(Bio)fouling is the most common problem in membrane processes used in water production. It is also a reported unavoidable problem, with mitigation strategies being frequently ineffective in addressing this problem. An ultrapure water plant (UPW) in Emmen (The Netherlands), fed with secondary effluent, comprises the following subsequent treatment steps: ultrafiltration (UF), biological oxygen-dosed activated carbon (BODAC) filtration and reverse osmosis (RO). The BODAC filters were designed to prevent fouling in RO membranes, and for ten years, they have been operated without significant fouling issues. The present work aims to provide insight into the role of the full-scale UF + BODAC in fouling prevention, by conducting a mass balance (MB) analysis to assess the removal/release of common fouling precursors. Positive MB results were noticed for particulate organic compounds, iron (Fe) and manganese (Mn) meaning their constant removal in the UF + BODAC. The UF + BODAC was shown to be an effective nitrification system, effectively converting all the ammonium and nitrite to nitrate. In conclusion, the combined removal of organics, Fe, and Mn species and nitrification by UF + BODAC is most likely an important factor in downstream fouling prevention, making this system an attractive process for fouling prevention. Nevertheless, further investigations to discover the mechanisms involved are needed.

For the anaerobic biological treatment of saline wastewater, Anaerobic Digestion (AD) is currently a possibility, even though elevated salt concentrations can be a major obstacle. Anaerobic consortia and especially methanogenic archaea are very sensitive to fluctuations in salinity. When working with Upflow Sludge Blanket Reactor (UASB) technology, in which the microorganisms are aggregated and retained in the system as a granular biofilm, high sodium concentration negatively affects aggregation and consequently process performances. In this research, we analysed the structure of the biofilm and granules formed during the anaerobic treatment of high salinity (at 10 and 20 g/L of sodium) synthetic wastewater at lab scale. The acclimated inoculum was able to accomplish high rates of organics removal at all the salinity levels tested. 16S rRNA gene clonal analysis and Fluorescence In Situ Hybridization (FISH) analyses identified the acetoclastic Methanosaeta harundinacea as the key player involved acetate degradation and microbial attachment/granulation. When additional calcium (1 g/L) was added to overcome the negative effect of sodium on microbial aggregation, during the biofilm formation process microbial attachment and acetate degradation decreased. The same result was observed on granules formation: while calcium had a positive effect on granules strength when added to UASB reactors, Methanosaeta filaments were not present and the degradation of the partially acidified substrate was negatively influenced. This research demonstrated the possibility to get granulation at high salinity, bringing to the forefront the importance of a selection towards Methanosaeta cells growing in filamentous form to obtain strong and healthy granules.