A novel membrane distillation-thermophilic bioreactor system: biological stability and trace organic compound removal

Advances in membrane distillation for wastewater treatment: Innovations, challenges, and sustainable opportunities

Water pollution and the growing demand for zero liquid discharge solutions have driven the development of advanced wastewater treatment technologies. Membrane distillation (MD) is a promising thermal-based process capable of treating high-salinity brines and wastewater. This review provides an in-depth analysis of MD configurations, operating principles, and membrane characteristics while addressing key challenges such as fouling and pore wetting which hinder large-scale implementation. To overcome these limitations, various membrane fabrication and modification strategies, including physical and chemical approaches, have been explored. The integration of MD with other processes (hybrid MD) for wastewater treatment is also examined. A comprehensive discussion on the mechanisms of organic, inorganic, and biological fouling and their impact on MD performance is presented. Additionally, recent advancements in antifouling strategies, including surface modifications, novel materials, and operational optimizations, are reviewed. Furthermore, the review critically analyzes membrane wetting, its governing mechanisms, and mitigation techniques. By summarizing the current challenges and future prospects, this work provides valuable insights into improving MD performance for practical applications. The findings serve as a foundation for further research and technological advancements in the field of wastewater treatment using MD.

Development and optimization of a silica-bound laccase biocatalyst and its application in hospital wastewater treatment

Laccase from Trametes hirsuta was immobilized on amino-functionalized silica by adsorption and covalent binding using glutaraldehyde (GLA) and glyoxal (GLX) as cross-linkers. The immobilization process was optimized applying the Box-Behnken methodology. The immobilized biocatalysts were characterized using scanning electron microscopy, Brunauer-Emmett-Teller surface area and Barrett-Joyner-Halenda pore size analyses, and elemental analysis. Covalent immobilization proved to be better than adsorption based on the specific activity, immobilization yield, and stability in hospital wastewater (HWW) of the biocatalysts. The biocatalyst prepared using GLA under optimized conditions (laccase loading: 10 kU/L, pH 5, temperature: 5 °C, immobilization time: 8 h, and GLA amount: 100 mM) demonstrated better stability to pH, temperature, and other denaturants, compared to free laccase. It exhibited good catalytic potential to remove phenolic compound acetaminophen (83%) and other trace organic contaminants (TrOCs) such as mefenamic acid (86%), indomethacin (73%), carbamazepine (62%), ibuprofen (43%), naproxen (37%), and ketoprofen (27%), in a mixture from a real non-treated hospital effluent spiked with 1 µg/L of each of the above compounds. In addition, the measured catalytic parameters (Km, kcat and kcat/Km) of acetaminophen (free laccase vs. immobilized laccase (AFHMS-GLA-Lac)) are relatively similar. This is one of the first evaluative studies on different immobilization strategies using the Box-Behnken optimization method to develop efficient and stable laccase biocatalysts by immobilization on amino-functionalized silica for real hospital wastewater treatment.

Assessment of temperature dynamics and microbial community responses in aerobic membrane bioreactors from mesophilic to hyper-thermophilic conditions

This study investigates the impact of temperature variations on the performance of an aerobic membrane bioreactor (MBR) as it transitions from mesophilic (30 °C) to hyper-thermophilic (65 °C) conditions. The microbial community structure was analyzed using 16S rRNA gene sequencing to assess how temperature influences microbial diversity and composition. In mesophilic conditions, the system exhibited high alpha diversity with a Shannon index of 5.92 and 224 observed species. As the temperature increased to 45 °C and 65 °C, diversity decreased significantly, with Shannon indices of 2.54 and 2.82, and 96 and 77 observed species, respectively. Additionally, nutrient removal efficiency, particularly for ammonia and phosphorus, declined at higher temperatures. COD removal efficiency reached 96.5% at 30 °C but decreased to 57% at 45 °C before recovering to 94% at 65 °C. Notably, biomass yield at hyper-thermophilic conditions was 37% lower than at mesophilic conditions, with a yield of 0.06 gVSS/gCODremoved. These findings highlight the potential advantages of operating under hyper-thermophilic conditions, including reduced sludge production, lower nutrient requirements, and increased organic loading capacity. The results provide valuable insights into optimizing high-temperature wastewater treatment processes for more efficient and sustainable industrial applications.

Innovative hyper-thermophilic aerobic submerged membrane distillation bioreactor for wastewater reclamation

For the first time, a hyper-thermophilic aerobic (>60 °C) bioreactor has been integrated with direct submerged membrane distillation (MD), highlighting its potential as an advanced wastewater treatment solution. The hyper-thermophilic aerobic bioreactor, operating up to 65 °C, is tailored for high organic removal, while MD efficiently produces clean water. Throughout the study, high removal rates of 99.5% for organic matter, 96.4% for ammonia, and 100% for phosphorus underscored the impressive adaptability of microorganisms to challenging hyper-thermophilic conditions and a successful combination with the MD process. Despite the extreme temperatures and substantial salinity accumulation reaching up to 12,532 μS/cm, the biomass of microorganisms increased by 1.6 times over a 92-day period, representing their remarkable resilience. The distillation flux ranged from 6.15 LMH to 8.25 LMH, benefiting from the temperature gradient in the hyper-thermophilic setting and the design of the tubular submerged MD membrane module. The system also excels in pH control, utilizing fewer alkali and nutritional resources than conventional systems. Meiothermus, Firmicutes, and Bacteroidetes, the three dominant species, played a crucial role, showcasing their significance in adapting to high salinity and decomposing organic matter.

Review of Hybrid Membrane Distillation Systems

Membrane distillation (MD) is an attractive separation process that can work with heat sources with low temperature differences and is less sensitive to concentration polarization and membrane fouling than other pressure-driven membrane separation processes, thus allowing it to use low-grade thermal energy, which is helpful to decrease the consumption of energy, treat concentrated solutions, and improve water recovery rate. This paper provides a review of the integration of MD with waste heat and renewable energy, such as solar radiation, salt-gradient solar ponds, and geothermal energy, for desalination. In addition, MD hybrids with pressure-retarded osmosis (PRO), multi-effect distillation (MED), reverse osmosis (RO), crystallization, forward osmosis (FO), and bioreactors to dispose of concentrated solutions are also comprehensively summarized. A critical analysis of the hybrid MD systems will be helpful for the research and development of MD technology and will promote its application. Eventually, a possible research direction for MD is suggested.

Membranes in Water Reclamation: Treatment, Reuse and Concentrate Management

In this article, an extensive examination is provided on the possible uses of membranes and hybrid processes in wastewater treatment. While membrane technologies face certain constraints, such as membrane fouling and scaling, the incomplete elimination of emerging contaminants, elevated expenses, energy usage, and brine disposal, there are approaches that can address these challenges. Methods such as pretreating the feed water, utilizing hybrid membrane systems and hybrid dual-membrane systems, and employing other innovative membrane-based treatment techniques can enhance the efficacy of membrane processes and advance sustainability.

High-retention membrane bioreactors for sugarcane vinasse treatment: Opportunities for environmental impact reduction and wastewater valorization

Ethanol production has increased over the years, and Brazil ranking second in the world using sugarcane as the main raw material. However, 10-15 L of vinasse are generated per liter of ethanol produced. Besides large volumes, this wastewater has high polluting potential due to its low pH and high concentrations of organic matter and nutrients. Given the high biodegradability of the organic matter, the treatment of this effluent by anaerobic digestion and membrane separation processes results in the generation of high value-added byproducts such as volatile fatty acids (VFAs), biohydrogen and biogas. Membrane bioreactors have been widely evaluated due to the high efficiency achieved in vinasse treatment. In recent years, high retention membrane bioreactors, in which high retention membranes (nanofiltration, reverse osmosis, forward osmosis and membrane distillation) are combined with biological processes, have gained increasing attention. This paper presents a critical review focused on high retention membrane bioreactors and the challenges associated with the proposed configurations. For nanofiltration membrane bioreactor (NF-MBR), the main drawback is the higher fouling propensity due to the hydraulic driving force. Nonetheless, the development of membranes with high permeability and anti-fouling properties is uprising. Regarding osmotic membrane bioreactor (OMBR), special attention is needed for the selection of a proper draw solution, which desirably should be low cost, have high osmolality, reduce reverse salt flux, and can be easily reconcentrated. Membrane distillation bioreactor (MDBR) also exhibit some shortcomings, with emphasis on energy demand, that can be solved with the use of low-grade and residual heat, or renewable energies. Among the configurations, MDBR seems to be more advantageous for sugarcane vinasse treatment due to the lower energy consumption provided by the use of waste heat from the effluent, and due to the VFAs recovery, which has high added value.

Treatment Trends and Combined Methods in Removing Pharmaceuticals and Personal Care Products from Wastewater-A Review

When discharged into wastewater, pharmaceuticals and personal care products (PPCPs) become microorganic contaminants and are among the largest groups of emerging pollutants. Human, animal, and aquatic organisms' exposures to PPCPs have linked them to an array of carcinogenic, mutagenic, and reproductive toxicity risks. For this reason, various methods are being implemented to remove them from water bodies. This report critically reviews these methods and suggests improvements to removal strategies. Biological, physical, and chemical methods such as biological degradation, adsorption, membrane filtration, and advanced electrical and chemical oxidation are the common methods used. However, these processes were not integrated into most studies to take advantage of the different mechanisms specific to each process and are synergistic in the removal of the PPCPs that differ in their physical and chemical characteristics (charge, molecular weight, hydrophobicity, hydrogen bonding, structure). In the review articles published to date, very little information is available on the use of such integrated methods for removing PPCPs. This report attempts to fill this gap with our knowledge.

Review of the environmental fate and effects of two UV filter substances used in cosmetic products

Sunscreens containing UV filters, such as octocrylene (OCR) and butyl-methoxydibenzoylmethane (BMDBM), have been increasingly used to protect human skin against UV radiation. Both substances have been detected in monitoring studies in the freshwater and marine environment, and there has been concern about potential effects on aquatic organisms. In the present work, the environmental fate and occurrence, bioaccumulation and ecotoxicity including endocrine effects of OCR and BMDBM are reviewed focusing on the aquatic environment. The two UV filters have low water solubilities and a high sorption potential. The available data indicate that OCR is poorly biodegradable. BMDBM lacks anaerobic and inherent biodegradability. However, it was biodegraded to variable degrees in simulation studies. Measured concentrations in the freshwater and marine environment were found to vary considerably between sites, depending on the extent of recreational activities or wastewater discharges. While the bioconcentration factor of OCR in fish is below the threshold value for bioaccumulation according to EU REACH, the available data for BMDBM do not allow a definitive conclusion on its bioaccumulation potential. Analysis of the aquatic toxicity data showed that data quality was often limited, e.g. in the case of effect concentrations substantially exceeding maximum achievable dissolved concentrations. Up to their limit of water solubility, OCR and BMDBM showed no toxicity to microorganisms, algae, and corals, and no acute toxicity to daphnids and fish. In chronic daphnid tests, OCR was highly toxic, whereas BMDBM lacked toxicity. Reliable water-sediment toxicity tests are required to further evaluate possible effects on benthic invertebrates. The available data do not provide evidence for endocrine effects of the two UV filters on fish. In order to assess potential environmental risks caused by OCR and BMDBM, a validated exposure model for estimating direct emission of UV filters into the aquatic environment and data from systematic, longer-term monitoring studies are needed.

A comprehensive review on application of bioreactor for industrial wastewater treatment

In the recent past, wastewater treatment processes performed a pivotal role in accordance with maintaining the sustainable environment and health of mankind at a proper hygiene level. It has been proved indispensable by government regulations throughout the world on account of the importance of preserving freshwater bodies. Human activities, predominantly from industrial sectors, generate an immeasurable amount of industrial wastewater loaded with toxic chemicals, which not only cause dreadful environmental problems, but also leave harmful impacts on public health. Hence, industrial wastewater effluent must be treated before being released into the environment to restrain the problems related to industrial wastewater discharged to the environment. Nowadays, biological wastewater treatment methods have been considered an excellent approach for industrial wastewater treatment process because of their cost-effectiveness in the treatment, high efficiency and their potential to counteract the drawbacks of conventional wastewater treatment methods. Recently, the treatment of industrial effluent through bioreactor has been proved as one of the best methods from the presently available methods. Reactors are the principal part of any biotechnology-based method for microbial or enzymatic biodegradation, biotransformation and bioremediation. This review aims to explore and compile the assessment of the most appropriate reactors such as packed bed reactor, membrane bioreactor, rotating biological contactor, up-flow anaerobic sludge blanket reactor, photobioreactor, biological fluidized bed reactor and continuous stirred tank bioreactor that are extensively used for distinct industrial wastewater treatment.

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.

Strategies to enhance micropollutant removal from wastewater by membrane bioreactors: Recent advances and future perspectives

Membrane bioreactor (MBR) has been widely implemented to advance wastewater treatment and reuse. Nevertheless, conventional MBRs with porous microfiltration or ultrafiltration membranes are not designed for the removal of micropollutants, which ubiquitously occur in wastewater at trace concentrations, but potentially exert detrimental impacts to the ecosystem. Several effective strategies have been applied to improve MBR performance for micropollutant removal, particularly the hydrophilic and recalcitrant compounds. These strategies mainly include the optimization of operational conditions, employment of high-retention membranes to replace porous ones, addition of functional materials into bioreactor, and integration of effluent purification processes. In particular, effluent purification by advanced oxidation processes (AOPs) and high-retention membranes can complement MBR to secure almost complete removal of micropollutants. Nevertheless, further research is still necessary to evaluate the technical and economic feasibility of these strategies, especially for long-term treatment performance, to screen the suitable techniques for industrial MBR applications.

Acid mine drainage and sewage impacted groundwater treatment by membrane distillation: Organic micropollutant and metal removal and membrane fouling

Groundwater is the dominant source of freshwater in many countries around the globe, and the deterioration in its quality by contaminants originating from anthropogenic sources raises serious concern. In this study, a scenario where groundwater is contaminated by acid mine drainage (AMD) from mining activities and/or sewage was envisaged, and the performance of a direct contact membrane distillation (DCMD) system was investigated comprehensively for different compositions of the AMD- and sewage-impacted groundwater. Regardless of the composition, MD membrane achieved 98-100% removal of metals and bulk organics, while the removal of the selected micropollutants ranged between 80 and 100%. Effective retention of contaminants by the MD led to their accumulation over time, which affected the hydraulic performance of the MD membrane by reducing the permeate flux by 29-76%. When persulfate (PS)-mediated oxidation process was integrated with the DCMD, degradation of bulk organics (50-71%) and micropollutants (50-100%) by PS reduced their accumulation. Characterisation of the fouling layer revealed the occurrence of membrane scaling that was mainly due to the deposition of iron oxide or oxyhydroxide precipitates. For an identical composition of the AMD- and sewage-impacted groundwater, flux decline was 10% less in PS-assisted DCMD as compared to that in the standalone DCMD. However, this did not prevent the formation of iron oxide scales on MD membrane during the operation of PS-assisted DCMD. This study demonstrates the long-term performance of a standalone and PS-assisted DCMD operated in continuous-flow mode to treat AMD- and sewage-impacted groundwater for the first time.

A review on effective removal of emerging contaminants from aquatic systems: Current trends and scope for further research

Wastewater is water that has already been contaminated by domestic, industrial and commercial activity that needs to be treated before it could be discharged into some other water bodies to avoid even more groundwater contamination supplies. It consists of various contaminants like heavy metals, organic pollutants, inorganic pollutants and Emerging contaminants. Research has been doing on all types of contaminates more than a decade, but this emerging contaminants is the contaminants which arises mostly from pharmaceuticals, personal care products, hormones and fertilizer industries. The majority of emerging contaminants did not have standardized guidelines, but may have adverse effects on human and marine organisms, even at smaller concentrations. Typically, extremely low doses of emerging contaminants are found in the marine environment and cause a potential risk to the aquatic animals living there. When contaminants emerge in the marine world, they are potentially toxic and pose many risks to the health of both man and livestock. The aim of this article is to review the Emerging contaminate sources, detection methods and treatment methods. The purpose of this study is to consider the adsorption as a beneficial treatment of emerging contaminants also advanced and cost effective emerging contaminates treatment methods.

WITHDRAWN: Progress in the removal of organic microcontaminants from wastewater using high retention membrane bioreactors: A critical review

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Impact of Inorganic Ions and Organic Matter on the Removal of Trace Organic Contaminants by Combined Direct Contact Membrane Distillation-UV Photolysis

This study investigated the degradation of five trace organic contaminants (TrOCs) by integrated direct contact membrane distillation (DCMD) and UV photolysis. Specifically, the influence of inorganic ions including halide, nitrate, and carbonate on the performance of the DCMD–UV process was evaluated. TrOC degradation improved in the presence of different concentrations (1–100 mM) of fluoride ion and chloride ion (1 mM). With a few exceptions, a major negative impact of iodide ion was observed on the removal of the investigated TrOCs. Of particular interest, nitrate ion significantly improved TrOC degradation, while bicarbonate ion exerted variable influence—from promoting to inhibiting impact—on TrOC degradation. The performance of DCMD–UV photolysis was also studied for TrOC degradation in the presence of natural organic matter, humic acid. Results indicated that at a concentration of 1 mg/L, humic acid improved the degradation of the phenolic contaminants (bisphenol A and oxybenzone) while it inhibited the degradation of the non-phenolic contaminants (sulfamethoxazole, carbamazepine, and diclofenac). Overall, our study reports the varying impact of different inorganic and organic ions present in natural water on the degradation of TrOCs by integrated DCMD–UV photolysis: the nature and extent of the impact of the ions depend on the type of TrOCs and the concentration of the interfering ions.

A novel thermophilic anaerobic granular sludge membrane distillation bioreactor for wastewater reclamation

Membrane distillation (MD) has a high heat requirement. Integrating MD with thermophilic bioreactors could remedy this problem. A laboratory-scale thermophilic anaerobic granular sludge membrane distillation bioreactor (ThAGS-MDBR) was used to treat wastewater with a high organic loading rate (OLR). Waste heat from ThAGS was used directly for the MD process to reduce energy consumption. The result demonstrated that the ThAGS-MDBR system achieved a high-efficiency removal of chemical oxygen demand (more 99.5%) and NH₄⁺-N (96.4%). Furthermore, the highest methane production from the proposed system was 332 mL/g COD_removed at OLR of 16 kg COD/m³/day. Specifically, an aggregate of densely packed diverse microbial communities in anaerobic granular sludge was the main mechanism for the enhancement of bioreactor tolerance with environmental changes. High-quality distillate water from ThAGS-MDBR was reclaimed in one step with total organic carbon less than 1.7 mg/L and electrical conductivity less than 120 μS/cm. Furthermore, the result of the DNA extraction kit recorded that Methanosaeta thermophila was a critical archaea for high COD removal and bioreactor stability.

Removal of Organic Micro-Pollutants by Conventional Membrane Bioreactors and High-Retention Membrane Bioreactors

The ubiquitous presence of organic micropollutants (OMPs) in the environment as a result of continuous discharge from wastewater treatment plants (WWTPs) into water matrices—even at trace concentrations (ng/L)—is of great concern, both in the public and environmental health domains. This fact essentially warrants developing and implementing energy-efficient, economical, sustainable and easy to handle technologies to meet stringent legislative requirements. Membrane-based processes—both stand-alone or integration of membrane processes—are an attractive option for the removal of OMPs because of their high reliability compared with conventional process, least chemical consumption and smaller footprint. This review summarizes recent research (mainly 2015–present) on the application of conventional aerobic and anaerobic membrane bioreactors used for the removal of organic micropollutants (OMP) from wastewater. Integration and hybridization of membrane processes with other physicochemical processes are becoming promising options for OMP removal. Recent studies on high retention membrane bioreactors (HRMBRs) such as osmotic membrane bioreactor (OMBRs) and membrane distillation bioreactors (MDBRs) are discussed. Future prospects of membrane bioreactors (MBRs) and HRMBRs for improving OMP removal from wastewater are also proposed.

Impact of salt accumulation in the bioreactor on the performance of nanofiltration membrane bioreactor (NF-MBR)+Reverse osmosis (RO) process for water reclamation

The impacts of salt accumulation, through adjusting the solid retention time (SRT), in the bioreactor on the bioprocess as well as membrane performance of a high retention nanofiltration membrane bioreactor (NF-MBR) and subsequent reverse osmosis (RO) process for water reclamation are addressed in this study. The build-up of salts (i.e., Ca, Mg, PO₄) is a function of SRT, hydraulic retention time (HRT) and membrane rejection. Despite the accumulation of salts, both NF-MBRs at SRT of 30 and 60 days, achieved (i) similar biodegradation efficiency; (ii) excellent organic removal (> 97%); and (iii) excellent ammonia removal (> 98%). Extending the SRT could improve the microbial bio-flocculation capability, but did not influence the microbial activity, viability, and community structure. However, more severe membrane fouling was observed in the NF-MBR with elevated salt levels, which was attributed to the greater formation of calcium phosphate scale and Ca-polysaccharides complex (i.e., irreversible fouling layer) as well as the cake-enhanced-osmotic-pressure (CEOP) effect. Although both NF-MBRs produced comparable quality of permeate, a higher RO membrane fouling rate was observed when the permeate of NF-MBR with SRT at 60 days was fed to the RO system, implying organic compositions in NF-MBR permeate may influence RO performance.

Understanding the mechanisms of trace organic contaminant removal by high retention membrane bioreactors: a critical review

High retention membrane bioreactors (HR-MBR) combine a high retention membrane separation process such as membrane distillation, forward osmosis, or nanofiltration with a conventional activated sludge (CAS) process. Depending on the physicochemical properties of the trace organic contaminants (TrOCs) as well as the selected high retention membrane process, HR-MBR can achieve effective removal (80-99%) of a broad spectrum of TrOCs. An in-depth assessment of the available literature on HR-MBR performance suggests that compared to CAS and conventional MBRs (using micro- or ultra-filtration membrane), aqueous phase removal of TrOCs in HR-MBR is significantly better. Conceptually, longer retention time may significantly improve TrOC biodegradation, but there are insufficient data in the literature to evaluate the extent of TrOC biodegradation improvement by HR-MBR. The accumulation of hardly biodegradable TrOCs within the bioreactor of an HR-MBR system may complicate further treatment and beneficial reuse of sludge. In addition to TrOCs, accumulation of salts gradually increases the salinity in bioreactor and can adversely affect microbial activities. Strategies to mitigate these limitations are discussed. A qualitative framework is proposed to predict the contribution of the different key mechanisms of TrOC removal (i.e., membrane retention, biodegradation, and sorption) in HR-MBR.

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.

Recent Progresses in Application of Membrane Bioreactors in Production of Biohydrogen

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

Volatile fatty acids and biogas recovery using thermophilic anaerobic membrane distillation bioreactor for wastewater reclamation

The effects of bioreactor temperatures and salinities of an anaerobic membrane distillation bioreactor (anMDBR) on the permeation performance and their potential recovery of bioresources were fully examined in this study. To the best of our knowledge, this is the first study of a lab-scale anMDBR process utilizing sub-merged hollow fiber membranes. The hybrid system utilizing both membrane distillation (MD) and anaerobic bioreactors achieved 99.99% inorganic salt rejection regardless the operation temperatures and high initial flux from (2-4 L m^-2 h^-1) at 45-65 °C. However, after 7-day operation, the flux dropped by 16-50% proportional to the bioreactor temperatures. It was found that the effects of bioreactor temperatures had strong impacts on both the permeation performance and fouling behavior while salinity had insignificant effect. A compact non-porous fouling layer was observed on the membrane surface from the bioreactor operated at 65 °C while only a few depositions was found on the membrane from 45 °C bioreactor. In the present study, the optimal anMDBR temperature was found to be 45 °C, showing a balanced biogas production and membrane permeation performance including less fouling formation. At this bioreactor temperature (45 °C), the biogas yield was 0.14 L/g COD_removal, while maintaining a methane recovery of 42% in the biogas, similar recovery to those at bioreactor temperatures of 55 and 65 °C. The potential recovery of volatile fatty acids made anMDBR a more economically efficient system, in addition to its lower operation cost and smaller footprint compared with most other technologies for on-site wastewater treatment.

An anaerobic membrane bioreactor - membrane distillation hybrid system for energy recovery and water reuse: Removal performance of organic carbon, nutrients, and trace organic contaminants

In this study, a direct contact membrane distillation (MD) unit was integrated with an anaerobic membrane bioreactor (AnMBR) to simultaneously recover energy and produce high quality water for reuse from wastewater. Results show that AnMBR could produce 0.3-0.5L/g COD_added biogas with a stable methane content of approximately 65%. By integrating MD with AnMBR, bulk organic matter and phosphate were almost completely removed. The removal of the 26 selected trace organic contaminants by AnMBR was compound specific, but the MD process could complement AnMBR removal, leading to an overall efficiency from 76% to complete removal by the integrated system. The results also show that, due to complete retention, organic matter (such as humic-like and protein-like substances) and inorganic salts accumulated in the MD feed solution and therefore resulted in significant fouling of the MD unit. As a result, the water flux of the MD process decreased continuously. Nevertheless, membrane pore wetting was not observed throughout the operation.

Removal of selected pesticides from groundwater by membrane distillation

The removal of five selected pesticide compounds in a brackish model groundwater solution was examined using a bench scale direct contact membrane distillation (DCMD) system. It was found that the rejection rate of the pesticides in DCMD is mainly influenced by its properties. Compounds with low hydrophobic characteristics and low vapour pressure showed a high rejection rate (70-99%), whereas compounds with a high vapour pressure or high hydrophobicity (LogD) showed a reduced rejection (30-50%) at a water recovery of 75%. The influence of groundwater feed solution contents such as the presence of organics (humic acid) and inorganic ions (Na⁺, Ca²⁺, Mg²⁺, Cl^- and SO₄^2-) as well as feed temperature (40, 55 and 70 °C) on the rejection of the pesticides in DCMD operation was also evaluated. The results showed that the presence of inorganic ions and organics in the feed solution influences the pesticides rejection in DCMD operation to a minor degree. In contrast, reduced rejection of pesticides with high vapour pressure was observed. A rapid small-scale column test (RSSCT) was carried out to study the removal of any remaining substances in the permeate by adsorption onto granular activated carbon (GAC). RSSCT showed promising performance of GAC as a post-treatment option.

Biocatalytic degradation of pharmaceuticals, personal care products, industrial chemicals, steroid hormones and pesticides in a membrane distillation-enzymatic bioreactor

Laccase-catalyzed degradation of a broad spectrum of trace organic contaminants (TrOCs) by a membrane distillation (MD)-enzymatic membrane bioreactor (EMBR) was investigated. The MD component effectively retained TrOCs (94-99%) in the EMBR, facilitating their continuous biocatalytic degradation. Notably, the extent of TrOC degradation was strongly influenced by their molecular properties. A significant degradation (above 90%) of TrOCs containing strong electron donating functional groups (e.g., hydroxyl and amine groups) was achieved, while a moderate removal was observed for TrOCs containing electron withdrawing functional groups (e.g., amide and halogen groups). Separate addition of two redox-mediators, namely syringaldehyde and violuric acid, further improved TrOC degradation by laccase. However, a mixture of both showed a reduced performance for a few pharmaceuticals such as primidone, carbamazepine and ibuprofen. Mediator addition increased the toxicity of the media in the enzymatic bioreactor, but the membrane permeate (i.e., final effluent) was non-toxic, suggesting an added advantage of coupling MD with EMBR.

Thermophilic membrane bioreactors: A review

This study undertakes a state-of-the-art review on thermophilic membrane bioreactors (ThMBRs). Thermophilic aerobic membrane bioreactors (ThAeMBR) and thermophilic anaerobic membrane bioreactors (ThAnMBR) have been widely tested for various high-temperature industrial wastewater treatments at lab- and pilot-scale studies and full-scale applications. The biological and membrane performances of the ThAeMBRs and ThAnMBRs could be better, comparable or poorer, as compared to the mesophilic ones. In general, sludge yield was much lower, biodegradation kinetic was higher, and microbial community was less diversity in the ThAeMBR and ThAnMBR systems. The results from the literature show that ThMBR technology has demonstrated many advantages and is a promising technology for industrial wastewater treatment and sludge digestion. Furthermore, challenges and opportunities of various ThMBRs for industrial applications are identified and discussed.

The fate of trace organic contaminants in sewage sludge during recuperative thickening anaerobic digestion

The aim of this work was to study the fate of trace organic contaminants (TrOCs) in sewage sludge during recuperative thickening anaerobic digestion. Sludge shearing at 3142s^-1 for 5minutes improved biogas production. By contrast, shearing at ≥6283s^-1 for 5minutes caused a notable reduction in biogas production and the removal of volatile solids. Results reported here showed the prevalent occurrence of 17 TrOCs in sewage sludge and highlights the importance of assessing TrOC removal via mass balance calculation by taking into account partitioning between the aqueous and solid phase as well as biodegradation. Hydrophilic and readily-biodegradable TrOCs (caffeine, trimethoprim, and paracetamol) were well removed and were not affected by shearing. TrOCs such as carbamazepine, gemfibrozil, and diuron showed biodegradation only at high shearing. It is possible that shearing can facilitate the circulation of TrOCs between aqueous and solid phases, thus, enhancing the biodegradation of some TrOCs.

Occurrence of trace organic contaminants in wastewater sludge and their removals by anaerobic digestion

This study aims to evaluate the occurrence of trace organic contaminants (TrOCs) in wastewater sludge and their removal during anaerobic digestion. The significant occurrence of 18 TrOCs in primary sludge was observed. These TrOCs occurred predominantly in the solid phase. Some of these TrOCs (e.g. paracetamol, caffeine, ibuprofen and triclosan) were also found at high concentrations (>10,000ng/L) in the aqueous phase. The overall removal of TrOCs (from both the aqueous and solid phase) by anaerobic digestion was governed by their molecular structure (e.g. the presence/absence of electron withdrawing/donating functional groups). While an increase in sludge retention time (SRT) of the digester resulted in a small but clearly discernible increase in basic biological performance (e.g. volatile solids removal and biogas production), the impact of SRT on TrOC removal was negligible. The lack of SRT influence on TrOC removal suggests that TrOCs were not the main substrate for anaerobic digestion.

Effects of salinity build-up on the performance and bacterial community structure of a membrane bioreactor

This study investigated the effects of salinity increase on bacterial community structure in a membrane bioreactor (MBR) for wastewater treatment. The influent salt loading was increased gradually to simulate salinity build-up in the bioreactor during the operation of a high retention-membrane bioreactor (HR-MBR). Bacterial community diversity and structure were analyzed using 454 pyrosequencing of 16S rRNA genes of MBR mixed liquor samples. Results show that salinity increase reduced biological performance but did not affect microbial diversity in the bioreactor. Unweighted UniFrac and taxonomic analyses were conducted to relate the reduced biological performance to the change of bacterial community structure. In response to the elevated salinity condition, the succession of halophobic bacteria by halotolerant/halophilic microbes occurred and thereby the biological performance of MBR was recovered. These results suggest that salinity build-up during HR-MBR operation could be managed by allowing for the proliferation of halotolerant/halophilic bacteria.

Trace organic contaminants in biosolids: Impact of conventional wastewater and sludge processing technologies and emerging alternatives

This paper critically reviews the fate of trace organic contaminants (TrOCs) in biosolids, with emphasis on identifying operation conditions that impact the accumulation of TrOCs in sludge during conventional wastewater and sludge treatment and assessing the technologies available for TrOC removal from biosolids. The fate of TrOCs during sludge thickening, stabilisation (e.g. aerobic digestion, anaerobic digestion, alkaline stabilisation, and composting), conditioning, and dewatering is elucidated. Operation pH, sludge retention time (SRT), and temperature have significant impact on the sorption and biodegradation of TrOCs in activated sludge that ends up in the sludge treatment line. Anaerobic digestion may exacerbate the estrogenicity of sludge due to bioconversion to more potent metabolites. Application of advanced oxidation or thermal pre-treatment may minimise TrOCs in biosolids by increasing the bioavailability of TrOCs, converting TrOCs into more biodegradable products, or inducing complete mineralisation of TrOCs. Treatment of sludge by bioaugmentation using various bacteria, yeast, or fungus has the potential to reduce TrOC levels in biosolids.

High retention membrane bioreactors: challenges and opportunities

Extensive research has focussed on the development of novel high retention membrane bioreactor (HR-MBR) systems for wastewater reclamation in recent years. HR-MBR integrates high rejection membrane separation with conventional biological treatment in a single step. High rejection membrane separation processes currently used in HR-MBR applications include nanofiltration, forward osmosis, and membrane distillation. In these HR-MBR systems, organic contaminants can be effectively retained, prolonging their retention time in the bioreactor and thus enhancing their biodegradation. Therefore, HR-MBR can offer a reliable and elegant solution to produce high quality effluent. However, there are several technological challenges associated with the development of HR-MBR, including salinity build-up, low permeate flux, and membrane degradation. This paper provides a critical review on these challenges and potential opportunities of HR-MBR for wastewater treatment and water reclamation, and aims to guide and inform future research on HR-MBR for fast commercialisation of this innovative technology.