This study addresses the pervasive challenge of biofouling in seawater desalination systems, which compromises membrane performance and longevity, by introducing a multifunctional PDA-SP-cTA coating. This bio-inspired coating effectively mitigates biofouling in seawater reverse osmosis systems without requiring biocide. The coating is applied to both hydrophilic polyamide membranes and hydrophobic polypropylene feed spacers through in-situ and ex-situ polymer deposition methods, involving a single-step process with polydopamine and sodium-periodate, followed by surface tailoring with citric acid-blended tannic acid. Extensive surface characterization, primarily conducted on polypropylene feed spacers, confirms coating deposition. Antibiofouling properties are evaluated through long-term biofouling tests simulating industrial conditions. The findings demonstrate that the ex-situ applied coating significantly reduces relative feed channel pressure drop increase due to biofilm growth by 75 % and lowers biomass accumulation (88 % total cell counts, 70 % adenosine-triphosphate, 91 % carbohydrates, and 69 % proteins). The coating inhibits the colonization of biofouling-causing bacterial genus Alteromonas, drastically decreases active bacterial gene copy numbers, and alters microbial composition, leading to reduced biofilm viability and loosely attached biofilms that could enhance cleaning efficiency. This comprehensive study encompasses the entire process from the strategic selection and systematic characterization of the coating to extensive biofouling tests and stability assessments offering a holistic solution to combat biofouling without biocides. With demonstrated durability and stability across various pH conditions over time, this coating could be a widely applicable and scalable solution for biofouling mitigation in diverse industrial contexts.

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Biofouling poses a significant challenge to reverse osmosis (RO) membrane systems, necessitating timely detection for effective control. This study evaluated the efficacy of flow cytometry (FCM) for early biofilm detection in comparison to conventional system performance indicators. Feed channel pressure drop and total cell concentration in the Membrane Fouling Simulator (MFS) flowcell cross-flow outlet water were monitored over time as early biofouling indicators. The results demonstrated the potential of increased bacterial cell concentration in cross-flow outlet water as a reliable indicator of biofouling development on the membrane. Water outlet monitoring enabled faster biofouling detection compared to feed channel pressure drop. Membrane autopsy confirmed biofilm presence prior to the pressure drop increase, highlighting the advantage of early detection in implementing corrective measures. Timely intervention reduces operational costs and energy consumption in membrane-based processes.@en

Nutrient limitation has been proposed as a biofouling control strategy for membrane systems. However, the impact of permeation on biofilm development under phosphorus-limited and enriched conditions is poorly understood. This study analyzed biofilm development in membrane fouling simulators (MFSs) with and without permeation supplied with water varying dosed phosphorus concentrations (0 and 25 µg P·L⁻¹). The MFSs operated under permeation conditions were run at a constant flux of 15.6 L·m^2·h−1 for 4.7 days. Feed channel pressure drop, transmembrane pressure, and flux were used as performance indicators. Optical coherence tomography (OCT) images and biomass quantification were used to analyze the developed biofilms. The total phosphorus concentration that accumulated on the membrane and spacer was quantified by using microwave digestion and inductively coupled plasma atomic emission spectroscopy (ICP-OES). Results show that permeation impacts biofilm development depending on nutrient condition with a stronger impact at low P concentration (pressure drop increase: 282%; flux decline: 11%) compared to a higher P condition (pressure drop increase: 206%; flux decline: 2%). The biofilm that developed at 0 µg P·L⁻¹ under permeation conditions resulted in a higher performance decline due to biofilm localization and spread in the MFS. A thicker biofilm developed on the membrane for biofilms grown at 0 µg P·L⁻¹ under permeation conditions, causing a stronger effect on flux decline (11%) compared to non-permeation conditions (5%). The difference in the biofilm thickness on the membrane was attributed to a higher phosphorus concentration in the membrane biofilm under permeation conditions. Permeation has an impact on biofilm development and, therefore, should not be excluded in biofouling studies.

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Biofouling is a problem that hinders sustainable membrane-based desalination and the stratification of bacterial populations over the biofilm’s height is suggested to compromise the efficiency of cleaning strategies. Some studies reported a base biofilm layer attached to the membrane that is harder to remove. Previous research suggested limiting the concentration of phosphorus in the feed water as a biofouling control strategy. However, the existence of bacterial communities growing under phosphorus-limiting conditions and communities remaining after cleaning is unknown. This study analyzes the bacterial communities developed in biofilms grown in membrane fouling simula-tors (MFSs) supplied with water with three dosed phosphorus conditions at a constant biodegradable carbon concentration. After biofilm development, biofilm was removed using forward flushing (an easy-to-implement and environmentally friendly method) by increasing the crossflow velocity for one hour. We demonstrate that small changes in phosphorus concentration in the feed water led to (i) different microbial compositions and (ii) different bacterial-cells-to-EPS ratios, while (iii) similar bacterial biofilm populations remained after forward flushing, suggesting a homogenous bacterial community composition along the biofilm height. This study represents an exciting advance towards greener desalination by applying non-expensive physical cleaning methods while manipulating feed water nutrient conditions to prolong membrane system performance and enhance membrane cleanability.

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