Impact of FeCl₃ dosing on AnMBR treatment of municipal wastewater

Effectiveness of cloth media filters on mitigating membrane fouling in anaerobic filter membrane bioreactors

Membrane fouling is a persistent challenge that has impeded the broader application of anaerobic membrane bioreactors (AnMBRs). To mitigate membrane fouling, between the outlet of the UASB anaerobic bioreactor and the PVDF membrane to form the anaerobic filter membrane bioreactor (AnFMBR) system. Through comprehensive experiments, the optimal pore size for cloth filters was determined to be 50 μm. A comprehensive assessment over 140 days of operation shows that the novel AnFMBR had significantly greater resistance to membrane pollution than the traditional AnMBR. The AnFMBR system membrane tank exhibited lower mixed liquor suspended solid and mixed liquor volatile suspended solid concentrations, smaller sludge particle sizes, increased hydrophilicity of sludge flocs, and optimized microbial community distribution compared to those of conventional AnMBRs. The total solids foulant accumulation rate in the AnMBR was 5.1 g/m2/day, while in the AnFMBR, the rate was 2.4 g/m2/day, marking a 53.7 % decrease in fouling rate for the AnFMBR compared with the AnMBR. This decrease indicates that integrating the filtration assembly significantly lowered the rate of solid foulant accumulation on the membrane surface, primarily by controlling the buildup of solid foulants in the cake layer, thereby alleviating membrane fouling. AnFMBR compared to AnMBR, the membrane fouling rate halved, effectively doubled the interval between membrane cleaning from seven days, as observed in the AnMBR system, to fourteen days. These findings underscore the potential of integrating cloth media filters into AnMBRs to improve operational efficiency, economic viability, and sustainability.

Iron Recycle-Driven Organic Capture and Sidestream Anaerobic Membrane Bioreactor for Revolutionizing Bioenergy Generation in Municipal Wastewater Treatment

The practicality of intensifying organic matter capture for bioenergy recovery to achieve energy-neutral municipal wastewater treatment is hindered by the lack of sustainable methods. This study developed innovative processes integrating iron recycle-driven organic capture with a sidestream anaerobic membrane bioreactor (AnMBR). Iron-assisted chemically enhanced primary treatment achieved elemental redirection with 75.2% of chemical oxygen demand (COD), 20.2% of nitrogen, and 97.4% of phosphorus captured into the sidestream process as iron-enhanced primary sludge (Fe-PS). A stable and efficient biomethanation of Fe-PS was obtained in AnMBR with a high methane yield of 224 mL/g COD. Consequently, 64.1% of the COD in Fe-PS and 48.2% of the COD in municipal wastewater were converted into bioenergy. The acidification of anaerobically digested sludge at pH = 2 achieved a high iron release efficiency of 96.1% and a sludge reduction of 29.3% in total suspended solids. Ultimately, 87.4% of iron was recycled for coagulant reuse, resulting in a theoretical 70% reduction in chemical costs. The novel system evaluation exhibited a 75.2% improvement in bioenergy recovery and an 83.3% enhancement in net energy compared to the conventional system (primary sedimentation and anaerobic digestion). This self-reliant and novel process can be applied in municipal wastewater treatment to advance energy neutrality at a lower cost.

In-depth insight on microbial electrochemical systems coupled with membrane bioreactors for performance enhancement: a review

A conventional activated sludge (CAS) system has traditionally been used for secondary treatment in wastewater treatment plants. Due to the high cost of aeration and the problem of sludge treatment, researchers are developing alternatives to the CAS system. A membrane bioreactor (MBR) is a technology with higher solid-liquid separation efficiency. However, the use of MBR is limited due to inevitable membrane fouling and high energy consumption. Membrane fouling requires frequent cleaning, and MBR components must be replaced, which reduces membrane lifetime and operating costs. To overcome the limitations of the MBR system, a microbial fuel cell-membrane bioreactor (MFC-MBR) coupling system has attracted the interest of researchers. The design of the novel bioelectrochemical membrane reactor (BEMR) can effectively couple microbial degradation in the microbial electrochemical system (MES) and generate a microelectric field to reduce and alleviate membrane fouling in the MBR system. In addition, the coupling system combining an MES and an MBR can improve the efficiency of COD and ammonium removal while generating electricity to balance the energy consumption of the system. However, several obstacles must be overcome before the MFC-MBR coupling system can be commercialised. The aim of this study is to provide critical studies of the MBR, MES and MFC-MBR coupling system for wastewater treatment. This paper begins with a critical discussion of the unresolved MBR fouling problem. There are detailed past and current studies of the MES-MBR coupling system with comparison of performances of the system. Finally, the challenges faced in developing the coupling system on a large scale were discussed.

Effects of wastewater pre-treatment on clogging of an intermittent sand filter

Intermittent sand filters (ISFs) are widely used in rural areas to treat domestic and dilute agricultural wastewater due to their simplicity, efficacy and relative low cost. However, filter clogging reduces their operational lifetime and sustainability. To reduce the potential of filter clogging, this study examined pre-treatment of dairy wastewater (DWW) by coagulation with ferric chloride (FeCl₃) prior to treatment in replicated, pilot-scale ISFs. Over the study duration and at the end of the study, the extent of clogging across hybrid coagulation-ISFs was quantified, and the results were compared to ISFs treating raw DWW without a coagulation pre-treatment, but otherwise operated under the same conditions. During operation, ISFs receiving raw DWW recorded higher volumetric moisture content (θ_v) than ISFs treating pre-treated DWW, which indicated that biomass growth and clogging rate was higher in ISFs treating raw DWW, which were fully clogged after 280 days of operation. The hybrid coagulation-ISFs remained fully operational until the end of the study. Examination of the field-saturated hydraulic conductivity (K_fs) showed that ISFs treating raw DWW lost approximately 85 % of their infiltration capacity in the uppermost layer due to biomass build-up versus 40 % loss for hybrid coagulation-ISFs. Furthermore, loss on ignition (LOI) results indicated that conventional ISFs developed five times the organic matter (OM) in the uppermost layer compared to ISFs treating pre-treated DWW. Similar trends were observed for phosphorus, nitrogen and sulphur, where proportionally higher values were observed for raw DWW ISFs than pre-treated DWW ISFs, with values decreasing with depth. Scanning electron microscopy (SEM) showed a clogging biofilm layer on the surface of raw DWW ISFs, while pre-treated ISFs maintained distinguishable sand grains on the surface. Overall, hybrid coagulation-ISFs are likely to sustain infiltration capacity for a longer period than filters treating raw wastewater; therefore, requiring smaller surface area for treatment and minimal maintenance.

In-situ membrane fouling control and performance improvement by adding materials in anaerobic membrane bioreactor: A review

Anaerobic membrane bioreactor (AnMBR) is a promising treatment technique for various types of wastewaters, and is preferred over other conventional aerobic and anaerobic methods. However, membrane fouling is considered a bottleneck in AnMBR system, which technically blocks membrane pores by numerous inorganics, organics, and other microbial substances. Various materials can be added in AnMBR to control membrane fouling and improve anaerobic digestion, and studies reporting the materials addition for this purpose are hereby systematically reviewed. The mechanism of membrane fouling control including compositional changes in extracellular polymeric substances (EPSs) and soluble microbial products (SMPs), materials properties, stimulation of antifouling microbes and alteration in substrate properties by material addition are thoroughly discussed. Nonetheless, this study opens up new research prospects to control membrane fouling of AnMBR, engineered by material, including compositional changes of microbial products (EPS and SMP), replacement of quorum quenching (QQ) by materials, and overall improvement of reactor performance. Regardless of the great research progress achieved previously in membrane fouling control, there is still a long way to go for material-mediated AnMBR applications to be undertaken, particularly for materials coupling, real scale application and molecular based studies on EPSs and SMPs, which were proposed for future researches.

Enhancement of struvite generation and anti-fouling in an electro-AnMBR with Mg anode-MF membrane module

Severe membrane fouling and the inability to remove/recover nitrogen and phosphorus are bottlenecks of anaerobic membrane bioreactors (AnMBRs) for large-scale application in wastewater treatment. Herein, an electrochemical AnMBR with a Mg anode-membrane module (electro-AnMBR) was built and showed good performance in terms of membrane fouling mitigation and nutrient recovery during sewage treatment. Compared with the traditional AnMBR, membrane fouling in the electro-AnMBR was reduced by up to 30%. The application of an electric field decreased the zeta potential, viscosity, and EPS concentration of the sludge-water liquor in the electro-AnMBR, which could improve the cake layer structure and thus enhance water permeability. Meanwhile, 26% of NH₄⁺ and 48% of PO₄^3- co-precipitated with Mg²⁺ generating from the sacrificial Mg anode and were recovered as struvite deposited onto cathode in the electro-AnMBR. Hydrogen evolution provided a relatively alkaline pH environment, resulting in struvite electrodeposition on the graphic cathode, which partly separated the formed struvite from the sludge with a purity of 77%. In the electro-AnMBR, the electrochemical reactions provided alkalinity and effectively inhibited anaerobic acidification. The applied voltage of 0.6 V reduced the relative abundance of methanosaeta, but increased that of methanosarcina, which is also beneficial for the membrane anti-fouling.

Electrochemical iron production to enhance anaerobic membrane treatment of wastewater

Although iron salts such as iron(III) chloride (FeCl₃) have widespread application in wastewater treatment, safety concerns limit their use, due to the corrosive nature of concentrated solutions. This study demonstrates that local, electrochemical generation of iron is a viable alternative to the use of iron salts. Three laboratory systems with anaerobic membrane processes were set up to treat real wastewater; two systems used the production of either in-situ or ex-situ electrochemical iron (as Fe²⁺ and Fe²⁺(Fe³⁺)₂O₄, respectively), while the other system served as a control. These systems were operated for over one year to assess the impact of electrochemically produced iron on system performance. The results showed that dosing of electrochemical iron significantly reduced sulfide concentration in effluent and hydrogen sulfide content in biogas, and mitigated organics-based membrane fouling, all of which are critical issues inherently related to sustainability of anaerobic wastewater treatment. The electrochemical iron strategy can generate multiple benefits for wastewater management including increased removal efficiencies for total and volatile suspended solids, chemical oxygen demand and phosphorus. The rate of methane production also increased with electrochemically produced iron. Economic analysis revealed the viability of electrochemical iron with total cost reduced by one quarter to a third compared with using FeCl₃. These benefits indicate that electrochemical iron dosing can greatly enhance the overall operation and performance of anaerobic membrane processes, and this particularly facilitates wastewater management in a decentralized scenario.

Membrane fouling mitigation by coagulation and electrostatic repulsion using an electro-AnMBR in kitchen wastewater treatment

Anaerobic membrane bioreactor (AnMBR) is considered an efficient technique for kitchen wastewater treatment; however, membrane fouling restricts their applicability. In this study, a novel AnMBR with an Fe anode and Ti membrane cathode (electro-AnMBR) was constructed. The reactor exhibited good performance in pollutant removal and antifouling in kitchen wastewater treatment. Compared with the traditional AnMBR, the electro-AnMBR increased phosphate removal by approximately 55% and reduced transmembrane pressure (TMP) by 50%. Coagulation from the Fe²⁺/Fe³⁺ released by the sacrificial anode increased the sludge floc size and porosity, significantly reducing the membrane fouling potential. In addition, the lower amounts of extracellular polymeric substances (EPS) in the electro-AnMBR, due to an increased Methanosarcina abundance, facilitated membrane-fouling mitigation. Almost no TMP difference was observed between the AnMBRs with Ti, ceramic, and polyvinylidene fluoride (PVDF) membranes. Quantitative analysis using an electrochemical quartz crystal microbalance with dissipation monitoring indicated that the electrostatic repulsion between EPS and cathodic membrane was positively correlated with the applied voltage. In addition, proteins in EPS had a higher membrane fouling potential than polysaccharides, and Fe³⁺ coagulation reduced adhesion capacity and alleviated membrane fouling. This study provides a perspective viewpoint for AnMBR membrane fouling mitigation and reactor design.

Energy-Efficient AnMBRs Technology for Treatment of Wastewaters: A Review

In recent years, anaerobic membrane bioreactor (AnMBRs) technology, a combination of a biological reactor and a selective membrane process, has received increasing attention from both industrialists and researchers. Undoubtedly, this is due to the fact that AnMBRs demonstrate several unique advantages. Firstly, this paper addresses fundamentals of the AnMBRs technology and subsequently provides an overview of the current state-of-the art in the municipal and domestic wastewaters treatment by AnMBRs. Since the operating conditions play a key role in further AnMBRs development, the impact of temperature and hydraulic retention time (HRT) on the AnMBRs performance in terms of organic matters removal is presented in detail. Although membrane technologies for wastewaters treatment are known as costly in operation, it was clearly demonstrated that the energy demand of AnMBRs may be lower than that of typical wastewater treatment plants (WWTPs). Moreover, it was indicated that AnMBRs have the potential to be a net energy producer. Consequently, this work builds on a growing body of evidence linking wastewaters treatment with the energy-efficient AnMBRs technology. Finally, the challenges and perspectives related to the full-scale implementation of AnMBRs are highlighted.

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.

Integrated anaerobic and algal bioreactors: A promising conceptual alternative approach for conventional sewage treatment

Conventional sewage treatment applying activated sludge processes is energy-intensive and requires great financial input, hampering widespread implementation. The introduction of anaerobic membrane bioreactors (AnMBR) followed by an algal reactor growing species of commercial interest, may present an alternative, contributing to the envisaged resource recovery at sewage treatment plants. AnMBRs can be applied for organic matter removal with energy self-sufficiency, provided that effective membrane fouling management is applied. Haematococcus pluvialis, an algal species with commercial value, can be selected for ammonium and phosphate removal. Theoretical analysis showed that good pollutant removal, positive financial output, as well as a significant reduction in the amount of hazardous activated sludge can be achieved by applying the proposed process, showing interesting advantages over current sewage treatment processes. Microbial contamination to H. pluvialis is a challenge, and technologies for preventing the contamination during continuous sewage treatment need to be applied.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid–liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

Important effects of temperature on treating real municipal wastewater by a submerged anaerobic membrane bioreactor: Removal efficiency, biogas, and microbial community

A submerged anaerobic membrane bioreactor (SAnMBR) was used in the treatment of real municipal wastewater at operation temperatures ranging from 15 °C to 25 °C and hydraulic retention time (HRT) of 6 h. The treatment process was evaluated in terms of organic removal efficiency, biogas production, sludge growth and membrane filtration. During long-term operation, the SAnMBR achieved chemical oxygen demand removal efficiencies of about 90% with a low sludge yield (0.12-0.19 g-VSS/g-COD_rem) at 20-25 °C. Approximately 1.82-2.27 kWh/d of electric energy was generated during the wastewater treatment process at 20-25 °C, 0.67 kWh/d was generated at 15 °C. The microbial community analysis results showed that microbial community was dominated by aceticlastic methanogens, coupled by hydrogenotrophic methanogens and a very small quantity of methylotrophic methanogens. It was also shown that the stabilization of the microbial community could be attributed to the carbohydrate-protein degrading bacteria and the carbohydrate degrading bacteria.

Efficient recovery of phosphorus and sulfur from Anaerobic Membrane Bioreactor (AnMBR) permeate using chemical addition of iron and evaluation of its nutrient availability for plant uptake

Anaerobic membrane bioreactors (AnMBRs) represent an emerging environmental biotechnology platform with the potential to simultaneously recover water, energy, and nutrients from concentrated wastewaters. The removal and beneficial capture of nutrients from AnMBR permeate has yet to be fully explored, therefore this study sought to foster iron phosphate recovery through a tertiary coagulation process, as well as characterize the recovered nutrient product (RNP) and assess its net phosphorus release, diffusion, and availability for plant uptake. One of the primary goals of this study was to optimize the dose of the coagulant, ferric chloride, and coagulant aid, aluminum chlorohydrate (ACH), for continuous application to the coagulation-flocculation-sedimentation (CFS) unit of an AnMBR pilot plant treating municipal wastewater, through controlled bench-scale jar tests. Anaerobic systems present unique challenges for nutrient capture, including high, dissolved hydrogen sulfide concentrations, along with settleability issues. The addition of the coagulant aid increases settleability, while enhancing phosphorus removal by up to 20%, decreasing iron demand. Water quality analysis indicated that a variety of factors affect nutrient capture, including the COD (chemical oxygen demand) concentration of the permeate and the limiting coagulant dose. COD >200 mg/L was shown to decrease the phosphorus removal efficiency by up to 15%. A combination of inductively coupled plasma optical emission spectrometer (ICP-OES) elemental analysis, inductively coupled plasma mass spectrometer (ICP-MS) elemental analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES) spectroscopy analysis was used to characterize the P-rich RNP which revealed a 2.58% w/w phosphorus content and the lack of a well-defined crystalline structure. Detailed studies on resin extractable phosphorus to assess the plant uptake potential also demonstrated that iron-based P-rich RNPs may not be an effective fertilizer product, as they can act as a phosphorus sink in some agricultural systems instead of a source.

Antifouling potential and microbial characterization of an electrochemical anaerobic membrane bioreactor utilizing membrane cathode and iron anode

Serious membrane fouling limits the application of anaerobic membrane bioreactors (AnMBRs) in sewage treatment. Herein, a novel electrochemical AnMBR (eAnMBR) was established by integrating electrocoagulation and a conductive membrane into an AnMBR. Compared with the traditional AnMBR, TP average removal rate increased by 24.97% and the membrane service cycle extended by 109.68% in the eAnMBR. Low extracellular polymeric substance concentration and large floc size were found in the mixed liquid of the eAnMBR due to the combined effect of coagulation and electric field, which induced a porous and hydrophilic cake layer, resulting in excellent water permeation capabilities. Additionally, the conductive membrane cathode effectively suppressed membrane fouling by the electrostatic repulsion and gas scouring. In the eAnMBR, the presence of an electric field and iron ions enriched the diversity of the microbial community, which may improve the adaptation of biochemical systems to environmental changes.

One-year operation of a 20-L submerged anaerobic membrane bioreactor for real domestic wastewater treatment at room temperature: Pursuing the optimal HRT and sustainable flux

A 20 L hollow-fiber submerged anaerobic membrane bioreactor (SAnMBR) was used to treat real domestic wastewater at 25 °C with hydraulic retention times (HRTs) ranging from 4 to 12 h. The process performance was evaluated by organic removal efficiency, biogas production, sludge yield, and filtration behaviors during one-year's operation. For HRTs ranging between 6 and 12 h, the AnMBR showed good organic removal efficiency with chemical oxygen demand (COD) and biochemical oxygen demand (BOD) removal efficiencies of about 89% and 93%, respectively. The biogas yield was 0.26 L-gas/g-COD_fed, with approximately 80% methane content, and the sludge yield was 0.07-0.11 g-VSS/g-COD_rem. While at an HRT of 4 h, with the higher wastewater treatment capacity and organic loading rate (OLR), the biogas production was lower (0.17 L-gas/g-COD_fed), and the sludge production was higher (0.22 g-VSS/g-COD_rem). The organic removal performance (COD 84% and BOD 89%) at HRT of 4 h was acceptable due to the effective separation effect of the membrane filtration process. According to COD balance analysis, the low biogas yield and high sludge yield at HRT of 4 h were due to insufficient biodegradation under an OLR of 2.05 g-COD/L-reactor/d. Theoretical calculations based on Henry's law indicate that the ideal methane content in the biogas should be 82-85% when the operational temperature was 25 °C. To achieve a high flux and sustainable AnMBR operation, the impact of mixed liquor suspended solid (MLSS) and gas sparging velocity (GSV) on the filtration performance was analyzed. The critical flux increased with increase in the GSV from 24.2 to 174.3 m/h, but decreased with increase in the MLSS concentration from 8.2 to 20.2 g/L. Therefore, decreasing fouling rate to 0.8-1.2 kPa/d by efficiently controlling GSV and MLSS, sustainable operation could be achieved at a flux of 0.34 m/d.

Self-forming dynamic membrane bioreactor for textile industry wastewater treatment

The robustness of anaerobic dynamic membrane bioreactor (AnDMBR) for synthetic textile wastewater treatment was investigated. Textile wastewater may contain high concentrations of NaCl and sulfate, hence their impact on the AnDMBR performance was investigated in detail. A dynamic membrane was formed on a 20-μm pore sized nylon support layer at a constant flux of around 8 LMH. In the absence of sulfate addition, total and filtered (soluble) COD averaged 96 ± 49 mg/L (91% removal) and 75 ± 35 mg/L (93% removal), respectively. Sulfate addition increased total COD in the permeate to 222 ± 68 mg/L (79% removal). Average SS concentration was lower than 30 mg/L in the permeate although its concentration in the bioreactor reached 10 g/L. Throughout the AnDMBR operation dye removal averaged >97%. Sludge filterability, which was assessed by specific resistance to filtration, supernatant filtration, capillary suction time and viscosity, decreased after sulfate addition. Organic and inorganic matters in the dynamic layer were characterized by SEM-EDS and FTIR analyses.

Effect of PAC on the Behavior of Dynamic Membrane Bioreactor Filtration Layer Based on the Analysis of Mixed Liquid Properties and Model Fitting

Recently, dynamic membrane bioreactor (DMBR) has gradually gained the interest of researchers for the development of membrane technology. In this paper, we set up parallel experiments to investigate the effect of powder activated carbon (PAC) on organic matter removal, transmembrane pressure, and filter cake layer characterization to make an overall performance assessment of DMBR. The results showed that DMBR has a good removal effect on organic matter removal, and with a chemical oxygen demand removal rate over 85%. Protein was found to be the main membrane fouling substance. Due to the electric double-layer effect, membrane fouling tended to be alleviated when the PN/PS value was low. Using a filtration model under constant current conditions, the filtration process through the cake layer was observed to be consistent with cake-intermediate model.

Performance Analysis for the Anaerobic Membrane Bioreactor Combined with the Forward Osmosis Membrane Bioreactor: Process Conditions Optimization, Wastewater Treatment and Sludge Characteristics

The anaerobic membrane bioreactors (AnMBR) were operated at 35 °C (H-AnMBR) and 25 °C (L-AnMBR) for long-term wastewater treatment. Two aerobic forward osmosis membrane bioreactors (FOMBRs) were utilized to treat the effluents of H-AnMBR and L-AnMBR, respectively. During the 180 days of operation, it is worth noting that the combined system was feasible, and the pollutant removal efficiency was higher. Though the permeate chemical oxygen demand (COD) of H-AnMBR (18.94 mg/L) was obviously lower than that of L-AnMBR (51.09 mg/L), the permeate CODs of the FOMBRs were almost the same with the average concentrations of 7.57 and 7.58 mg/L for the H-FOMBR and L-FOMBR, respectively. It was interesting that for both the AnMBRs, the permeate total nitrogen (TN) concentration was higher than that in bulk phase. However, the TN concentrations in the effluent remained stable with the values of 20.12 and 15.22 mg/L in the H-FOMBR and L-FOMBR effluents, respectively. For the two systems, the characteristics of activated sludge flocs were different for H-AnMBR-FOMBR sludge and L-AnMBR-FOMBR sludge. The viscosity of L-AnMBR-activated sludge (2.09 Pa·s) was higher compared to that of H-AnMBR (1.31 Pa·s), while the viscosity of activated sludge in L-FOMBR (1.44 Pa·s) was a little lower than that in H-FOMBR (1.48 Pa·s). The capillary water absorption time of L-AnMBR-activated sludge (69.6 s) was higher compared to that of H-AnMBR (49.5 s), while the capillary water absorption time of activated sludge in L-FOMBR (14.6 s) was little lower than that in H-FOMBR (15.6 s). The particle size of H-AnMBR-activated sludge (119.62 nm) was larger than that of L-AnMBR-activated sludge (84.92 nm), but the particle size of H-FOMBR-activated sludge (143.81 nm) was significantly smaller than that of L-FOMBR-activated sludge (293.38 nm). The observations of flocs indicated that the flocs of activated sludge in H-AnMBR were relatively loose, while the flocs of L-AnMBR were relatively tight. The fine sludge floc was less present in the L-FOMBR than in the H-FOMBR. Therefore, in the process of sewage treatment, the influent of each unit in the AnMBR-FOMBR system should have suitable organic content to maintain the particle sizes of sludge flocs.

Fouling Mitigation by Cationic Polymer Addition into a Pilot-Scale Anaerobic Membrane Bioreactor Fed with Blackwater

Cationic polymers have proven to be suitable flux enhancers (FEs) in large-scale aerobic membrane bioreactors (MBRs), whereas in anaerobic membrane bioreactors (AnMBRs) research is scarce, and so far, only done at lab-scale. Results from MBRs cannot be directly translated to AnMBRs because the extent and nature of membrane fouling under anaerobic and aerobic conditions are different. Our research focused on the long-term effect of dosing the cationic polymer Adifloc KD451 to a pilot AnMBR, fed with source-separated domestic blackwater. A single dosage of Adifloc KD451 at 50 mg L^-1 significantly enhanced the filtration performance in the AnMBR, revealed by a decrease in both fouling rate and total filtration resistance. Nevertheless, FE addition had an immediate negative effect on the specific methanogenic activity (SMA), but this was a reversible process that had no adverse effect on permeate quality or chemical oxygen demand (COD) removal in the AnMBR. Moreover, the FE had a long-term positive effect on AnMBR filtration performance and sludge filterability. These findings indicate that dosing Adifloc KD451 is a suitable strategy for fouling mitigation in AnMBRs because it led to a long-term improvement in filtration performance, while having no significant adverse effects on permeate quality or COD removal.

Study of Catalysts’ Influence on Photocatalysis/Photodegradation of Olive Oil Mill Wastewater. Determination of the Optimum Working Conditions

The high production of raw olive oil mill wastewater (OMW) is a current environmental problem due to its high organic load and phenol compounds. In this work, photo-Fenton reaction as an advanced oxidation process has been chosen for OMW treatment. In this sense, different iron salts (FeCl3, Fe2(SO4)3, FeSO4·7H2O, and Fe(ClO4)3) as catalysts were used in order to compare their effects on treatment. For each catalyst, different H2O2 concentrations (2.5, 5.0, 7.5, 10.0, 15.0, 20.0, and 30.0%, w/v) as oxidizing agents were tested. The common experimental conditions were temperature 20 °C, the catalyst/H2O2 ratio = 0.03, pH = 3, and ultraviolet light. The Lagergren kinetic model, in cases of total organic carbon removal, for the best H2O2 concentration per catalyst was used. During the experiments, the water quality was determined by measuring the removal percentages on chemical oxygen demand, total carbon, total organic carbon, total nitrogen, total phenolic compounds, total iron, turbidity and electric conductivity. The best catalyst was FeCl3 and the optimum H2O2 concentration was 7.5% (w/v). At these optimal conditions, the removal percentages for chemical oxygen demand, total phenolic compounds, total carbon, total organic carbon and total nitrogen were 60.3%, 88.4%, 70.1%, 63.2% and 51.5%, respectively.

Effect of ferric hydroxide on membrane fouling in membrane bioreactor treating pharmaceutical wastewater

Membrane fouling is considered as a main drawback for MBR technology especially treating industrial wastewater. Therefore, this study aimed to investigate the effect of fouling in membrane bioreactor (MBR) treating pharmaceutical wastewater with the addition of ferric hydroxide. Two identical lab-scale MBRs, namely, a control MBR (Co-MBR) and an enhanced MBR dosed with ferric hydroxide (Fe-MBR), were operated in parallel. The results demonstrate membrane fouling was retarded by 35% with the addition of iron. Further exploration of membrane fouling mechanisms showed iron addition resulted in increase in biomass floc size, enhancement of bacteria activity and reduction of dissolved organic concentration, especially carbohydrate, biopolymer and low molecular weight compounds concentrations in mixed liquor. There was also lower abundance of bacterial associated with biofilm formation in the Fe-MBR compared with the Co-MBR. These findings collectively contributed to the positive impacts on membrane fouling mitigation.

Size-dependent microbial diversity of sub-visible particles in a submerged anaerobic membrane bioreactor (SAnMBR): Implications for membrane fouling

Sub-visible particles, an often-overlooked fine particle (0.45-10 μm) with a size between sludge solids and soluble microbial products (SMP), have recently been identified as a critical foulant in anaerobic membrane bioreactors (AnMBRs), and our recent new insights into the size-fractionation and composition of sub-visible particles in AnMBRs have enabled fouling to be understood in more depth. Here, we investigated the microbial diversity of the sub-visible particles in three size fractions (i.e., 5-10, 1-5, and 0.45-1 μm) from bulk and cake solutions in a lab-scale AnMBR, and their fouling potential was further explored based on their filtration behavior and biofilm formation. Results show that with decreasing particle size, a significant shift in microbial communities was observed for the sub-visible particles in both bulk and cake solutions; (a) with notable decreases in filamentous microbes in the order SJA-15, GCA004, and Anaerolineales of phylum Chloroflexi, and, (b) with substantial increases in sulfate-reducing bacteria (i.e., the family Syntrophobacteraceae, genus DCE29 of family Thermodesulfovibrionaceae, Desulfovibrio, and Geobacter). More importantly, the filamentous microbes associated with micro-particles (5-10 μm) led to higher cake fouling resistances while free living cells in the form of colloidal particles (0.45-1 μm) induced severer pore blocking. Moreover, the micro-particles had an enhanced capacity to favor biofilm formation (OD595 = 1.0-2.5, categorized as highly positive), thus potentially aggravating biofouling. This work advances our knowledge on the effect of particle size on communities and underlying fouling behavior of microbes associated with fine particles in AnMBRs.

Anaerobic membrane bioreactors for wastewater treatment: Novel configurations, fouling control and energy considerations

Water shortage, public health and environmental protection are key motives to treat wastewater. The widespread adoption of wastewater as a resource depends upon development of an energy-efficient technology. Anaerobic membrane bioreactor (AnMBR) technology has gained increasing popularity due to their ability to offset the disadvantages of conventional treatment technologies. However there are several hurdles, yet to climb over, for wider spread and scale-up of the technology. This paper reviews fundamental aspects of anaerobic digestion of wastewater, and identifies the challenges and opportunities to the further development of AnMBRs. Membrane fouling and its implications are discussed, and strategies to control membrane fouling are proposed. Novel AnMBR configurations are discussed as an integrated approach to overcome technology limitations. Energy demand and recovery in AnMBRs is analyzed. Finally key issues that require urgent attention to facilitate global penetration of AnMBR technology are highlighted.

Application of anaerobic membrane bioreactors to municipal wastewater treatment at ambient temperature: A review of achievements, challenges, and perspectives

This review surveys the implementation of anaerobic membrane bioreactors in municipal wastewater treatment at ambient temperature. High chemical oxygen demand (COD) removal efficiencies and methane conversion rates were achieved under various conditions, while also achieving a low sludge yield of 0.04-0.09 g volatile suspended solids (VSS)/g COD. A survey of energy demands for pilot-scale anaerobic membrane bioreactors showed that they could be energy neutral or even positive, even though high energy (0.08-0.35 kWh/m³) is required to clear membrane fouling. Thus, the use of anaerobic membrane bioreactors in municipal wastewater treatment at ambient temperature is very promising. However, some challenges such as membrane fouling control, methane in effluent, low COD/SO₄^2--S ratio, and deficiencies in alkalinity should be addressed, especially the latter. Future research perspectives relating to the challenges and further research are proposed.

Dynamic characterization of a FeCl3-dosed anaerobic membrane bioreactor (AnMBR) treating municipal wastewater

A transient study was conducted at pilot scale to assess the impact of Fe dosage on the dynamics of biological and membrane performance of an anaerobic membrane bioreactor (AnMBR) treating authentic municipal wastewater. A transient model of the AnMBR system was employed to assist with interpretation of the observed responses in the mixed liquor under different FeCl₃ dosages. A high dosage (43 mg FeCl₃/L_Sewage) resulted in a significant accumulation of fixed suspended solids and volatile suspended solids (VSS) and reduction of colloidal COD in the mixed liquor. The elevated dosages appeared to reduce the biodegradability of VSS that was present in the raw wastewater. Intermediate dosages of FeCl₃ (21-12 mg/L) had less effect on these responses and did not appear to affect VSS biodegradation. Membrane performance was significantly affected by FeCl₃ dosage as indicated by reversible resistance (RR) and physically irreversible resistance (IR). RR was closely related to the colloidal COD in the mixed liquor, thus responded quickly to Fe dosage. Physically, IR had a delayed response to changes in the colloidal COD concentrations in the mixed liquor and this was attributed to the effect of slow mass transfer of colloidal matter between the mixed liquor and the membrane.

Current status of the pilot-scale anaerobic membrane bioreactor treatments of domestic wastewaters: A critical review

This review presented the performances of the pilot-scale anaerobic membrane bioreactors (AnMBRs) treating domestic wastewater. High COD removal efficiencies and low biosolids productions were achieved at HRTs comparable to conventional aerobic processes under ambient temperatures. The energy demands for fouling control in the pilot-scale AnMBRs ranged from 0.04 to 1.35kWh/m³, which is lower than those of lab-scale AnMBRs and aerobic MBRs. The energy demands for fouling control were in the order of gas sparging>particle sparging>rotating membrane AnMBR. Two major factors affecting the energy demand in gas sparging AnMBRs were specific gas demands (SGD_m) and operating flux. The energy potentials in wastewater were significantly affected by the influent sulfate concentrations. Energy balances indicated that five out of nine pilot-scale AnMBRs was energy positive. However, further improvements of the AnMBRs are required to implement the energy positive wastewater treatment process.

Fouling reduction using adsorbents/flocculants in a submerged anaerobic membrane bioreactor

Using adsorbents/flocculants in anaerobic membrane bioreactors (AnMBRs) to reduce membrane fouling is comparatively rare. This study evaluated 8 additives: 3 powdered activated carbons, 2 granular activated carbons, 1 cationic polymer, and 2 metal salts to identify the best additive and dose to minimise membrane fouling. Small cross flow filtration tests showed 400mg/L PAC SAE2, or 150mg/L FeCl₃, reduced the transmembrane pressure (TMP) rise from 0.94 to 0.06kPa/h, indicating excellent fouling reduction. The best filtration performance correlated with a significant reduction in supernatant supracolloidal particles, colloids and SMPs. FESEM-EDX showed that PAC SAE 2 and FeCl₃ reduced the thickness of the fouling layer dramatically, while FeCl₃ increased sludge floc size and particle size of the colloids, while decreasing the negative charge of colloids, and SMP size. Furthermore, Fe was not found in the supernatant or effluent, but precipitated with the solids, which is beneficial for its long-term use.

Fouling in membrane bioreactors: An updated review

The goal of the current article is to update new findings in membrane fouling and emerging fouling mitigation strategies reported in recent years (post 2010) as a follow-up to our previous review published in Water Research (2009). According to a systematic review of the literature, membrane bioreactors (MBRs) are still actively investigated in the field of wastewater treatment. Notably, membrane fouling remains the most challenging issue in MBR operation and attracts considerable attention in MBR studies. In this review, we summarized the updated information on foulants composition and characteristics in MBRs, which greatly improves our understanding of fouling mechanisms. Furthermore, the emerging fouling control strategies (e.g., mechanically assisted aeration scouring, in-situ chemical cleaning, enzymatic and bacterial degradation of foulants, electrically assisted fouling mitigation, and nanomaterial-based membranes) are comprehensively reviewed. As a result, it is found that the fundamental understanding of dynamic changes in membrane foulants during a long-term operation is essential for the development and implementation of fouling control methods. Recently developed strategies for membrane fouling control denoted that the improvement of membrane performance is not our ultimate and only goal, less energy consumption and more green/sustainable fouling control ways are more promising to be developed and thus applied in the future. Overall, such a literature review not only demonstrates current challenges and research needs for scientists working in the area of MBR technologies, but also can provide more useful recommendations for industrial communities based on the related application cases.

Performance of an anaerobic membrane bioreactor in which granular sludge and dynamic filtration are integrated

To alleviate the fouling of a filter, simple substrates, dynamic filtration, and granular sludge were applied in an anaerobic membrane bioreactor (AnMBR). The results showed that under a transmembrane pressure < 20 kPa, the filter flux ranged between 15 and 20 l (m^-2 h)^-1 for a period of 30 days. The flux was higher than the typical flux of AnMBRs with conventional membranes and most current dynamic filters. In addition, the low cost of the filter avoided the need for a higher flux. Moreover, a stable granular sludge bed, which consumed all volatile fatty acids, was maintained. A compact fouling/filtration layer formed on the filter, which contributed to low effluent chemical oxygen demand concentrations and turbidity. In addition, substrate scarcity in the filtration zone resulted in the evolution of diverse bacteria on the filter.

Start-up of an anaerobic fluidized bed reactor treating synthetic carbohydrate rich wastewater

The present work studied the start-up process of a mesophilic (37 ± 2 °C) anaerobic fluidized bed reactor (AFBR) operated at a hydraulic retention time (HRT) of 20 days using synthetic carbohydrate rich wastewater. Anox Kaldness-K1 carriers were used as biofilm carrier material. The reactor performance and biofilm formation were evaluated during the process. The start-up process at lower liquid recirculation flow rate enhanced the biofilm formation and reactor performance. The organic substrate composition had a major impact on early colonization of methanogenic archaea onto the surface of the Kaldness carriers during the start-up process. Specific organic substrates favouring the growth of methanogenic archaea, such as acetate, are preferred in order to facilitate the subsequent biofilm formation and AFBR start-up. The supply of 'bio-available' nutrients and trace elements, in particular iron, had an important role on optimal methanogenic activity and speeding-up of the biofilm development on the Kaldness carriers. This paper provides possible strategies to optimize the various operational parameters that influence the initial biofilm formation and development in an AFBR and similar high rate anaerobic reactors, hence can be used to reduce the long time required for process start-up.

An enhanced anaerobic membrane bioreactor treating bamboo industry wastewater by bamboo charcoal addition: Performance and microbial community analysis

In this study, two anaerobic membrane bioreactors (AnMBRs) were operated for 150days to treat bamboo industry wastewater (BIWW), and one of them was enhanced with bamboo charcoal (B-AnMBR). During the steady period, average chemical oxygen demand (COD) removal efficiencies of 94.5±2.9% and 89.1±3.1% were achieved in B-AnMBR and AnMBR, respectively. The addition of bamboo charcoal (BC) increased the amount of biomass and improved the performance of the systems. A higher biogas production and methane yield were also observed in B-AnMBR. Regarding the issue of membrane fouling, BC lowered the soluble microbial product (SMP) content by approximately 62.73mg/L and decreased the membrane resistance, thereby mitigating membrane fouling. Analysis of the microbial communities demonstrated that BC increased the microbial diversity and promoted the activity of Methanosaeta, Methanospirillum, and Methanobacterium, which are dominant in methane production.

Effects of FeCl3 addition on the operation of a staged anaerobic fluidized membrane bioreactor (SAF-MBR)

The effects on sulfur removal and membrane fouling resulting from FeCl(3) addition to an anaerobic fluidized membrane bioreactor (AFMBR) in a staged AFMBR (SAF-MBR) was investigated. Total sulfur removal in the SAF-MBR was 42-59% without FeCl(3) addition, but increased to 87-95% with FeCl(3) addition. Sulfide removal in the AFMBR increased to 90% with addition of FeCl(3) at a molar Fe(3+)/S ratio of 0.54 and to 95% when the ratio was increased to 0.95. Effluent sulfide concentration then decreased to 0.3-0.6 mg/L. Phosphate removals were only 19 and 37% with the above added FeCl(3) ratios, indicating that iron removed sulfide more readily than phosphate. Neither chemical oxygen demand nor biochemical oxygen demand removal efficiencies were affected by the addition of FeCl(3). When the AFMBR permeate became exposed to air, light brown particles were formed from effluent Fe(2+) oxidation to Fe(3+). FeCl(3) addition, while beneficial for sulfide removal, did increase the membrane fouling rate due to the deposition of inorganic precipitates in the membrane pores.

Preliminary evaluation of biosolids characteristics for anaerobic membrane reactors treating municipal wastewaters

This study assessed the characteristics of biosolids of a pilot-scale anaerobic membrane bioreactor (AnMBR) treating municipal wastewater. The production of total solids (TS) and volatile solids (VS) was comparable to that reported for the extended aeration system at solids residence time (SRT) longer than 40 days. The yields of TS and VS were reduced as SRT increased from 40 to 100 days and increased with the addition of 26 mg/L of FeCl3. The AnMBR destroyed 60-82% of the VS loading in feed wastewater and hence it was concluded the biosolids met the requirements for vector attraction reduction for land application. The concentrations of volatile suspended solids and total suspended solids in the sludge were less than those reported after anaerobic digestion of conventional primary and secondary sludge mixtures, and hence dewatering of the waste stream may be required for some applications. The nutrient content in terms of total Kjeldahl nitrogen and total phosphorus was similar to that of anaerobically digested municipal sludges. The dewaterability of the biosolids was poorer than that reported for sludges from aerobic treatment and anaerobically digested sludges. Dewaterability was improved by addition of FeCl3 and reduced SRT. The biosolids met standards for land application with regards to the concentration of heavy metals but would need further treatment to meet Class B pathogen indicator criteria.