Role of dissolved air flotation (DAF) and liquid ferrate on mitigation of algal organic matter (AOM) during algal bloom events in RO desalination

Abstract

Harmful Algal Blooms (HABs) are considered a major contributor to membrane biofouling in Seawater Reverse Osmosis (SWRO) desalination plants. The presence of HABs in the raw feed water leads to an increase in membrane fouling rate, increase of chemical consumption, and can cause temporary shutdown of plants. Effective pretreatment can reduce the amount of organic foulants reaching the RO membrane and alleviate the problem of flux decline during RO operation and frequent membrane cleaning using chemicals. This study compared the effect of in-situ generated liquid ferrate and ferric chloride in combination with dissolved air flotation (DAF) as a pretreatment strategy to remove algal cells and algal organic matter (AOM) during algal bloom events. Experiments were performed using a bench-scale DAF unit. HABs conditions were simulated by harvesting AOM from cultivating Chaetoceros affinis (CA) in raw seawater to a concentration of around 10 mg C/L of dissolved organic carbon (DOC). The liquid ferrate was generated in-situ by wet oxidation of ferric chloride in an alkaline media. The best performance was achieved with the combined use of liquid ferrate and DAF, removing up to 100% of algal cells, 99.99% of adenosine tri-phosphate (ATP), and up to 92% of AOM.