Comparison of long-term ceramic membrane bioreactors without and with in-situ ozonation in wastewater treatment: Membrane fouling, effluent quality and microbial community

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

New insight into the irreversible membrane fouling in different pore-sized ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater treatment

Despite great achievements in ceramic membrane bioreactor applications, membrane fouling, which decreases the permeability and separation performance of bioreactors and is associated with increased operational costs and energy consumption, remains a problem. The aim of this study was to expand our understanding of the fouling behavior in the long-term performance of ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater reclamation. Using real textile wastewater effluent, the effects of ultrafiltration (UF) membrane pore sizes, cleaning strategies, and foulant distribution were systematically evaluated over more than three months of continuous operation. The results showed that UCMBR system achieved chemical oxygen demand and total nitrogen removal efficiencies as high as 91-95% and 39-43%, respectively. The high PN concentration can easily increase the viscosity of mixed liquor samples, contributing to a fouling layer on the membrane surface. In addition, the fouling layer formed on the surface of small-pore-sized ceramic UF membranes was not completely reversible but was difficult to eliminate by simple physical cleaning. Soluble extracellular polymeric substances, especially proteins and low molecular weight neutrals, remained, resulting in irreversible fouling on the UF membrane. However, saturated CO₂ backwash showed great potential for enhancing the system through efficient fouling control without using environmentally unfriendly cleaning chemicals. The cake-intermediate and complete-standard models were suitable for explaining the fouling mechanism in the large- and small-pore-sized UF membranes, respectively.

Biofouling in Membrane Bioreactors: Mechanism, Interactions and Possible Mitigation Using Biosurfactants

Biofouling roots damage to membrane bioreactors (MBRs), such as physical, functional and organisational changes and even therefore clogging of the membrane pores and successive microbial degradation. Further, it blocks the pores, results into a biomass cake and in due course reduces the membrane flux and leads to an increase in the operational costs. MBR fouling contributed to the rise in transmembrane pressure (TMP) and decrease in permeate flux (in case of constant pressure operation mode). Chemical surfactants adopted for the cleaning of membrane surfaces have certain disadvantages such as toxicity manifestations, damage to the membranes and high CMC concentrations. Biosurfactant surfactants have attained increasing interest due to their low toxicity, biodegradability, stability to extreme environmental conditions such as temperatures, pH and tolerance to salinity. The biosurfactants trapped the foulants via micelle formation, which distresses hydrophobic interactions amongst bacteria and the surface. Rhamnolipids as an anionic biosurfactant pose a significant interfacial potential and have affinity to bind organic matter. The present review discusses the problem of biofouling in MBRs, type and interactions of foulants involved and also highlights the mechanisms of biosurfactant cleaning, effect of different parameters, effect of concentration, TMP, flux recovery, permeability, mitigation practices and challenges.

Study on the performance and mechanism of bio-electrochemical system to mitigate membrane fouling in bioreactors

To alleviate membrane fouling, a membrane of the membrane bioreactor was directly used as the anode of the bio-electrochemical system. On the 14th day, the control group had blocked, while the experimental group with a current of 0.44 mA, the increase in ΔTMP was only 2.2 kPa. The polysaccharide and protein concentrations in the open-circuit group were 4.2 and 2.9 times higher than those in the closed-circuit group, respectively. Three-dimensional fluorescence spectroscopy and gas chromatography mass spectrometry showed that most of the deposition in the control group contained high-molecular-weight compounds, especially long-chain ester derivatives, phenols, and complex hydrocarbons, whereas the experimental group was the opposite. Therefore, current (electrons) can change the composition of the cake layer. High-throughput sequencing indicated that a significantly higher abundance of electroactive microorganisms on the experimental than control group. Two-dimensional correlation spectroscopy showed that electrons promote the degradation of polysaccharides, thereby alleviating membrane fouling.

Ceramic nanofiber membrane anchoring nanosized Mn2O3 catalytic ozonation of sulfamethoxazole in water

Catalytic ceramic nanofiber membranes (Mn@CNMs) were prepared by anchoring Mn₂O₃ nanoparticles on the pits of attapulgite (APT) nanofibers via an impregnation and in-situ precipitation method. An integrated catalytic ozonation/membrane filtration process applying Mn@CNM was employed to degrade sulfamethoxazole (SMX) and the removal achieved up to 81.3% during a 7-h continuous filtration. The reactive oxygen species (ROS) quenching and radical detection experiments were conducted to determine the contribution of ¹O₂, ·OH and O₂^·- towards the catalytic degradation of SMX. Moreover, Mn@CNM exhibited wide applicability for real water matrix and the total removal of various kinds of emerging contaminants in real hospital wastewater reached up to 98.5%. The excellent performances of Mn@CNM were attributed to the nano-confinement effect in the membrane layer. First, anchoring Mn₂O₃ nanoparticles on the pits of the APT surface suppressed the growth and aggregation of nanosized Mn₂O₃, providing abundant reactive sites for catalytic ozonation. Second, the interlaced APT nanofibers formed nano-sized network structures, where ROS and SMX were confined in close vicinity and ROS have more chances to attack SMX. This work provides a promising strategy for the preparation of catalytic ceramic membrane with high catalytic efficiency for degradation of emerging contaminants in water.

The phylogeny, ecology and ecophysiology of the glycogen accumulating organism (GAO) Defluviicoccus in wastewater treatment plants

This comprehensive review looks critically what is known about members of the genus Defluviicoccus, an example of a glycogen accumulating organism (GAO), in wastewater treatment plants, but found also in other habitats. It considers the operating conditions thought to affect its performance in activated sludge plants designed to remove phosphorus microbiologically, including the still controversial view that it competes with the polyphosphate accumulating bacterium Ca. Accumulibacter for readily biodegradable substrates in the anaerobic zone receiving the influent raw sewage. It looks at its present phylogeny and what is known about it's physiology and biochemistry under the highly selective conditions of these plants, where the biomass is recycled continuously through alternative anaerobic (feed); aerobic (famine) conditions encountered there. The impact of whole genome sequence data, which have revealed considerable intra- and interclade genotypic diversity, on our understanding of its in situ behaviour is also addressed. Particular attention is paid to the problems in much of the literature data based on clone library and next generation DNA sequencing data, where Defluviicoccus identification is restricted to genus level only. Equally problematic, in many publications no attempt has been made to distinguish between Defluviicoccus and the other known GAO, especially Ca. Competibacter, which, as shown here, has a very different ecophysiology. The impact this has had and continues to have on our understanding of members of this genus is discussed, as is the present controversy over its taxonomy. It also suggests where research should be directed to answer some of the important research questions raised in this review.

Immobilization of hexavalent chromium in contaminated soil by nano-sized layered double hydroxide intercalated with diethyldithiocarbamate: Fraction distribution, plant growth, and microbial evolution

Soil contamination by hexavalent chromium (Cr(VI)) poses great risks to human health and ecosystem safety. We introduced a new cheap and efficient layered double hydroxide intercalated with diethyldithiocarbamate (DDTC-LDH) for in-situ remediation of Cr(VI)-contaminated soil. The content of Cr(VI) in contaminated soil (134.26 mg kg^-1) was rapidly reduced to 1.39 mg kg^-1 within 10 days by 0.5% of DDTC-LDH. This result attains to or even exceeds the effectiveness of most of reported soil amendments for Cr(VI) removal in soils. The production cost of DDTC-LDH ($4.02 kg^-1) was relatively low than some common materials, such as nano zero-valent iron ($22.80-140.84 kg^-1). The growth of water spinach became better with the increase of DDTC-LDH dose from 0% to 0.5%, suggesting the recovery of soil function. DDTC-LDH significantly altered the structure and function of soil microbial communities. The species that have Cr(VI)-resistant or Cr(VI)-reductive ability were enriched in DDTC-LDH remediated soils. Network analysis revealed a significant functional niche differentiation of soil microbial communities. In addition to the enhancement of Cr(VI) reduction, the stimulation of plant growth promoting traits, including siderophore biosynthesis, oxidation resistance to reactive oxygen species, and phosphorus availability by DDTC-LDH was another essential mechanism for the immediate remediation of Cr(VI)-contaminated soil.

Novel strategy for membrane biofouling control in MBR with nano-MnO2 modified PVDF membrane by in-situ ozonation

In this study, ozonation catalyst nano-MnO₂ blended polyvinylidene fluoride (PVDF) membrane was fabricated via phase inversion method and applied to membrane bioreactors (MBR), and then coupled with in-situ ozonation to study the anti-biofouling performance and reveal its mechanism. Results showed that, compared with pristine PVDF membrane (MBR_M₀), 0.75 wt% and 1.00 wt% nano-MnO₂ modified PVDF membrane (MBR_M_0.75 and MBR_M_1.00) could mitigate the membrane biofouling rate. Meanwhile MBR_M_1.00 coupled with in-situ ozonation could increase the membrane cleaning cycle to 1.5 and 2.7 times, compared with MBR_M₀ and MBR_M_0.75 without in-situ ozonation. The possible mechanisms included that the nano-MnO₂ modification coupled with in-situ ozonation directly removed the biofouling on the membrane surface, improved the hydrophilicity of the membrane surface and enhanced the chemical oxidation and biodegradation of membrane biofouling contaminants in the sludge mixture. The results of this work provide a new strategy for the control of membrane biofouling in MBR to treat industrial wastewater.

Antibacterial effect of TiO2 modified with poly-amidoamine dendrimer - G3 on S. aureus and E. coli in aqueous solutions

This study investigated bacterial removal using TiO₂ nanoparticles (NPs) modified with poly-amidoamine dendrimer macromolecule (PAMAM, G3). The PAMAM G3/TiO₂ (nanohybrid) was used to specify antibacterial properties via broth microdilution (MBC-Minimum Bactericidal Concentration and MIC-Minimum Inhibitory Concentration-determination), paper disc diffusion, and surface plate count methods. The nanohybrid was characterized via the different techniques. The effects of different factors including initial bacteria count, run time, solution pH, and the nanohybrid concentration were studied. The nanohybrid cytotoxicity was studied on AGS and MKN45 cells line by MTT assay. It was revealed that the nanohybrid was effective in intercepting both bacterial strains growth. The MIC value for S. aureus and E. coli were determined to be 4 and 2 μg/mL, respectively. The MBC value for both strains were calculated to be 32 μg/mL. The results showed removal efficiency of 100% for S. aureus and E. coli bacteria in optimum situation. The decrease in cell viability in the dosage of 32 μg/mL after 72 h treatment for AGS and MKN45 cells line were shown to be 6.2 and 4.6%, respectively. The nanohybrid was able to decrease the S. aureus and E. coli count in solution, which meets the drinking water criterions aligned with WHO guidelines.

Organics removal from shale gas wastewater by pre-oxidation combined with biologically active filtration

Biological treatment technology is increasingly explored in shale gas wastewater (SGW) treatment owing to its cost effectiveness and requires efforts to improve its efficacy. In this work, ozone and ferrate(VI) oxidation pre-treatment were evaluated to enhance the performance of the subsequent biologically active filtration (BAF) in the removal of organic contaminants. The oxidation improved the SGW biodegradability and organic composition under relative high salinity (~20 g/L). Due to the degradation activity of microorganisms, the organics removal efficiency in the BAF system was observed to gradually improve and then reaching stability in long-term continuous-mode operation. The removal rate of dissolved organic carbon (DOC) of the ozone-BAF (O₃-BAF) and the ferrate(VI)-BAF (Fe(VI)-BAF) systems was 83.2% and 82.8% , respectively, higher than that of BAF alone (80.9%). This increase was attributed to higher activity and content of microorganisms in O₃-BAF and Fe(VI)-BAF systems. Two uncultured bacterial species with high abundance of 7.2-21.0% and 2.24-22.31% in genus Rehaibacterium and genus Methyloversatilis were significantly correlated with DOC removal and fluorescent organics removal, respectively. More research is needed to understand whether the species were new and their specific function. This study provides valuable suggestions for extracting safe water from SGW with an efficient treatment train.

Emerging organic contaminants and odorous compounds in secondary effluent wastewater: Identification and advanced treatment

This study aims to address organic micropollutants in secondary effluents from municipal wastewater treatment plants (WWTPs) by first identification of micropollutants in different treatment units, and second by evaluating an advanced treatment process for removals of micropollutants. In secondary effluents, 28 types of pharmaceutical and personal care products (PPCPs), 5 types of endocrine disrupting chemicals (EDCs) and 3 types of odorous compounds are detected with total concentrations of 513 ± 57.8 ng/L, 991 ± 36.5 ng/L, 553 ± 48.3 ng/L, respectively. An integrated process consisting of in-situ ozonation, ceramic membrane filtration (CMF) and biological active carbon (BAC) filtration is investigated in a pilot scale (1000 m³/d) for removal of micropollutants in secondary effluents. The total removal efficiencies of PPCPs, EDCs and odorous compounds are 98.5%, 95.4%, and 91.1%, respectively. Removal mechanisms of emerging organic contaminants (EOCs) and odorous compounds are discussed based on their physicochemical properties. The remarkable removal efficiencies of micropollutants by the pilot system is attributed to synergistic effects of combining ozonation, ceramic membrane filtration and BAC filtration. This study provides a cost-effective and robust technology with the capability of treating secondary effluents for reuse applications.

Mechanism concerning the occurrence and removal of antibiotic resistance genes in composting product with ozone post-treatment

The soil application of composting product will probably cause the spread of antibiotic resistance genes (ARGs) to environment, thereby it is crucial to remove ARGs in composting product. Ozone was adopted for the first time as a post-treatment method to remove the ARGs in composting product in this study. Ozone treatment significantly removed the total ARGs and mobile genetic elements (MGEs) once ozonation process finished. After 10-day storage stage, although the amount of total intracellular ARGs and MGEs increased, the total extracellular ARGs and MGEs decreased in the ozone-treated compost product. Correlation analysis revealed that the reduction in intracellular 16S rRNA contributed to intracellular tetQ and tetW removal, while the variations of other ARGs after ozonation related to MGEs abundance. Network analysis suggested that the reduction of potential host bacteria, as well as the decline in NH₄⁺-N and TOC after the ozonation, contributed to the intracellular ARGs removal.

Elucidating the impacts of intermittent in-situ ozonation in a ceramic membrane bioreactor: Micropollutant removal, microbial community evolution and fouling mechanisms

In this study, impacts of in-situ ozonation applied directly in the membrane tank of a ceramic MBR (Oz-MBR) were assessed to elucidate its implications on micropollutant removal, microbial taxa and membrane fouling. The basic effluent quality (i.e., bulk organics and nutrients) of the MBR without and with in-situ ozonation was comparable. Importantly, pollutant-specific (10-26%) improvement in micropollutant removal was achieved by the Oz-MBR, which could be attributed to the increase in the abundance of microbial taxa responsible for the removal of structurally complex pollutants and/or ozone-assisted oxidation. In-situ ozonation affected the abundance of denitrifying bacteria and functional genes but total nitrogen removal by the Oz-MBR was comparable to that achieved by the control (C)-MBR. Improved mixed liquor properties, and the reduced accumulation of foulants on the membrane surface resulted in membrane fouling alleviation (53%) in the Oz-MBR. In addition, fouling models evaluated for the first time in the case of Oz-MBR indicated that the cake-complete model was suitable to explain membrane fouling mechanism. This comprehensive study demonstrates the performance of MBR coupled with in-situ ozonation, and the obtained results would serve as a useful reference for its implementation at pilot- and/or full-scale.

Powdered activated carbon - Membrane bioreactor (PAC-MBR): Impacts of high PAC concentration on micropollutant removal and microbial communities

In this study, the effect of a high concentration of powdered activated carbon (PAC) on pollutant removal and microbial communities was systematically investigated. Micropollutant removal by the 'control' MBR (without PAC addition) was pollutant-specific and was mainly controlled by their molecular properties. The PAC-MBR achieved enhanced removal of micropollutant by 10% (ofloxacin) to 40% (caffeine). Analysis of the microbial communities in the sludge samples collected from both MBRs indicated an increase in the abundance of 24 (out of 31) genera following PAC addition. Notably, bacterial diversity enriched, particularly in the anoxic zone of the PAC-MBR, indicating a positive impact of recirculating mixed liquor containing PAC from the aerobic to the anoxic zone. In addition, PAC improved the abundance of Comamonas and Methanomethylovorans (up to 2.5%) that can degrade recalcitrant micropollutants. According to the quantitative PCR (qPCR) analysis, the copies of functional genes (nirS, nosZ and narG) increased in PAC-MBR. This study demonstrated that MBR could be operated at a high PAC concentration without compromising the pollutant removal and microbial community evolution during wastewater treatment.

Electrochemical membrane bioreactors: State-of-the-art and future prospects

Integration of an electrochemical process with membrane bioreactor (MBR) has attracted considerable attention in the last decade for simultaneous improvement in pollutant removal and hydraulic performance of MBR. Electrochemical MBR (eMBR) with sacrificial anodes has been observed to achieve enhanced phosphorus (up to 40%) and micropollutant removal (5-60%). This is because direct anodic oxidation, indirect oxidation by reactive oxygen species and electrocoagulation can supplement the biological process. The application of an electric field can substantially reduce membrane fouling by 10% to 95% in the eMBR as compared to the conventional MBR. Sacrificial electrodes (e.g., iron or aluminium) have been reported to be more suitable for fouling mitigation than non-sacrificial electrodes (e.g., titanium). However, during prolonged operation, metal ions released from sacrificial electrodes can adversely affect microbial activity and could accumulate in activated sludge. Depending on the current density and electrode material (sacrificial or non- sacrificial), anodic oxidation, electrocoagulation, electrophoresis and/or electroosmosis mechanisms are responsible for suppressing membrane fouling propensity. This paper critically reviews the current status of the electrochemical MBR technology and presents a concise summary of eMBR configurations and electrode materials. Comparative removal of bulk organics, nutrients and micropollutants in the eMBR and conventional MBR is discussed, and performance governing factors are elucidated. Impacts of operating conditions such as current density on mixed liquor properties (e.g., floc size and zeta potential) and microbial activity are elucidated. The extent of membrane fouling mitigation along with associated mechanisms as well as energy consumption is explained and critically analysed. Future research directions are suggested to fast track the scalability of eMBR, which include but are not limited to electrode lifetime, development of self-cleaning conductive membranes, optimisation of operating parameters, removal of emerging micropollutants, accumulation of toxic metals in activated sludge, and degradation by-products and ecotoxicity.

An integrated process for the advanced treatment of hypersaline petrochemical wastewater: A pilot study

An integrated process combining ozonation, ceramic membrane filtration with biological activated carbon filtration (O₃+CMF + BAC process) was designed and evaluated using a pilot scale (10 m³/d) test for the advanced treatment of hypersaline petrochemical wastewater in a coastal wastewater plant. The membrane flux and ozone dosage were optimized for the optimal treatment performance of this integrated process. The results showed that this integrated process performed well in pollutant removal. The concentrations of COD_Cr, phosphate and color in the effluents were 17.9 mg/L, 0.25 mg/L, and 5 dilution times in average, respectively. The effluent quality met the local discharge standard even under a high influent COD concentration (195 mg/L in average). The synergistic effect of the ozonation and ceramic membrane filtration was investigated through the fluorescence characteristics and hydrophobic/hydrophilic properties of organic compounds. It revealed that ozonation mitigated the membrane fouling and the nanopores in the ceramic membranes enhanced the ozonation efficiency. Meanwhile, the Fenton process had a slightly better effluent quality than the integrated process, but Fenton process consumed much more chemicals and required the sludge disposal, resulting in higher cost. The estimated unit cost for this integrated process was only 34% of that for the Fenton process. Overall, the integrated process demonstrated high stability, reliable effluents and low cost, providing a promising and cost-efficient technology for the treatment of hypersaline petrochemical wastewater.

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.

Optimization of In Situ Backwashing Frequency for Stable Operation of Anaerobic Ceramic Membrane Bioreactor

The cost-effective and stable operation of an anaerobic ceramic membrane bioreactor (AnCMBR) depends on operational strategies to minimize membrane fouling. A novel strategy for backwashing, filtration and relaxation was optimized for stable operation of a side stream tubular AnCMBR treating domestic wastewater at the ambient temperature. Two in situ backwashing schemes (once a day at 60 s/day, and twice a day at 60 s × 2/day) maintaining 55 min filtration and 5 min relaxation as a constant were compared. A flux level over 70% of the initial membrane flux was stabilized by in situ permeate backwashing irrespective of its frequency. The in situ backwashing by permeate once a day was better for energy saving, stable membrane filtration and less permeate consumption. Ex situ chemical cleaning after 60 days’ operation was carried out using pure water, sodium hypochlorite (NaOCl), and citric acid as the order. The dominant cake layer was effectively reduced by in situ backwashing, and the major organic foulants were fulvic acid-like substances and humic acid-like substances. Proteobacteria, Firmucutes, Epsilonbacteria and Bacteroides were the major microbes attached to the ceramic membrane fouling layer which were effectively removed by NaOCl.

Genome sequencing as a new window into the microbial community of membrane bioreactors - A critical review

Recent developed sequencing techniques have resulted in a new and unprecedented way to study biological wastewater treatment, in which most organisms are uncultivable. This review provides (i) an insight on state-of-the-art sequencing techniques and their limitations; (ii) a critical assessment of the microbial community in biological reactor and biofouling layer in a membrane bioreactor (MBR). The data from high-throughput sequencing has been used to infer microbial growth conditions and metabolisms of microorganisms present in MBRs at the time of sampling. These data shed new insight to two fundamental questions about a microbial community in the MBR process namely the microbial composition (who are they?) and the functions of each specific microbial assemblage (what are their function?). The results to date also highlight the complexity of the microbial community growing on MBRs. Environmental conditions are dynamic and diverse, and can influence the diversity and structural dynamics of any given microbial community for wastewater treatment. The benefits of understanding the structure of microbial communities on three major aspects of the MBR process (i.e. nutrient removal, biofouling control, and micropollutant removal) were symmetrically delineated. This review also indicates that the deployment of microbial community analysis for a practical engineering context, in terms of process design and system optimization, can be further realized.

Fenton cleaning strategy for ceramic membrane fouling in wastewater treatment

Membrane fouling is an obstacle impeding the wide applications of ceramic membranes and organics are responsible for most of the membrane fouling issues in wastewater treatment. In this study, Fenton cleaning strategy was firstly proposed to clean ceramic membrane fouling in wastewater treatment. Fe²⁺ efficiently catalyzed fouling cleaning with H₂O₂ (1.5%) to recover the filterability of ceramic membrane. The maximum ∆TMP recovery (over 99%) was achieved at an optimal Fe²⁺ dosage of 124 mg/L after 6 hr of immersion cleaning. The total residual membrane fouling resistance decreased gradually from this optimum value as the Fe²⁺ dosage increased above 124 mg/L. The residual hydraulically reversible fouling resistance accounted for most of the membrane fouling and was basically removed (≤3.0 × 10⁹ m^-1) when Fe²⁺ dosages higher than 124 mg/L were used. The foulants responsible for the formation of a residual hydraulically reversible fouling layer (DOC (dissolved organic carbon), proteins, polysaccharides, EEM (fluorescence excitation-emission matrix spectra), SS (suspended solids), and VSS (volatile suspended solids)) were gradually removed as the Fe²⁺ dosage increased. These residual organic foulants were degraded from biopolymers (10-200 kDa) to low molecular weight substances (0.1-1 kDa), and the particle size of these residual foulants decreased significantly as a result. The strong oxidation power of hydrogen peroxide/hydroxy radicals towards organic foulants was enhanced by Fe²⁺. Fe²⁺ played a significant role in the removal of hydraulically reversible fouling and irreversible fouling from the ceramic membrane. However, Fe²⁺ (≥124 mg/L) increased the likelihood of forming secondary iron-organics aggregates.

Fe(II)-dosed ceramic membrane bioreactor for wastewater treatment: Nutrient removal, microbial community and membrane fouling analysis

Ferrous dosing is used to reduce phosphorus concentration and alleviate polymeric membrane fouling in membrane bioreactor (MBR). However, limited studies have been conducted to investigate the impacts of ferrous dosing on ceramic membrane fouling, nutrient removal efficiency and microbial community. Accordingly, the aim of this study was to investigate the effect of intermittent ferrous dosing with Fe/P molar ratios of 2 and 1 (with a dosing frequency of every two days) on the overall nutrient removal, functional microbial changes and membrane fouling in ceramic membrane bioreactors (CMBR) in treatment of wastewater. TP concentration of 10 mg/L in influent decreased to 1.94 ± 0.62 mg/L (control), 0.38 ± 0.22 mg/L (Fe/P = 1) and 0.31 ± 0.18 mg/L (Fe/P = 2) in the effluent, respectively. Meanwhile, the effluent total nitrogen (TN) concentrations with Fe/P = 1 treatment (6.80 ± 2.02 mg/L) and Fe/P = 2 treatment (5.12 ± 2.28 mg/L) were lower than that of the control (7.72 ± 2.36 mg/L). Compared to Fe/P = 1, the TN removal performance was better for Fe/P = 2 mainly due to the increased abundance of denitrifying bacteria (Zoogloea and Acinetobacter). In addition, excess iron dose might have toxic effects on bacterial physiology, however the Fe concentrations that cause cell damage vary for different bacteria. The relative abundance of Zoogloea (aerobic denitrifying bacteria) continuously increased with ferrous addition (Fe/P = 2), while other bacteria including Dechloromonas, Hyphomicrobium and Thauera (anoxic denitrifying bacteria), Nitrospira (nitrifying bacteria) and Candidatus Accumulibacter (phosphorus accumulating organism) decreased sharply. Furthermore, membrane fouling was effectively moderated by ferrous dosing and Fe/P = 1 treatment showed improved membrane fouling mitigation than Fe/P = 2. Overall, intermittent ferrous addition in CMBR with Fe/P molar ratio of 1 was beneficial to the removal of nutrients (TP, TN and organics), enhanced succession of microbial community and membrane fouling mitigation.

Effects of biomass pyrolysis derived wood vinegar on microbial activity and communities of activated sludge

The effects of wood vinegar (WVG) on microbial activity and communities of activated sludge were investigated in a sequencing batch reactor (SBR) process. Results showed that the optimal WVG concentration was 4 μL/L when the pollutants removal efficiency and microbial activity were promoted by a WVG dilution factor of 1000. WVG could reduce the increase in microbial species richness, which led to a more notable variety of microbial species diversity. The enhanced microbial activity and communities were addressed to the promotion of 7 main classes of microbes in Proteobacteria, Bacteroidetes, Acidobacteria, and Nitrospirae phyla. The growth of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and main genera of denitrifying bacteria (DNB), phosphorus-accumulating organisms (PAOs), and glycogen-accumulating organisms (GAOs) could be promoted by WVG, which improved the sewage treatment effectiveness in a SBR.