Fouling Rate Research Articles

Developing PVDF hollow fiber membrane enhanced by braided tube and modified by bionic coating for treating aldehyde-containing wastewater

This study originates from the difficulties encountered in the wastewater treatment from a large-scale methionine production line. Despite the superior performance of the polytetrafluoroethylene (PTFE) membrane, significant issues still persist. The PTFE layer tend to peer off leading to substandard effluent quality, and membrane fouling rate is relatively rapid. To overcome the peeling issue, braided tubes were used to enhance the mechanical strength. To improve the interface bonding between the PVDF layer and braided tubes, two modifiers are introduced to modify the surfaces of braided tubes. Then, the embedded braided tube enhanced PVDF membrane is prepared. On this basis, the one-step bionic coating PVDF (OSBC-PVDF) membrane was prepared by utilizing the polydopamine coating, polyethylene glycol and Cu nanoparticles. It was found that the embedded structure resembling “teeth and gums” formed, significantly improving the mechanical properties to prevent the peeling off of the separation layer. The optimal reaction temperature, reaction time and modifier dosage for preparing the OSBC-PVDF membrane are separately 25 °C, 2 h and 20 g. More importantly, the OSBC-PVDF membrane has withstood the test of 300 days of continuous operation. The stable water quality of the effluent demonstrated that the above issues had been overcome.

Dual-layer coated photocatalytic membranes for surface water treatment: Insight of membrane fouling restriction

The combination of carbon-based material adsorption and photocatalytic oxidation is a crucial approach to eliminate natural organic substances and mitigate membrane fouling induced by them. In this investigation, Bi2O3-TiO2 (BT) was incorporated with three varieties of carbon-based substances (such as powdered activated carbon (PAC), ordered mesoporous carbon CMK-3 (OMCs), and carbon nanotubes (CNTs)) and employed as a dual-layer coating on the surface of the ultrafiltration membrane to reduce membrane fouling induced by natural organics during the treatment of actual water bodies. Under light conditions, the BT/CMK-3 coating outperforms BT/PAC and BT/CNTs coatings in reducing membrane fouling, with a flux recovery rate of up to 80.4 % and an irreversible fouling rate as low as 19.5 %, while also improving the removal rates of UV254 and DOC to 55.2 % and 77.9 %, respectively. Based on the analyses of three-dimensional fluorescence PARAFAC and liquid chromatography, the BT/CMK-3 coating efficiently removes humic substances and protein-like compounds via adsorption and photocatalytic oxidation, achieving a 24.1 % removal rate of humic acid and a 93.7 % removal rate of low molecular weight neutral substances. Under the synergy of CMK-3 adsorption and BT photocatalytic oxidation, reactive oxygen species effectively degraded and transformed the membrane foulants enriched by CMK-3, reducing and increasing the Zeta potential and free energy on the membrane surface to −4.2 mV and 15.1mJ/m2, respectively. The interaction force between the foulant and the membrane changed into a repulsive force, and the fouling mechanism changed from complete blockage to intermediate blockage, thereby shortening the transition time. This advancement provides significant promise for the development and broader application of photocatalytic membrane filtration technology.

Copper Acetate Monohydrate/Nickel Chloride Impregnated PVDF Ultrafiltration Membrane: An Antifouling Membrane for Peat Water Treatment

AbstractThis study examines the polyvinylidene fluoride (PVDF) ultrafiltration membrane impregnated with the copper acetate monohydrate/nickel chloride/thiourea (CuNit) nanoparticle through its physical properties, chemical properties, water flux, humic rejection, and antifouling properties against peat water. The ultrafiltration membrane was fabricated via phase inversion by blending CuNit nanoparticles (1, 3, and 5 wt/wt PVDF %) and PVDF (16 wt %) in N‐Methyl‐2‐pyrrolidone (NMP, 42 wt %) as the solvent. The humic rejection and fouling test are conducted using peat water collected from the Beladin water treatment plant. As a result, M03, which has 1 wt/wt PVDF % of CuNit nanoparticle, gives a better result of pure water flux, humic rejection, and fouling recovery rate with a value of 82 L/m2 h, 93 %, and 40 % compared to pristine PVDF membrane. The fouling of M03 recorded a low total rate of fouling (76 %) that is caused by high reversible fouling and low irreversible fouling with a value of 0.16 and 0.59, respectively, compared to the pristine PVDF membrane. In conclusion, due to the agglomeration that occurs in the further addition of CuNit nanoparticles, coating or encapsulation must be done to improve the stability of nanoparticles and reduce the leach‐out problem as well as provide a good distribution between the nanoparticle and casting solution during the membrane fabrication.

TiO2-embedded dual-layer mullite hollow fiber membranes for efficient removal of Persistent organic pollutants from wastewater

Persistent organic pollutants (POPs) are toxic pollutants that harm the environment and ecosystems. This study presents a novel approach to develop a dual-layer hollow fiber ceramic membrane for phenolic compound removal. A co-extrusion-based phase inversion process and co-sintering techniques were employed to fabricate the membrane, and the effects of TiO2 loadings on the outer layer were investigated. Characterization techniques, including FTIR, SEM, EDX, and zeta potential analysis, were used to analyze the mullite and TiO2 powders and membranes. The membrane’s performance was evaluated through rejection tests of POPs at various concentrations (10, 500, and 1000 ppm) and fouling assessments were conducted. The results showed that the M−MT0.6 membrane, with a mean pore size of 0.0245 μm, effectively rejected benzoic acid (81.45 %), gallic acid (91.45 %), and hydroquinone (74.49 %) from wastewater, achieving the highest permeate flux (1320.50 L/m2·h) for gallic acid at 10 ppm. Additionally, M−MT0.6 exhibited minimal fouling over a 1-h filtration cycle, with the lowest fouling rate (35.1 %) recorded at 1000 ppm for BA, attributed to effective backwashing. However, higher fouling rates were observed at 10 ppm for BA (90.10 %) and HQ (83.50 %). Overall, this study demonstrates the potential of the novel membrane for effective removal of POPs from industrialwastewater.

Pattern Size Relative to Oil Droplet Size Effect on Oil Fouling in Nanofiltration

Membrane fouling is a major issue in many membrane applications. There are numerous methods used in attempt to mitigate membrane fouling, with one method being membrane surface patterning. However, it is still unclear how the ratio of foulant size to pattern size affects membrane fouling. In this study, we investigated constant foulant size while varying the pattern size on the membrane surface to be smaller than (300-nm), equal to (10-μm), and larger than (50-μm) the foulant (10-μm) on polyamide nanofiltration membranes. These membranes were compared to a commercial nanofiltration membrane and a control flat synthesized membrane. The membranes were tested with water, 2,000 ppm Na2SO4, and three cycles of a n-dodecane (as oil) brine solution in a dead-end cell to assess the fouling resistance and flux recovery ability of each polyamide membrane type. From the fouling experiments, it was determined that none of the pattern sizes significantly affect the flux recovery ratio, but smaller than and larger than patterns decreased the fouling rate on the polyamide membranes by a small margin.

Sustainable control of microplastics in wastewater using the electrochemically enhanced living membrane bioreactor

Wastewater treatment plant (WWTP) discharges are major contributors to the release of microplastics (MPs) into the environment. This research work aimed to assess the performance of the novel living membrane bioreactor (LMBR), which utilizes a biological layer as a membrane filter for the removal of polyethylene (PE) MPs from wastewater. The impact of an intermittently applied low current density (0.5 mA/cm2) on the reduction of MPs in the electrochemically enhanced LMBR (e-LMBR) has also been examined. The reactors were also compared to a conventional membrane bioreactor (MBR) and an electro-MBR (e-MBR). 1H nuclear magnetic resonance spectroscopy (1H NMR) was implemented for the MPs detection and quantification in terms of mass per volume of sample.The LMBR and MBR achieved comparable mean PE MPs reduction at 95% and 96%, respectively. The MPs mass reduction in the e-LMBR slightly decreased by 2% compared to that achieved in the LMBR. This potentially indicated the partial breakdown of the MPs due to electrochemical processes. Decreasing and inconsistent NH4-N and PO4-P removal efficiencies were observed over time due to the addition of PE MPs in the MBR and LMBR. In contrast, the integration of electric field in the e-MBR and e-LMBR resulted in consistently high values of conventional contaminant removals of COD (99.72–99.77 %), NH4-N (97.96–98.67%), and PO4-P (98.44–100.00%), despite the MPs accumulation.Integrating electrochemical processes in the e-LMBR led to the development of a stable living membrane (LM) layer, as manifested in the consistently low effluent turbidity 0.49 ± 0.33 NTU. Despite the increasing MPs concentration in the mixed liquor, applying electrochemical processes reduced the fouling rates in the e-LMBR. The e-LMBR achieved comparable efficiencies in contaminant reductions as those observed in the e-MBR, while using a low-cost membrane material.

A comprehensive study on the effects of electrocoagulation integrated in a membrane bioreactor treating sunflower oil refinery wastewater on treatment performance, biological properties, and fouling behavior.

This study evaluated the effects of electrocoagulation integrated in a laboratory-scale membrane bioreactor (MBR), namely EC-MBR, on the treatment performance, activated sludge morphological characterization, and membrane fouling of MBR treating actual sunflower oil refinery wastewater. The EC-MBR system exhibited significantly higher chemical oxygen demand (COD) and oil and grease (O&G) removal efficiency compared to the MBR system. Additionally, both systems achieved excellent turbidity removal, with a percentage above 99%. The membrane fouling rate was higher in the EC-MBR system compared to the MBR system. Despite the decrease in the soluble microbial product (SMP) and extracellular polymeric substance (EPS) concentration in the EC-MBR system, especially their protein fraction, the significant increase in MLSS and carbohydrates/protein ratio, and the decrease in the mixed liquor and the cake layer particles size were the main membrane fouling factors. The membrane fouling resistance distribution showed that the EC-MBR system had a higher percentage of pore blocking resistance compared to the MBR. FTIR analysis identified a greater proportion of carbohydrate compounds in the cake layer of the EC-MBR system. SEM images revealed dense microbial clusters, mainly rod- and oval-shaped bacteria, in the EC-MBR system. Furthermore, EDX analysis detected elements such as Ca, K, O, Al, and P in both systems, with the EC-MBR system showing a higher Al content. The EC-MBR system showed low energy consumption (0.431kWhm-3) and total operating costs ($0.90m-3), showcasing its effectiveness and affordability for sustainable wastewater management.

Enhanced anti-fouling and selective performance of GO-modified nanofiltration membranes for lithium extraction from salt lake brine

Nanofiltration (NF) is a promising method in lithium extraction from salt lake brine with a high Mg2+/Li+ mass ratio. However, membrane fouling challenges its applicability and productivity. This study incorporated graphene oxide (GO) into the polyamide (PA) selective layer of NF membranes to enhance anti-fouling properties and improve lithium extraction from brine. Membrane structure analyses revealed that 0.002 wt% and 0.01 wt% GO facilitated the interfacial polymerization reaction. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) results indicated that the PA selective layers in the GO-0.002 % and GO-0.01 % membranes were denser, smoother, and thinner. In contrast, the addition of 0.05 wt% GO resulted in the Turing structures on the membrane surface. Adsorption kinetics indicated pollutant adhesion in the following order: GO-0.05 % > GO-0 % > GO-0.002 % > GO-0.01 %, which was attributed to calcium-carboxyl complexation, as directly measured by AFM and consistent with carboxyl density. The GO-0.002 % and GO-0.01 % NF membranes demonstrated excellent anti-fouling properties in brines, with lower initial fouling rates and higher flux recovery after cleaning, underscoring the significant role of calcium-carboxyl complexation in membrane fouling. The retention of Mg2+ increased to 95 %, while that of Li+ decreased to below −28 % for GO-0.002 % and GO-0.01 % membranes, indicating promising potential for Mg and Li separation. This study provides valuable insights into developing NF membranes with high Mg/Li selectivity and anti-fouling capabilities for lithium extraction from salt lake brine.

Manufacture and performance assessment of PVDF-La@TiO2 Photocatalyst implanted membrane for efficient produced water treatment via ozonation-adsorption process under visible-light exposure

This research aims to develop a visible light-activated photocatalytic membranes for produced water treatment system by employing the phase inversion technique for implantation of La@TiO2 photocatalytic nanoparticles into PVDF membrane at concentrations varying from 0 % to 2 % wt. The results demonstrated significant amplification of COD and NH3-N removal efficiency. Implantation of the photocatalyst into PVDF membranes via bulk mixing, coupled with elemental doping and combination with La@TiO2 appreciably reduces band gap energy and increases visible light absorption thereby improves membrane's optical properties. SEM-EDX analysis confirms uniform distribution of La@TiO2 nanoparticles on the membrane surface, which leads to amplify membrane's hydrophilicity and water absorption. The modified membrane facilitated concurrent photocatalytic degradation and filtration processes that lead to remarkable reductions in TDS, COD, and NH3-N pollutants, with the highest flux was achieved when 1.5 % wt. La@TiO2 was incorporated into the membrane matrix. Obviously, adsorption and ozonation processes promote synergistic effect and amplify pollutant flux and efficiency to a greater extent. Furthermore, the modified membrane exhibited extraordinary antifouling properties and stability, providing excellent reusability with a 96.22 % fouling reduction rate after five consecutive cycle tests.

Mitigation of Membrane Fouling in Membrane Bioreactors Using Granular and Powdered Activated Carbon: An Experimental Study

This experimental study explores the mitigation of membrane fouling in membrane bioreactors (MBRs) through the combined use of granular activated carbon (GAC) and powdered activated carbon (PAC). The research assesses the impact of these materials on the fouling resistance, critical flux, and permeate quality using various mixed liquor suspended solids concentrations and carbon dosages. The results indicate that the GAC-PAC combination significantly reduces the total filtration resistance, particularly the cake layer resistance, by 11.7% to 13.6% compared to setups without activated carbon or with the individual carbon types. The study also reveals that this combination decreased the fouling rate by 15% to 24% at critical flux steps, demonstrating substantial improvements in fouling mitigation and operational efficiency. Furthermore, the GAC-PAC combination, which produces an adsorption process, enhances the permeate quality, achieving the near-complete removal of organic matter, total nitrogen, and turbidity, with total phosphorus removal reaching 99%. These findings demonstrate that the combined use of GAC and PAC not only reduces membrane fouling but also improves the overall MBR performance, making it a viable strategy for enhancing the efficiency of wastewater treatment processes.

A comparison study on membrane fouling in A/O-MBR and A/A-MBR at different mixed liquor-suspended solids concentrations

ABSTRACT Membrane fouling leads to decreased membrane flux, increases the frequency of membrane tissue replacement and membrane cleaning, and increases the operating cost of membrane bioreactor. In this study, the pollutant removal effects, membrane fouling differences and microbial characteristics of anaerobic/aerobic MBR (A/O-MBR) and anaerobic/anoxic MBR (A/A-MBR) were investigated at different mixed liquor suspended solids (MLSS) concentrations. The results showed that the chemical cleaning cycle of membrane contamination was 12, 28, 44 h and 24, 40, 104 h, respectively, and the cycle was prolonged with the increase of MLSS concentration (from 6000 to 9000 mg L−1). A/O-MBR was 1.4–2.4 times the rate of membrane fouling of A/A-MBR. In irreversible resistance, extracellular polymer substances (EPS) were the most significant contributors to membrane fouling. EPS concentration in A/A-MBR (118.33, 73.75, 54.26 mg/gMLSS) was lower than that in A/O-MBR (171.68, 91.92, 62.33 mg/gMLSS). Therefore, increasing MLSS concentration could mitigate membrane fouling. 16S rRNA high-throughput sequencing demonstrated that filamentous bacteria was the primary reason for the membrane fouling difference. Filamentous bacteria were more likely to be attached to the surface of the membrane, causing membrane fouling. The abundance percentage of filamentous bacteria in A/A-MBR was smaller than that in A/O-MBR. In summary, The excellent performance of A/A-MBR in membrane fouling behaviour, resistance analysis, EPS and microorganisms proved that A/A-MBR is more promising than A/O-MBR in wastewater nitrogen and phosphorus removal. This study can provide a theoretical basis for the application of MBR in the field of sewage treatment.

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.

Spray-coated PDA-wrapped carboxylic CNT/PES membrane to augment fouling mitigation, organic removal, and membrane stability in electrochemical membrane filtration

This study introduces robust and conductive polydopamine (PDA)-wrapped carboxylic carbon nanotube (C-CNT)-coated polyethersulfone (PES) membrane for electrochemical membrane filtration to treat greywater. Self-polymerized dopamine was prepared directly under oxidative conditions on the CNT strands, followed by their immobilizations on the surface of the PES membrane through a novel spray-coating technique. The spraying coating technique improved both the durability of the coating layer and membrane permeability by 27 % higher than that prepared by the conventional vacuum filtration method. The spraying coating technique enhanced the electroactive properties of the PDA/C-CNT membrane so that the fouling rate was reduced more effectively than the C-CNT membrane or bare PES membrane. Fouling mitigation of the PDA/C-CNT membrane was attributed to the combined effect of electrostatic repulsions between the foulants and the conductive membrane surface along with degradation of organic compounds by electrochemical oxidation. The constant current density profile also confirmed the structural stability of the conductive layer on the membrane under both cathodic and anodic conditions. Furthermore, the fouling layer formed by membrane filtration was removed effectively by in-situ anodic cleaning. Over 80% of water permeability was recovered without losing the membrane integrity up to 3 consecutive anodic cleaning cycles.

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.

Functionalised carbon nanotube thin film nanocomposite membranes: A comparison study on the role of backbone monomers and hydraulic pressure on membrane's performance and fouling

Thin film nanocomposite (TFN) reverse osmosis (RO) and nanofiltration (NF) membranes have attracted considerable attention for industrial applications in recent years. Among recent nanomaterials used in the fabrication of TFN membranes, carbon nanotubes (CNTs) have gained significant interest due to their unique structure (e.g., tubular shape, mechanical strength, porosity, etc.). Here, the effects of multi-walled carbon nanotubes (MWCNTs) with different functional groups as one of the well proven nanchannel structures and their interaction with two typical monomers, MPD and PIP, were thoroughly investigated. All fabricated membranes were analysed using SEM, FTIR, AFM and contact angle analyzer. Pressure variation significantly affected the performance of membranes over 24 hours of testing. The membranes incorporated with polypyrrole (PPy) modified MWCNTs showed promising results with nearly 37 % and 99 % water flux improvement for the TFN-RO and NF membranes, respectively, compared to the bare (unmodified) TFC RO/NF membranes. Specifically, the water flux of the RO OX-MWCNTs-PPy membrane increased from 18.9 to 25.5 L.m−2.h−1, while the NF OX-MWCNTs-PPy membrane's water flux rose from 45.2 to 90.1 L.m−2.h−1. The salt rejection of RO and NF remained relatively high, with over 90 % salt rejection against NaCl and Na2SO4 for RO and NF membranes. The NF OX-MWCNTs-PPy membrane exhibited a 98.2 % rejection rate for Na2SO4, and the RO OX-MWCNTs-PPy membrane showed around a 98.8 % rejection rate for NaCl. The TFN membranes showed less fouling tendency compared to the TFC membranes. In general, the integration of MWCNTs with various functional groups significantly enhanced the water flux and salt rejection properties of these membranes. Specifically, the modified membranes showed considerable improvements in water flux and maintained high salt rejection rates. Additionally, the interaction between MWCNTs and PIP monomers in TFN-NF membranes exhibited a stronger affinity compared to MPD monomers in TFN-RO membranes, indicating a more promising performance for NF applications. The findings suggest that TFN-NF membranes incorporating MWCNTs hold great promise for future industrial use, offering enhanced performance and reduced fouling rates.

Effectiveness of cloth media filters on mitigating membrane fouling in anaerobic filter membrane bioreactors

Membrane fouling is a persistent challenge that has impeded the broader application of anaerobic membrane bioreactors (AnMBRs). To mitigate membrane fouling, between the outlet of the UASB anaerobic bioreactor and the PVDF membrane to form the anaerobic filter membrane bioreactor (AnFMBR) system. Through comprehensive experiments, the optimal pore size for cloth filters was determined to be 50 μm. A comprehensive assessment over 140 days of operation shows that the novel AnFMBR had significantly greater resistance to membrane pollution than the traditional AnMBR. The AnFMBR system membrane tank exhibited lower mixed liquor suspended solid and mixed liquor volatile suspended solid concentrations, smaller sludge particle sizes, increased hydrophilicity of sludge flocs, and optimized microbial community distribution compared to those of conventional AnMBRs. The total solids foulant accumulation rate in the AnMBR was 5.1 g/m2/day, while in the AnFMBR, the rate was 2.4 g/m2/day, marking a 53.7 % decrease in fouling rate for the AnFMBR compared with the AnMBR. This decrease indicates that integrating the filtration assembly significantly lowered the rate of solid foulant accumulation on the membrane surface, primarily by controlling the buildup of solid foulants in the cake layer, thereby alleviating membrane fouling. AnFMBR compared to AnMBR, the membrane fouling rate halved, effectively doubled the interval between membrane cleaning from seven days, as observed in the AnMBR system, to fourteen days. These findings underscore the potential of integrating cloth media filters into AnMBRs to improve operational efficiency, economic viability, and sustainability.

Treatment of azo dye-containing wastewater in a combined UASB-EMBR system: Performance evaluation and membrane fouling study

This work investigated the treatment of azo dye-containing wastewater in an upflow anaerobic sludge blanket (UASB) reactor combined with an electro-membrane bioreactor (EMBR). Current densities of 20 A m−2 and electric current exposure mode of 6′ON/30′OFF were applied to compare the performance of the EMBR to a conventional membrane bioreactor (MBR). The results showed that dye (Drimaren Red CL-7B) removal occurred predominantly in the UASB reactor, which accounted for 57% of the total dye removal achieved by the combined system. When the MBR was assisted by electrocoagulation, the overall azo dye removal efficiency increased from 60.5 to 67.1%. Electrocoagulation batch tests revealed that higher decolorization rates could be obtained with a current density of 50 A m−2. Over the entire experimental period, the combined UASB-EMBR system exhibited excellent performance in terms of chemical oxygen demand (COD) and NH4+-N removal, with average efficiencies above 97%, while PO43--P was only consistently removed when the electrocoagulation was used. Likewise, a consistent reduction in the absorption spectrum of aromatic amines was observed when the MBR was electrochemically assisted. In addition to improving the pollutants removal, the use of electrocoagulation reduced the membrane fouling rate by 68% (0.25–0.08 kPa d−1), while requiring additional energy consumption and operational costs of 1.12 kWh m−3 and 0.32 USD m−3, respectively. Based on the results, it can be concluded that the combined UASB-EMBR system emerges as a promising technological approach for textile wastewater treatment.

Anaerobic fluidized membrane bioreactors with low strength wastewater: A long-term study on the impact of conductive polyaniline modified fluidized biocarrier on biomethane production

Polyaniline (PANI) is used as a coating material to create a conductive surface on polyvinylidene fluoride (PVDF) substrate. This was implemented as a biocarrier in an anaerobic fluidized membrane bioreactor (AFMBR) to treat low-strength wastewater consisting of glucose. The results of parallel operation using AFMBRs indicate that the fouling rate was invariably similar in both AFMBR 1 and AFMBR 2 throughout the operation of 400 days for uncoated and PANI coated PVDF pellet as substrate, respectively. The conductive coating in AFMBR 2 enhanced the electron transfer between organic matter and microbes. The AFMBR 2 with PANI-PVDF biocarrier exhibited a methane yield that was 62 % more per gram soluble chemical oxygen demand (SCOD) removed at 12 h HRT than its uncoated counterpart in AFMBR 1. The results of the surface analysis of the biocarrier indicated the enhanced biomass attachment on the conductive surface owing to the roughness (which is 1.6 times more) created by PANI coating over PVDF supporting material. The findings of our study indicate that the utilization of conductive polymeric-based biocarrier has the potential to significantly enhance the kinetics of AFMBR during the treatment of low-strength wastewater.

Impact of membrane characteristics and chemical ageing on algal protein fouling behaviour of ultrafiltration membranes

Membrane characteristics can exacerbate the prevailing challenges associated with membrane fouling in industry. However, the combined impact of deliberate membrane modifications and the unavoidable effects of chemical ageing on fouling behaviour is still not well understood. In this study, three polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes with different pore size and surface roughness were selected and subject to chemical ageing with 5000 ppm sodium hypochlorite (NaOCl) at pH 10.5, selected to simulate accelerated ageing conditions. The impact of NaOCl on membrane characteristics was assessed for exposure times from 1.2 x 105 to 25.2 x 105 ppm·h using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, contact angle, and clean water resistance analysis. The fouling behaviour of each pristine and aged membrane was compared using 10 mg C·L−1 dissolved organic carbon algal protein feed containing 18 % biopolymeric compounds. The membrane with intermediate pore size presented lower overall filtration resistance compared to the membrane with smaller pores that developed rapid foulant cake layers. It also displayed less susceptibility to fouling via pore blocking mechanisms compared to membranes with larger pores where greater surface area available in pore walls leads to higher foulant adhesion.

Observing and identifying fouled ballast bed: On-site testing with infrared thermography (IRT) and uncovering thermodynamic transfer mechanisms within the ballast bed

The ballast bed serves as the foundation of the ballasted track, and its performance is maintained through periodic ballast cleaning. Early detection of fouled ballast bed significantly reduces maintenance workload and capital investment. Some scholars have studied the feasibility of utilizing infrared thermography (IRT) for detecting fouled ballast bed (DBF) and have made some progress. Existing studies have predominantly employed simulated boxes to simulate the ballast bed. To better reflect real-world conditions, this study established two sections of ballast bed on a newly constructed line: one with clean ballast and the other fouled, with a volumetric fouling rate (VFR) of 27.6 % (FI ≈ 21.5 %). Moreover, this paper takes a pivotal step in exploring the thermodynamic transfer mechanisms within the ballast bed, the influences of meteorological factors on the detection effectiveness of IRT, and other detection indicators that could be used for DBF.The results demonstrate that the different void fractions and composition substances of the clean and fouled ballast beds (CFB) contribute to their distinct thermodynamic properties. Furthermore, the high specific heat capacity of water exacerbates the thermodynamic property difference between the CFB. In terms of meteorological factors, both the solar radiation intensity (S) and air temperature (T) have a significant positive impact on the temperature of the ballasted structure (STT) and the temperature difference between the CFB (CF-S). Throughout the day, as the S and T increase, the ballast bed surface absorbs more solar heat than it loses, leading to an increase in its surface temperature. When it exceeds the soil temperature (S-S), heat is transferred downward. Since the poor heat conduction of the clean ballast bed, it has a higher surface temperature. As the S and T decrease, heat convection and conduction become dominant, leading to a decrease in the surface temperature of the ballast bed (BT-S). When the BT-S is lower than the S-S, heat is transferred upward, causing the surface temperature of the fouled ballast bed (F-S) to potentially exceed that of the clean ballast bed (C-S). Furthermore, the humidity (H) has a strong negative impact on the STT, while on sunny days following rain, it has a significantly positive impact on the CF-S. The effects of wind speed (W) on the STT and the CF-S are not prominently observed due to its low values during the experiment. Without considering rainfall, higher S and T, combined with reduced W, result in a greater CF-S and are more conducive to advancing fouling detection. Hence, the CF-S can reach up to about 3 °C on a sunny day and may even rise to about 5 °C after rainfall. Nonetheless, the CF-S is only around 0.71 °C on a cloudy day and 0.25 °C at night. Unexpectedly, there is a significant temperature difference between the sleeper and the ballast bed or the steel rail. These indicators could potentially be used for DBF on cloudy days. Overall, these findings demonstrate the feasibility of using IRT for DBF in the field, provding a broader theoretical support for its advancement and implementation.