Holloway et al. [ 22] compared FO and RO membrane fouling when investigating the concentration of anaerobic digester centrate. They reported that the rate of flux decline was higher with RO than FO (Figure 10) and that the FO fouling was reversible, whereas the RO fouling was not. They further speculated that the reason for both the lower rate of fouling and its reversibility was due to the affects of hydraulic pressure on the foulants on the membrane surface, which occurs rapidly in RO