Development of a reporter for prediction of membrane fouling potential and application of nitric oxide for biofouling control

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Membrane fouling that results in increases in operational and maintenance costs is a major obstacle to the widespread application of membrane technology. The concentration of assimilable organic carbon (AOC) is directly correlated with the growth of heterotrophic bacteria in water systems. AOC has been widely used as a biofouling indicator for the prediction of biofouling in reverse osmosis (RO) systems. In addition to new methodologies to predict fouling, new membrane cleaning technologies are also being developed. One new cleaning method is the application of nitric oxide (NO), which is a biologically active signaling molecule that has been shown to induce biofilm dispersal at nanomolar concentrations. In this study, potential AOC reporter strains were isolated for use in desalination RO systems. The results show that strains BLS2, CBSW3 and CBSW4 grew on seawater medium, with maximum cell densities of 5.1 x 10⁵, 4.5 x 10⁵ and 7.2 x 10⁵ colony forming unit (CFU) ml⁻¹, respectively. In addition, all three strains were able to metabolise humic substances which are a major component of AOC in seawater, reaching maximum cell numbers of 5.0 x 10⁴ - 2.1 x 10⁵ CFU ml⁻¹. With 𝘝. 𝘤𝘩𝘰𝘭𝘦𝘳𝘢𝘦 A1552 (pUC19-𝘭𝘶𝘹𝘈𝘉), there was a linear relationship between bioluminescent intensity and glucose concentrations ranging from 0 to 100 μg C L⁻¹, with a coefficient (R²) of 0.9761. The limit detection was 20 μg C L⁻¹. Our findings provide a more rapid AOC assay, which can quickly determine AOC concentrations within 10 min compared to 30 min performed by 𝘝. 𝘧𝘪𝘴𝘤𝘩𝘦𝘳𝘪 MJ1. Pyrosequencing analysis revealed that there was a total of 1,372,739 16S rDNA gene V4 region reads obtained from 9 activated sludge and 10 biofilm samples. RDP Classifier identified 36 phyla, 101 classes and 527 genera of bacteria. The significant changes in relative abundance of the most dominant OTUs associated with the sudden TMP increases demonstrated that species of unclassified 𝘉𝘢𝘤𝘵𝘦𝘳𝘰𝘪𝘥𝘦𝘵𝘦𝘴, 𝘚𝘢𝘱𝘳𝘰𝘴𝘱𝘪𝘳𝘢𝘤𝘦𝘢𝘦, 𝘊𝘰𝘮𝘢𝘮𝘰𝘯𝘢𝘥𝘢𝘤𝘦𝘢𝘦 and unclassified TM7-3 may play important roles in membrane fouling, and that 𝘚𝘢𝘱𝘳𝘰𝘴𝘱𝘪𝘳𝘢𝘤𝘦𝘢𝘦 and unclassified TM7-3 may be primary colonisers of the membrane. Unclassified 𝘉𝘢𝘤𝘵𝘦𝘳𝘰𝘪𝘥𝘦𝘵𝘦𝘴 and 𝘊𝘰𝘮𝘢𝘮𝘰𝘯𝘢𝘥𝘢𝘤𝘦𝘢𝘦 (𝘊𝘰𝘮𝘢𝘮𝘰𝘯𝘢𝘴 in particular) may be secondary colonisers of the biofilms on the MBR membranes. Treatment of the membranes with 40 μM DETA NONOate led to a reduction of the TMP by 35% compared to 21% obtained by control distilled water backwash (P value < 0.05), indicating that DETA NONOate was effective in delaying TMP increase.
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