Impact of membrane biofouling in the sequential development of performance indicators: feed channel pressure drop, permeability, and salt rejection

Biofouling development is affected by a variety of factors that change over the length of membrane modules in pressure vessels. Spatially resolved biofouling formation was studied under conditions representative to practice using a validated one-meter Long Channel Membrane Test Cells (LCMTCs), enabling the monitoring of permeability and salt rejection for five segments over the test cell length. Biofouling was induced by dosing an easily assimilable substrate to the feed water. The impact of biofouling on membrane performance was investigated spatially resolved as indicated in feed channel pressure drop over four LCMTCs and as indicated in permeability and salt rejection over five segments of each LCMTC. Results showed that all membrane performance indicators: feed channel pressure drop, permeability and salt rejection were impacted by biofouling formation. The feed channel pressure (FCP) drop increase was impacted earliest and strongest followed by permeability and salt rejection decline, underlining that FCP drop is a sensitive biofouling monitoring indicator. Spatially resolved biofouling investigations revealed that most biofouling was formed in the lead sections of membrane installations with a decreasing gradient over length, linked to substrate availability in the system. In this study, FCP drop played a crucial role: the severe FCP drop increase at the lead parts of the membrane installation caused performance losses in flux and salt rejection at the tail parts of the membrane installation. Minimizing the effect of biofouling on membrane performance should be pursued by a combination of strategies involving (i) early detection and preventive cleaning, (ii) substrate limitation for delaying biofouling built-up and (iii) optimized (early) cleaning procedures for more effective biofilm removal.