Evaluation of the fouling potential of sludge in a membrane bioreactor integrated with microbial fuel cell

Performance of modified hollow fiber membrane silver nanoparticles-zeolites Na-Y/PVDF composite used in membrane bioreactor for industrial wastewater treatment

Membrane bioreactor (MBR) deteriorates due to fouling on the membrane pores, which can reduce the membrane performance. To reduce membrane fouling, the addition of inorganic filler can enhance the antifouling properties. This study investigates two different membrane preparation by thermally induced phase separation (TIPS) and dip coating methods to modify hollow fiber membrane with Silver Nanoparticles (AgNPs)-Zeolites used in MBR for industrial wastewater treatment. Performance was evaluated by analyzing the flux of water and wastewater, rejection, water content, and antifouling properties. Characterization result represented the synthesized silver nanoparticles had similar diffraction peak with commercial AgNPs, then the micrograph of AgNPs and zeolites addition membrane showed that the inorganic material had an octahedral shape representing zeolite crystal and irregular shape representing AgNPs. The addition of zeolites and AgNPs resulted in satisfying performance, increased flux, rejection, and antifouling properties.

Impact of sandwich-type composite anodic membrane on membrane fouling and methane recovery from sewage sludge and food waste via electrochemical anaerobic membrane bioreactor

Membrane fouling presents a big challenge for the real-world implementation of anaerobic membrane bioreactors (AnMBRs) in digesting high-solid biowastes. In this study, an electrochemical anaerobic membrane bioreactor (EC-AnMBR) with a novel sandwich-type composite anodic membrane was designed and constructed for controlling membrane fouling whilst improving the energy recovery. The results showed that EC-AnMBR produced a higher methane yield of 358.5 ± 74.8 mL/d, rising by 12.8% compared to the AnMBR without applied voltage. Integration of composite anodic membrane induced a stable membrane flux and low transmembrane pressure through forming an anodic biofilm while total coliforms removal reached 97.9%. The microbial community analysis further provided compelling evidence that EC-AnMBR enriched the relative abundance of hydrolyzing (Chryseobacterium 2.6%) bacteria and methane-producing (Methanobacterium 32.8%) archaea. These findings offered new insights into anti-biofouling performance and provided significant implications for municipal organic waste treatment and energy recovery in the new EC-AnMBR.

Smart utilisation of reverse solute diffusion in forward osmosis for water treatment: A mini review

Forward osmosis (FO) has been widely studied as a promising technology in wastewater treatment, but undesirable reverse solute diffusion (RSD) is inevitable in the FO process. The RSD is generally regarded as a negative factor for the FO process, resulting in the loss of draw solutes and reduced FO efficiency. Conventional strategies to address RSD focus on reducing the amount of reverse draw solutes by fabricating high selective FO membranes and/or selecting the draw solute with low diffusion. However, since RSD is inevitable, doubts have been raised about the strategies to cope with the already occurring reverse draw solutes in the feed solution, and the feasibility to positively utilise the RSD phenomenon to improve the FO process. Herein, we review the state-of-the-art applications of RSD and their benefits such as improving selectivity and maintaining the stability of the feed solution for both independent FO processes and FO integrated processes. We also provide an outlook and discuss important considerations, including membrane fouling, membrane development and draw/feed solution properties, in RSD utilisation for water and wastewater treatment.

A new insight into the low membrane fouling tendency of liquid-liquid hollow fiber membrane contactor capturing ammonia from human urine

To unravel the low membrane fouling tendency and underlying membrane fouling mechanism of liquid-liquid hollow fiber membrane contactor (LL-HFMC) capturing ammonia from human urine, the ammonia flux decline trend, membrane fouling propensity, foulant-membrane thermodynamic interaction energy and microscale force analysis at different feed urine pH were comprehensively investigated. The 21-d continuous experiments showed that the ammonia flux decline trend and membrane fouling propensity significantly strengthened with the decrease of feed urine pH. The calculated foulant-membrane thermodynamic interaction energy decreased with the decreasing feed urine pH and agreed with the ammonia flux decline trend and membrane fouling propensity. The microscale force analysis showed that the absence of hydrodynamic water permeate drag force resulted in the foulant located at long distance from the membrane were difficult to approach the membrane surface, thus considerably alleviating membrane fouling. Additionally, the vital thermodynamic attractive force near the membrane surface increased with the decrease of feed urine pH, which made the membrane fouling further relieved at high pH condition. Therefore, the absence of water permeate drag force and operating at high pH condition minimized the membrane fouling during the LL-HFMC ammonia capture process. The obtained results provide a new insight into the low membrane tendency mechanism of LL-HFMC.

Modification of reinforced hollow fiber membranes with WO3 nanosheets for treatment of textile wastewater by membrane bioreactor

In this study, performance of braid reinforced hollow fiber membrane containing polyvinylidene fluoride (PVDF) embedded with tungsten trioxide (WO₃) nanosheets in a membrane bioreactor (MBR) was examined for textile wastewater treatment. The WO₃ nanosheets was synthesized and blended at different concentrations (0.1-0.02 wt%) in casting solutions of the membranes. The WO₃ nanosheets characterized using various tests such as XRD, FTIR, SEM, EDS, dot-mapping, and TEM. Furthermore, the effects of the increased WO₃ nanosheets into the PVDF matrix on the membrane morphology, hydrophilicity, permeability, antifouling, and COD and color removal efficiency was investigated. The addition of 0.1 wt% of the nanosheets reduces the water contact angle from 69.3° to 62.5° while increasing overall porosity from 37.5 to 43.2%. COD and color removal for PVDF/0.10 wt% WO₃ membrane was between 86-89% and 72-76%, respectively. While the TMP of modified WO₃ membranes did not significantly increase due to antimicrobial properties of the WO₃ nanosheets, the TMP of the pure PVDF membrane increase, indicating considerable cake layer fouling. The results of this study showed that modification of PVDF braid reinforced hollow fiber membrane using WO₃ nanosheets is promising membrane for MBR systems.

Anti-Pectin Fouling Performance of Dopamine and (3-Aminopropy) Triethoxysilane-Coated PVDF Ultrafiltration Membrane

Due to the diversity and complexity of the components in traditional Chinese medicine (TCM) extracts, serious membrane fouling has become an obstacle that limits the application of membrane technology in TCM. Pectin, a heteropolysaccharide widely existing in plant cells, is the main membrane-fouling substance in TCM extracts. In this study, a hydrophilic hybrid coating was constructed on the surface of a polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane co-deposited with polydopamine (pDA) and (3-Aminopropy) triethoxysilane (KH550) for pectin antifouling. Characterization analysis showed that hydrophilic coating containing hydrophilic groups (–NH₃, Si-OH, Si-O-Si) formed on the surface of the modified membrane. Membrane filtration experiments showed that, compared with a matched group (FRR: 28.66%, Rr: 26.87%), both the flux recovery rate (FRR) and reversible pollution rate (Rr) of the pDA and KH550 coated membrane (FRR: 48.07%, Rr: 44.46%) increased, indicating that pectin absorbed on the surface of membranes was more easily removed. Based on the extended Derjaguin–Laudau–Verwey–Overbeek (XDLVO) theory, the fouling mechanism of a PVDF UF membrane caused by pectin was analyzed. It was found that, compared with the pristine membrane (144.21 kT), there was a stronger repulsive energy barrier (3572.58 kT) to confront the mutual adsorption between the coated membrane and pectin molecule. The total interface between the modified membrane and the pectin molecule was significantly greater than the pristine membrane. Therefore, as the repulsion between them was enhanced, pectin molecules were not easily adsorbed on the surface of the coated membrane.

Investigation and evaluation of membrane fouling in a microbial fuel cell-membrane bioreactor systems (MFC-MBR)

Two membrane bioreactors with and without adding an electric circuit (named as MFC-MBR and C-MBR, respectively) were established to investigate the effects of micro-electric field on membrane fouling. With the aeration rate of 1.5 L/min, the synergistic effect of aeration and micro-electric field was the best in reducing membrane fouling and COD in treatment of a simulated phenol wastewater. Compared with C-MBR, the running time of MFC-MBR was extended for 16 days. Scanning electron microscope (SEM) and energy-dispersive X-ray detector (SEM-EDX) demonstrated that less foulants were attached to the membrane and the attachment was loosend in MFC-MBR. The decreased absolute value of zeta potential indicated repulsion among the negatively-charged sludge particles was reduced and flocculation of the sludge was improved, which alleviated the membrane fouling. The soluble microbial products (SMP) and loosely-bound extracellular polymeric substances (LB-EPS) were also decreased in MFC-MBR. It was found that migration and neutralization of the negatively-charged particles, and degradation of microorganisms contributed to the alleviation of membrane fouling. Moreover, the decreases of carbohydrates in LB-EPS led to higher protein/carbohydrates (PN/PS) ratio, which was a key parameter for alleviating membrane fouling. Meanwhile, the increase of tightly bound extracellular polymeric substances (TB-EPS) could also slow down membrane fouling. Because TB-EPS can be used as a binder to strengthen the flocculation of sludge particles.

Mitigating membrane biofouling in biofuel cell system – A review

A biofuel cell (BFC) system can transform chemical energy to electrical energy through electrochemical reactions and biochemical pathways. However, BFC faced several obstacles delaying it from commercialization, such as biofouling. Theoretically, the biofouling phenomenon occurs when microorganisms, algae, fungi, plants, or small animals accumulate on wet surfaces. In most BFC, biofouling occurs by the accumulation of microorganisms forming a biofilm. Amassed biofilm on the anode is desired for power production, however, not on the membrane separator. This phenomenon causes severities toward BFCs when it increases the electrode’s ohmic and charge transfer resistance and impedes the proton transfer, leading to a rapid decline in the system’s power performance. Apart from BFC, other activities impacted by biofouling range from the uranium industry to drug sensors in the medical field. These fields are continuously finding ways to mitigate the biofouling impact in their industries while putting forward the importance of the environment. Thus, this study aims to identify the severity of biofouling occurring on the separator materials for implementation toward the performance of the BFC system. While highlighting successful measures taken by other industries, the effectiveness of methods performed to reduce or mitigate the biofouling effect in BFC was also discussed in this study.

Study of membrane fouling mechanism during the phenol degradation in microbial fuel cell and membrane bioreactor coupling system

This study evaluated the feasibility of phenol degradation in microbial fuel cell (MFC) and membrane bioreactor (MBR) coupling system, and explored the mechanism of MBR membrane fouling. Four aspects were researched in open and closed circuit conditions: the degradation capacity of the coupling system, the increase of trans-membrane pressure (TMP), and the adhesion of phenol degradation products and microorganisms on the membrane. The results showed that the degradation of phenol and COD in the closed circuit coupling system was higher than that in the open circuit. The micro-electric field can inhibit the growth of TMP and keep dodecamethylcyclohexasiloxane away from the membrane, meanwhile can also reduce the abundance and species diversity of microorganisms. Nevertheless, the micro-electric field could not completely eliminate the membrane fouling due to the fact that the phenol degradation product of ethanethiol, microorganisms of Proteobacteria and Actinobacteria were more favorable on the membrane.

Fouling potentials and properties of foulants in an innovative algal-sludge membrane bioreactor

This study focused on the effect of algae on the fouling potential and dynamic fouling variation of foulants in an innovative algal-sludge membrane bioreactor (AS-MBR). Filtration experiments revealed that the soluble extracellular polymeric substance (S-EPS) released by the algal-sludge flocs showed a slower diminishing rate of flux than that released by the sludge flocs. The intermediate blocking and cake filtration models demonstrated the major mechanisms, which implied a reduction in the driving force of pore blocking and fouling layer formation induced by the algal-bacterial S-EPS. Furthermore, the relative flux decrements of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) in the AS-MBR were lower than those of the control without algae, indicating a reduction in the fouling potential of the bound EPS (B-EPS) in the algal-sludge flocs compared to the control. This could be attributed to the reduction in the membrane intercepts for LB- and TB-EPS, respectively. Specifically, S-EPS and B-EPS released by algal-sludge flocs had a lower free energy of cohesion (ΔG_coh) than those released by sludge flocs (decreased of 19.14%, 45.93%, and 43.34% for the S-EPS, LB-EPS, and TB-EPS, respectively). Furthermore, these changes could contribute to the decrease in the relative abundance of adsorbed polysaccharide- and protein-like substances in the B-EPS (released by algal-sludge flocs) filtration membrane, leading to the formation of less rough peaks and valleys in the fouling layer in the AS-MBR. Accordingly, the lower fouling propensity and weaker cohesion energy of S-EPS and B-EPS tend to decrease the hydrophobicity and the free energy of the floc surface and further provide less driving force to adhere to the membrane, resulting in significant mitigation of membrane fouling in the AS-MBR. Therefore, the overall fouling behavior caused by S-EPS, B-EPS and flocs should be comprehensively considered to achieve an underlying understanding of the algal effect on membrane fouling control.

Minimizing salinity accumulation via regulating draw solute concentration in a bioelectrochemically assisted osmotic membrane bioreactor

A suitable draw solute (DS) concentration in bioelectrochemically assisted osmotic membrane bioreactor (BEA-OMBR) can convert the "negative effect" of salinity accumulation into a "beneficial effect" by using the reverse-fluxed DS as a buffer agent or a carbon source supplement. Herein, the effect of DS concentration from acid buffer solution (i.e., ammonium chloride, NH₄Cl), alkaline buffer solution (i.e., sodium bicarbonate, NaHCO₃), and organic solution (i.e., sodium acetate, NaOAc) on salinity accumulation was systematically investigated. Salinity accumulation with NaHCO₃ DS mainly derived from reversal fluxed sodium ion (Na⁺, major contributor with DS concentration ≤0.25 M) and bicarbonate ion (main contributor with DS concentration ≥0.50 M): Na⁺ accumulation could be mitigated by Na⁺ transport dominant by electrically driven migration (i.e., 21.3-62.1% of reverse-fluxed Na⁺), and bicarbonate accumulation could be reduced by buffer system. A medium-low concentration of 0.25 M NH₄Cl DS had a better performance on current density of 165.0 ± 23.0 A m^-3 and COD removal efficiency of 91.5 ± 3.4% by taking advantage that 77.7 ± 1.3% of reverse-fluxed ammonium could be removed by biological treatment and ammonium transport. A high NaOAc DS concentration (i.e., ≥0.05 M) exhibited a higher current density of 145.3-146.0 A m^-3 but a lower COD removal efficiency due to the limited carbon source utilization capacity of anaerobic bacteria. Both concentration diffusion (20.9-28.3%) and electrically driven migration (29.5-39.4%) promoted reverse-fluxed Na⁺ transport to catholyte and thus mitigated Na⁺ accumulation in the feed/anolyte. These findings have provided an optimal DS concentration for BEA-OMBR operation and thus encourage its further development.