Biological Activated Carbon (BAC) is a water purification process that combines physical adsorption onto granular activated carbon (AC) and biodegradation to remove pollutants. The technology helps to prevent the saturation and replacement of the AC through biodegradation. At the Puurwaterfabriek (Emmen, the Netherlands), ultrafiltration (UF), a BAC pre-filter, a BAC polishing-filter, and Reserve Osmosis (RO) are subsequently applied to produce ultrapure water. This ultrapure water plant has been in operation for over nine years without the need for AC regeneration and without major RO membrane fouling issues. This research aims to understand how fouling is prevented.