New insights into membrane fouling during direct membrane filtration of municipal wastewater and fouling control with mechanical strategies

Gradient purification of surface water and ultrafiltration membrane fouling mitigation based on Fe(VI) multifunctional integration characteristics: Is a sedimentation unit necessary?

Ferrate (Fe(VI)) can provide oxidation and in-situ coagulation/adsorption for the removal of emerging contaminants and natural organic matter, and can be used in conjunction with ultrafiltration (UF) membrane to enhance the removal of composite contaminants and mitigate UF membrane fouling. Based on the Fe(VI) multifunctional integration characteristics, the study objectively and comprehensively verified the gradient purification of surface water and the UF membrane fouling mitigation by Fe(VI)-UF and sulfite (S(IV)) activated Fe(VI) (S(IV)/Fe(VI))-UF, elucidated the effect of sedimentation unit on the UF mechanism and the membrane fouling behaviors, and revealed the free energy changes throughout the UF process. The experimental results demonstrated that S(IV)/Fe(VI)-UF showed superior purification performance and UF membrane fouling mitigation than Fe(VI)-UF. S(IV)/Fe(VI)-UF achieved removals of sulfamethoxazole, DOC, and UV254 up to 77.73 %, 61.86 %, and 86.33 %, and was able to significantly mitigate UF membrane fouling by prolonging the transition stage and positively shifting the interfacial free energy. Innovatively, the absence of a sedimentation unit was found to adversely affect the initial stages of Fe(VI)-UF and S(IV)/Fe(VI)-UF by lowering the energy barriers, while negligibly affecting cake filtration. Additionally, the water treatment cost of S(IV)/Fe(VI) was 0.3 yuan per ton, indicating notable economic benefits and engineering potential. While deepening the understanding of Fe(VI) multifunctional integration characteristics, the above results provided theoretical and data support for S(IV)/Fe(VI)-UF and Fe(VI)-UF treatment of surface water, and enriched the application scenarios of Fe(VI)-related technologies.

Effect of substrate concentration on sulfamethoxazole wastewater treatment by osmotic microbial fuel cell: Insight into operational efficiency, dynamic changes of membrane fouling and microbial response

To solve the problems of antibiotic pollution, water resources and energy shortage, an osmotic microbial fuel cell (OsMFC) was adopted innovatively to treat antibiotic wastewater containing sulfamethoxazole (SMX), and achieved SMX removal, water production and electricity generation. Substrate concentration was one of the key factors affecting the performances of OsMFC, but there were few relevant studies This study explored the effect of substrate concentration on system performances, clarified the dynamic changes of membrane fouling under different substrate concentrations, and further revealed the response of microbial communities. The results showed that the stable removal efficiency of SMX exceeded 98.8 % due to the efficient interception of forward osmosis (FO) membrane. Compared with the 1.0 g/L NaAc system, the SMX degradation efficiency and maximum output voltage in the 2.0 g/L NaAc system were only increased by 3.9 % and 6.3 %, respectively. However, the initial water flux decreased by 30.1 % in the 7th cycle due to more serious FO membrane fouling. In addition, there were significant differences in the dynamic formation process of FO membrane fouling. Higher substrate concentration increased the relative abundance of Desulfobacterota and Geobacter. Functional prediction analysis showed that increasing substrate concentration promoted carbohydrate metabolism pathways and relative abundance of sulfur respiration functional groups, thereby improving COD and SMX removal rates. However, the biosynthesis of other secondary metabolites was significantly improved, resulting in increased contents of EPS and SMP, which aggravated membrane fouling. Overall, the system performed better when the substrate concentration was 1.0 g/L. This study would provide certain guidance for the performance optimization and membrane fouling mitigation of OsMFC, thereby promoting its practical application in antibiotic wastewater treatment.

Effect of micro-granular activated carbon on bacteriophage MS2 removal and fouling control in flat-plate MBR

Pathogenic microorganisms pose a severe risk to the aquatic environment and human health. Membrane bioreactors (MBRs) have attracted much attention due to their simultaneous biological treatment and virus retention, but membrane fouling is the main obstacle. This study explored the effect of micro-granular activated carbon (μGAC) on bacteriophage MS2 removal efficiency and membrane fouling in a flat-plate MBR. The results showed that the μGAC addition with a particle size of 180-300 μm improved the removal of MS2 (LRVMBR of 4.77 log) and enhanced the removal of COD and ammonia nitrogen. The μGAC integrated MBR (μGAC-MBR) exhibited a higher MS2 retention rate by the membrane filter layers with an average LVRMem of 2.03 log compared to that of a control reactor (C-MBR) of 1.89 log. Meanwhile, the total membrane filter layer resistance of μGAC-MBR was significantly lower than that of C-MBR, particularly in terms of cake layer resistance and organic pore-blocking exclusion. The μGAC addition slightly reduced MS2 adsorption by the activated sludge while significantly altering the extracellular polymeric substances (EPS) profiles. The fluorescent components in the bound EPS and PN/PS ratio of the activated sludge were reduced. We found that μGAC enhanced membrane surface roughness and hydrophilicity. Notably, the μGAC significantly influenced the quorum sensing (QS) systems, reducing the abundance and synthesis of AHL-related genes. The synthase luxI in the AHL-QS system was reduced by 93.21% in μGAC-MBR. The AHL-QS system is closely related to biofilm formation, and the total EPS of the surface filer layer of μGAC-MBR decreased by 57.73%, and PN in LB-EPS and TB-EPS decreased by 91.33% and 54.44% compared with C-MBR, indicating a significant reduction in biofilm formation. This study exhibited a new perspective on promoting MS2 removal with the synergistic effect of alleviating fouling in the MBR process.

A practical study on the near-zero discharge of rainwater and the collaborative treatment and regeneration of rainwater and sewage

Non-conventional water recovery, recycling, and reuse have been considered imperative approaches to addressing water scarcity in China. The objective of this study was to evaluate the technical and economic feasibility of Water Reclamation Plants (WRP) based on an anaerobic-anoxic-oxic membrane bioreactor (A2O-MBR) system for unconventional water resource treatment and reuse in towns (domestic sewage and rainwater). Rainwater is collected and stored in the rainwater reservoir through the rainwater pipe network, and then transported to the WRP for treatment and reuse through the rainwater reuse pumping station during the peak water demand period. During a year of operation and evaluation process, a total of 610,000 cubic meters of rainwater were reused, accounting for 10.4 % of the treated wastewater. In the A2O-MBR operation, the average effluent concentrations for COD (chemical oxygen demand), NH4+-N (ammonium), TN (total nitrogen), and TP (total phosphorus) were 14.23 ± 4.07 mg/L, 0.22 ± 0.26 mg/L, 11.97 ± 1.54 mg/L, and 0.13 ± 0.09 mg/L, respectively. The effluent quality met standards suitable for reuse in industrial cooling water or for direct discharge. The WRP demonstrates a positive financial outlook, with total capital and operating costs totaling 0.16 $/m3. A comprehensive cost-benefit analysis indicates a positive net present value for the WRP, and the estimated annualized net profit is 0.024 $/m3. This research has achieved near-zero discharge of wastewater and effective allocation of rainwater resources across time and space.

Molecular level unveils anion exchange membrane fouling induced by natural organic matter via XDLVO and molecular simulation

Membrane fouling, critically determined by the interplay of interfacial interaction between foulant and membrane, is a critical impediment that limits application extension of electrodialysis (ED) process. In this study, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) model and molecular simulation were performed to quantify the interaction energy barrier for revealing anion exchange membranes (AEMs) fouling mechanisms of calcium ions coexisted with natural organic matter (NOM) (sodium alginate, humic acid, and bovine serum albumin). The insight gained from DMol3 module was also utilized to interpret the adhesion process of NOM at the molecular level. The interaction energy suggested that the presence of Ca-NOM complex magnify the adhesion on the surface cavities of AEMs structures. The molecular simulation and XDLVO presented a good agreement in predicting the fouling trajectory based on the experimental findings. The short-path acid-base interaction exerted a predominant influence on exploring the fouling formation process. In addition, the sodium alginate displayed more stable adhesion behavior through calcium ions bridges stimuli than humic acid and bovine serum albumin. In particular, the molecular simulation calculations exhibited a superior level of concurrence with colloid growth of membrane fouling. Combined XDLVO theory with DMol3 model proposed a new approach to understand membrane fouling mechanisms in ED process.

Hybrid electrolysis and membranes system for apple packing houses water treatment

The apple industry uses high flows of potable quality water to transport and clean the apple, which is regularly contaminated. Thus, it is necessary to implement an efficient water treatment system during the industrial process, providing reductions in the intake and release flows. A hybrid system was developed by applying the electrolytic treatment by electrocoagulation using a batch process (Step 1) and a continuous process (Step 2), followed by a microfiltration membrane separation (MSP) process (Step 3). The optimal conditions for removal of organic matter, chemical oxygen demand, total suspended solids (TSS), turbidity, color, and fungi obtained in Step 1 were a hydraulic detention time of 40 min, stirring at 40 rpm, current density of 20 A/m2, pH of 8.00, and temperature of 10 °C. These findings led to a successful implementation in Step 2, which evolved into Step 3, where tests in the combined continuous electrolytic reactor together with MSP showed significant removal rates, notably reaching up to 54% organic matter (OM) removal, 72% chemical oxygen demand (COD) removal, 83% TSS removal, 92% haze and color removal, and 100% mildew removal. The hybrid system proved to be a promising alternative for implementation in the processing industry, minimizing environmental impacts and costs.

Membrane processes for environmental remediation of nanomaterials: Potentials and challenges

Nanomaterials have gained huge attention with their wide range of applications. This is mainly driven by their unique properties. Nanomaterials include nanoparticles, nanotubes, nanofibers, and many other nanoscale structures have been widely assessed for improving the performance in different applications. However, with the wide implementation and utilization of nanomaterials, another challenge is being present when these materials end up in the environment, i.e. air, water, and soil. Environmental remediation of nanomaterials has recently gained attention and is concerned with removing nanomaterials from the environment. Membrane filtration processes have been widely considered a very efficient tool for the environmental remediation of different pollutants. Membranes with their different operating principles from size exclusions as in microfiltration, to ionic exclusion as in reverse osmosis, provide an effective tool for the removal of different types of nanomaterials. This work comprehends, summarizes, and critically discusses the different approaches for the environmental remediation of engineered nanomaterials using membrane filtration processes. Microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) have been shown to effectively remove nanomaterials from the air and aqueous environments. In MF, the adsorption of nanomaterials to membrane material was found to be the main removal mechanism. While in UF and NF, the main mechanism was size exclusion. Membrane fouling, hence requiring proper cleaning or replacement was found to be the major challenge for UF and NF processes. While limited adsorption capacity of nanomaterial along with desorption was found to be the main challenges for MF.

Livestock and poultry farm wastewater treatment and its valorization for generating value-added products: Recent updates and way forward

Livestock and poultry wastewater poses a potent risk factor for environmental pollution accelerating disease load and premature deaths. It is characterized by high chemical oxygen demand, biological oxygen demand, suspended solids, heavy metals, pathogens, and antibiotics, among other contaminants. These contaminants have a negative impact on the quality of soil, groundwater, and air, and is a potential hazard to human health. Depending on the specific characteristics of wastewater, such as the type and concentration of pollutants present; several physical, chemical and biological strategies have been developed for wastewater treatment. This review aims at providing comprehensive overview of the profiling of livestock wastewater from the dairy, swine and poultry sub-sectors along with the biological (annamox and genetically modified bacteria) and physico-chemical treatment methodologies, and valorisation for the generation of value-added products such as bioplastics, biofertilizers, biohydrogen and microalgal-microbial fuel cells. Additionally, future perspectives for efficient and sustainable wastewater treatment are contemplated.

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.