Lower Fouling Rate Research Articles

Optimizing full-scale MBR performance: A dual-phase approach for real-time air-scouring and permeate flow modifications

This study reports on an advanced fuzzy logic control system designed to optimize air-scour and permeate flow rates in membrane bioreactors, targeting enhanced energy efficiency and reduced fouling. Developed in two stages, the system integrates real-time monitoring of transmembrane pressure and permeability trends to adjust air-scour rates in response to fouling indicators. The initial simulations indicated potential for a 50 % reduction in air-scour rates, suggesting considerable energy savings. The second stage's refinements, based on empirical validations, yielded a more responsive system, albeit with more conservative operational adjustments for energy savings.Over eight months of full-scale testing, the advanced control system implemented in one of eight filtration lines exhibited lower fouling rates and maintained superior permeability values compared to the other lines. This performance translated into reduced chemical cleaning frequency, thereby affirming the system's efficiency in fouling management. These findings validate the application of fuzzy logic in MBR operations and offer a promising approach for energy-efficient and sustainable wastewater treatment.

Sludge bound-EPS solubilization enhance CH4 bioconversion and membrane fouling mitigation in electrochemical anaerobic membrane bioreactor: Insights from continuous operation and interpretable machine learning algorithms

Bound extracellular polymeric substances (EPS) are complex, high-molecular-weight polymer mixtures that play a critical role in pore clogging, foulants adhesion, and fouling layer formation during membrane filtration, owing to their adhesive properties and gelation tendencies. In this study, a novel electrochemical anaerobic membrane bioreactor (EC-AnMBR) was constructed to investigate the effect of sludge bound-EPS solubilization on methane bioconversion and membrane fouling mitigation. During the 150-days’ operation, the EC-AnMBR demonstrated remarkable performance, characterized by an exceptionally low fouling rate (transmembrane pressure (TMP) < 4.0 kPa) and high-quality effluent (COD removal > 98.2 %, protein removal > 97.7 %, and polysaccharide removal > 98.5 %). The highest methane productivity was up to 38.0 ± 3.1 mL/Lreactor/d at the applied voltage of 0.8 V with bound-EPS solubilization, 107.6 % higher than that of the control stage (18.3 ± 2.4 mL/Lreactor/d). Morphological and multiplex fluorescence labeling analyses revealed higher fluorescence intensities of proteins, polysaccharides, total cells and lipids on the surface of the fouling layer. In contrast, the interior exhibited increased compression density and reduced activity, likely attributable to compression effect. Under the synergistic influence of the electric field and bound-EPS solubilization, biomass characteristics exhibited a reduced propensity for membrane fouling. Furthermore, the bio-electrochemical regulation enhanced the electroactivity of microbial aggregates and enriched functional microorganisms, thereby promoting biofilm growth and direct interspecies electron transfer. Additionally, the potential hydrogenotrophic and methylotrophic methanogenesis pathways were enhanced at the cathode and anode surfaces, thereby increasing CH₄ productivity. The random forest-based machine learning model analyzed the nonlinear contributions of EPS characteristics on methane productivity and TMP values, achieving R² values of 0.879 and 0.848, respectively. Shapley additive explanations (SHAP) analysis indicated that S-EPSPS and S-EPSPN were the most critical factors affecting CH₄ productivity and membrane fouling, respectively. Partial dependence plot analysis further verified the marginal and interaction effects of different EPS layers on these outcomes. By combining continuous operation with interpretable machine learning algorithms, this study unveils the intricate impacts of EPS characteristics on methane productivity and membrane fouling behaviors, and provides new insights into sludge bound-EPS solubilization in EC-AnMBR.

Experience in Processing Alternative Crude Oils to Replace Design Oil in the Refinery

A comprehensive investigation of a highly complex petroleum refinery (Nelson complexity index of 10.7) during the processing of 11 crude oils and an imported atmospheric residue replacing the design Urals crude oil was performed. Various laboratory oil tests were carried out to characterize both crude oils, and their fractions. The results of oil laboratory assays along with intercriteria and regression analyses were employed to find quantitative relations between crude oil mixture quality and refining unit performance. It was found that the acidity of petroleum cannot be judged by its total acid number, and acid crudes with lower than 0.5 mg KOH/g and low sulphur content required repeated caustic treatment enhancement and provoked increased corrosion rate and sodium contamination of the hydrocracking catalyst. Increased fouling in the H-Oil hydrocracker was observed during the transfer of design Urals crude oil to other petroleum crudes. The vacuum residues with higher sulphur, lower nitrogen contents, and a lower colloidal instability index provide a higher conversion rate and lower fouling rate in the H-Oil unit. The regression equations developed in this work allow quantitative assessment of the performance of crucial refining units like the H-Oil, fluid catalytic cracker, naphtha reformer, and gas oil hydrotreatment based on laboratory oil test results.

Self-cleaning foulant attachment on near-infrared responsive photocatalytic membrane for continuous dynamic removing antibiotics in sewage effluent environment

Bifunctional photocatalytic nanofiltration (PNF) membrane has become a reliable frontier technique for removing refractory organic micropollutants. However, the active mitigated fouling mechanism from the microscopic perspective during its long-term operation of purifying real micro-polluted water is rarely studied. Herein, with an integrated use of QSense Explorer and confocal laser scanning microscope techniques, self-cleaning foulant attachment on an activated and customized near-infrared responsive polymeric PNF (termed as nPNF) membrane with good service performance for continuous dynamic removing antibiotics in sewage effluent environment was firstly elucidated. Time-dependent changes in dissipation oscillation frequency, sensed mass and the visualized foulant spatial distribution all indicated that there were only sporadic foulant attachment, an extremely low fouling layer thickness and irreversible fouling rate on/of the activated nPNF membrane top surface, thereby endowing it with excellent self-cleaning characteristic. This is probably because the reactive oxygen species (mainly •O2− and •OH) concurrently destroys the integrity of fouling layer and its internal adhesion structure, transforming part of the irreversible fouling on nPNF membrane surface into reversible one that is easy to wash off. These new horizons provided useful insight on the fate of selected antibiotics in the to-be-removed stage and self-cleaning foulant attachment of PNF membrane.

Long-term operation optimization of circulating cooling water systems under fouling conditions

Fouling caused by excess metal ions in hard water can negatively impact the performance of the circulating water system (CCWS) by depositing ions on the heat exchanger's surface. Currently, the operation optimization of CCWS often prioritizes short-term flow velocity optimization for minimizing power consumption, without considering fouling. However, low flow velocity promotes fouling. Therefore, it’s crucial to balance fouling and energy/water conservation for optimal CCWS long-term operation. This study proposes a mixed-integer nonlinear programming (MINLP) model to achieve this goal. The model considers fouling in the pipeline, dynamic concentration cycle, and variable frequency drive to optimize the synergy between heat transfer, pressure drop, and fouling. By optimizing the concentration cycle of the CCWS, water conservation and fouling control can be achieved. The model can obtain the optimal operating parameters for different operation intervals, including the number of pumps, frequency, and valve local resistance coefficient. Sensitivity experiments on cycle and environmental temperature reveal that as the cycle increases, the marginal benefits of energy/water conservation decrease. In periods with minimal impact on fouling rate, energy/water conservation can be achieved by increasing the cycle while maintaining a low fouling rate. Overall, the proposed model has significant energy/water saving effects and can comprehensively optimize the CCWS through its incorporation of fouling and cycle optimization.

Performance of an aerobic granular sludge membrane filtration in a full-scale industrial plant.

This study quantifies the hydraulic performance of a pilot-scale ultrafiltration system integrated into a full-scale industrial aerobic granular sludge (AGS) plant. The treatment plant consisted of parallel AGS reactors, Bio1 and Bio2, with similar initial granular sludge properties. During the 3-month filtration test, a chemical oxygen demand (COD) overloading episode took place, affecting the settling properties, morphology, and microbial community composition in both reactors. The impact on Bio2 was more severe than on Bio1, with higher maximal sludge volume index values, a complete loss of granulation, and the excessive appearance of filamentous bacteria extending from the flocs. The membrane filtration properties of both sludges, with these different sludge qualities, were compared. The permeability in Bio1 varied between 190.8 ± 23.3 and 158.9 ± 19.2 L·m-2·h-1·bar-1, which was 50% higher than in Bio2 (89.9 ± 5.8 L·m-2·h-1·bar-1). A lab-scale filtration experiment using a flux-step protocol showed a lower fouling rate for Bio1 in comparison with Bio2. The membrane resistance due to pore blocking was three times higher in Bio2 than in Bio1. This study shows the positive impact of granular biomass on the long-term membrane filtration properties and stresses the importance of granular sludge stability during reactor operation.

Nanomaterial‐Incorporated Membrane Distillation Membranes: Characteristics, Fabrication Techniques, and Applications

AbstractMembrane distillation (MD), a temperature‐driven membrane separation process, is used for various applications due to its less complicated design. MD operations encounter major issues such as permeate flux decrease, membrane fouling, and wetting. A lot of research has been conducted in the past years on the modification of MD membranes by incorporating nanomaterials to overcome these obstacles and considerably increase their performance. Nanomaterials incorporated into the membranes improve the water permeability, mechanical strength, and fouling. The incorporation of next‐generation nanomaterials like metal oxide nanoparticles, carbon‐based nanomaterials, graphene‐based membranes, quantum dots, and metal‐organic frameworks in the MD membranes is investigated. Essential membrane properties for MD operations are comprehensively studied, including higher liquid entry pressure, permeability, porosity, hydrophobicity, thermal stability, mean pore size, and low fouling rate. Significant advances in the application of nanomaterials to the modification of MD membranes as well as other membrane fabrication techniques adopted for the incorporation of nanoparticles like surface grafting, interfacial polymerization, plasma polymerization, and dip coating are reviewed. Important future aspects are discussed.

Nanofiltration-Based Membrane Bioreactor Operated under an Ultralow Flux: Fouling Behavior and Feasibility toward a Low-Carbon System for Municipal Wastewater Reuse

Compared to a conventional membrane bioreactor (MBR) with a porous microfiltration (MF) membrane (MBRMF), a nanofiltration (NF)-based MBR (MBRNF) shows highly attractive features such as high permeate water quality. However, the practical applications of MBRNF are often hindered by the high driven pressures and severe membrane fouling. To address these two critical issues, this study investigated the feasibility of operating MBRNF at an ultralow flux (ULF, e.g., <5 L·m–2·h–1) toward the reuse of municipal wastewater in a single step. We operated the ULF MBRNF at a flux of 2 L·m–2·h–1 and benchmarked its performance against a conventional system using a MBRMF followed by a subsequent NF treatment (MBRMF + NF, both at a constant flux of 20 L·m–2·h–1). The results show that the ULF MBRNF achieved substantial removal of most pollutants, with low negative impacts of ultralow fluxes on pollutant rejections. Besides, the ultralow-flux operation led to a very low fouling rate (0.18 kPa·d–1). More importantly, the ULF MBRNF reduced carbon emissions by 45.2% compared with the MBRMF + NF, mainly due to less energy consumption by pumping. Our findings highlight the simplicity and great potential of ULF MBRNF for wastewater reuse.

Comparison of NaOH and NaOCl on-line chemical enhanced backwash on membrane fouling of high flux membrane bioreactor treating sewage

Different physio-chemical and biological methods have been applied to reduce membrane fouling and to maintain the flux of membrane bioreactor (MBR). Periodic chemically enhanced backwash (CEB) has been recently developed and displayed good performance to recover the membrane permeability. However, the comparative effect of on-line CEB (using NaOCl and NaOH) on fouling mitigation and the effluent quality of MBR was poorly known. This study aimed to evaluate the changes in membrane resistance, membrane fouling and the effluent quality with and without CEB in MBR to reveal the effect of different NaOCl and NaOH concentrations. Lab-scale MBR treating sewage at high flux were operated for 8 min continuously at a flux of 20 L/(m2.h) followed by a backwash duration of 30 s. In reference MBR permeate (without chemical) was used as a backwash solution. The study found that MBR with CEB has higher operational time and lower fouling rates than reference MBR. Overall, backwash with NaOH increased the run-time by 29% – 45% compared to the control MBR, and backwash with NaOCl increased run-time from 34% to 61% compared to the control MBR. NaOCl was significantly more effective by 7% – 28% compared to NaOH in fouling reduction at different concentrations. CEB has no significant (p > 0.05) effect on the removal efficiencies of different pollutants. The chemical oxygen demand removal efficiencies varied between 82 and 84%. The removals of total kjeldahl nitrogen (50 – 54%) and total phosphorus (45 – 52%) were lower due to the short solids and hydraulic retention time. This study highlights the potential of periodic CEB and concentrations of chemicals on MBR fouling and provides insights into potential approaches for mitigating this issue in MBR systems.

Efficient Recovery of Organic Matter from Municipal Wastewater by a High-Rate Membrane Bioreactor Equipped with Flat-Sheet Ceramic Membranes

High-rate processes have been investigated for the recovery of organic matter from municipal wastewater. High-rate membrane bioreactors (HR-MBRs) may simultaneously achieve the increased recovery of carbon and high effluent quality, although control of membrane fouling is extremely difficult. To address the severe fouling in HR-MBRs, the combination of granular scouring and frequent chemically enhanced backwashing was examined. The use of robust flat-sheet ceramic membranes enabled the application of those cleaning strategies. Experiments were carried out at an existing wastewater treatment plant. To operate as a high-rate system, the bioreactor solid residence time and hydraulic residence time were set at 0.5 days and 1.6 h, respectively. Although a relatively high flux of 20 L m-2 h-1 was applied, the proposed HR-MBR exhibited a very low fouling rate of 1.3 kPa/day. The system could recover >70% of the carbon from raw wastewater, whereas the concentration of chemical oxygen demand in the effluent was lowered to <20 mg/L. The performance of the proposed HR-MBR observed in this study was clearly superior to those reported in previous related studies.

Chemical cleaning−solvent treatment−hydrophilic modification strategy for regenerating end-of-life PVDF membrane

Membrane will inevitably reach its end of life during long-term application. The current disposal approach of replacing end-of-life (EOL) membranes by new membranes constrains the economic efficiency and sustainability of the membrane-based wastewater treatment. Herein, we conducted a proof-of-concept study of regenerating EOL polyvinylidene fluoride (PVDF) membranes from a full-scale membrane bioreactor (MBR), to achieve an economical and sustainable membrane-based wastewater treatment. A novel chemical cleaning−solvent treatment−hydrophilic modification strategy was proposed for regenerating the EOL PVDF membranes. After the regeneration, the water permeance of the EOL membrane could be recovered from 43.7 ± 8.8 to 426.0 ± 40.3 L m−2 h−1 bar−1, which was comparable with that of the new membrane. The solvent treatment slightly dissolved the membrane matrix and facilitated the detachment of recalcitrant foulants, which was responsible for the markedly recovered water permeance. The hydrophilic modification using polydopamine coating effectively improved surface hydrophilicity of membrane, endowing the regenerated membrane with better antifouling performance over the solvent treated membrane. The regenerated membrane was tested in an MBR for real municipal wastewater treatment, where the regenerated membrane possessed a comparable effluent quality, as well as a lower fouling rate over EOL, chemical cleaned, and solvent treated membranes. Compared with the conventional way of membrane replacement, the reduction in expenditure and carbon emission of membrane regeneration was ∼3.0 USD/m2-membrane/year and 0.059 kg CO2-e/membrane module, respectively. This proof-of-concept study offers a promising strategy of the EOL membrane regeneration to achieve economical and sustainable membrane-based wastewater treatment.

Experimental investigation of temperature and hydrodynamics on CaCO3 fouling during convective heat transfer and subcooled flow boiling

Deposit formation in heat exchangers is an undesirable process in many industries. Severe fouling can potentially reduce the performance of heat exchangers compromising the efficiency of operating units. This research aimed to examine experimentally the effect of fluid bulk temperature (Tb) during deposition of CaCO3 solution under convective heat transfer and subcooled flow boiling conditions. To do so, several tests were performed at a constant concentration of CaCO3 solution (0.2 g/l) and Tb values of 55–75 °C. Heat flux ranging from 13 to 83 kW/m2 and fluid flow rates of 2 to 4 l /min) were also applied to investigate experimentally fouling resistance and heat transfer coefficient of CaCO3 solution. It was found that Tb would significantly affect the mechanism of deposit formation which has been less discussed in the past. Higher Tb changed the propensity of fouling resistance curve from linear to asymptotic, and the crystal type of deposit layer from aragonite to calcite. Results also showed that at low Tb (55 °C), an increase in heat flux enhanced the fouling rate while at high Tb, an increase in heat flux reduced the fouling, due to increasing the evaporation rate of the solution. In addition, at low heat flux (13 kW/m2), an increase in the fluid flow rate led to higher fouling rate, whereas at high heat flux, increasing the fluid flow rate resulted in lower fouling rate.

Influence of Dispersed TiO2 Nanoparticles via Steric Interaction on the Antifouling Performance of PVDF/TiO2 Composite Membranes.

Herein, the influence of various contents of polyethylene glycol (PEG) on the dispersion of TiO2 nanoparticles and the comprehensive properties of PVDF/TiO2 composite membranes via the steric hindrance interaction was systematically explored. Hydrophilic PEG was employed as a dispersing surfactant of TiO2 nanoparticles in the pre-dispersion process and as a pore-forming additive in the following membrane preparation process. The slight overlap shown in the TEM image and low TSI value (&lt;1) of the composite casting solution indicated the effective dispersion and stabilization under the steric interaction with a PEG content of 6 wt.%. Properties such as the surface pore size, the development of finger-like structures, permeability, hydrophilicity and Zeta potential were obviously enhanced. The improved antifouling performance between the membrane surface and foulants was corroborated by less negative free energy of adhesion (about -42.87 mJ/m2), a higher interaction energy barrier (0.65 KT) and low flux declination during the filtration process. The high critical flux and low fouling rate both in winter and summer as well as the long-term running operation in A/O-MBR firmly supported the elevated antifouling performance, which implies a promising application in the municipal sewage treatment field.

Advanced wastewater treatment and membrane fouling control by electro-encapsulated self-forming dynamic membrane bioreactor

An advanced concept of aerobic membrane bioreactors (MBRs) for highly efficient wastewater treatment has been disclosed by introduction of an electro and encapsulated self-forming dynamic biomembrane (e-ESFDM). The biological filtering membrane is intercalated between two woven polyester fabrics as supports that assist the formation and protect the biomembrane. The innovative architecture of the e-ESFDM in combination with electrocoagulation processes resulted in efficient and cost-effective wastewater treatment and control of the membrane fouling. The performance of the e-ESFDMBR was compared to a yet highly efficient ESFDMBR, where the electric field was not present. The ESFDM-based reactors both showed comparable results in the removal of organic matter, in terms of COD and DOC. On the other hand, e-ESFDMBR exceeded the performance of the ESFDMBR in the reduction of nitrogen- and phosphorous-containing pollutants, responsible for eutrophication processes in the environment, and recalcitrant molecules, such as humic-like substances. In addition, an extremely low fouling rate was observed for the e-ESFDM bioreactor. Insights on the biological processes involved in the developed MBR were provided by investigations on the microbiological diversity found in reactor mixed liquor, ESFDM layer and treated wastewater.

Membrane fouling of raw coking wastewater in membrane distillation: Identification of fouling potential of hydrophilic and hydrophobic components

The flux decline of raw coking wastewater in membrane distillation (MD) is not serious as expected, yet little is known for such phenomenon. This study provides a systematic analysis of the fouling potential of hydrophilic substances (HIS) and hydrophobic fractions (HOA, HOB, HON) extracted from real coking wastewater. The results showed that HIS had a similar flux decline as compared to raw wastewater, whilst HOA and HOB demonstrated an obviously higher initial flux but a higher fouling rate as well. SEM, AFM and XPS analysis proved that a dense layer was formed for HIS, similar as for raw coking wastewater. However, the pores of HOA, HOB and HON fouled membranes remained open and little inorganic elements were presented. Surface charge results confirmed that hydrophobic fractions were negatively charged but the hydrophilic fraction was nearly neutral. Considering the negatively charged membrane surface, HIS was more readily to form a dense layer. With such a hydrophilic protective layer, the heat transfer resistance increased suddenly, leading to a lower initial flux but a lower fouling rate at the same time. This study provides a theoretical fundamental for understanding membrane fouling of high-strength organic wastewater, which is helpful for further development of MD technology.

A Novel Anaerobic Gravity-Driven Dynamic Membrane Bioreactor (AnGDMBR): Performance and Fouling Characterization.

Despite numerous studies undertaken to define the development and significance of the dynamic membrane (DM) formed on some coarse materials, the optimization of reactor configuration and the control of the membrane fouling of anaerobic dynamic membrane bioreactor (AnDMBR) need to be further investigated. The aim of this study was to design a novel anaerobic gravity-driven dynamic membrane bioreactor (AnGDMBR) for the effective and low-cost treatment of municipal wastewater. An 800 mesh nylon net was determined as the optimal support material based on its less irreversible fouling and higher effluent quality by the dead-end filtration experiments. During the continuous operation period of 44 days, the reactor performance, DM filtration behavior and microbial characteristics were studied and compared with the results of recent studies. AnGDMBR had a higher removal rate of chemical oxygen demand (COD) of 85.45 ± 7.06%. Photometric analysis integrating with three-dimensional excitation–emission matrix fluorescence spectra showed that the DM effectively intercepted organics (46.34 ± 16.50%, 75.24 ± 17.35%, and 66.39 ± 17.66% for COD, polysaccharides, and proteins). The addition of suspended carriers effectively removed the DM layer by mechanical scouring, and the growth rate of transmembrane pressure (TMP) and the decreasing rate of flux were reduced from 18.7 to 4.7 Pa/h and 0.07 to 0.01 L/(m2·h2), respectively. However, a dense and thin morphological structure of the DM layer was still observed in the end of reactor operation and plenty of filamentous microorganisms (i.e., SJA-15 and Anaerolineaceae) and the acidogens (i.e., Aeromonadaceae) predominated in the DM layer, which was also embedded in the membrane pore and led to severe irreversible fouling. In summary, the novel AnGDMBR has a superior performance (higher organic removal and lower fouling rates), which provides useful information on the configuration and operation of AnDMBRs for municipal wastewater treatment.

Cake layer reformation rates on self forming dynamic membranes and performance comparison with microfiltration membranes

Dynamic membranes (DMs) keep on attracting attention progressively as an alternative to conventional membranes because they can be operated with relatively higher fluxes and lower fouling rates. However, there are many factors affecting the performance of DMs, such as DM pore size, structure, and operating conditions. In this study, mainly focused on the investigation of cake formation rates both in initial formation and reformation rates after physical/chemical cleaning. In this context, it has been evaluated the performances of DMs with different pore sizes (171 μm, 90 μm, and 30 μm) and different structures under the same conditions and compared their performances with microfiltration (MF) membranes (0.45 μm and 0.22 μm) in a single reactor. In the study, the effects of different fluxes (15-, 20-, 25 L/m2·h (LMH), SADm (1-, 0.8-, 0.5 m3-air /m2·h) and F/M (0.095, 0.125, 0.19 g-COD/g-MLSS·day) conditions on the treatment and filtration performance of DMs were investigated. High COD (>95%) and turbidity (<10 NTU) removals were obtained in this study. In particular, the 30 μm DM (0.65 ± 0.47 NTU) produced quite close effluent turbidity compared to MFs (0.12 ± 0.05 NTU). Low SADm and high F/M values resulted in increased effluent COD concentrations and turbidity values. By decreasing the SADm, the cake formation rate and the fouling rate increased, which showed that there is a definite relationship between the cake formation rates and the fouling rates. Additionally, considering all the results, the most stable operation was obtained in the 30 μm DM, although it has been occurred the least fouling in the 90 μm membrane in the study. This study, focused on cake reformation rates, attempts to show that DMs can be used as an alternative to MBRs. Especially, when taking into account the results of the reformation rate of 30 μm DM (6.09 NTU/h) and other high filterability features.

Enhanced dissolved methane recovery and energy-efficient fouling mitigation via membrane vibration in anaerobic membrane bioreactor

This work successfully developed a novel vibrating AnMBR (VAnMBR) and investigated its long-term performance, fouling control and energy recovery compared to the conventional biogas-sparging AnMBR (BSAnMBR). The VAnMBR achieved better organics removal compared to the BSAnMBR due to the lower content of biopolymers in its effluents. Moreover, the VAnMBR retarded the early TMP rise to alleviate membrane fouling efficaciously with 49.7%–80.2% lower fouling rates than the BSAnMBR. Reduced amounts of nano-particles were consistently observed in the supernatants of the VAnMBR, revealing its benefits to restrict fouling sources for better fouling control. Importantly, the VAnMBR could save 81.9%–94.1% energy of the BSAnMBR and enhance 11.1%–35.0% biogas recovery resulting from minimised dissolved methane, inducing more net energy production during wastewater treatment. The favourable performance of the VAnMBR makes it a promising technology to replace the conventional wastewater treatment plant as a next-generation resource recovery facility.

Stable fouling resistance of polyethylene (PE) separator membrane via oxygen plasma plus zwitterion grafting

Low-cost and fouling resistant microfiltration/ultrafiltration membranes for wastewater treatment has been a challenging task when balancing the membrane cost and performance stability. Herein, a low-cost polyethylene (PE) lithium-ion battery separator was explored as a potential solution. To tackle the intrinsic hydrophobic character which incurs severe fouling, a novel cascade process of plasma treatment plus zwitterion grafting was designed: first oxygen plasma to endow oxygen-containing groups for hydrophilicity and supply “grafting sites”, and grafting zwitterion 3-[[3-(trimethoxysilane)-propyl] amino] propane-1-sulfonic acid (TMAPS) for robust fouling resistance. The membranes were analyzed by water contact angle, Fourier-transform Infrared Spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS). Challenged by two typical foulants, e.g., humic acid (HA) and bovine serum albumin (BSA), the zwitterion grafted membrane showed the best antifouling performance. Oxygen plasma treated PE membrane presented a better performance towards HA than to BSA. The Resistance-in-Series model revealed that the plasma-treated membrane showed improvement in reversible resistance but not in irreversible resistance. Migration of hydrophobic PE segment to the surface due to the low glass transition temperature was attributed to the low fouling resistance of the plasma-treated membrane. However, the zwitterion-grafted membrane led to stabilized hydrophilicity and inhibited the hdrophobic-hydrophobic interaction between the membrane and foulant, thus resulting to significantly improved flux recovery and low irreversible fouling rate. This study clarified that oxygen plasma alone is not sufficient to provide sufficient fouling resistance, but grafting with zwitterion provides stable hydrophilicity and fouling resistance.

Insights on fouling development and characteristics during different fouling stages between a novel vibrating MBR and an air-sparging MBR for domestic wastewater treatment

Membrane fouling remains a major hindrance to a prevalent application of membrane bioreactor (MBR) for wastewater treatment. Vibrating membrane technology has recently attracted increasing attention in energy-efficient fouling control in MBR compared to air sparging. However, little is known about its fundamental fouling control mechanism and whether the vibrating MBR (VMBR) is a highly effective strategy to control fouling constitutions and fouling sources compared to the conventional air-sparging MBR (ASMBR). This study operated two parallel MBRs with vibrating or air-sparging membrane modules for long-term (215 d) real domestic wastewater treatment. Effects of air sparging and vibration rates on fouling control, fouling development and fouling sources across three fouling stages were comprehensively evaluated. Results showed that the VMBR achieved 70% lower fouling rates compared to the ASMBR due to a remarkable retardation in each fouling stage by membrane vibration. The VMBR significantly reduced over 62.7% of colloidCL and SMPCL within the cake layer (CL) to simultaneously alleviate the reversible and irreversible fouling compared to the ASMBR. The comparatively lower dissolved organic matter (DOM) and biopolymer contents in the cake layer of the VMBR resulted in a slower TMP rise. The main DOMs in the foulants of both MBRs were found in the following order: aromatic protein > soluble microbial by-products > other organics. EPSML from mixed liquor (ML) contributed more DOMs to form membrane foulant than the SMPML in both MBRs. Aromatic proteins and soluble microbial products in the EPSML were markedly reduced in the VMBR but increased in the ASMBR in high-shear phase, demonstrating higher effectiveness in fouling control by membrane vibration. This study provided insights into understanding fouling control, fouling development characteristics and fouling mechanisms between the VMBR and ASMBR, which might guide the researchers and engineers to apply novel vibrating MBRs to better control membrane fouling for holistic wastewater treatment in full scale.