Detection of dynamic biofouling from adenosine triphosphate measurements in water concentrated from reverse osmosis desalination of seawater

The evaluation of fouling behavior, including biofouling, is crucial to increase efficiency in the reverse osmosis (RO) seawater desalination process (SDP). This paper reports on biofouling behavior in seawater in the SDP, detected by monitoring intracellular, extracellular, and total adenosine triphosphates (ATPs) in the cross-flow RO filtration system as bacterial activity tracers. The first-stage ultrafiltration (UF) treatment of raw seawater reduced the ATP range to approximately 25%, while the ATP concentration in seawater did not decrease significantly on average between the subsequent four stages until the RO membrane treatment. The results demonstrated temporal variation of ∆ATPs, the deference in ATPs between in RO concentrated water and in RO feed water, occurs randomly, as the membrane fouling index, evaluated from pressure measurements, increases to the level of fouling that requires cleaning. The significant increase in ∆ATPs despite a residence time of only approximately fifteen seconds over the RO module reflects bacteria cell detachment from biofilm. The large reduction in ∆ATPs reflects bacteria cell adhesion and biofilm growth on RO membrane surfaces. It is concluded that the temporal increase and decrease in ∆ATP in RO concentrated water capture the dynamic biofouling behavior and the formation process of biofilm on RO membrane surfaces.