Biofouling removal of drinking water filters

Pure culture studies have shown that biofilm dispersal can be stimulated by limiting the supply of nutrients by stopping the flow. Stimulating biofilm dispersal in this manner would provide a sustainable manner to control unwanted biofilm growth in industrial settings, for instance on synthetic membranes used to purify water. The response of multispecies biofilms to nutrient limitation has not been thoroughly studied. To assess biomass dispersal during nutrient limitation, it is common practise to flush the biofilm after the stop-period. Hence, flow-stop-induced biomass removal could occur as a response to nutrient limitation and because of mechanical removal due to biofilm flushing (e.g. biofilm detachment). Here we investigated the feasibility to reduce membrane biofouling by stopping the flow and flushing the membrane. Using a membrane fouling simulator, biomass removal from synthetic membranes after different stop-periods was determined, and biomass removal at different flow velocities was determined. We show that biomass removal from membrane surfaces depends on the period of nutrient limitation and on the flow velocity during the biofilm flush. When flushed at a low flow velocity, the length of the stop-period has a large effect on the biomass removal rate, but when the flow velocity is increased, the duration of the stop period becomes less substantial. Repetition of the stop-period and biofilm flushing after three repetitive biofouling cycles led to a stable bacterial community. This increase in bacterial community stability coincided with a decrease in cleaning effectivity to restore membrane performance.