A comparison study on membrane fouling in a sponge-submerged membrane bioreactor and a conventional membrane bioreactor

Sustainable hydrogen production via microalgae: Technological advancements, economic indicators, environmental aspects, challenges, and policy implications

Hydrogen has emerged as an alternative energy source to meet the increasing global energy demand, depleting fossil fuels and environmental issues resulting from fossil fuel consumption. Microalgae-based biomass is gaining attention as a potential source of hydrogen production due to its green energy carrier properties, high energy content, and carbon-free combustion. This review examines the hydrogen production process from microalgae, including the microalgae cultivation technological process for biomass production, and the three main routes of biomass-to-hydrogen production: thermochemical conversion, photo biological conversion, and electrochemical conversion. The current progress of technological options in the three main routes is presented, with the various strains of microalgae and operating conditions of the processes. Furthermore, the economic and environmental perspectives of biomass-to-hydrogen from microalgae are evaluated, and critical operational parameters are used to assess the feasibility of scaling up biohydrogen production for commercial industrial-scale applications. The key finding is the thermochemical conversion process is the most feasible process for biohydrogen production, compared to the pyrolysis process. In the photobiological and electrochemical process, pure hydrogen can be achieved, but further process development is required to enhance the production yield. In addition, the high production cost is the main challenge in biohydrogen production. The cost of biohydrogen production for direct bio photolysis it cost around $7.24 kg-1; for indirect bio photolysis it costs around $7.54 kg-1 and for fermentation, it costs around $7.61 kg-1. Therefore, comprehensive studies and efforts are required to make biohydrogen production from microalgae applications more economical in the future.

Integrating electrochemical pre-treatment with carrier-based membrane bioreactor for efficient treatment of municipal waste transfer stations leachate

An integrated process of electrochemical pre-treatment with carrier-based membrane bioreactor (MBR) was constructed for fresh leachate from waste transfer stations with high organic and NH₄⁺-N content. Results showed that within a hydraulic retention time 40 h, the removal efficiencies of chemical oxygen demand (COD), NH₄⁺-N, suspended solids (SS) and total phosphorus (TP) were over 98.5%, 91.2%, 98.3% and 98.4%, respectively, with the organic removal rate of 18.7 kg/m³. The effluent met the Grade A Standard of China (GB/T31962-2015). Pre-treatment contributed about 70 % of the degraded refractory organics and almost all the SS, with the transformation of the humic-like acid to readily biodegradable organics. Biotreatment further removed over 50% of nitrogen pollutants through simultaneous nitrification and denitrification (SND) and consumed about 30% of organics. Meanwhile, the addition of carriers in the oxic MBR enhanced the attached biomass and denitrification enzyme activity, alleviating membrane fouling.

Enhanced membrane fouling control through self-forming dynamic membrane and sponge-wrapped membrane: A novel membrane bioreactor

Membrane technology offers a wide variety of advantages in wastewater treatment, but fouling impedes its widespread applications. Hence, in this study, a novel method was tried to control membrane fouling by combining the self-forming dynamic membrane (SFDM) with a sponge-wrapped membrane bioreactor. The configuration is termed a "Novel-membrane bioreactor" (Novel-MBR). To compare the performance of Novel-MBR, a conventional membrane bioreactor (CMBR) was operated under similar operating conditions. CMBR and Novel-MBR were run consequently for 60 and 150 days, respectively. The Novel-MBR was composed of SFDMs in two compartments before a sponge-wrapped membrane in the membrane compartment. In Novel-MBR, the formation times for SFDMs on coarse (125 μm) and fine (37 μm) pore cloth filers were 43 and 13 min, respectively. The CMBR experienced more frequent fouling; the maximum fouling rate was 5.83 kPa/day. In CMBR, the membrane fouling due to cake layer resistance (6.92 × 10¹²  m^-1 ) was high, and that alone contributed to 84% of fouling. In Novel-MBR, the fouling rate was 0.0266 kPa/day, and the cake layer resistance was 0.329 × 10¹²  m^-1 . Also, the Novel-MBR experienced 21 times less reversible fouling and 36 times less irreversible fouling resistance than the CMBR. In Novel-MBR, the formed SFDM and the sponge wrapped on the membrane helped to reduce both reversible and irreversible fouling. With the modification tried in the present study, the Novel-MBR experienced less fouling, and the maximum transmembrane pressure at the end of 150 days of operation was 4 kPa. PRACTITIONER POINTS: CMBR experienced frequent fouling, and the maximum fouling rate was 5.83 kPa/day. Cake layer resistance was dominant in CMBR and contributed to 84% of fouling. The fouling rate of Novel-MBR at the end of the operation was 0.0266 kPa/day. Novel-MBR is expected to perform for ≈3380 days to reach the maximum TMP of 35 kPa.

Organosilicon and inorganic silica inhibit polystyrene nanoparticles uptake in rice

Nanoplastics (NPs) have become an emerging global environmental problem, and the toxicity of polystyrene nanoplastics (PS-NPs) in rice plants has received widespread attention. However, few studies have focused on silicon (Si)-mediated interactions between PS-NPs and rice. Thus, two forms of Si (organosilicon/inorganic silica) treated rice cells were exposure of positively or negatively charged NPs, PS-NH₂ and PS-COOH, to evaluate the effects of Si for defense against PS-NPs toxicity in rice. The result showed PS-NH₂ nanoparticles were accumulated at relatively low levels in cells compared with that of PS-COOH, but induced a higher accumulation of hydrogen peroxide (H₂O₂) and superoxide radicals (O₂^•-). However, both organosilicon and inorganic silica can generate more negative potential on the surfaces of cell wall to absorb large numbers of positively charged PS-NH₂. In addition, they can prevent the uptake of both PS-NH₂ and PS-COOH through reducing the porosity on the surface of the cell walls. These finally alleviated the toxicity of oxidative stress caused by PS-NPs and improved the viability of rice cells. Our findings demonstrated the significant contribution of Si in combating PS-NPs in rice.

Varied promotion effects and mechanisms of biochar on anaerobic digestion (AD) under distinct food-to-microorganism (F/M) ratios and biochar dosages

Biochar (BC) promotes the performance of anaerobic digestion (AD) through different routes, such as enriching microbes, buffering pH and promoting electron transfer. However, the mechanisms and processes of AD that enhanced by BC under various food to microorganism (F/M) ratios are still unclear. The organic transformations, bioelectrochemical characteristics and microbial consortia under the different BC dosages and F/M ratios were studied to reveal the role of BC in an AD process. The electron transfer system (ETS) was proportional to BC dosage and considered to be a key for AD promotion. At the F/M ratios of 0.5 and 1.0, BC accelerated methane production mainly by promoting ETS. The most enhanced specific methanation activities (SMAs) were obtained with 10.0 g/L BC, and the promotion efficiency under the F/M ratio of 1.0 was significantly higher (P < 0.05) than that under the F/M ratio of 0.5. Under the higher F/M ratio of 2.0, BC shortened the entire AD duration for 5.0 ∼ 13.0 days and guaranteed the resilience of AD by expanding the thermodynamic window of syntrophic methanogenesis via direct interspecies electron transfer (DIET). The COD balance analysis and the ecological functional profiles of microbes demonstrated that BC promoted both the anabolism and catabolism of anaerobes, and enhanced the DIET by converting hydrotrophic methanogenesis into acetolastic methanogenesis pathway. Besides, excessive BC enhanced SMA and simultaneously triggered superfluous biomass growth and thus decreased CH₄ yield. This study provided an important reference for further application of BC under various F/M ratios and dosages in AD.

Performance evaluation of membrane bioreactor coupled with self-forming dynamic membrane

In the present study, Conventional Membrane Bioreactor (C-MBR) and Modified Membrane Bioreactor (M-MBR) were run consequently to compare the fouling reduction through incorporated modification. M-MBR was developed by introducing a Self-forming dynamic membrane (SFDM) formed on a nylon cloth filter ahead of a flat sheet membrane. The coarse cloth filter and fine cloth filter had a pore size of 125 μm and 37 μm, respectively and it took 45 min and 12 min to form a dynamic membrane on them. The C-MBR experienced frequent fouling with cake layer resistance (R_C) as the dominant one which contributed to 83.98% of total resistance (R_T). Whereas in M-MBR the cake layer resistance (67.86% of R_T) and pore blocking resistance (R_P) (1.31% of R_T) was less compared to C-MBR. The formed SFDM on nylon cloth filters led to the reduced R_C and R_P in M-MBR. Therefore, the operation of M-MBR was prolonged, which took 150 days to reach 8.6 KPa (0.057 KPa/day). Eventually, it was concluded that the modification made in this study significantly reduced the fouling.

Exploring the Function of Quorum Sensing Regulated Biofilms in Biological Wastewater Treatment: A Review

Quorum sensing (QS), a type of bacterial cell–cell communication, produces autoinducers which help in biofilm formation in response to cell population density. In this review, biofilm formation, the role of QS in biofilm formation and development with reference to biological wastewater treatment are discussed. Autoinducers, for example, acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2, present in both Gram-negative and Gram-positive bacteria, with their mechanism, are also explained. Over the years, wastewater treatment (WWT) by QS-regulated biofilms and their optimization for WWT have gained much attention. This article gives a comprehensive review of QS regulation methods, QS enrichment methods and QS inhibition methods in biological waste treatment systems. Typical QS enrichment methods comprise adding QS molecules, adding QS accelerants and cultivating QS bacteria, while typical QS inhibition methods consist of additions of quorum quenching (QQ) bacteria, QS-degrading enzymes, QS-degrading oxidants, and QS inhibitors. Potential applications of QS regulated biofilms for WWT have also been summarized. At last, the knowledge gaps present in current researches are analyzed, and future study requirements are proposed.

Impacts of bio-carriers on the characteristics of cake layer and membrane fouling in a novel hybrid membrane bioreactor for treating mariculture wastewater

Membrane fouling is generally considered as a major bottleneck to the wide application of membrane bioreactor (MBR) for high saline mariculture wastewater treatment. Though numerous researches have investigated the membrane fouling of MBR combined with bio-carriers, few studies reveal the impacts of bio-carriers on the characteristics of cake layer and the mechanism of bio-carriers alleviating membrane fouling. In this study, two systems, namely carriers-enhanced MBR (R1) and conventional MBR (R2) were parallel operated, drawing a conclusion that bio-carriers effectively improved the characteristics of cake layer, thus mitigating membrane fouling. Fluorescence excitation emission matrix (EEM) analysis indicated that bio-carriers reduced the adhesion of proteins and humic acid-like materials on membrane surface. Molecular weight (Mw) distribution suggested that soluble microbial products (SMP) with small Mw (6-20 kDa) and biopolymers in extracellular polymeric substances (EPS) (50-300 kDa) was easier to accumulate on membrane surface in R2. The above results indicated that the presence of bio-carriers could effectively reduce the attachment of these organics on membrane surface, contributing to a larger porosity of cake layer and thus mitigating membrane fouling. Meanwhile, gas chromatography-mass spectrometry (GC-MS) clarified that more components were present in R2 than R1. Moreover, the majority of compounds in the SMP were present in both systems, while only 14 compounds in the EPS were the same between R1 and R2. Noticeably, certain aromatics only existed in R2, suggesting that bio-carriers effectively reduced the accumulation of recalcitrant materials, especially aromatics. These results revealed that bio-carriers shifted the precise composition of cake layers.

Insight into the Impacts and Removal Pathways of Perfluorooctanoic Acid (PFOA) in Anaerobic Digestion

Perfluorooctanoic acid (PFOA) that accumulates in wastewater and excess sludge interact with the anaerobes and deteriorate the energy recovery and pollutants removal performance in the anaerobic digestion (AD) system. However, the interaction between PFOA and microbial metabolism in the AD systems remains unclear. This study aimed to clarify the effects and mechanism of PFOA on the AD process as well as the removal pathways of PFOA in an AD system. The results showed that the methane recovery efficiency was inhibited by 7.6–19.7% with the increased PFOA concentration of 0.5–3.0 mg/L, and the specific methanogenesis activity (SMA) was inhibited by 8.6–22.3%. The electron transfer system (ETS) was inhibited by 22.1–37.3% in the PFOA-containing groups. However, extracellular polymeric substance (EPS) gradually increased due to the toxicity of PFOA, and the ratio of protein to polysaccharide shows an upward trend, which led to the formation of sludge aggregates and resistance to the toxic of PFOA. The PFOA mass balance analysis indicated that 64.2–71.6% of PFOA was removed in the AD system, and sludge adsorption was the main removal pathway, accounting for 36.1–61.2% of the removed PFOA. In addition, the anaerobes are proposed to have the potential to reduce PFOA through biochemical degradation since 10.4–28.2% of PFOA was missing in the AD system. This study provides a significant reference for the treatment of high-strength PFOA-containing wastes.

Recent advances in attached growth membrane bioreactor systems for wastewater treatment

To tackle membrane fouling and limited removals of pollutants (nutrients and emerging pollutants) that hinder the wide applications of membrane bioreactor (MBR), attached growth MBR (AGMBR) combining MBR and attached growth process has been developed. This review comprehensively presents the up-to-date developments of media used in both aerobic and anaerobic AGMBRs for treating wastewaters containing conventional and emerging pollutants. It also elaborates the properties of different media, characteristics of attached biomass, and their contributions to AGMBR performance. Conventional media, such as biological activated carbon and polymeric carriers, induce formation of aerobic, anoxic and/or anaerobic microenvironment, increase specific surface area or porous space for biomass retention, improve microbial activities, and enrich diverse microorganisms, thereby enhancing pollutants removal. Meanwhile, new media (i.e. biochar, bioaugmented carriers with selected strain/mixed cultures) do not only eliminate conventional pollutants (i.e. high concentration of nitrogen, etc.), but also effectively remove emerging pollutants (i.e. micropollutants, nonylphenol, adsorbable organic halogens, etc.) by forming thick and dense biofilm, creating anoxic/anaerobic microenvironments inside the media, enriching special functional microorganisms and increasing activity of microorganisms. Additionally, media can improve sludge characteristics (i.e. less extracellular polymeric substances and soluble microbial products, larger floc size, better sludge settleability, etc.), alleviating membrane fouling. Future studies need to focus on the development and applications of more new functional media in removing wider spectrum of emerging pollutants and enhancing biogas generation, as well as scale-up of lab-scale AGMBRs to pilot or full-scale AGMBRs.

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.

Preparation and Characterization of MWCNTs/PVDF Conductive Membrane with Cross-Linked Polymer PVA and Study on Its Anti-Fouling Performance

Based on carboxylated multi-walled carbon nanotubes (MWCNTs-COOH), a MWCNTs/PVDF conductive membrane was prepared by a vacuum filtration cross-linking method. The surface compositions and morphology of conductive membranes were studied by X-ray photoelectron spectroscopy and high-resolution field emission scanning electron microscopy, respectively. The effects of cross-linked polymeric polyvinyl alcohol (PVA) on the conductive membrane properties such as the porosity, pore size distribution, pure water flux, conductivity, hydrophilicity, stability and antifouling properties were investigated. Results showed that the addition of PVA to the MWCNTs/PVDF conductive membrane decreased the pure water flux, porosity and the conductivity. However, the hydrophilicity of the modified MWCNTs/PVDF conductive membrane was greatly improved, and the contact angle of pure water was reduced from 70.18° to 25.48° with the addition of PVA contents from 0 wt% to 0.05 wt%. Meanwhile, the conductive membranes with higher content had a relatively higher stability. It was found that the conductive functional layer of the conductive membrane had an average mass loss rate of 1.22% in the 30 min ultrasonic oscillation experiment. The tensile intensity and break elongation ratio of the conductive membrane are improved by the addition of PVA, and the durability of the conductive membrane with PVA was superior to that without PVA added. The electric assisted anti-fouling experiments of modified conductive membrane indicated that compared with the condition without electric field, the average flux attenuation of the conductive membrane was reduced by 11.2%, and the membrane flux recovery rate reached 97.05%. Moreover, the addition of PVA could accelerate the clean of the conductive membranes.

Enhanced decolorization of dyeing wastewater in a sponges-submerged anaerobic reactor

This study was conducted to assess the potential of a sponges-submerged anaerobic baffled reactor (SS-ABR) for enhancing the processing performance of azo dye-contaminated wastewater. A lab-scale four-compartment SS-ABR, with a total volume of 10 L, was operated at 30 °C for 180 days. A total of 14 polyurethane sponges were added in each compartment to treat synthetic wastewater including a commercial azo dye Hellozol HSR Reactive Black. During the entire operation, in synthetic wastewater, starch was used as a sole carbon source, and the true color level was maintained at 1050 ± 98 Pt/Co. Meanwhile, the hydraulic retention time (HRT) and total COD (T-COD) in the influent were changed to evaluate the SS-ABR treatment performance. After the start-up phase, true color and T-COD removal efficiencies were recorded as 65 ± 3% and 83 ± 2%, 68 ± 5% and 81 ± 4%, and 70 ± 5% and 84 ± 2% for HRT and influent T-COD concentration of 18.6 h and 260 mg L^-1, 14.6 h and 260 mg L^-1, and 14.6 h and 460 mg L^-1, respectively. The microbial community analysis showed that bacterial groups involved in dye degradation, such as Clostridium sp., and sulfate-reducing bacteria Desulfomonile sp. and Desulfovibrio sp. were detected prominently in the SS-ABR. Interestingly, the SS-ABR exhibited the dominance of both Geobacter sp. and Methanosarcina sp., and their occurrences in all columns were proportional to each other, revealing the formation of syntrophic relationships.

Microbial community response to ciprofloxacin toxicity in sponge membrane bioreactor

This study aims to offer insights into how ciprofloxacin (CIP) impact bacterial community structures in the Sponge-MBR process when CIP is spiked into hospital wastewater. We found that the CIP toxicity decreased richness critical phylotypes such as phylum class ẟ-, β-, ɣ-proteobacteria, and Flavobacteria that co-respond to suppress denitrification and cake fouling to 37% and 28% respectively. Cluster analysis shows that the different community structures were formed under the influence of CIP toxicity. CIP decreased attached growth biomass by 2.3 times while increasing the concentration of permeate nitrate by 3.8 times, greatly affecting TN removal by up to 26%. Ammonia removal was kept stable by inflating the ammonia removal rate (p < 0.003), with the wealthy Nitrospira genus guaranteeing the nitrification activity. In addition, we observed an increasing richness of Chloroflexi and Planctomycetes, which may play a role in fouling reduction in the Sponge-MBR. Therefore, if the amount of antibiotics in hospital wastewater continues to increase, it is so important to extend biomass retention for denitrification recovery.

Effects of coarse and fine bubble aeration on performances of membrane filtration and denitrification in moving bed membrane bioreactors

In this study, two lab-scale Moving Bed Membrane Bioreactors (MBMBR) were setup and operated in parallel to study the effect of coarse and fine bubble aeration on the performances of membrane filtration and denitrification treating domestic wastewater. The bacterial populations in the two MBMBRs were further analyzed to investigate the mechanisms involved in the different denitrification performances. The results showed that coarse bubble aeration could effectively mitigate membrane fouling by decreasing the formation of cake layer, although smaller sizes of bio-flocs were induced. In addition, coarse bubble aeration could also maintain dissolved oxygen (DO) at a relatively lower level without compromising the moving of bio-carriers, which achieved 10% higher total nitrogen removal rate due to anoxic zone created at inner layers of biofilms on bio-carriers. Accumulation of denitrifier (Thiobacillus denitrificans) on the bio-carriers was found under the coarse bubble aeration system, which can explain its superior denitrification performance.

Improving sulfonamide antibiotics removal from swine wastewater by supplying a new pomelo peel derived biochar in an anaerobic membrane bioreactor

Sulfonamide antibiotics (SMs), as a class of antibiotics commonly used in swine industries, pose a serious threat to animal and human health. This study aims to evaluate the performance of an anaerobic membrane bioreactor (AnMBR) with and without supplying a new pomelo peel derived biochar to treat swine wastewater containing SMs. Results show that 0.5 g/L biochar addition could increase more than 30% of sulfadiazine (SDZ) and sulfamethazine (SMZ) removal in AnMBR. Approximately 95% of chemical oxygen demand (COD) was removed in the AnMBR at an influent organic loading rate (OLR) of 3.27 kg COD/(m³·d) while an average methane yield was 0.2 L/g COD_removed with slightly change at a small dose 0.5 g/L biochar addition. SMs inhibited the COD removal and methane production and increased membrane fouling. The addition of biochar could reduce the membrane fouling by reducing the concentration of SMP and EPS.

Impacts of sulfadiazine on the performance and membrane fouling of a hybrid moving bed biofilm reactor-membrane bioreactor system at different C/N ratios

The performance and membrane fouling of a hybrid moving bed biofilm reactor-membrane bioreactor (MBBR-MBR) system was evaluated when exposed to 0.5 mg/L of antibiotic sulfadiazine (SDZ). Results indicated that although SDZ reduced the removal efficiency of NH₄⁺-N and TN (up to 12%) and TOC (up to 6%) at low C/N (2.5 and 4), it had no significant effect at high C/N (6 and 9). It was found that SDZ was removed 75% and 58% at high C/N of 9 and low C/N of 2.5, respectively. SDZ decreased the ratio of volatile biomass/total biomass and sludge particle size and increased the concentrations of extracellular polymeric substance (EPS) and soluble microbial product (SMP) in MBR. Consequently, this accelerated the membrane fouling rates, with an average increase of 6.85 kPa/d at low C/N (2.5) and 0.513-0.701 kPa/d at medium and high C/N (4, 6 and 9).

Performance evaluation of conventional membrane bioreactor and moving bed membrane bioreactor for synthetic textile wastewater treatment

In this study, conventional membrane bioreactor (MBR) and moving bed-membrane bioreactor (MB-MBR) processes were compared in synthetic textile wastewater treatment. For this purpose, the bioreactors were operated as a conventional MBR, an MB-MBR with a biocarrier filling ratio of 20 % and an MB-MBR with a biocarrier filling ratio of 10 %, respectively. In the conventional MBR operation, 93.1 % chemical oxygen demand (COD) and 87.1 % color (Reactive Red 390) removal efficiencies were obtained. In both MB-MBR operations, almost equal COD and color removal efficiencies were found as 98.5 % and 89.5 %, respectively. Moreover, offline physical and chemical membrane cleaning processes were applied every other day and every 15 days throughout the conventional MBR operation, respectively, while no physical or chemical membrane cleaning was required during both MB-MBR operations. Furthermore, lower polysaccharide concentrations of extracellular polymeric substances (EPS) and floc sizes of sludge and higher zeta potential of sludge were determined in MB-MBR. Considering the obtained results, it may be stated that the MB-MBR process is an attractive treatment technology for reducing membrane fouling propensity for treatment of textile wastewater.

Membrane fouling mitigation in different biofilm membrane bioreactors with pre-anoxic tanks for treating mariculture wastewater

This study compared the membrane fouling mitigation in two novel types of biofilm membrane bioreactor coupled with a pre-anoxic tank (BF-AO-MBR)-namely a fixed biofilm membrane bioreactor (FB-MBR) with fiber bundle bio-carriers and a moving-bed biofilm membrane bioreactor (MB-MBR) with suspended bio-carriers-relative to an anoxic/oxic MBR (AO-MBR), at salinities ranging from zero to 60 g/L. The results showed that the FB-MBR mitigated membrane fouling to a greater degree than the MB-MBR and AO-MBR. During operation, the FB-MBR exhibited the lowest fouling development, with three membrane filtration cycles, while the AO-MBR and MB-MBR had 22 and nine cycles, respectively. The key fouling factor in all reactors was cake layer resistance (R_C), which contributed to 89.61, 62.20, and 83.17% of the total fouling resistance (R_T) in AO-MBR, FB-MBR and MB-MBR, respectively. Additionally, in the FB-MBR, the pore blocking resistance (30.07%) was also an important cause of fouling. Fiber bundle bio-carriers and suspended bio-carriers reduced the R_T by 37.68% and 21.24% (mainly the R_C) compared to that of AO-MBR. Furthermore, FB-MBR and MB-MBR caused a decrease of suspended biomass (80.14 and 15.90%, respectively), and the latter exhibited a higher sludge particle size than AO-MBR, possibly resulting in the cake layer decline. The studied BF-AO-MBRs further alleviated the fouling propensity by reducing the amount of soluble microbial product (SMP) and extracellular polymeric substances (EPS) under all salinity levels, especially the FB-MBR. Among the protein components, the amounts of tryptophan protein-like substance and aromatic protein-like substance were significantly lower in the FB-MBR compared to the AO-MBR and MB-MBR. Additionally, at 60 g/L salinity, the structure of the microbial community in the FB-MBR had a lower abundance of Bacteroidetes and more biomacromolecule degraders, which may have contributed to the moderation of membrane fouling.

Perspectives and challenges of micro/nanoplastics-induced toxicity with special reference to phytotoxicity

Plastic pollution has become a global concern for ecosystem health and biodiversity conservation. Concentrations of plastics are manifold higher in the terrestrial system than the aquatic one. Micro/nanoplastics (M/NP) have the ability to alter soil enzymatic system, soil properties and also affect soil borne microorganisms and earthworms. Despite, the knowhow regarding modulatory effects of plastics are acquired from the study on aquatic system and reports on their phytotoxic potentials are limited. The presence of cell wall that could restrict M/NP invasion into plant roots might be the putative cause of this limitation. M/NP inhibit plant growth, seed germination and gene expression; and they also induce cytogenotoxicity by aggravating reactive oxygen species generation. Dynamic behavior of cell wall; the pores formed either by cell wall degrading enzymes or by plant-pathogen interactions or by mechanical injury might facilitate the entry of into roots M/NP. This review also provides a possible mechanism of large sized microplastics-induced phytotoxicity especially for those that cannot pass through cell wall pores. As M/NP affect soil microbial community and soil parameters, it is hypothesized that they could have the potential to affect N₂ fixation and research should be conducted in this direction. Reports on M/NP-induced toxicity mainly focused only on one polymer type (polystyrene) in spite of the toxicological relevancies of other polymer types like polyethylene, polypropylene etc. So, the assessment of phytotoxic potential of M/NP should be done using other plastic polymers in real environment as they are known to intract with other environmental stressors as well as can alter the the soil-microbe-plant interaction.

Anaerobic hybrid membrane bioreactor for treatment of synthetic leachate: Impact of organic loading rate and sludge fractions on membrane fouling

In the present study, the treatment of synthetic landfill leachate was carried out using a lab-scale anaerobic hybrid membrane bioreactor (An-HMBR). The reactor was operated for 250 days at two days of hydraulic retention time (HRT). Average chemical oxygen demand (COD) removal efficiency was ≥ 88% at steady-state conditions at 100% raw leachate. As organic loading rate (OLR) increased from 1.6 to 13.9 Kg COD m^-3 d^-1, flux gradually declined from 70 to 52 L/m² h (LMH) within 250 days. Chemical membrane cleaning enhanced the flux up to 75% of the initial flux at the final stage of the reactor. Reversible fouling (>90%) dominated over irreversible fouling (<8%). Membrane fouling was mainly caused by extracellular polymeric substances (EPS) fraction, which resulted in cake layer formation on the ceramic membrane used in the An-HMBR system. Membrane resistance increased with variables in the following order OLR > MLSS (mixed liquor suspended solids) > EPS > SMP (soluble microbial products). A nonlinear regression model developed for prediction of membrane resistance at different OLR can predict with an error of ±7%.

Impact of static biocarriers on the microbial community, nitrogen removal and membrane fouling in submerged membrane bioreactor at different COD:N ratios

The polyvinyl formal (PVFM) biocarrier addition in a membrane bioreactor (MBR) was evaluated at high and low carbon/nitrogen (C/N) ratio of 20.0 and 6.7. Results indicated that static biocarrier addition could enrich nitrification and denitrification bacteria, dominating by Tauera, Amaricoccus and Nitrosospira at the genus level and slightly improved the total nitrogen removal even at a low C/N ratio. The bulk sludge characteristics (such as bigger particle size, lower SMP, lower SMP P/C) were also significantly changed in the hybrid MBR (HMBR), leading to a more sustainable membrane operation. The biocarrier addition also reduced the relative abundance of Sphingobacterials_unclassified, Ohtaekwangia and Rhodocyclaceae_unclassified at the genus level, indicating less membrane fouling in the HMBR. Consequently, HMBR with static PVFM addition could partially overcome the drawback of low C/N ratio for total nitrogen removal and membrane fouling control, providing a more resilient MBR to the undesirable environment such as low C/N ratio.

Performance and microbial communities of different biofilm membrane bioreactors with pre-anoxic tanks treating mariculture wastewater

The performance of pollutant removals, activated sludge characteristics, and microbial communities of two biofilm membrane bioreactors coupled with pre-anoxic tanks (BF-AO-MBRs) (one using fiber bundle bio-carriers (FB-MBR) and the other using suspended bio-carriers (MB-MBR)) were compared at the salinity between zero and 60 g/L. At all salinities, three bioreactors showed good COD average removal efficiencies (>94.1%), and FB-MBR showed the best TN removal efficiency (90.4% at 30 g/L salinity). Moreover, FB-MBR had the faster process start-up time and better salt shock resistance. At high salinities (30-60 g/L), more extracellular polymeric substances were produced by the BF-AO-MBRs to avoid the penetration of salt and protect the bacterial community. Because of the different attachment patterns of biofilms, the microbial community structure in the FB-MBR exposed to 30 g/L salinity had higher nitrite-oxidizing/ammonia-oxidizing bacteria ratio (6.44) with more abundance of denitrifiers, which contribute to higher TN removal efficiency and lower nitrite accumulation.

Simultaneous nitrification-denitrification using baffled osmotic membrane bioreactor-microfiltration hybrid system at different oxic-anoxic conditions for wastewater treatment

The efficacy of a baffled osmotic membrane bioreactor-microfiltration (OMBR-MF) hybrid system equipped with thin film forward osmosis membrane for wastewater treatment was evaluated at laboratory scale. The novel OMBR-MF hybrid system involved baffles, that separate oxic and anoxic zones in the aerobic reactor for simultaneous nitrification and denitrification (SND), and a bioreactor comprised of thin film composite-forward osmosis (TFC-FO) and polyether sulfone-microfiltration (PES-MF) membranes. The evaluation was conducted under four different oxic-anoxic cycle patterns. Changes in flux, salinity build-up, and microbial activity (e.g., extracellular polymeric substances (EPS) were assessed. Over the course of a 34 d test, the OMBR-MF hybrid system achieved high removal of total organic carbon (TOC) (86-92%), total nitrogen (TN) (63-76%), and PO₄-P (57-63%). The oxic-anoxic cycle time of 0.5-1.5 h was identified to be the best operating condition. Incorporation of MF membrane effectively alleviated salinity build-up in the reactor, allowing stable system operation.

Revisiting the effects of powdered activated carbon on membrane fouling mitigation in an anaerobic membrane bioreactor by evaluating long-term impacts on the surface layer

Two submerged anaerobic membrane bioreactors (AnMBRs) with and without powdered activated carbon (PAC) were studied to revisit the effect of PAC on membrane fouling performance by long-term operation when treating synthetic sewage. The results showed that PAC remained efficient for membrane fouling control after long-term operation (over 140 d), and it reduced the fouling rate at a hydraulic retention time of 8 h from 3.12 to 0.89 kPa/d. PAC mainly mitigated the membrane fouling by restraining the formation of a cake layer while generating a gel layer on the membrane surface, which was attributed to the PAC-induced microbial community change in mixed liquor and the membrane surface. Microbial community analysis indicated the genera Pseudomonas (26.5%) and Methanothrix (79.21%) were the predominant bacteria and archaea, respectively, in the gel layer, and this result is completely different from the presence of a high abundance of Levilinea (7.1%), Aminivibrio (4.9%) and Methanothrix (90.04%) in the cake layer on the membrane surface without PAC. The significant difference in the predominant microbes in the membrane surface layer was attributed to the reduced enrichment of Levilinea and Methanothrix with PAC addition.

Comparing powdered and granular activated carbon addition on membrane fouling control through evaluating the impacts on mixed liquor and cake layer properties in anaerobic membrane bioreactors

Concerning the lack of comprehensive study on the impact of powdered and granular activated carbon (PAC and GAC) on AnMBR, their impact on treatment performance, mixed liquor and cake layer properties and membrane fouling behaviors were further investigated. High COD removal efficiencies (>90%) and COD converting to CH₄ rates (>70%) were achieved. GAC greatly increased extracellular polymeric substances (EPS) production in mixed liquor, but significantly reduced biosolids deposited on membrane surface; while PAC largely increased proteins and polysaccharides on membrane surface. In addition, PAC decreased, whereas GAC increased particle sizes. Fouling rates showed PAC and GAC addition effectively alleviated membrane fouling at HRT 8 h, and GAC remarkably postponed the occurrence of the transmembrane pressure jump and extended membrane service time. This study clarified the roles of GAC and PAC on membrane fouling control over long-term operation, which provides the basis for decision-making in practical application.

Pre-coagulation coupled with sponge-membrane filtration for organic matter removal and membrane fouling control during drinking water treatment

A new hybrid system was developed in this study for the treatment of drinking water consisting of pre-coagulation using polyaluminium chloride (PACl) and membrane filtration (MF) with sponge cubes acting as biomass carriers (P-SMF). When compared to a conventional MF (CMF) and a MF after coagulation by utilizing PACl (P-MF), better removal of nutrients, UV₂₅₄ and dissolved organic carbon (DOC) (>65%) was obtained from the P-SMF. The accumulation of biopolymers (including polysaccharides and proteins), humic substances, hydrophilic organics, and other small molecular weight (MW) organic matter in the CMF led to the most severe membrane fouling coupled with the highest pore blocking and cake resistance. Pre-coagulation was ineffective in eliminating small MW and hydrophilic organic matter. Conversely, the larger MW organics (i.e. biopolymers and humic substances), small MW organics and hydrophilic organic compounds could be removed in significantly larger quantities in the P-SMF by PACl coagulation. This was achieved via adsorption and the biodegradation by attached biomass on these sponges and by the suspended sludge. Further analyses of the microbial community indicated that the combined addition of PACl and sponges generated a high enrichment of Zoolgloea, Amaricoccus and Reyranella leading to the reduction of biopolymers, and Flexibacter and Sphingobium were linked to the degradation of humic substances. Moreover, some members of Alphaproteobacteria in the P-SMF may be responsible for the removal of low MW organics. These results suggest that the pre-coagulation process coupled with adding sponge in the MF system is a promising technology for mitigating membrane fouling.

Strategy for Flux Enhancement in Biofilm Ceramic Membrane Bioreactor Applying Prepolymerized and Non-Prepolymerized Inorganic Coagulants

Considering new legislative and economic restrictions caused by the water crisis, this work focuses on a more efficient wastewater treatment process, which combines biological treatment in a moving bed biofilm system with a membrane bioreactor (BF-MBR) and coagulation, particularly addressing fouling alleviation in the separation stage. The study justifies the positive impact of coagulant dosing in BF-MBR regarding membrane flux and fouling rate. Statistical techniques connect the results of coagulation and membrane separation experiments with properties of mixed liquor, obtained after biotreatment in the representative pilot plant and characteristics of prepolymerized and non-prepolymerized inorganic coagulants. Research results substantiate the need for a pH-controlled coagulation of mixed liquor in BF-MBR depending on coagulant type, which influences charge, hydrophobicity and size of flocs and organic content of the system. It is suggested, that the adsorption/charge neutralization mechanism dominates in flux enhancement in BF-MBR, giving the best results in the case of prepolymerized aluminium coagulants. Together with high quality of permeate, the application of prepolymerized aluminium chloride of medium basicity entails a tenfold increase in filtration time of the membrane separation cycle and increases net membrane flux by 30–56%. The results of the study are practically significant for the development of an automated control system for BF-MBR, optimizing treatment rates together with membrane separation efficiency.

A Brief Review on the Resistance-in-Series Model in Membrane Bioreactors (MBRs)

The cake layer deposited on the membrane modules of membrane bioreactors (MBRs), especially under a submerged configuration, represents a relevant and fundamental mechanism deeply influencing the development of membrane fouling. It negatively affects the total resistance to filtration, while exerting a positive effect as a "pre-filter" promoting the "dynamic membrane" that protects the physical membrane from internal fouling. These two opposite phenomena should be properly managed, where the submerged membranes are usually subjected to a periodical cake layer removal through ordinary (permeate backwashing and air scouring) and/or irregular cleaning actions (manual physical cleaning). In this context, the physical removal of the cake layer is needed to maintain the design filtration characteristics. Nevertheless, the proper evaluation of the effect of physical cleaning operations is still contradictory and under discussion, referring in particular to the correct evaluation of fouling mechanisms. The aim of the present work was to summarize the different aspects that influence the fouling investigations, based on simple models for the evaluation of the resistance to filtration due to the cake layer, through physical cleaning operations.

Simultaneous nitrification-denitrification and membrane fouling alleviation in a submerged biofilm membrane bioreactor with coupling of sponge and biodegradable PBS carrier

Simultaneous nitrification-denitrification (SND) was achieved in submerged biofilm membrane bioreactor (SBF-MBR) treating low carbon/nitrogen (C/N) ratio wastewater. A novel bio-carrier coupling of sponge and biodegradable poly(butanediol succinate) (PBS) was applied as external carbon source and biofilm carrier. Result represented that NH₄⁺-N and total nitrogen removal efficiencies were high of 99.1% and 94.3% in the SBF-MBR. Protein (PN) contents from SND-biofilm were reduced by 10.5% and 44.3% in TB-EPS and LB-EPS, while polysaccharides (PS) were reduced by 45.8% and 34.8%, respectively. 3D-EEM spectra indicated that protein-like, humic acid-like and fulvic acid-like substances were the main components in EPS and their peak intensities were reduced. Additionally, membrane fouling of SBF-MBR was improved after the achievement of biofilm. Microbial community analysis showed that Simplicispira, Thauera, Desulfovibrio, Dechlorobacter and Acinetobacter were dominant genus, which indicated co-existence of nitrifying bacteria, heterotrophic denitrifiers and aerobic denitrifiers in the SBF-MBR.

New insight into the fouling behavior of hydrophobic and hydrophilic polypropylene membranes in integrated membrane bioreactors

To investigate the effect of hydrophobic and hydrophilic polypropylene hollow fiber membranes (PPHFMs) applied in membrane bioreactors (MBR), the fouling behaviors of membrane surfaces and pores have been tested. The structural and morphological features on the membrane surface were characterized using attenuated total reflection-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, atomic force microscope, energy dispersive X-ray spectroscopy and laser granularity distribution analysis. The results showed that significantly more polysaccharide, protein and inorganic ingredients were accumulated in the original membrane compared to the hydrophilic membrane. Furthermore, it was found that the pore size influenced the particle distribution and accumulation, such that smaller pore size membranes tended to contain fewer pollutants and a narrow size distribution. Under a constant flux of 11.5 L/m² h, the transmembrane pressure (TMP) varied narrowly between 38 and 53 KPa. Alongside this, a relatively hydrophilic membrane (PP-g-AA) showed the characteristics of lower TMP in comparison to hydrophobic membranes (PP). Indeed, the flux recovery was 30% higher than those of the original PPHFM. This investigation broadens our understanding of membrane modifying and fouling behavior in integrated MBRs.

Removal and degradation mechanisms of sulfonamide antibiotics in a new integrated aerobic submerged membrane bioreactor system

A novel laboratory-scale aerobic submerged membrane bioreactor integrating sponge-plastic biocarriers (SPSMBR) was conducted to study the removal and degradation mechanisms of sulfonamide antibiotics (SAs). Experimental results indicated that SPSMBR had a better removal of sulfadiazine (91% SDZ) and sulfamethoxazole (88% SMZ) than that of a conventional aerobic submerged membrane bioreactor (CSMBR) (76% SDZ and 71% SMZ, respectively). Material balance calculations suggested that biodegradation is the primary removal mechanism of SDZ and SMZ. Protein (tyrosine-like materials) significantly affected the removal of SAs. Moreover, the SPSMBR exhibited its better performance in removing SAs due to more abundance of tyrosine-like materials. The 16S rRNA sequencing showed that biocarriers could promote the enrichment of slow growing bacteria, especially Thermomonas, associated with the removal of SAs. Valuable insights into the removal and degradation mechanisms of SAs in the SPSMBR systems are documented here.

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.

Specific approach for membrane fouling control and better treatment performance of an anaerobic submerged membrane bioreactor

This paper investigated a strategy to minimize membrane fouling and increase treatment efficiency through an investigation of a specific approach by adding sponges into a conventional submerged anaerobic membrane bioreactor (CAnSMBR). During the operation, the protein-based soluble microbial products as the main factor affecting the membrane fouling could be reduced by sponge addition in the CAnSMBR (SAnSMBR). Furthermore, reducing HRT from 18 h to 12 h could shorten the membrane fouling cycle to 62% and 87% in CAnSMBR and SAnSMBR, respectively. At the initial of COD/NO₃ ratio ranges from 5 to 4, only 88% of nitrogen in CAnSMBR was removed, while the SAnSMBR could remove more than 90%. TOC removal efficiency could reach more than 95% under a good stirring scenario. It is evident that the SAnSMBR is a promising solution for improving overall CAnSMBR performance and substantially mitigating membrane fouling.

The characteristic evolution of soluble microbial product and its effects on membrane fouling during the development of sponge membrane bioreactor coupled with fiber bundle anoxic bio-filter for treating saline wastewater

Membrane fouling mitigation was observed during the development of novel sponge membrane bioreactor coupled with fiber bundle anoxic bio-filter (AF-MBMBR). Soluble microbial product (SMP) was found to be positively correlated with membrane fouling. To further clarify the mechanism of fouling mitigation, the effects of bio-carriers (sponge and fiber bundles) on characteristics and fouling potential of SMP were investigated. Characterization of SMP implied that as a consequence of employing bio-carriers, tyrosine and tryptophan in SMP significantly decreased, instead relative proportions of humic and fulvic acids increased. Meanwhile, batch filtration tests demonstrated that fouling potential of SMP was significantly alleviated, flux decline caused by filtrating SMP decreased from 84.5% to 60.1%. Further analysis on foulants and filtrate revealed that proteins performed high adhesion propensity on membrane while humic and fulvic acids mainly can pass through the membrane; this finding could well explain the mitigation of SMP fouling potential induced by bio-carriers.

Multivariate Chemometric Analysis of Membrane Fouling Patterns in Biofilm Ceramic Membrane Bioreactor

Membrane fouling highly limits the development of Membrane bioreactor technology (MBR), which is among the key solutions to water scarcity. The current study deals with the determination of the fouling propensity of filtered biomass in a pilot-scale biofilm membrane bioreactor to enable the prediction of fouling intensity. The system was designed to treat domestic wastewater with the application of ceramic microfiltration membranes. Partial least squares regression analysis of the data obtained during the long-term operation of the biofilm-MBR (BF-MBR) system demonstrated that Mixed liquor suspended solids (MLSS), diluted sludge volume index (DSVI), chemical oxygen demand (COD), and their slopes are the most significant for the estimation and prediction of fouling intensity, while normalized permeability and its slope were found to be the most reliable fouling indicators. Three models were derived depending on the applied operating conditions, which enabled an accurate prediction of the fouling intensities in the system. The results will help to prevent severe membrane fouling via the change of operating conditions to prolong the effective lifetime of the membrane modules and to save energy and resources for the maintenance of the system.

Effect of magnetic powder on membrane fouling mitigation and microbial community/composition in membrane bioreactors (MBRs) for municipal wastewater treatment

This study aims to investigate the usefulness of magnetic powder addition in membrane bioreactors (MBRs) for membrane fouling mitigation and its effect on microbial community and composition. The comparison between the two MBRs (one with magnetic powder (MAS-MBR) and one without magnetic powder (C-MBR)) was carried out to treat synthetic municipal wastewater. Results showed that bioflocculation and adsorption of magnetic powder contributed only minimally to membrane fouling mitigation while the slower fouling rate might be ascribed to magnetic bio-effect. The macromolecules (larger than 500 kDa and 300-500 kDa) of soluble microbial product from the MAS-MBR were reduced by 24.06% and 11.11%, respectively. High-throughput sequencing demonstrated the most abundant genera of biofilm sludge indicated lower abundance in bulk sludge from the MAS-MBR compared to the C-MBR. It is possible that less membrane fouling is connected to reductions in large molecules and pioneer bacteria from bulk sludge.

Performance and membrane fouling of a step-fed submerged membrane sequencing batch reactor treating swine biogas digestion slurry

To identify the performance of step-fed submerged membrane sequencing batch reactor (SMSBR) treating swine biogas digestion slurry and to explore the correlation between microbial metabolites and membrane fouling within this novel reactor, a lab-scale step-fed SMSBR was operated under nitrogen loading rate of 0.026, 0.052 and 0.062 g NH₄⁺-N (gVSS·d)^-1. Results show that the total removal efficiencies for NH₄⁺-N, total nitrogen and chemical oxygen demand in the reactor (>94%, >89% and >97%, respectively) were high during the whole experiment. However, the cycle removal efficiency of NH₄⁺-N decreased significantly when the nitrogen loading rate was increased to 0.062 g NH₄⁺-N (gVSS·d)^-1. The total removal efficiency of total phosphorus in the step-fed SMSBR was generally higher than 75%, though large fluctuations were observed during the experiments. In addition, the concentrations of microbial metabolites, i.e., soluble microbial products (SMP) and extracellular polymeric substances (EPS) from activated sludge increased as nitrogen loading rate increased, both showing quadratic equation correlations with viscosity of the mixed liquid in the step-fed SMSBR (both R² > 0.90). EPS content was higher than SMP content, while protein (PN) was detected as the main component in both SMP and EPS. EPS PN was found to be well correlated with transmembrane pressure, membrane flux and the total membrane fouling resistance. Furthermore, the three-dimensional excitation-emission matrix fluorescence spectroscopy results suggested the tryptophan-like protein as one of the main contributors to the membrane fouling. Overall, this study showed that the step-fed SMSBR could be used to treat swine digestion slurry at nitrogen loading rate of 0.052 g NH₄⁺-N (gVSS·d)^-1, and the control strategy of membrane fouling should be developed based on reducing the tryptophan-like PN in EPS.

Effect of hydraulic retention time on the performance of a hybrid moving bed biofilm reactor-membrane bioreactor system for micropollutants removal from municipal wastewater

This study evaluated micropollutants removal and membrane fouling behaviour of a hybrid moving bed biofilm reactor-membrane bioreactor (MBBR-MBR) system at four different hydraulic retention times (HRTs) (24, 18, 12 and 6h). The results revealed that HRT of 18h was the optimal condition regarding the removal of most selected micropollutants. As the primary removal mechanism in the hybrid system was biodegradation, the attached growth pattern was desirable for enriching slow growing bacteria and developing a diversity of biocoenosis. Thus, the efficient removal of micropollutants was obtained. In terms of membrane fouling propensity analysis, a longer HRT (e.g. HRTs of 24 and 18h) could significantly mitigate membrane fouling when compared with the shortest HRT of 6h. Hence, enhanced system performance could be achieved when the MBBR-MBR system was operated at HRT of 18h.

Effects of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor for municipal wastewater treatment

This study aimed to evaluate the impact of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor (SAAMB-AnGMBR) in municipal wastewater treatment. The results showed that organic removal efficiencies were above 94% at all C/N conditions. Nutrient removal was over 91% at C/N ratio of 100/5 but was negatively affected when decreasing C/N ratio to 100/10. At lower C/N ratio (100/10), more noticeable membrane fouling was caused by aggravated cake formation and pore clogging, and accumulation of extracellular polymeric substances (EPS) in the mixed liquor and sludge cake as a result of deteriorated granular quality. Foulant analysis suggested significant difference existed in the foulant organic compositions under different C/N ratios, and humic substances were dominant when the fastest fouling rate was observed. The performance of the hybrid system was found to recover when gradually increasing C/N ratio from 100/10 to 100/5.

Prediction of membrane fouling using artificial neural networks for wastewater treated by membrane bioreactor technologies: bottlenecks and possibilities

Membrane fouling is a major concern for the optimization of membrane bioreactor (MBR) technologies. Numerous studies have been led in the field of membrane fouling control in order to assess with precision the fouling mechanisms which affect membrane resistance to filtration, such as the wastewater characteristics, the mixed liquor constituents, or the operational conditions, for example. Worldwide applications of MBRs in wastewater treatment plants treating all kinds of influents require new methods to predict membrane fouling and thus optimize operating MBRs. That is why new models capable of simulating membrane fouling phenomenon were progressively developed, using mainly a mathematical or numerical approach. Faced with the limits of such models, artificial neural networks (ANNs) were progressively considered to predict membrane fouling in MBRs and showed great potential. This review summarizes fouling control methods used in MBRs and models built in order to predict membrane fouling. A critical study of the application of ANNs in the prediction of membrane fouling in MBRs was carried out with the aim of presenting the bottlenecks associated with this method and the possibilities for further investigation on the subject.

Removal of antibiotics in sponge membrane bioreactors treating hospital wastewater: Comparison between hollow fiber and flat sheet membrane systems

Hollow fiber (HF) and flat sheet (FS) Sponge MBRs were operated at 10-20 LMH flux treating hospital wastewater. Simultaneous nitrification denitrification (SND) occurred considerably with TN removal rate of 0.011-0.020mg TN mgVSS^-1d^-1. Furthermore, there was a remarkable removal of antibiotics in both Sponge MBRs, namely Norfloxacin (93-99% (FS); 62-86% (HF)), Ofloxacin (73-93% (FS); 68-93% (HF)), Ciprofloxacin (76-93% (FS); 54-70% (HF)), Tetracycline (approximately 100% for both FS and HF) and Trimethoprim (60-97% (FS); 47-93% (HF). Whereas there was a quite high removal efficiency of Erythromycin in Sponge MBRs, with 67-78% (FS) and 22-48% (HF). Moreover, a slightly higher removal of antibiotics in FS than in HF achieved, with the removal rate being of 0.67-32.40 and 0.44-30.42µgmgVSS^-1d^-1, respectively. In addition, a significant reduction of membrane fouling of 2-50 times was achieved in HF-Sponge MBR for the flux range.

Influence of relaxation modes on membrane fouling in submerged membrane bioreactor for domestic wastewater treatment

Relaxation and backwashing have become an integral part of membrane bioreactor (MBR) operations for fouling control. This study was carried out on real municipal wastewater to evaluate the influence of different operational strategies on membrane fouling at equivalent water yield. Four relaxation modes (MBR_10+0, MBR₁₀₊₁, MBR_10+1.5 and MBR₁₀₊₂) were tested to analyze membrane fouling behavior. For the optimization of relaxation modes, fouling rate in terms of trans-membrane pressure, hydraulic resistances and characteristics of fouling fractions were analyzed. It has been observed that cake layer resistance was minimum in MBR_10+1.5 but pore blockage resistance was increased in all relaxation modes. Moreover, high instantaneous flux contributed significantly to fouling rate at the initial stage of MBR operations. Relaxation modes were also efficient in removing irreversible fouling to some extent. Under all relaxation modes, COD removal efficiency ranged from 92 to 96.5%. Ammonium and TP removal were on the lower side due to the short solids and hydraulic retention time.