Low energy single-staged anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for wastewater treatment

Innovative high-performance and energy-positive Co-treatment of organic kitchen waste and domestic wastewater using a fluidized bed ceramic membrane bioreactor

The aim of the study was to efficiently treat organic kitchen waste (FW) and domestic wastewater (DWW) together in an anaerobic fluidized bed bioreactor equipped with a ceramic membrane (AnFCMBR) through a sustainable approach considering energy recovery. The system operated continuously for 519 days at room temperature, and different filtration fluxes (1.7 and 5 L/m2/h), hydraulic retention times (HRTs) (22 h and 7 h), and organic loading rate (OLRs) (0.46, 1.52, 3.42, 6.08 kg/m3.d) were tested. The amount of organic matter in DWW may be insufficient for feasible gas production, but this challenge can be resolved through the addition of food waste. Influent chemical oxygen demand (COD) of 500 ± 143 mg/L gradually increased to 2000 ± 196 mg/L by increasing the portion of FW. The COD removal ranged from 92 to 98% throughout the study, with the membrane and the cake layer contributing 5-8% to the performance. Average supernatant SMP and EPS concentrations increased from 5 ± 1 to 45 ± 5 mg COD/L and from 54 ± 7 to 254 ± 26 mg COD/g VSS, respectively, when the highest amount of FW was added to the synthetic wastewater. This significant increase in SMP and EPS concentrations due to the addition of FW negatively impacted the filtration performance. SRF and CST values also increased with rising OLR, especially with the supplementation of synthetic wastewater with FW. After FW started to be mixed with DWW, the methane production increased approximately 5.5 times. With the use of AnFCMBR for the co-treatment of FW and DWW, it is possible to achieve energy-positive treatment with high-quality effluent that can be reused for various applications, such as irrigation. The methane produced provided 12 times more energy than was needed to operate the bioreactor. This is the first study evaluating the co-treatment of FW and DWW in AnFCMBR under varying operational parameters.

Synergistic effects of biochar addition and filtration mode optimization on mitigating membrane fouling in high-solid anaerobic membrane bioreactors

In this study, a high-solid anaerobic membrane bioreactor was established for treating food waste, and membrane fouling rates were regulated through multivariate modulation. The anaerobic membrane bioreactor operated stably at a high organic loading rate of 28.75 gCOD/L/d achieved a methane production rate of 8.03 ± 0.61 L/L/d. Experimental findings revealed that the most effective control of membrane fouling was achieved at a filtration- relaxation ratio (F/R) of 10/90 s. This indicates that a higher relaxation frequency provided improved the mitigation of membrane fouling. Compared with single F/R modulation, the combined modulation of biochar and F/R provided enhanced control over membrane fouling. Moreover, the addition of biochar altered the sludge properties of the reactor, thereby preventing the formation of a dense cake layer. Additionally, biochar enhanced the sheer force of the fluid on the membrane surface and facilitated the separation of pollutants during the relaxation stage, thereby contributing to improved control of membrane fouling.

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.

Response of the mainstream anammox process to the biodegradable carbon sources in the granule-based systems: The difference in self-stratification of the microbial community

The inevitable introduction of biodegradable carbon sources (such as monosaccharides and volatile fatty acids) originating from pretreatment units might affect the performance of the mainstream anaerobic ammonium oxidation (anammox) process. Two model carbon sources (glucose and acetate) were selected to investigate their effects on granule-based anammox systems under mainstream conditions (70 mg total nitrogen (TN) L^-1, 15 °C). At a nitrogen loading rate of 2.87 ± 0.80 kg N m^-3 d^-1, a satisfactory effluent quality (TN < 10 mg L^-1) was achieved in the presence of glucose or acetate at a chemical oxygen demand (COD/N) ratio of 0.5. The contribution of anammox to nitrogen removal decreased with increasing COD/N ratio to 1.0 because the expression of anammox functional genes was inhibited, whereas the expression of denitrifying functional genes was promoted. However, the nitrogen removal efficiency of the two considered reactors was maintained above 80 %. Self-stratification of the microbial community along the reactor height facilitated a functional balance through the retention of anammox bacteria in granules but resulted in washout of denitrifying bacteria in flocs under a high-flow pattern. These findings highlighted the advantages of granule-based systems in the mainstream anammox process due to their inherent biomass self-segregation property and the need for the development of targeted biomass retention strategies.

Evaluation of the start-up of hydraulic conditions of a fluidised bed system

The development of this research was based on the analysis of an anaerobic fluidised bed reactor from the assembly of its components to the sealing of the system and further fluidisation. A hydrometer and a Venturi were used to identify the best means of measuring the flow rate. Results produced by both devices were similar, however, the latter was less effective due to the low flow rates necessary to operate the system. The hydrometer was the most adequate device for flow rate measurements in the range between 0.1 and 1.0 m³/h, whereas the Venturi proved to be an adequate device for the flow in the range between 0.3 and 0.7 m³/h. Sand with grain sizes varying from 357 to 1000 µm was used as support material. It was not observed statistically significant differences between the minimum fluidisation velocities related to the amount of supported material of 20% and 40% (V_SM/V_usable) added to the reactor. Forty percent of the usable volume occupied with sand is adequate to reach fluidisation, instead of only the expansion of the bed. The fluidisation velocities for the sand grain size of 357 µm were 8.4 m/h ± 0.25 for 20%, and 8.6 m/h ± 0.30 for 40%, whereas for the 505 µm they were, respectively for 20% and 40%, 9.2 m/h ±0.70 and 10.1 m/h ± 0.37. The hydraulic tests allow to stress that sand grain sizes varying from 357 to 505 µm are recommended to be used in a system with similar characteristics.

Process characteristics and energy self-sufficient operation of a low-fouling anaerobic dynamic membrane bioreactor for up-concentrated municipal wastewater treatment

Up-concentration of municipal wastewater using physico-chemical methods can effectively enrich organic matter, facilitating subsequent anaerobic digestion of up-concentrated wastewater for enhanced methanogenesis at reduced energy consumption. An anaerobic dynamic membrane bioreactor (AnDMBR) assisted with biogas-sparging was developed to treat up-concentrated municipal wastewater, focusing on the effects of operating temperature and hydraulic retention time (HRT) as well as COD mass balance and energy balance. The COD removal stabilized at about 98 % over the experimental period, while gaseous and dissolved methane contributed 43-49 % and 2-3 % to the influent COD reducing greenhouse gas emissions. The formed dynamic membrane exists mainly as a heterogeneous cake layer with a uneven distribution feature, ensuring the stable effluent quality. Without adopting any physico-chemical cleaning, the transmembrane pressure (TMP) maintained at a low range (2.7 to 14.67 kPa) with the average TMP increasing rate of 0.089 kPa/d showing a long-term low-fouling operation. Increasing the concentration ratio, the methane production rate decreased from 0.18 to 0.15 L CH₄/gCOD likely due to the accumulation of particulate organics. Microbial community analysis indicated the predominant methanogenic pathway shifted from hydrogenotrophic to acetoclastic methanogenesis in response to the temperature change. Net energy balance (0.003-0.600 kWh/m³) can be achieved only under room temperature (25 °C) rather than mesophilic conditions (36 °C).

Applications of submerged and staged membrane systems for pollutant removal from effluents and mechanism studies - a review

Membrane based filtration is one of the promising technologies for rehabilitation of wastewater streams for reuse and recycle. Many advancements have emerged with the use of novel materials and innovative integrated technologies. The present investigation focuses on the treatment methods based on submerged and stages systems of membranes for water purification. Ceramic, polymeric and mixed matrix type of membranes fabricated for specific type of effluents, their modification methods for accelerating the rejection efficiency, permeability, durability, stability and antifouling properties are detailed in this review. Graphene oxide is the most considered membrane material for adsorption purposes as it exhibits larger surface area, abundant functional groups contain oxygen and has good supply of ligands which is responsible in metal adsorption as it enhances electrostatic interaction by bonding metal ions with graphene oxide nanosheets. Energy derivation in terms of biogas production was also reported in some integrated methods. In many cases, embedded nanomaterial matrices yielded maximum efficiencies in both the submerged and staged operations. However, submerged type of membranes are reported more than the staged type due to simpler configuration with relatively lesser equipment, operational and maintenance issues. In treatment of a low strength wastewater, aluminum oxide based membrane in fluidized bed assembly was reported to yield promising results with reduced power requirement.

Gravity-driven high flux filtration behavior and microbial community of an integrated granular activated carbon and dynamic membrane bioreactor for domestic wastewater treatment

A gravity-driven dynamic membrane bioreactors (DMBR) with GAC addition (G-DMBR) was operated under constant pressure filtration mode (using 20 cm water head) for real domestic wastewater treatment. During the stable operation period, the treatment performance, DM filtration behavior and mechanism as well as microbial properties were studied and compared with a control DMBR (C-DMBR). Both DMBRs showed stable removal of chemical oxygen demand (COD) and ammonia (NH₄⁺-N) with average removal rates over 88% and 98%, respectively. GAC addition effectively enhanced dynamic membrane (DM) permeability with a stable flux of 17 to 65 L/m²h, which was approximately four times higher than that in the C-DMBR without GAC addition. Filtration resistance analysis indicated the DM formation can be divided to three stages: the formation of the initial DM layer, the development of mature DM layer and dynamic equilibrium stage of the DM layer. Filtration model analysis illustrated that added GAC could be the skeleton of the DM, resulting in a more porous and incompressible DM layer. Additionally, microbial community analysis revealed that in the G-DMBR several fouling-causing phyla including Proteobacteria reduced while other phyla preferring attached growth such as Bacteroidetes and Gemmatimonadetes increased. Thus, adding GAC to the DMBR can be an effective strategy for achieving stable and high-flux operation by modifying DM properties and regulating DM formation process and structure.

Hollow-Fiber Membrane Contactor for Biogas Recovery from Real Anaerobic Membrane Bioreactor Permeate

This study demonstrates the application of hollow-fiber membrane contactors (HFMCs) for the recovery of biogas from the ultrafiltration permeate of an anaerobic membrane bioreactor (AnMBR) and synthetic effluents of pure and mixed CH₄ and CO₂. The developed membrane degassing setup was coupled with a pilot-scale AnMBR fed with synthetic domestic effluent working at 25 °C. The membrane degassing unit was able to recover 93% of the total dissolved CH₄ and 83% of the dissolved CO₂ in the first two hours of permeate recirculation. The initial recovery rates were very high (0.21 mg CH₄ L⁻¹ min⁻¹ and 8.43 mg CO₂ L⁻¹ min⁻¹) and the membrane was able to achieve a degassing efficiency of 95.7% for CH₄ and 76.2% for CO₂, at a gas to liquid ratio of 1. A higher mass transfer coefficient of CH₄ was found in all experimental and theoretical evaluations compared to CO₂. This could also be confirmed from the higher transmembrane mass transport resistance to CO₂ rather than CH₄ found in this work. A strong dependency of the selective gas transport on the gas and liquid side hydrodynamics was observed. An increase in the liquid flow rate and gas flow rate favored CH₄ transport and CO₂ transport, respectively, over each component. The results confirmed the effectiveness of the collective AnMBR and membrane degassing setup for biogas recovery. Still, additional work is required to improve the membrane contactor’s performance for biogas recovery during long-term operation.

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.

Membrane bioreactors for the production of value-added products: Recent developments, challenges and perspectives

The potential of membrane bioreactors to produce value-added products such as biofuels, biopolymers, proteins, organic acids and lipids at high productivities is emerging. Despite the promising results at laboratory scale, industrial deployment of this technology is hindered due to challenges associated with scale-up. This review aims to address these challenges and create a framework to encourage further research directed towards industrial application of membrane bioreactors to produce value-added products. This review describes the current state-of-the art in such bioreactor systems by exploiting membranes to increase the mass transfer rate of the limiting substrates, reach high cell concentrations and separate the inhibitory substances that may inhibit the bioconversion reaction. It also covers the current trends in commercialization, challenges linked with membrane usage, such as high costs and membrane fouling, and proposes possible future directions for the wider application of membrane bioreactors.

Volatile Fatty Acid Production from Organic Waste with the Emphasis on Membrane-Based Recovery

In recent years, interest in the biorefinery concept has emerged in the utilization of volatile fatty acids (VFAs) produced by acidogenic fermentation as precursors for various biotechnological processes. This has attracted substantial attention to VFA production from low-cost substrates such as organic waste and membrane based VFA recovery techniques to achieve cost-effective and environmentally friendly processes. However, there are few reviews which emphasize the acidogenic fermentation of organic waste into VFAs, and VFA recovery. Therefore, this article comprehensively summarizes VFA production, the factors affecting VFA production, and VFA recovery strategies using membrane-based techniques. Additionally, the outlook for future research on VFA production is discussed.

Wind speed pattern data and wind energy potential in Pakistan: current status, challenging platforms and innovative prospects

Energy is an essential parameter for the economic growth and sustainable development of any country. Due to the rapid increase in energy demand, depletion of fossil fuels and environmental concerns, many developing and developed countries are moving towards alternative renewable resources such as solar energy, wind energy and biomass. Wind energy as a renewable energy source is gaining a lot of significant attention. Wind energy is a sustainable solution to produce energy having potential benefits such as clean source, reduced toxic gases emission and environmental friendly protocol for operation. Pakistan is among the top countries facing the worst energy crisis due to different political and financial issues. Pakistan is blessed with a huge potential of wind energy having all the basic requirements such as windy regions and good wind speed for harnessing energy. Pakistan can utilize the potential of wind energy to reduce the problem of energy outrage in the country and also take steps towards green economy from conventional fuel economy. This critical review highlights the current status, potential and the steps taken in the past and present to overcome the energy shortage in Pakistan by employing wind energy. Outlook on wind speed data, deployment of wind energy, environmental effect of wind energy and its barriers in the adoption are discussed with recommendations and suggestions to utilize this clean energy in an effective way. Graphical abstract.

Combined Effect of Activated Carbon Particles and Non-Adsorptive Spherical Beads as Fluidized Media on Fouling, Organic Removal and Microbial Communities in Anaerobic Membrane Bioreactor

The combined effect of acrylonitrile butadiene styrene (ABS) spherical beads and granular activated carbon (GAC) particles as fluidized media on the performance of anaerobic fluidized bed membrane bioreactor (AFMBR) was investigated. GAC particles and ABS beads were fluidized together in a single AFMBR to investigate membrane fouling and organic removal efficiency as well as energy consumption. The density difference between these two similarly sized media caused the stratified bed layer where ABS beads are fluidized above the GAC along the membrane. Membrane relaxation was effective to reduce the fouling and trans-membrane pressure (TMP) below 0.25 bar could be achieved at 6 h of hydraulic retention time (HRT). More than 90% of soluble chemical oxygen demand (SCOD) was removed after 80 d operation. Biogas consisting of 65% of methane was produced by AFMBR, suggesting that combined use of GAC and ABS beads did not have any adverse effect on methane production during the operational period. Scanning Electron Microscope (SEM) examinations showed the adherence of microbes to both media. However, 16S rRNA results revealed that fewer microbes attached to ABS beads than GAC. There were also compositional differences between the ABS and GAC microbial communities. The abundance of the syntrophs and exoelectrogens population on ABS beads was relatively low compared to that of GAC. Our result implied that syntrophic synergy and possible occurrence of direct interspecies electron transfer (DIET) might be facilitated in AFMBR by GAC, while traditional methanogenic pathways were dominant in ABS beads. The electrical energy required was 0.02 kWh/m3, and it was only about 13% of that produced by AFMBR.

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.

Greener and sustainable production of bioethylene from bioethanol: current status, opportunities and perspectives

The economic value of bioethylene produced from bioethanol dehydration is remarkable due to its extensive usage in the petrochemical industry. Bioethylene is produced through several routes, such as steam cracking of hydrocarbons from fossil fuel and dehydration of bioethanol, which can be produced through fermentation processes using renewable substrates such as glucose and starch. The rise in oil prices, environmental issues due to toxic emissions caused by the combustion of fossil fuel and depletion of fossil fuel resources have led a demand for an alternative pathway to produce green ethylene. One of the abundant alternative renewable sources for bioethanol production is biomass. Bioethanol produced from biomass is alleged to be a competitive alternative to bioethylene production as it is environmentally friendly and economical. In recent years, many studies have investigated catalysts and new reaction engineering pathways to enhance the bioethylene yield and to lower reaction temperature to drive the technology toward economic feasibility and practicality. This paper critically reviews bioethylene production from bioethanol in the presence of different catalysts, reaction conditions and reactor technologies to achieve a higher yield and selectivity of ethylene. Techno-economic and environmental assessments are performed to further development and commercialization. Finally, key issues and perspectives that require utmost attention to facilitate global penetration of technology are highlighted.

Effects of Solids Retention Time on the Anaerobic Membrane Bioreactor with Yttria-Based Ceramic Membrane Treating Domestic Wastewater at Ambient Temperature

The effects of solid retention times (SRTs) (100 days, 50 days, 25 days) on the performance, microbial community, and membrane fouling of a lab-scale anaerobic yttria-based ceramic membrane bioreactor (AnCMBR) treating synthetic domestic wastewater at ambient temperature (31.2 ± 2.7 °C) were examined. The soluble chemical oxygen demand (SCOD) removal was higher (89.6%) at 25 days SRT compared with 50 days (39.61%) and 100 days (34.3%) SRT. At 100 days SRT, more Bacteroidetes, Firmicutes, and Proteobacteria were present in the microbial community. At 25 days SRT, more Chloroflexi, Synergistetes, and Pastescibacteria emerged, contributing to the stable performance. The SRT of 25 days has resulted in a more stable microbial community compared with 50 days and 100 days SRT. Both bacterial and archaeal community diversities were higher at 25 days SRT, and the specific production of soluble microbial by-products (SMPs) and extracellular polymeric substances (EPSs) were higher at 25 days SRT as well. Consequently, the membrane flux was lower at 25 days SRT with the increased particle size and the enhanced SMPs and EPSs production. Fourier transform infrared spectroscopy analysis (FTIR) and three-dimensional excitation and emission matrix (3D-EEM) analysis showed that protein and SMPs were the major membrane foulants at all SRT stages. In this study, SRT at 25 days was favorable for the stable operation of an AnCMBR treating domestic wastewater at ambient temperature.

Fluidized bed membrane bioreactor achieves high sulfate reduction and filtration performances at moderate temperatures

The study explored the potential of an up-flow sulfate reducing fluidized-bed membrane bioreactor (SR-FMBR) for biogenic sulfide generation at room temperature together with evaluation of filtration and fouling characteristics developed under various operational conditions. The SR-FMBR was tested at different COD/sulfate (mg/mg) ratios for a total of 127 days, initially at 35 °C and then at 23 °C. SR-FMBR was able to achieve COD oxidation and sulfate reduction efficiencies up to 98%, and allowed for biogenic sulfide generation up to 600 mg/L (97% of theoretical value) at room temperature. Alkalinity was generated as a result of sulfate reduction and averaged around 1900 mgCaCO₃/L in the permeate. Hence, starting the bioreactor operation at 35 °C and then decreasing it to 23 °C did not adversely affect the process performance. High filtration fluxes up to 9.3 L/m²/h (LMH) could be maintained at employed hydraulic retention times between 24 h and 6 h. Observing relatively high filtration performance was due to keeping a high fraction of biomass attached to the carrier material, which decreased the cake formation potential on the membrane surface compared to conventional MBR operation. The SR-FMBR performance may further be tested for heavy metal removal under sulfidogenic conditions for acid mine drainage treatment.

Ceramic nanocomposite membranes and membrane fouling: A review

Membrane technologies have broad applications in the removal of contaminants from drinking water and wastewater. In recent decades, ceramic membrane has made rapid progress in industrial/municipal wastewater treatment and drinking water treatment owing to their advantageous properties over conventional polymeric membrane. The beneficial characteristics of ceramic membranes include fouling resistance, high permeability, good recoverability, chemical stability, and long life time, which have found applications with the recent innovations in both fabrication methods and nanotechnology. Therefore, ceramic membranes hold great promise for potential applications in water treatment. This paper mainly reviews the progress in the research and development of ceramic membranes, with key focus on porous ceramic membranes and nanomaterial-functionalized ceramic membranes for nanofiltration or catalysis. The current state of the available ceramic membranes in industry and academia, and their potential advantages, limitations and applications are reviewed. The last section of the review focuses on ceramic membrane fouling and the efforts towards ceramic membrane fouling mitigation. The advances in ceramic membrane technologies have rarely been widely reviewed before, therefore, this review could be served as a guide for the new entrants to the field, as well to the established researchers.

Recent advancement on biological technologies and strategies for resource recovery from swine wastewater

Swine wastewater is categorized as one of the agricultural wastewater with high contents of organics and nutrients including nitrogen and phosphorus, which may lead to eutrophication in the environment. Insufficient technologies to remove those nutrients could lead to environmental problems after discharge. Several physical and chemical methods have been applied to treat the swine wastewater, but biological treatments are considered as the promising methods due to the cost effectiveness and performance efficiency along with the production of valuable products and bioenergies. This review summarizes the characteristics of swine wastewaters in the beginning, and briefly describes the current issues on the treatments of swine wastewaters. Several biological techniques, such as anaerobic digestion, A/O process, microbial fuel cells, and microalgae cultivations, and their future aspects will be addressed. Finally, the potentials to reutilize biomass produced during the treatment processes are also presented under the consideration of circular economy.

A Review on the Mechanism, Impacts and Control Methods of Membrane Fouling in MBR System

Compared with the traditional activated sludge process, a membrane bioreactor (MBR) has many advantages, such as good effluent quality, small floor space, low residual sludge yield and easy automatic control. It has a promising prospect in wastewater treatment and reuse. However, membrane fouling is the biggest obstacle to the wide application of MBR. This paper aims at summarizing the new research progress of membrane fouling mechanism, control, prediction and detection in the MBR systems. Classification, mechanism, influencing factors and control of membrane fouling, membrane life prediction and online monitoring of membrane fouling are discussed. The research trends of relevant research areas in MBR membrane fouling are prospected.

Enhancement of sustainable flux by optimizing filtration mode of a high-solid anaerobic membrane bioreactor during long-term continuous treatment of food waste

Membrane fouling or flux limitation is the major bottleneck that hinders anaerobic membrane bioreactor (AnMBR) application. An AnMBR with a working volume of 15 L was operated for 180 days to investigate the maximum sustainable flux at different high solid concentrations during the anaerobic treatment of food waste. A total of eight filtration-to-relaxation (F/R) ratios were incorporated, with a fixed filtration time of 3 min and varied relaxation times (decreased from 12 to 1 min). Besides, a total of five instantaneous fluxes were applied: 12, 14, 16, 18 and 20 L/m²/h (LMH). Results showed that sustainable flux was greatly enhanced by filtration mode optimization. The optimal F/R ratios were 3:1, 3:1, 3:1 and 3:6 at mixed liquor total solid (MLTS) concentrations of 10, 15, 20 and 25 g/L, respectively. The corresponding sustainable flux values were 13.2 ± 0.3, 10.1 ± 0.4, 9.3 ± 0.2 and 4.0 ± 0.3 LMH, respectively. These values were 29%, 35%, 52% and 21% higher than the critical flux determined by the flux-stepping technique. The results of this study were used to perform a mathematical simulation. The obtained regression equation between the maximum sustainable flux and MLTS concentration can be used to predict the sustainable flux at other MLTS concentrations. This work provides valuable insight into the design and operation of high-solid AnMBRs, and is expected to contribute to further advances in the application of AnMBRs in industry.

Membrane distillation as post-treatment for anaerobic fluidized bed membrane bioreactor for organic and nitrogen removal

To observe feasibility of membrane distillation (MD) as post-treatment for anaerobic fluidized bed membrane bioreactor (AFMBR), removals of organic and total nitrogen were investigated by using the commercial polyvinylidene difluoride (PVDF) membrane for direct contact membrane distillation (DCMD) at various operational conditions. Test solutions for MD experiments were permeate produced by staged AFMBR (SAF-MBR), permeate from single AFMBR and synthetic wastewater fed to both reactors. Increasing in feed temperature improved permeate flux through PVDF membrane, but it decreased total nitrogen (TN) removal efficiency. Effect of chemical oxygen demand (COD) concentrations in feed solutions for DCMD on TN removal efficiency was almost negligible. However, the COD removal efficiency was lower at lower feed concentration in DCMD operation. At constant feed temperature, TN removal efficiency was improved by increasing a recirculation flow rate on PVDF membrane across DCMD system. Both organic and inorganic fouling were observed on PVDF membrane surface and pore matrix after conducting DCMD operation. The organic fouling on PVDF membrane consisted mainly of protein and fatty acids, supporting that the permeate produced by AFMBR should have potentials to foul the membrane applied in DCMD system as post-treatment.

Impact of sludge recirculation ratios on the performance of anaerobic membrane bioreactor for wastewater treatment

The performance of a lab scale anaerobic membrane bioreactor (AnMBR) was evaluated for wastewater treatment. The efficacy of the system was determined at different operating conditions in terms of fluxes and recirculation ratios (R); 10.28 L/m² h (R = 1, Phase I), 8.8 L/m² h (R = 2, Phase II and R = 3, Phase III) and 6 L/m² h (R = 2, Phase IV and R = 3, Phase V), respectively. In comparison with all the operating conditions tested, optimum efficacy of the system was found at flux of 6 L/m² h and R of 3 in terms of highest COD removal (96.7%), and maximum biogas yield (0.44 L/g COD_removed). The MLSS and MLVSS concentrations under optimum phase were 6.23 and 4.83 g/L, respectively at OLR of 0.46 kg COD/m³ day. The system also exhibited significant reduction of foulants i.e. extracellular polymeric substances (EPS) and soluble microbial products (SMP) resulting in longer membrane runs in optimized phase.

Applying a dynamic membrane filtration (DMF) process for domestic wastewater preconcentration: Organics recovery and bioenergy production potential analysis

Wastewater is increasingly recognized as a valuable resource rather than as a waste, motivating a shift in the perspective of wastewater treatment from pollution control to resource recovery. This study proposes the recovery of organic matter from domestic wastewater for the production of bioenergy through a novel process of wastewater preconcentration based on dynamic membrane filtration (DMF). The selection of a dynamic membrane (DM) supporting material, the preconcentration performance of organics, and the biomethane production potential (BMP) of the organic concentrate were investigated. The process optimization results indicated that a DM module with a supporting material of a 25 μm stainless steel mesh with a three-layer structure, assisted by internal suspended particles derived from raw wastewater, enabled the rapid DM layer formation within 1 h. The DMF process operated under a constant high flux of 30-60 L/m² h at a trans-membrane pressure (TMP) of less than 40 kPa. During the continuous DMF operation, the average chemical oxygen demand (COD) of the influent, effluent and concentrate was 305, 113 and 2000-2500 mg/L, respectively, while the removal performance of other pollutants(such as nitrogen and phosphorus) varied, indicating differential retention effects for the various pollutants by the DM layer. Air back-flushing can effectively regenerate the DM layer and maintain long-term stable operation, but higher rates of TMP increase were observed for later filtration cycles, probably due to the accumulation of physically irremovable fouling. The BMP of the DMF concentrate was 0.20 L CH₄/g COD, which was comparable to the ordinary biogas yield from municipal wastewater by anaerobic digestion. The DMF process integrated with anaerobic digestion can be a promising alternative for energy-sufficient wastewater treatment.

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.

Newly Designed Hydrolysis Acidification Flat-Sheet Ceramic Membrane Bioreactor for Treating High-Strength Dyeing Wastewater

Cost-effective treatment of dyeing wastewater remains a challenge. In this study, a newly designed hydrolysis acidification flat-sheet ceramic membrane bioreactor (HA-CMBR) was used in treating high-strength dyeing wastewater. The start-up phase of the HA-CMBR was accomplished in 29 days by using cultivated seed sludge. Chemical oxygen demand (COD) removal rate reached about 62% with influent COD of 7800 mg/L and an organic loading rate of 7.80 kg-COD/(m³·d). Chromaticity removal exceeded 99%. The results show that the HA-CMBR has good removal performance in treating dyeing wastewater. The HA-CMBR could run with low energy consumption at trans-membrane pressure (TMP) <10 kPa due to the good water permeability of the flat-sheet ceramic membrane. New strains with 92%⁻96% similarity to Alkalibaculum bacchi, Pseudomonas sp., Desulfovibrio sp., and Halothiobacillaceae were identified in the HA-CMBR. Microbial population analysis indicated that Desulfovibrio sp., Deltaproteobacteria, Halothiobacillaceae, Alkalibaculum sp., Pseudomonas sp., Desulfomicrobium sp., and Chlorobaculum sp. dominated in the HA-CMBR.

Fluidized bed bioreactor for multiple environmental engineering solutions

Fluidized bed bioreactors (FBR) are characterized by two-phase mixture of fluid and solid, in which the bed of solid particles is fluidized by means of downward or upward recirculation stream. FBRs are widely used for multiple environmental engineering solutions, such as wastewater treatment, as well as some industrial applications. FBR offers many benefits such as compact bioreactor size due to short hydraulic retention time, long biomass retention on the carrier, high conversion rates due to fully mixed conditions and consequently high mass transfer rates, no channelling of flow, dilution of influent concentrations due to recycle flow, suitability for enrichment of microbes with low K_m values. The disadvantages of FBRs include bioreactor size limitations due to the height-to-diameter ratio, high-energy requirements due to high recycle ratios, and long start-up period for biofilm formation. This paper critically reviews some of the key studies on biomass enrichment via immobilisation of low growth yield microorganisms, high-rates via fully mixed conditions, technical developments in FBRs and ways of overcoming toxic effects via solution recycling. This technology has many potential new uses as well as hydrodynamic characteristics, which enable high-rate environmental engineering and industrial applications.

Investigating membrane fouling associated with GAC fluidization on membrane with effluent from anaerobic fluidized bed bioreactor in domestic wastewater treatment

Effect of mechanical scouring driven by granular activated carbon (GAC) fluidization on membrane fouling was investigated using a laboratory-scaled, fluidized membrane reactor filtering the effluent from anaerobic fluidized bed bioreactor (AFBR) in domestic wastewater treatment. The GAC particles were fluidized by recirculating a bulk solution only through the membrane reactor to control membrane fouling. The membrane fouling was compared with two different feed solutions, effluent taken from a pilot-scaled, AFBR treating domestic wastewater and its filtrate through 0.1-μm membrane pore size. The GAC fluidization driven by bulk recirculation through the membrane reactor was very effective to reduce membrane fouling. Membrane scouring under GAC fluidization decreased reversible fouling resistance effectively. Fouling mitigation was more pronounced with bigger GAC particles than smaller ones as fluidized media. Regardless of the fluidized GAC sizes, however, there was limited effect on controlling irreversible fouling caused by colloidal materials which is smaller than 0.1 μm. In addition, the deposit of GAC particles that ranged from 180 to 500 μm in size on membrane surface was very significant and accelerated fouling rate. Biopolymers rejected by the membranes were thought to play a role as binding these small GAC particles on membrane surface strongly.

Impact of reactor configuration on treatment performance and microbial diversity in treating high-strength dyeing wastewater: Anaerobic flat-sheet ceramic membrane bioreactor versus upflow anaerobic sludge blanket reactor

In this study, an anaerobic flat-sheet ceramic membrane bioreactor (AnCMBR) was used to treat high-strength dyeing wastewater, and compared with an upflow anaerobic sludge blanket (UASB) reactor. The start-up phases of the AnCMBR and UASB reactor were accomplished within 60 d by using cultivated seed sludge. The results showed that the AnCMBR had better COD, TN, and TP removal rates than the UASB reactor. The CH₄ production of the AnCMBR was higher than that of the UASB reactor. The AnCMBR was operated with low energy consumption due to good water permeability of the flat-sheet ceramic membrane. The AnCMBR and UASB reactor had similar CH₄-producing Archaea; Methanosaeta, Methanosarcina, and Methanomassiliicoccus were the most abundant. The AnCMBR had a higher proportion of Desulfovibrio sp. and Desulfomicrobium sp., which are reported to have the potential to degrade reactive dyes. A large number of sulfate-reducing enzymes were deduced to contribute to the sulfate-reducing pathway.

Psychrophilic anaerobic dynamic membrane bioreactor for domestic wastewater treatment: Effects of organic loading and sludge recycling

Two upflow anaerobic dynamic membrane bioreactors (AnDMBRs) with and without sludge recycling were operated in parallel at varied organic loadings and psychrophilic temperature for domestic wastewater treatment. A 75 μm nylon mesh, used as a supporting material, enabled quick and stable dynamic membrane formation. The AnDMBRs could operate continuously without relaxation at a high flux rate of 22.5 L/m²h; however, high organic loading accelerated the increasing rate of trans-membrane pressure (TMP). High chemical oxygen demand removal was achieved in both AnDMBRs with removal efficiencies of 70-90%. Sludge recycling enhanced the cross-flow velocity but negatively affected the effluent turbidity, sludge properties (particle size reduction and biopolymer release) and dynamic membrane filterability. Although increased organic loading enhanced biogas yield, the low biogas production was related to the dissolved methane loss in the effluent. Easy-operation, minimal maintenance and low-energy consumption makes the AnDMBR process cost-effective for practical wastewater treatment in temperate areas.

Anaerobic membrane bioreactors for biohydrogen production: Recent developments, challenges and perspectives

Biohydrogen as one of the most appealing energy vector for the future represents attractive avenue in alternative energy research. Recently, variety of biohydrogen production pathways has been suggested to improve the key features of the process. Nevertheless, researches are still needed to overcome remaining barriers to practical applications such as low yields and production rates. Considering practicality aspects, this review emphasized on anaerobic membrane bioreactors (AnMBRs) for biological hydrogen production. Recent advances and emerging issues associated with biohydrogen generation in AnMBR technology are critically discussed. Several techniques are highlighted that are aimed at overcoming these barriers. Moreover, environmental and economical potentials along with future research perspectives are addressed to drive biohydrogen technology towards practicality and economical-feasibility.

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

The use of anaerobic membrane bioreactor technology (AnMBR) is rapidly expanding. However, depending on the application, AnMBR design and operation is not fully mature, and needs further research to optimize process efficiency and enhance applicability. This paper reviews state-of-the-art of AnMBR focusing on modelling and control aspects. Quantitative environmental and economic evaluation has demonstrated substantial advantages in application of AnMBR to domestic wastewater treatment, but detailed modelling is less mature. While anaerobic process modelling is generally mature, more work is needed on integrated models which include coupling between membrane performance (including fouling) and the biological process. This should include microbial factors, which are important to generation of specific foulants such as soluble and particulate inert organics. Mature and well-established control tools, including better feedback control strategies are also required for both the process, and for fouling control.

Anaerobic membrane bioreactors for antibiotic wastewater treatment: Performance and membrane fouling issues

Antibiotic wastewater has become a major concern due to the toxicity and recalcitrance of antibiotics. Anaerobic membrane bioreactors (AnMBRs) are considered alternative technology for treating antibiotic wastewater because of their advantages over the conventional anaerobic processes and aerobic MBRs. However, membrane fouling remains the most challenging issue in the AnMBRs' operation and this limits their application. This review critically discusses: (i) antibiotics removal and antibiotic resistance genes (ARGs) in different types of AnMBRs and the impact of antibiotics on membrane fouling and (ii) the integrated AnMBRs systems for fouling control and removal of antibiotics. The presence of antibiotics in AnMBRs could aggravate membrane fouling by influencing fouling-related factors (i.e., sludge particle size, extracellular polymeric substances (EPS), soluble microbial products (SMP), and fouling-related microbial communities). Conclusively, integrated AnMBR systems can be a practical technology for antibiotic wastewater treatment.

The data on the removal of turbidity and biological agents in spent filter backwash by bed ceramic in water treatment process

The use of a ceramic membrane is not only a new and modern technique, but reduce the use of chemicals and coagulants as well, and also having high mechanical and chemical resistance reduces costs over consecutive years. The aim of this research was to remove turbidity and biological agents such as Diatoms, Chlorophyte, Cyanophyceae, Protozoa, and Nematodes by using of ceramic membranes. A ceramic pilot plant was designed and constructed. Titanium oxide (TiO₂) and aluminum oxide (Al₂O₃) ultrafiltration membrane with the length, diameter and pore sizes of 25 cm, 2.7 cm, and 50 nm was used. The inlet flow was the effluent resulted from the backwashing of a sand filter. This data showed that the possibility of removing of this agent was high by comparing the size of the agents and ceramic membrane pore size. Therefore, the construction of a pilot plant of ceramic membranes with 50 nm pore size and dimension (H = 1.5 m, Y = 20 cm, X = 50 cm) was offered a constant flow filtration, and sampling was performed at different times. The results showed that all biological agents except diatoms have a removal efficiency of 100% and the effluent׳s turbidity was 0.1 NTU.

Enhancing anaerobic treatment of domestic wastewater: State of the art, innovative technologies and future perspectives

Recent concerns over public health, environmental protection, and resource recovery have induced to look at domestic wastewater more as a resource than as a waste. Anaerobic treatment, owing to attractive advantages of energy saving, biogas recovery and lower sludge production, has been suggested as an alternative technology to the traditional practice of aerobic wastewater treatment, which is energy intensive, produces high excess of sludge, and fails to recover the potential resources available in wastewater. Sewage treatment by high-rate anaerobic processes has been widely reported over the last decades as an attractive method for providing a good quality effluent. Among the available high-rate anaerobic technologies, membrane bioreactors feature many advantages over aerobic treatment and conventional anaerobic systems, since high treatment efficiency, high quality effluent, pathogens retention and recycling of nutrients, were generally achieved. The objective of this paper is to review the currently available knowledge on anaerobic domestic wastewater treatment for the mostly applied high-rate systems and membrane bioreactors, presenting benefits and drawbacks, and focusing on the most promising emerging technologies, which need more investigation for their scale-up.

Submerged low-cost pyrophyllite ceramic membrane filtration combined with GAC as fluidized particles for industrial wastewater treatment

Submerged ceramic membrane reactor treating industrial wastewater was combined with granular activated carbon (GAC) particles to control membrane fouling and organic removal efficiency. The GAC particles were suspended along the membrane surface under bulk recirculation only through the reactor without any gas sparging. Membrane support coated with Al₂O₃ layer (CPM) and uncoated one (UPM) was compared at constant flux mode of filtration. The membrane support consisted of 80% of pyrophyllite and 20% of alumina. Under up-flow velocity of 0.031 m s^-1 through bulk recirculation only without GAC particles, the fouling rates were observed as 0.011 and 0.013 bar h^-1 for the CPM and UPM, respectively. With suspension of GAC particles, fouling mitigation was enhanced considerably and this effect was more pronounced with CPM than UPM under the same upflow velocity (90 vs. 57%). In addition, the GAC suspension increased critical flux by 46% higher with CPM than that observed without the carbon particles. The organic removal efficiency of the UPM was lower than that of CPM while the fouling rate was much greater probably due to pore blocking caused by organic dye compounds. For the both membranes, suspension of GAC particles along the membrane surface increased organic removal efficiency higher than 90%. The organic removal efficiency was enhanced by increasing permeate flux, but it became lower as upflow velocity was higher.

Pilot study of cold-rolling wastewater treatment using single-stage anaerobic fluidized membrane bioreactor

A pilot-scale single-stage anaerobic fluidized membrane bioreactor (AFMBR) was firstly used in this study to treat cold-rolling emulsion wastewater from steel industry. It was continuously operated for 302 days with influent COD concentration of 860-1120 mg/L. Under a hydraulic retention time of 1.5 d, the average effluent COD concentration of 72 mg/L achieved corresponding 90% of COD removal. The permeate flux was varied between 1.7 and 2.9 L/m²/h during operation which decreased with increased biomass concentration inside AFMBR. The trans-membrane pressure (TMP) was generally around 35-40 kPa, however, it increased up to 60 kPa when volatile suspended solid increased to above 2.5 g/L. Both flux and TMP data reveal the importance of biomass control for AFMBR operation. Results from terminal restriction fragment length polymorphism (T-RFLP) show the genus Methanosaeta was dominant on GAC and it shared dominance with the genera Methanomethylovorans and Methanosarcina in suspended sludge.