such modelling allows the consideration of specific functioning conditions and optimization problems together with the estimation and monitoring of Performance Index (PIs). This paper reviews the diversity of those problems criteria used in performance assessment. Dividing issues that can be addressed either off-line or online, it is shown that integrated models have attained an important degree of maturity. Several recommendations for mainstreaming the optimization of MBRs using such integrated models. The key findings of this work show that there is room for improving and optimizing the functioning of MBRs using integrated modelling and that this integrated modelling approach is necessary to link functioning conditions together with PI estimation and monitoring.

Boosting nutrient recovery from AnMBR effluent by means of electrodialysis technology: Operating parameters assessing

This work describes a comprehensive assessment of operating parameters of a bench-scale electrodialysis (ED) plant for nutrient concentration from an Anaerobic Membrane BioReactor (AnMBR) effluent. The ED bench-scale plant serves a dual purpose. Firstly, to generate a concentrated stream with a high nutrient content, and secondly, to produce high-quality reclaimed water in the diluted stream, both sourced from real wastewater coming from the effluent of an AnMBR. Two sets of experiments were conducted: 1) short-term experiments to study the effect of some parameters such as the applied current and the type of anionic exchange membrane (AEM), among others, and 2) a long-term experiment to verify the feasibility of the process using the selected parameters. The results showed that ED produced concentrated ammonium and phosphate streams using a 10-cell pair stack with 64 cm2 of unitary effective membrane area, working in galvanostatic mode at 0.24 A, and operating with an Acid-100-OT anionic exchange membrane. Concentrations up to 740 mg/L and 50 mg/L for NH4-N and PO4-P, respectively, were achieved in the concentrated stream along with removal efficiencies of 70% for ammonium and 60% for phosphate in the diluted stream. The average energy consumption was around 0.47 kWh·m-3.

Dynamic Modelling, Process Control, and Monitoring of Selected Biological and Advanced Oxidation Processes for Wastewater Treatment: A Review of Recent Developments

This review emphasizes the significance of formulating control strategies for biological and advanced oxidation process (AOP)-based wastewater treatment systems. The aim is to guarantee that the effluent quality continuously aligns with environmental regulations while operating costs are minimized. It highlights the significance of understanding the dynamic behaviour of the process in developing effective control schemes. The most common process control strategies in wastewater treatment plants (WWTPs) are explained and listed. It is emphasized that the proper control scheme should be selected based on the process dynamic behaviour and control goal. This study further discusses the challenges associated with the control of wastewater treatment processes, including inadequacies in developed models, the limitations of most control strategies to the simulation stage, the imperative requirement for real-time data, and the financial and technical intricacies associated with implementing advanced controller hardware. It is discussed that the necessity of the availability of real-time data to achieve reliable control can be achieved by implementing proper, accurate hardware sensors in suitable locations of the process or by developing and implementing soft sensors. This study recommends further investigation on available actuators and the criteria for choosing the most appropriate one to achieve robust and reliable control in WWTPs, especially for biological and AOP-based treatment approaches.

Membrane-based technology in water and resources recovery from the perspective of water social circulation: A review

In this review, the application of membrane-based technology in water social circulation was summarized. Water social circulation encompassed the entire process from the acquirement to discharge of water from natural environment for human living and development. The focus of this review was primarily on the membrane-based technology in recovery of water and other valuable resources such as mineral ions, nitrogen and phosphorus. The main text was divided into four main sections according to water flow in the social circulation: drinking water treatment, agricultural utilization, industrial waste recycling, and urban wastewater reuse. In drinking water treatment, the acquirement of water resources was of the most importance. Pressure-driven membranes, such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were considered suitable in natural surface water treatment. Additionally, electrodialysis (ED) and membrane capacitive deionization (MCDI) were also effective in brackish water desalination. Agriculture required abundant water with relative low quality for irrigation. Therefore, the recovery of water from other stages of the social circulation has become a reasonable solution. Membrane bioreactor (MBR) was a typical technique attributed to low-toxicity effluent. In industrial waste reuse, the osmosis membranes (FO and PRO) were utilized due to the complex physical and chemical properties of industrial wastewater. Especially, membrane distillation (MD) might be promising when the wastewater was preheated. Resources recovery in urban wastewater was mainly divided into recovery of bioenergy (via anaerobic membrane bioreactors, AnMBR), nitrogen (utilizing MD and gas-permeable membrane), and phosphorus (through MBR with chemical precipitation). Furthermore, hybrid/integrated systems with membranes as the core component enhanced their performance and long-term working ability in utilization. Generally, concentrate management and energy consumption control might be the key areas for future advancements of membrane-based technology.

Biological processes modelling for MBR systems: A review of the state-of-the-art focusing on SMP and EPS

A mathematical correlation between biomass kinetic and membrane fouling can improve the understanding and spread of Membrane Bioreactor (MBR) technology, especially in solving the membrane fouling issues. On this behalf, this paper, produced by the International Water Association (IWA) Task Group on Membrane modelling and control, reviews the current state-of-the-art regarding the modelling of kinetic processes of biomass, focusing on modelling production and utilization of soluble microbial products (SMP) and extracellular polymeric substances (EPS). The key findings of this work show that the new conceptual approaches focus on the role of different bacterial groups in the formation and degradation of SMP/EPS. Even though several studies have been published regarding SMP modelling, there still needs to be more information due to the highly complicated SMP nature to facilitate the accurate modelling of membrane fouling. The EPS group has seldom been addressed in the literature, probably due to the knowledge deficiency concerning the triggers for production and degradation pathways in MBR systems, which require further efforts. Finally, the successful model applications showed that proper estimation of SMP and EPS by modelling approaches could optimise membrane fouling, which can influence the MBR energy consumption, operating costs, and greenhouse gas emissions.

Development of a dynamic model for effective mitigation of membrane fouling through biogas sparging in submerged anaerobic membrane bioreactors (SAnMBRs)

The deterministic mechanistic model derived from the fundamental of the dynamical fouling system was investigated to estimate fouling parameters, with theoretical biogas sparging performance evaluated of a Submerged Anaerobic Membrane Bioreactor treating trade wastewater. The result showed that the sparging effectiveness of EPSc removal was average, 35% higher than the sparging effectiveness of EPSp, with the coefficient of fouling removal characterizing the dynamic time behaviour increasing with the organic loading rate. The dynamic system analysis predicted that the process gain for SAnMBR-1 was more than 30% compared with SAnMBR-2, which supported a widely known theory of fouling dependence of organic loading rate.

Modeling and assessment of the transfer effectiveness in integrated bioreactor with membrane separation

Integrating a reaction process with membrane separation allows for effective product removal, favorable shifting of the reaction equilibrium, overcoming eventual inhibitory or toxic effects of the products and has the advantage of being energy and space saving. It has found a range of applications in innovative biotechnologies, generating value-added products (exopolysaccharides, antioxidants, carboxylic acids) with high potential for separation/ concentration of thermosensitive bioactive compounds, preserving their biological activity and reducing the amount of solvents and the energy for solvent recovery. Evaluating the effectiveness of such integrated systems is based on fluid dynamics and mass transfer knowledge of flowing matter close to the membrane surface – shear deformation rates and shear stress at the membrane interface, mass transfer coefficients. A Computational Fluid Dynamics (CFD)-based approach for assessing the effectiveness of integrated stirred tank bioreactor with submerged membrane module is compiled. It is related to the hydrodynamic optimization of the selected reactor configuration in two-phase flow, as well as to the concentration profiles and analysis of the reactor conditions in terms of reaction kinetics and mass transfer.

Enhanced organic degradation and biogas production of domestic wastewater at psychrophilic temperature through submerged granular anaerobic membrane bioreactor for energy-positive treatment

This study deals with the conversion of organic matter into methane at ambient temperature, during anaerobic digestion of domestic wastewater combined with a submerged ultrafiltration membrane with no gas-sparging. A one-stage submerged granular anaerobic membrane bioreactor (G-AnMBR) and a control anaerobic digester (UASB type) were operated during four months, after 500 days of biomass acclimatization to psychrophilic and low loading rate conditions. Membrane barrier led to the retention of biomass, suspended solids and dissolved and colloidal organic matter which greatly enhanced total COD (tCOD) removal (92.3%) and COD to methane conversion (84.7% of tCOD converted into dissolved and gaseous CH4). G-AnMBR overcame the usual long start-up period and led to a higher sludge heterogeneity, without altering the granular biomass activity. The feasibility of the G-AnMBR without gas-sparging was also assessed and the net positive energy balance was estimated around + 0.58 kWh.m^-3.

Recovery of Nutrients from Residual Streams Using Ion-Exchange Membranes: Current State, Bottlenecks, Fundamentals and Innovations

The review describes the place of membrane methods in solving the problem of the recovery and re-use of biogenic elements (nutrients), primarily trivalent nitrogen N^III and pentavalent phosphorus P^V, to provide the sustainable development of mankind. Methods for the recovery of NH₄⁺ − NH₃ and phosphates from natural sources and waste products of humans and animals, as well as industrial streams, are classified. Particular attention is paid to the possibilities of using membrane processes for the transition to a circular economy in the field of nutrients. The possibilities of different methods, already developed or under development, are evaluated, primarily those that use ion-exchange membranes. Electromembrane methods take a special place including capacitive deionization and electrodialysis applied for recovery, separation, concentration, and reagent-free pH shift of solutions. This review is distinguished by the fact that it summarizes not only the successes, but also the “bottlenecks” of ion-exchange membrane-based processes. Modern views on the mechanisms of NH₄⁺ − NH₃ and phosphate transport in ion-exchange membranes in the presence and in the absence of an electric field are discussed. The innovations to enhance the performance of electromembrane separation processes for phosphate and ammonium recovery are considered.

Comparison of three anaerobic digestion reactors for low-carbon wastewater treatment

In this study, three anaerobic digestion reactors using up-flow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (AnSBR), and anaerobic membrane bioreactor (AnMBR) were studied. The chemical oxygen demand (COD), gas production, sludge performance, and microbial characteristics of the anaerobic digestion process were assessed. The results showed that the average COD removal efficiencies reached 86%, 83%, and 85%, with corresponding removed rates of 2.49, 0.48, and 0.79 kg COD m-3 d-1 in UASB, AnSBR, and AnMBR, respectively. After the reactors attained stable operation, both extracellular polymeric substances and soluble microbial products decreased in all the reactors compared with the seed sludge. Methanothrix was the dominant archaea for methane production in the UASB, the relative abundance of which increased from 58.3% to 83.4%. These results identify UASB as the most suitable reactor for anaerobic digestion when treating wastewater with low carbon. Such reactors are important for the application and development of the energy self-sufficiency in sewage treatment. PRACTITIONER POINTS: UASB, SBR, and MBR were adopted to treat low-carbon wastewater using anaerobic digestion process. UASB performed the highest COD removal from low-carbon wastewater. The main microorganisms in UASB were Methanothrix, Methanomassiliicoccus, and Methanobacterium.

Role of microparticles in membrane fouling from acidogenesis to methanogenesis phases in an anaerobic baffled reactor

Microparticles (0.45-10 μm) have been recognized as key foulants in anaerobic membrane bioreactors (AnMBRs). However, their characteristics and fouling behaviors are often understood in single-stage and completely mixed reactors, failing to elucidate the occurrence of microparticles in the multi-stage anaerobic bioprocess. Here, a lab-scale anaerobic baffled reactor with four compartments (C1-C4) was employed to explore the composition and fouling potential of microparticles in different compartments. Photometric analysis showed that the microparticles had an increasing percentage in the total organics of the top supernatant but a decreasing concentration from C1 to C4. Long-term filtration and dead-end filtration tests revealed that the top supernatant in C1 had much higher fouling potential than those in C2-C4. The supernatant microparticles significantly accumulated in the cake layers for each compartment (68-95% of the total organics), particularly the fraction of 1-5 μm, and the fouling rate was positively correlated with the biomass accumulation rate. Based on reactor performance and 16S rRNA gene sequences, a significant bio-phase separation occurred between C1 (acidogenesis) and C2-C4 (methanogenesis). And hydrolytic and fermentative bacteria in the family Veillonellaceae, Streptococcaceae, and Enterobacteriaceae were dominant in the supernatant microparticles, particularly in C1, which had a positive correlation with the fouling rate and biomass accumulation rate. These above results all revealed that the microparticles in the acidogenesis phase had higher fouling potential. In summary, our results suggest that the tactic of pre-hydrolysis and acidification with feedstocks and constructing AnMBRs by coupling with multi-phase anaerobic bioprocesses and membrane units could be beneficial to fouling control.

Optimising the Flux Enhancer Dosing Strategy in a Pilot-Scale Anaerobic Membrane Bioreactor by Mathematical Modelling

Flux enhancers (FEs) have been successfully applied for fouling mitigation in membrane bioreactors. However, more research is needed to compare and optimise different dosing strategies to improve the filtration performance, while minimising the use of FEs and preventing overdosing. Therefore, the goal of this research is to develop an optimised control strategy for FE dosing into an AnMBR by developing a comprehensive integrated mathematical model. The integrated model includes filtration, flocculation, and biochemical processes to predict the effect of FE dosing on sludge filterability and membrane fouling rate in an AnMBR. The biochemical model was based on an ADM1, modified to include FEs and colloidal material. We developed an empirical model for the FE-induced flocculation of colloidal material. Various alternate filtration models from the literature and our own empirical models were implemented, calibrated, and validated; the best alternatives were selected based on model accuracy and capacity of the model to predict the effect of varying sludge characteristics on the corresponding output, that is fouling rate or sludge filterability. The results showed that fouling rate and sludge filterability were satisfactorily predicted by the selected filtration models. The best integrated model was successfully applied in the simulation environment to compare three feedback and two feedforward control tools to manipulate FE dosing to an AnMBR. The modelling results revealed that the most appropriate control tool was a feedback sludge filterability controller that dosed FEs continuously, referred to as ∆R20_10. Compared to the other control tools, application of the ∆R20_10 controller resulted in a more stable sludge filterability and steady fouling rate, when the AnMBR was subject to specific disturbances. The simulation environment developed in this research was shown to be a useful tool to test strategies for dosing flux enhancer into AnMBRs.

Anaerobic membrane bioreactors (AnMBRs) for municipal wastewater treatment- potential benefits, constraints, and future perspectives: An updated review

The application of Anaerobic Membrane Bioreactors (AnMBRs) for municipal wastewater treatment has been made sufficiently sustainable for practical implementations. The potential benefits are significant as AnMBRs effectively remove a broad range of contaminants from wastewater for water reuse, degrade organics in wastewater to yield methane-rich biogas for resultant energy production, and concentrate nutrients for subsequent recovery for fertilizer production. However, there still exist some concerns requiring vigilant considerations to make AnMBRs economically and technically viable. This review paper briefly describes process fundamentals and the basic AnMBR configurations and highlights six major factors which obstruct the way to AnMBRs installations affecting their performance for municipal wastewater treatment: (i) organic strength, (ii) membrane fouling, (iii) salinity build-up, (iv) inhibitory substances, (v) temperature, and (vi) membrane stability. This review also covers the energy utilization and energy potential in AnMBRs aiming energy neutrality or positivity of the systems which entails the requirement to further determine the economics of AnMBRs. The implications and related discussions have also been made on future perspectives of the concurrent challenges being faced in AnMBRs operation.

Resource recovery from sugarcane vinasse by anaerobic digestion - A review

The increase in biofuel production by 2030, driven by the targets set at the 21st United Nations Framework Convention on Climate Change (COP21), will promote an increase in ethanol production, and consequently more vinasse generation. Sugarcane vinasse, despite having a high polluting potential due to its high concentration of organic matter and nutrients, has the potential to produce value-added resources such as volatile fatty acids (VFA), biohydrogen (bioH₂) and biomethane (bioCH₄) from anaerobic digestion. The objective of this paper is to present a critical review on the vinasse treatment by anaerobic digestion focusing on the final products. Effects of operational parameters on production and recovery of these resources, such as pH, temperature, retention time and type of inoculum were addressed. Given the importance of treating sugarcane vinasse due to its complex composition and high volume generated in the ethanol production process, this is the first review that evaluates the production of VFAs, bioH₂ and bioCH₄ in the treatment of this organic residue. Also, the challenges of the simultaneous production of VFA, bioH₂ and bioCH₄ and resources recovery in the wastewater streams generated in flex-fuel plants, using sugarcane and corn as raw material in ethanol production, are presented. The installation of flex-fuel plants was briefly discussed, with the main impacts on the treatment process of these effluents either jointly or simultaneously, depending on the harvest season.

Anaerobic MBR technology for treating municipal wastewater at ambient temperatures

An innovative way to treat municipal wastewater and produce energy at the same time is anaerobic treatment. Anaerobic processes are traditionally used for high-strength wastewater or municipal sludge treatment and only recently have been applied for the treatment of low strength municipal wastewater To investigate the performance of anaerobic wastewater treatment through the incorporation of membrane technology, a 40 L laboratory scale Anaerobic Membrane Bioreactor (AnMBR) with a flat sheet submerged membrane along with a 40 L reservoir for trapping and measuring the biogas produced have been installed and set in operation. The scope of this study is to examine, through long term bench scale experiments, the impact that different temperatures and also different operating conditions have on the efficiency of AnMBR in order to identify the possibility of integrating this technology into Wastewater Treatment Plants (WWTPs). This paper evaluates the efficiency of AnMBR in the temperature range 14-26 °C, operating at three different hydraulic retention times (HRTs). The three different HRTs examined were 2 d, 1 d and 12 h. Each HRT is divided into two different temperature ranges. As the HRT decreased the effluent quality decreased and the membrane fouled more rapidly. AnMBR was able to produce permeate water with an average COD of 51 ± 8 mg L^-1 at an HRT of 2 d during the summer period with an average temperature of 24 °C. The effluent COD increased to 67 ± 10 mg L^-1 and reached 91 ± 5 mg L^-1 for HRT 1 d and 12 h respectively for the same temperature range.

Anaerobic membrane bioreactors for wastewater treatment: Challenges and opportunities

Anaerobic membrane bioreactors (AnMBRs) have become a new mature technology and entered into the wastewater market, but there are several challenges to be addressed for wide applications. In this review, we discuss challenges and potentials of AnMBRs focusing on wastewater treatment. Nitrogen and dissolved methane control, membrane fouling and its control, and membrane associated cost including energy consumption are main bottlenecks to facilitating AnMBR application in wastewater treatment. Accumulation of dissolved methane in AnMBR permeate decreases the benefit of methane energy and contributes to methane gas emissions to atmosphere. Separate control units for nitrogen and dissolved methane add system complexity and increase capital and operating and maintenance (O & M) costs in AnMBR-centered wastewater treatment. Alternatively, methane-based denitrification can be an ideal nitrogen control process due to simultaneous removal of nitrogen and dissolved methane. Membrane fouling and energy associated with membrane fouling control are major limitations, in addition to membrane cost. More efforts are required to decrease capital and O & M costs associated with the control of dissolved methane nitrogen and membrane fouling to facilitate AnMBRs for wastewater treatment. PRACTITIONER POINTS: AnMBRs can accelerate anaerobic wastewater treatment including dilute wastewater. Nitrogen and dissolved methane control is detrimental for AnMBR application to wastewater treatment. Membrane biofilm reactors using gas-permeable membranes are suitable for simultaneous nitrogen and dissolved methane control. High capital and O & M costs from membranes are a major bottleneck to wide application of AnMBRs. Dynamic membranes could be an option to reduce capital and O & M costs for AnMBRs.

Widening the applicability of AnMBR for urban wastewater treatment through PDMS membranes for dissolved methane capture: Effect of temperature and hydrodynamics

AnMBR technology is a promising alternative to achieve future energy-efficiency and environmental-friendly urban wastewater (UWW) treatment. However, the large amount of dissolved methane lost in the effluent represents a potential high environmental impact that hinder the feasibility of this technology for full-scale applications. The use of degassing membranes (DM) to capture the dissolved methane from AnMBR effluents can be considered as an interesting alternative to solve this problem although further research is required to assess the suitability of this emerging technology. The aim of this study was to assess the effect of operating temperature and hydrodynamics on the capture of dissolved methane from AnMBR effluents by DMs. To this aim, a commercial polydimethylsiloxane (PDMS) DM was coupled to an industrial prototype AnMBR (demonstration scale) treating UWW at ambient temperature. Different operating temperatures have been evaluated: 11, 18, 24 and 30 °C. Moreover, the DM was operated at different ratios of liquid flow rate to membrane area (Q_L:A) ranging from 22 to 190 Lh^-1m^-2 in order to study the resistance of the system to methane permeation. Methane recovery was maximized when temperature raised and Q_L:A was reduced, giving methane recovery efficiencies (MRE) of about 85% at a temperature of 30 °C and a Q_L:A of 25 Lh^-1m^-2. The study showed that high Q_L:A ratios hinder methane recovery by the perturbation of the DM fibers, being this effect intensified at lower temperatures probably due the higher liquid viscosities. Also, the performed fouling evaluation showed that not significant membrane fouling may be expected in the DM unit at the short-term when treating AnMBR effluents. A resistance-in-series model was proposed to predict the overall mass transfer of the system according to operating temperature and Q_L:A, showing that methane capture was controlled by the liquid phase, which represented up to 80-90% of total mass transfer resistance. The energy and environmental evaluation performed in this study revealed that PDMS DMs would enhance energy recovery and environmental feasibility of AnMBR technology for UWW treatment, especially when operating at low temperatures. When MRE was maximized, the combination of AnMBR with DM achieved net energy productions and net greenhouse gas reductions of up to 0.87 kWh and 0.216 kg CO₂-eq per m³ of treated water.

A review of the characteristics of Fenton and ozonation systems in landfill leachate treatment

The development and application of Fenton and ozonation systems in landfill leachate treatment over the last 20 years, and the current research status are reviewed in this paper, with an emphasis on the technical and economic characteristics of Fenton and ozonation systems used to treat different types of landfill leachate. To date, a total of 101 and 78 articles have been published regarding leachate treatment by Fenton and ozonation systems, respectively. These articles considered the use of two systems to treat aged leachate, biologically treated leachate and leachate comprising the concentrated solution resulting from reverse osmosis (RO). The oxidization mechanisms of the two systems used to treat landfill leachate significantly differed in terms of their optimal process parameters (e.g., initial pH value, reagent dosage, and reaction time) and removal efficiency. The Fenton and ozonation systems outperformed persulfate-based advanced oxidation technology in terms of their improved biodegradability of landfill leachate and engineering practicability. The cost of the reagents required to treat landfill leachate by Fenton and ozonation systems accounted for at least 85% of the total operating cost. In contrast to the ozonation system, the Fenton system was more cost-effective when both systems were used to treat the same type of landfill leachate. This study provides a theoretical basis for the operation of Fenton and ozonation systems and also offers technical support for landfill leachate disposal companies that opt to use these technologies.

Maximising resource recovery from wastewater grown microalgae and primary sludge in an anaerobic membrane co-digestion pilot plant coupled to a composting process

A pilot-scale microalgae (Chlorella spp.) and primary sludge anaerobic co-digestion (ACoD) plant was run for one year in an anaerobic membrane bioreactor (AnMBR) at 35 °C, 70 d solids retention time and 30 d hydraulic retention time, showing high stability in terms of pH and VFA concentration. The plant achieved a high degree of microalgae and primary sludge substrate degradation, resulting in a methane yield of 370 mLCH₄·gVS_inf^-1. Nutrient-rich effluent streams (685 mgN·L^-1 and 145 mgP·L^-1 in digestate and 395 mgNH₄-N·L^-1 and 37 mgPO₄-P·L^-1 in permeate) were obtained, allowing posterior nutrient recovery. Ammonium was recovered from the permeate as ammonia sulphate through a hydrophobic polypropylene hollow fibre membrane contactor, achieving 99% nitrogen recovery efficiency. However, phosphorus recovery through processes such as struvite precipitation was not applied since only 26% of the phosphate was available in the effluent. Composting process of the digestate coming from the ACoD pilot plant was assessed on laboratory-scale Dewar reactors, as was the conventional sludge compost from an industrial WWTP digestion process, obtaining similar values from both. Sanitised (free of Escherichia coli and Salmonella spp.) and stable compost (respirometric index at 37 °C below 0.5 mgO ₂ g organic matter^-1·h^-1) was obtained from both sludges.

Performance of AnMBR in Treatment of Post-consumer Food Waste: Effect of Hydraulic Retention Time and Organic Loading Rate on Biogas Production and Membrane Fouling

Anaerobic digestion of food waste (FW) is typically limited to large reactors due to high hydraulic retention times (HRTs). Technologies such as anaerobic membrane reactors (AnMBRs) can perform anaerobic digestion at lower HRTs while maintaining high chemical oxygen demand (COD) removal efficiencies. This study evaluated the effect of HRT and organic loading rate (OLR) on the stability and performance of a side-stream AnMBR in treating diluted fresh food waste (FW). The reactor was fed with synthetic FW at an influent concentration of 8.24 (± 0.12) g COD/L. The OLR was increased by reducing the HRT from 20 to 1 d. The AnMBR obtained an overall removal efficiency of >97 and >98% of the influent COD and total suspended solids (TSS), respectively, throughout the course of operation. The biological process was able to convert 76% of the influent COD into biogas with 70% methane content, while the cake layer formed on the membrane gave an additional COD removal of 7%. Total ammoniacal nitrogen (TAN) and total nitrogen (TN) concentrations were found to be higher in the bioreactor than in the influent, and average overall removal efficiencies of 17.3 (± 5) and 61.5 (± 3)% of TAN and TN, respectively, were observed with respect to the bioreactor concentrations after 2 weeks. Total phosphorus (TP) had an average removal efficiency of 40.39 (± 5)% with respect to the influent. Membrane fouling was observed when the HRT was decreased from 7 to 5 d and was alleviated through backwashing. This study suggests that the side-stream AnMBR can be used to successfully reduce the typical HRT of wet anaerobic food waste (solids content 7%) digesters from 20 days to 1 day, while maintaining a high COD removal efficiency and biogas production.

Virus removal by membrane bioreactors: A review of mechanism investigation and modeling efforts

The increasing pressure on the global water supply calls for more advanced solutions with higher efficiency and better sustainability, leading to the promptly developing water reclamation and reuse schemes including treatment technologies and risk management strategies where microbial safety is becoming a crucial aspect in the interest of public health. Backed up by the development of membrane technology, membrane bioreactors (MBR) have received substantial attention for their superiority over conventional treatment methods in many ways and are considered promising in the water reclamation realm. This review paper provides an overview of the efforts made to manage and control the potential waterborne viral disease risks raised by the use of effluent from MBR treatment processes, including the mechanisms involved in the virus removal process and the attempts to model the dynamics of the removal process. In principle, generalized and integrated virus removal models that provide insight into real-time monitoring are urgently needed for advanced real-time control purpose. Future studies of approaches that can well handle the inherent uncertainty and nonlinearity of the complex removal process are crucial to the development and promotion of related technologies.

Anaerobic membrane bioreactor performance at different wastewater pre-concentration factors: An experimental and economic study

This research evaluated the performance of a lab-scale anaerobic membrane bioreactor (AnMBR) treating municipal sewage pre-concentrated by forward osmosis (FO). The organic loading rate (OLR) and sodium concentrations of the synthetic sewage stepwise increased from 0.3 to 2.0 g COD L^-1 d^-1 and from 0.28 to 2.30 g Na⁺ L^-1 to simulate pre-concentration factors of 1, 2, 5 and 10. No major operational problems were observed during AnMBR operation, with COD removal efficiencies ranging between 90 and 96%. The methane yield progressively increased from 214 ± 79 to 322 ± 60 mL CH₄ g^-1 COD as the pre-concentration factor increased from 1 to 10. This was mainly attributed to the lower fraction of methane dissolved lost in the permeate at higher OLRs. Interestingly, at the highest pre-concentration factor (2.30 g Na⁺ L^-1) the difference between the permeate and the digester soluble COD indicated that membrane biofilm also played a role in COD removal. Finally, a preliminary energy and economic analysis showed that, at a pre-concentration factor of 10, the AnMBR temperature could be increased 10 °C and achieve a positive net present value (NPV) of 4 M€ for a newly constructed AnMBR treating 10,000 m³ d^-1 of pre-concentrated sewage with an AnMBR lifetime of 20 years.

Microbially induced carbonate precipitation via methanogenesis pathway by a microbial consortium enriched from activated anaerobic sludge

AIMS

Various applications of microbially induced carbonate precipitation (MICP) has been proposed. However, most studies use cultured pure strains to obtain MICP, ignoring advantages of microbial consortia. The aims of this study were to: (i) test the feasibility of a microbial consortium to produce MICP; (ii) identify functional micro-organisms and their relationship; (iii) explain the MICP mechanism; (iv) propose a way of applying the MICP technique to soil media.

METHODS AND RESULTS

Anaerobic sludge was used as the source of the microbial consortium. A laboratory anaerobic sequencing batch reactor and beaker were used to perform precipitation experiment. The microbial consortium produced MICP with an efficiency of 96·6%. XRD and SEM analysis showed that the precipitation composed of different-size calcite crystals. According to high-throughput 16S rRNA gene sequencing, the functional micro-organisms included acetogenic bacteria, acetate-oxidizing bacteria and archaea Methanosaeta and Methanobacterium beijingense. The methanogenesis acetate degradation provides dissolved inorganic carbon and increases pH for MICP. A series of reactions catalysed by many enzymes and cofactors of methanogens and acetate-oxidizers are involved in the acetate degradation.

CONCLUSION

This work demonstrates the feasibility of using the microbial consortium to achieve MICP from an experimental and theoretical perspective.

SIGNIFICANCE AND IMPACT OF THE STUDY

A method of applying the microbial-consortium MICP to soil media is proposed. It has the advantages of low cost, low environmental impact, treatment uniformity and less limitations from natural soils. This method could be used to improve mechanical properties, plug pores and fix harmful elements of soil media, etc.

Quorum quenching altered microbial diversity and activity of anaerobic membrane bioreactor (AnMBR) and enhanced methane generation

A facultative bacterium Microbacterium sp. (QQ strain) was found significantly mitigated membrane biofouling and also increased methane production. It was found genera Nitrospira, norank-c-Bacterodetes vadinHA17, Trichococcus and family Anaerolineaceae were likely responsible for membrane biofouling. The presence of QQ strain increased the total abundance of fermentative and acetogenic genera by 0.61% and 379.61%, respectively, but had a minor effect on the abundance of methanogens. The increased methane production was likely due to the strengthened methanogenic activity and more available substrates. Homo-acetogenic Treponema was enriched (9.01%) in the presence of QQ strain suggesting that apart from hydrogenotrophic methanogenic pathway, extra CH₄ could be also produced from the additional acetate synthesized via homo-acetogenic pathway. This study advances knowledge about the effects of QQ strain on microbial communities, microbiota biofouling behavior and anaerobic fermentation process in AnMBRs.

Anaerobic membrane bioreactor (AnMBR) scale-up from laboratory to pilot-scale for microalgae and primary sludge co-digestion: Biological and filtration assessment

This research work proposes the scale-up evaluation in terms of biological and filtration performance from laboratory to pilot-scale of an anaerobic membrane bioreactor (AnMBR) co-digesting raw microalgae and primary sludge. Best operating conditions for this scale-up were energetically and economically assessed based on laboratory results. Economic balance showed 3% higher annual costs when operating a reactor at 100 d solids retention time (SRT) compared to 70 d SRT. Energetic balance showed a 5.5-fold increase in heat demand working at thermophilic temperature comparing to mesophilic. The AnMBR operating conditions were set at 70 d SRT and 35 °C. The pilot-scale and lab-scale co-digesters performed similarly in terms of biogas production and system stability. 154 mLbiogas·d^-1·L^-1_reactor were produced at pilot-scale, corresponding to methane yield of 215 mLCH₄·gCOD_inf^-1. AnMBR filtration at both laboratory and pilot-scale showed stability working at permeate fluxes of 4.2-5.8 L·m^-2·h^-1.

Anaerobic membrane bioreactors (AnMBR) treating urban wastewater in mild climates

Feasibility of an AnMBR demonstration plant treating urban wastewater (UWW) at temperatures around 25-30 °C was assessed during a 350-day experimental period. The plant was fed with the effluent from the pre-treatment of a full-scale municipal WWTP, characterized by high COD and sulfate concentrations. Biodegradability of the UWW reached values up to 87%, although a portion of the biodegradable COD was consumed by sulfate reducing organisms. Effluent COD remained below effluent discharge limits, achieving COD removals above 90%. System operation resulted in a reduction of sludge production of 36-58% compared to theoretical aerobic sludge productions. The membranes were operated at gross transmembrane fluxes above 20 LMH maintaining low membrane fouling propensities for more than 250 days without chemical cleaning requirements. Thus, the system resulted in net positive energy productions and GHG emissions around zero. The results obtained confirm the feasibility of UWW treatment in AnMBR under mild and warm climates.

Modeling the anaerobic treatment of sulfate-rich urban wastewater: Application to AnMBR technology

Although anaerobic membrane bioreactors (AnMBR) are a core technology in the transition of urban wastewater (UWW) treatment towards a circular economy, the transition is being held back by a number of bottlenecks. The dissolved methane released from the effluent, the need to remove nutrients (ideally by recovery), or the energy lost by the competition between methanogenic and sulfate-reducing bacteria (SRB) for the biodegradable COD have been identified as the main issues to be addressed before AnMBR becomes widespread. Mathematical modeling of this technology can be used to obtain further insights into these bottlenecks plus other valuable information for design, simulation and control purposes. This paper therefore proposes an AnMBR anaerobic digestion model to simulate the crucial SRB-related process since these bacteria degrade more than 40% of the organic matter. The proposed model, which is included in the BNRM2 collection model, has a reduced but all-inclusive structure, including hydrolysis, acidogenesis, acetogenesis, methanogenesis and other SRB-related processes. It was calibrated and validated using data from an AnMBR pilot plant treating sulfate-rich UWW, including parameter values obtained in off-line experiments and optimization methods. Despite the complex operating dynamics and influent composition, it was able to reproduce the process performance. In fact, it was able to simulate the AD of sulfate-rich UWW considering only two groups of SRB: heterotrophic SRB growing on both VFA (propionate) and acetate, and autotrophic SRB growing on hydrogen. Besides the above-mentioned constraints, the model reproduced the dynamics of the mixed liquor solids concentration, which helped to integrate biochemical and filtration models. It also reproduced the alkalinity and pH dynamics in the mixed liquor required for assessing the effect of chemical precipitation on membrane scaling.

A mathematical approach to predict the solids concentration in anaerobic membrane bioreactos (AnMBR): Evaluation of the volatile solids solubilization

Anaerobic Membrane Bioreactors (AnMBR) are gaining attention as a suitable approach for sustainable low-strength wastewater treatment, as they bring together the advantages of both anaerobic treatments and membrane bioreactors. However, increasing the sludge retention time (SRT) necessary to favor hydrolysis increases the suspended solids concentration potentially leading to decreased permeate flux. Therefore, the availability of a mathematical approach to predict the solids concentration within an AnMBR can be very useful. In this work, a mathematical model describing the volatile solids concentration within the reactor as a function of the operating parameters and the influent characteristics is developed. The solubilization of organic particulates was clearly influenced by temperature and the SRT, whereas the hydraulic retention time influence was negligible. Furthermore, the activation energy value of about 20 kJ mol^-1 confirms the idea that diffusion of hydrolytic enzymes from the bulk solution to the particle surface is the rate-limiting step of hydrolysis.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Food-processing wastes

Literature published in 2018 and literature published in 2019 related to food-processing wastes treatment for industrial applications are reviewed. This review is a subsection of the Treatment Systems section of the annual Water Environment Federation literature review and covers the following food-processing industries and applications: general, meat and poultry, fruits and vegetables, dairy and beverage, and miscellaneous treatment of food wastes. PRACTITIONER POINTS: This article summarizes literature reviews published in 2018 and in 2019 related to food processing wastes treatment for industrial applications are reviewed. This review is a subsection of the Treatment Systems section of the annual Water Environment Federation literature review and covers the following food processing industries and applications: general, meat and poultry, fruits and vegetables, dairy and beverage, and miscellaneous treatment of food wastes.

A brief review of anaerobic membrane bioreactors emphasizing recent advancements, fouling issues and future perspectives

This review summarizes the recent development and studies of anaerobic membrane bioreactor (AnMBR) to control fouling issues. AnMBR is an emerging waste water treatment technology mainly because of its low sludge residual, high volumetric organic removal rate, complete liquid-solid separation, better effluent quality, efficient resource recovery and the small footprint. This paper surveys the fundamental aspects of AnMBRs, including its applications, membrane configurations, and recent progress for enhanced reactor performance. Furthermore, the membrane fouling, a major restriction in the practical application of AnMBR, its mechanism and antifouling strategies like membrane cleaning, quorum quenching, ultrasonic treatment, membrane modifications, and antifouling agents are briefly discussed. Based on the review, the key issues that require urgent attention to facilitate large scale and integrated application of AnMBR technology are identified and future research perspectives relating to the prevalent issues are proposed.

Anaerobic membrane bioreactors for treatment of emerging contaminants: A review

Emerging contaminants (ECs) are synthetic organic chemicals that released into the environment, which pose a serious threat to the ecosystem and human health. Due to the high costs of physicochemical methods and the possibility of secondary pollution, and conventional biological treatment techniques are not efficient to remove ECs. Thus, there is a need to develop novel technologies to treat ECs. Anaerobic digestion (AD) is reported to degrade most ECs. Anaerobic membrane bioreactor (AnMBR) is an upgraded AD technology that has high system stability and microbial community abundance. The biogas production and EC biodegradation efficiency in the AnMBR system are markedly higher than those in the traditional AD system. In recent years, AnMBR is widely used to remove environmental ECs. This review analyzes the feasibility and challenges of AnMBR in the treatment of ECs and provides useful insights for improving the performance and efficiency of AnMBR to treat ECs.

Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-Of-The-Art and Performance Analysis

Wastewater reuse as a sustainable, reliable and energy recovery concept is a promising approach to alleviate worldwide water scarcity. However, the water reuse market needs to be developed with long-term efforts because only less than 4% of the total wastewater worldwide has been treated for water reuse at present. In addition, the reclaimed water should fulfill the criteria of health safety, appearance, environmental acceptance and economic feasibility based on their local water reuse guidelines. Moreover, municipal wastewater as an alternative water resource for non-potable or potable reuse, has been widely treated by various membrane-based treatment processes for reuse applications. By collecting lab-scale and pilot-scale reuse cases as much as possible, this review aims to provide a comprehensive summary of the membrane-based treatment processes, mainly focused on the hydraulic filtration performance, contaminants removal capacity, reuse purpose, fouling resistance potential, resource recovery and energy consumption. The advances and limitations of different membrane-based processes alone or coupled with other possible processes such as disinfection processes and advanced oxidation processes, are also highlighted. Challenges still facing membrane-based technologies for water reuse applications, including institutional barriers, financial allocation and public perception, are stated as areas in need of further research and development.

Micro-macro transition for numerical simulation of submerged membrane bioreactor

The objective of this work is numerical simulation of the membrane by direct analysis at micro, meso and macro level. This approach includes first a defining and modeling of a basic structural unit, after that simulation of a fragment as a representative element of the membrane structure. Then the results obtained to transfer for the entire membrane module and finally modeling of the membrane as porous media with calculated permeability. The numerical simulation was done with Ansys CFX, using the Darcy’s equation for flow through porous media with configuration of the membrane and second order backward Euler transient scheme for solving the Navier-Stokes equations.

The permeability of the membrane is determined at a micro and macro level by computer simulation for different fluids, which allows to evaluating the influence of the viscosity on the flow passing through the membrane. This micro-macro approach is quite efficient and cost-effective because it saves time and requires less computer capacity and allows direct analysis of the complex structure of the membrane modules.

Influence of COD/SO42- ratio on vinasse treatment performance by two-stage anaerobic membrane bioreactor

Vinasse is sulfate-rich wastewater due to sulfuric acid dosage in some ethanol production steps. The vinasse sulfate concentration is subject to seasonal variations. A two-stage anaerobic membrane bioreactor (2S-AnMBR) was operated to evaluate the influence of COD/SO₄^2- ratio on vinasse treatment performance by using a real vinasse sample under natural seasonal COD/SO₄^2- variation. This ratio directly affects the sulfidogenesis efficiency, which is responsible for different forms of inhibition in the anaerobic treatment of sulfate-rich wastewater. The bioreactor presented a stable performance at the highest COD/SO₄^2- ratios (50-94), with high removal of chemical oxygen demand (COD) (97.5 ± 0.4%) and volatile fatty acids (VFA) (98.0 ± 0.6%), but low removal of sulfate (69.9 ± 9.5%), indicating lower sulfate reducing bacteria (SRB) activity. In the lowest COD/SO₄^2- ratios (9-20), a deterioration in the removal of organic matter (87.0 ± 1.3%) and VFA (69.8 ± 15.5%) was observed, accompanied by sulfate removal increase (92.9 ± 2.6%). A significant correlation between COD fractions removed via methanogenesis and sulfidogenesis and the COD/SO₄^2- ratio was found, indicating that the increase of this ratio is beneficial to the methanogenic archaea activity. The occurrence of sulfidogenesis, favored by the lower COD/SO₄^2- ratios, induced the microbial soluble products (SMP) and extracellular polymeric substances (EPS) release and protein/carbohydrate ratio increase in the mixed liquor, contributing to the filtration resistance increase.

Aeration control in membrane bioreactor for sustainable environmental footprint

In this study different scenarios were scrutinized to minimize the energy consumption of a membrane bioreactor system for wastewater treatment. Open-loop and closed-loop scenarios were investigated by two-step cascade control strategies based on dissolved oxygen, ammonia and nitrite concentrations. An integrated MBR model which includes also the greenhouse gas formation/emission processes was applied. A substantial energy consumption reduction was obtained for the closed-loop scenarios (32% for Scenario 1 and 82% for Scenario 2). The air flow control based on both ammonia and nitrite concentrations within the aerobic reactor (Scenario 2) provided excellent results in terms of reduction of operating cost reduction (64%), direct (10%) and indirect (81%) emissions.

Review on microaeration-based anaerobic digestion: State of the art, challenges, and prospectives

Microaeration (dosing small quantities of air or oxygen) is an effective approach to facilitate anaerobic digestion (AD) process and has gained increased attention in recent years. The underlying mechanisms of the facilitation effect of microaeration on AD process were reviewed in terms of accelerating hydrolysis, scavenging hydrogen sulfide, and affecting microbial diversity. Process parameters and control strategies were summarized to reveal considerable factors in implementing microaeration-based AD process. In addition, current applications, including lab-, pilot- and full-scale level cases, were summarized to provide guidance for further improvement in large-scale applications. The challenges and future perspectives were also highlighted to promote the development of AD process associated with microaeration.

New frontiers from removal to recycling of nitrogen and phosphorus from wastewater in the Circular Economy

Nutrient recovery technologies are rapidly expanding due to the need for the appropriate recycling of key elements from waste resources in order to move towards a truly sustainable modern society based on the Circular Economy. Nutrient recycling is a promising strategy for reducing the depletion of non-renewable resources and the environmental impact linked to their extraction and manufacture. However, nutrient recovery technologies are not yet fully mature, as further research is needed to optimize process efficiency and enhance their commercial applicability. This paper reviews state-of-the-art of nutrient recovery, focusing on frontier technological advances and economic and environmental innovation perspectives. The potentials and limitations of different technologies are discussed, covering systems based on membranes, photosynthesis, crystallization and other physical and biological nutrient recovery systems (e.g. incineration, composting, stripping and absorption and enhanced biological phosphorus recovery).

Unveiling microbial structures during raw microalgae digestion and co-digestion with primary sludge to produce biogas using semi-continuous AnMBR systems

Methane production from microalgae can be enhanced through anaerobic co-digestion with carbon-rich substrates and thus mitigate the inhibition risk associated with its low C:N ratio. Acclimated microbial communities for microalgae disruption can be used as a source of natural enzymes in bioenergy production. However, co-substrates with a certain microbial diversity such as primary sludge might shift the microbial structure. Substrates were generated in a Water Resource Recovery Facility (WRRF) and combined as follows: Scenedesmus or Chlorella digestion and microalgae co-digestion with primary sludge. The study was performed using two lab-scale Anaerobic Membrane Bioreactors (AnMBR). During three years, different feedstocks scenarios for methane production were evaluated with a special focus on the microbial diversity of the AnMBR. 57% of the population was shared between the different feedstock scenarios, revealing the importance of Anaerolineaceae members besides Smithella and Methanosaeta genera. The addition of primary sludge enhanced the microbial diversity of the system during both Chlorella and Scenedesmus co-digestion and promoted different microbial structures. Aceticlastic methanogen Methanosaeta was dominant in all the feedstock scenarios. A more remarkable role of syntrophic fatty acid degraders (Smithella, Syntrophobacteraceae) was observed during co-digestion when only microalgae were digested. However, no significant changes were observed in the microbial composition during anaerobic microalgae digestion when feeding only Chlorella or Scenedesmus. This is the first work revealing the composition of complex communities for semi-continuous bioenergy production from WRRF streams. The stability and maintenance of a microbial core over-time in semi-continuous AnMBRs is here shown supporting their future application in full-scale systems for raw microalgae digestion or co-digestion.

A review on the applications of ultrasonic technology in membrane bioreactors

Membrane bioreactors (MBRs) have received increasing attention in the field of wastewater treatment in recent years. However, membrane fouling is the main problem of MBRs, limiting their widespread and large applications. Membrane cleaning methods can be mainly classified into four types including chemical, physical, physico-chemical and biological clean the fouled membrane. In recent years, ultrasonication has been reported as a promising cleaning technique for the membranes fouled in MBRs. Ultrasonic irradiation can clean the fouled membrane by creating important physical phenomena including microjets, microstreams and shock waves. Moreover, the ultrasonic method can be combined with other cleaning methods e.g. chemical cleaning and backwashing in order to improve the cleaning efficiency. It should be noted that the application of ultrasonic in the MBR system is not limited to the cleaning of membrane. The pretreatment of the wastewater by ultrasonic irradiation or ultrasound coupled with other methods, e.g. ozonation, prior to MBR system, can decrease the organic loading of the wastewater and subsequently postpone the fouling of the membrane. This paper critically reviews the recent advances in the applications of ultrasound in MBR systems. Emerging issues associated with application of on-line ultrasound and also hybrid on-line ultrasound for controlling the membrane fouling in MBR systems are critically reviewed. Moreover, application of the ultrasound in ex-situ form for cleaning the fouled membranes and pretreatment of wastewater prior to the MBR system is discussed.

Recent Progresses in Application of Membrane Bioreactors in Production of Biohydrogen

Biohydrogen is a clean and viable energy carrier generated through various green and renewable energy sources such as biomass. This review focused on the application of membrane bioreactors (MBRs), emphasizing the combination of these devices with biological processes, for bio-derived hydrogen production. Direct biophotolysis, indirect biophotolysis, photo-fermentation, dark fermentation, and conventional techniques are discussed as the common methods of biohydrogen production. The anaerobic process membrane bioreactors (AnMBRs) technology is presented and discussed as a preferable choice for producing biohydrogen due to its low cost and the ability of overcoming problems posed by carbon emissions. General features of AnMBRs and operational parameters are comprehensively overviewed. Although MBRs are being used as a well-established and mature technology with many full-scale plants around the world, membrane fouling still remains a serious obstacle and a future challenge. Therefore, this review highlights the main benefits and drawbacks of MBRs application, also discussing the comparison between organic and inorganic membranes utilization to determine which may constitute the best solution for providing pure hydrogen. Nevertheless, research is still needed to overcome remaining barriers to practical applications such as low yields and production rates, and to identify biohydrogen as one of the most appealing renewable energies in the future.

Selective production of volatile fatty acids at different pH in an anaerobic membrane bioreactor

This study investigated the production of major volatile fatty acid (VFA) components in an anaerobic membrane bioreactor (AnMBR) to treat low-strength synthetic wastewater. No selective inhibition was applied for methane production and solvent-extraction method was used for VFA extraction. The results showed acetic and propionic acid were the predominant VFA components at pH 7.0 and 6.0 with concentrations of 1.444 ± 0.051 and 0.516 ± 0.032 mili-mol/l respectively. At pH 12.0 isobutyric acid was the major VFA component with a highest concentration of 0.712 ± 0.008 mili-mol/l. The highest VFA yield was 48.74 ± 1.5 mg VFA/100 mg COD_feed at pH 7.0. At different pH, AnMBR performance was evaluated in terms of COD, nutrient removal and membrane fouling rate. It was observed that the membrane fouled at a faster rate in both acidic and alkaline pH conditions, the slowest rate in membrane fouling was observed at pH 7.0.