Measuring the bacterial growth potential of seawater reverse osmosis (SWRO) feed water is an issue that is receiving growing attention. This study developed and demonstrated the applicability of the flow-cytometry (FCM)-based bacterial growth potential (BGP) method to assess the biofouling potential in SWRO systems using natural microbial consortium. This method is relatively fast (2-3 days) compared to conventional bioassays. The effect of the potential introduction of nutrients during measurement has been studied thoroughly to achieve the lowest measure value of about 45,000 cells/mL, which is equivalent to about (10 µg-C glucose/L). The BGP method was applied in two full-scale SWRO plants that included (i) dissolved air flotation (DAF) and ultra-filtration (UF); (ii) dual-media filtration (DMF) and cartridge filter (CF), which were compared with the cleaning frequency of the plants. A significant reduction (54%) in BGP was observed through DAF-UF as pre-treatment (with 0.5 mg Fe3+/L), while there was a 40% reduction by DMF-CF (with 0.8 mg Fe3+/L). In terms of the absolute number, the SWRO feed water after DAF-UF supports 1.5 × 106 cells/mL, which is 1.25 times higher than after DMF-CF. This corresponds to the higher cleaning-in-place (CIP) frequency of SWRO with DAF-UF compared to DMF-CF as pre-treatment, indicating that the BGP method has an added value in monitoring the biofouling potential in SWRO systems.
Keywords: bacterial growth potential; biofouling; flow cytometry; pre-treatment; seawater reverse osmosis.