Dissolved air flotation pretreatment for low-pressure membranes in water treatment: A review of fouling mitigation and product water quality

Coagulation/flocculation/dissolved air flotation (CF-DAF) has garnered increased interest in recent years as pretreatment for low-pressure membranes (LPM) due to its ability to treat colored and algal-laden waters. These challenging water types are now more frequently encountered due to eutrophication and the effects of climate change, which necessitates pretreatment to prevent severe LPM fouling. In this study, pertinent literature regarding CF-DAF as pretreatment for LPMs in water treatment applications is reviewed. Specifically, the paper presents a brief overview of CF-DAF, compares CF-DAF pretreatment performance with other coagulation alternatives, outlines relationships between CF-DAF treated water quality and LPM fouling, reviews the treated water quality from the integrated system (i.e., CF-DAF-LPM), and finally discusses cost considerations of CF-DAF implementation as LPM pretreatment. When comparing CF-DAF with inline coagulation and coagulation/flocculation/sedimentation as pretreatment strategies for LPM fouling mitigation, it was found that the relative performance is influenced by both the feed water quality and the membrane configuration/type. CF-DAF pretreatment improved removal of hydrophobic organics (as measured by UV254 and SUVA) and for the limited waters tested resulted in reduced irreversible fouling measures, which are critical to long-term economic operation. According to the knowledge gaps identified throughout the study, the manuscript concludes by outlining guidance on potential foci of future research.