Antibiofouling Characteristics and Mechanisms in an Anammox Membrane Bioreactor Based on an Optimized Photocatalytic Technology─Photocatalytic Optical Fibers

Abstract

As an ecofriendly photocatalytic antifouling technology for membrane bioreactors (MBRs), photocatalytic optical fibers (POFs) can decrease the replacement cost of modified membranes and prevent the proliferation of photosynthetic bacteria caused by direct light illumination. Here, POFs were applied in situ in an anaerobic ammonium oxidation (anammox) MBR for membrane biofouling control. Compared with the control MBR without POFs treatment, the average fouling cycle of the POFs-loaded MBR was extended by 137%, and the energy consumption caused by membrane fouling was saved by 18%. In the antibiofouling process, •OH was the key photocatalytic reactive species. On the fouled POFs-loaded membranes, the membrane-adhered foulant was significantly decreased by photocatalytic degradation of the proteins, polysaccharides and humic substances in the microbial metabolites. The membrane-attached bacteria were inactivated by the POFs by the mechanisms of cell-membrane destruction and cell-membrane permeabilization, which caused bacterial necrosis and apoptosis, respectively. Moreover, the total nitrogen-removal efficiencies of the two MBRs were maintained at 85.3–90.4%, and the abundance of anammox bacteria increased from 21.3% to 46.2% during the 202 days of operation, indicating an efficient anammox process with excellent nitrogen-removal performance, biomass retention, and anammox bacteria enrichment. The systematic insights into the antibiofouling performance and mechanisms of POFs in anammox MBRs will promote application and development of membrane-filtration technology in wastewater treatment using environmentally friendly and energy-efficient antifouling strategies.

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement

“…Furthermore, the illumination of light within MBRs can impact the microbial community structure by promoting the proliferation of photosynthetic bacteria or algae. In response to these challenges, surface-loaded photocatalytic optical fibers (POFs) have emerged as a novel antifouling strategy in MBRs, serving as an alternative to membrane modification and avoiding the disadvantages associated with direct light exposure (Figure c). , These aerobically and anaerobically applicable POFs were fabricated by coating Zr-MOFs/rGO/Ag 3 PO 4 Z-scheme heterojunctions onto optical fibers, subsequently utilized in-situ in an anammox MBR after installation on the membrane surface . During a 202-d operation, the average fouling cycle of the POFs-loaded MBR was extended by 137%, leading to an 18% reduction in energy consumption resulting from membrane fouling when compared to the control MBR .…”

“…The additional electricity consumption attributed to the EO for inhibiting membrane fouling occupied only 2.38% of the total energy consumption . The extra electricity consumption associated with membrane fouling control in eMBRs utilizing conductive flat membranes was also found to be minimal in comparison to the standard energy consumption of MBRs used for wastewater treatment. , Through EO with in-situ free chlorine generation, the fouling mitigation in eMBRs equipped with Ti/IrO 2 anodes and Ti/Pt cathodes led to a substantial reduction in air scouring and energy costs, which accounted for up to 60% of the overall operating expenses. , The additional electricity consumption (approximately 0.03 kWh/m 3 ) was negligible when compared to a typical MBR system. , Similar findings were also reported in the antifouling process of electro-Fenton MBRs. , In MBRs integrated with ozonation, despite the requirement for extra electricity consumption related to air preparation, ozone generation, and ozone contacting, the inhibited membrane fouling resulted in significantly reduced energy usage due to decreased filtration pressure and reduced frequencies of aeration and backwashing. ,, Similarly, in terms of photocatalytic oxidation, the application of both POFs and Bi 2 MoO 6 /CuS modified photocatalytic membrane led to a > 18% reduction in energy consumption for addressing membrane fouling during MBRs operation. , …”

“…143 During a 202-d operation, the average fouling cycle of the POFs-loaded MBR was extended by 137%, leading to an 18% reduction in energy consumption resulting from membrane fouling when compared to the control MBR. 142 Through photocatalytic oxidation, the foulants adhered to the membrane, primarily microbial metabolites, were notably degraded, and the membrane-attached bacteria were inactivated via cell-membrane destruction and permeabilization. 142 3.2.4.…”

“…142 Through photocatalytic oxidation, the foulants adhered to the membrane, primarily microbial metabolites, were notably degraded, and the membrane-attached bacteria were inactivated via cell-membrane destruction and permeabilization. 142 3.2.4. Suspended Photocatalyst.…”

Phenotypic and Transcriptional Responses of Pseudomonas aeruginosa Biofilms to UV-C Irradiation via Side-Emitting Optical Fibers: Implications for Biofouling Control

“…Attaching LEDs to SEOFs described herein offers a new design strategy to deliver light to large surface areas in narrow or curved channels. While the focus herein is on UV-C light inactivation, optical fibers with catalytic surfaces that produce reactive oxygen species (ROS) via photocatalysis have been proposed suitable for application in other geometries, including their use as spacers to prevent biofilms from fouling membrane surfaces. − Future research should continue to explore and improve strategies to utilize optical fibers with different surface coatings to mitigate biofilm-associated water quality problems.…”