Advanced coagulation with liquid ferrate as SWRO desalination pretreatment during severe algal bloom. Process performance, environmental impact, and cost analysis

Abstract

Harmful algal bloom (HABs) events represent a major operational challenge for seawater reverse osmosis (SWRO) desalination plants, leading to severe membrane fouling, increased chemical consumption and plant shutdowns. Current pretreatment practice applying conventional coagulation, flocculation, and sedimentation (CFS) with ferric chloride has shown limited capability in reducing seawater fouling potential during HABs events. The use of in-situ generated liquid ferrate (Fe(VI)) has recently been proposed for CFS pretreatment due to its capability of acting simultaneously as a coagulant, oxidant, and disinfectant. In this study, the use of ferric chloride (conventional coagulation) was compared to liquid ferrate (advanced coagulation) during HABs events, in terms of process performance, life-cycle assessment (LCA) and cost analysis. Results show that a 10 times lower concentration of Fe salt was required in advanced coagulation compared to conventional coagulation to achieve a similar performance in terms of turbidity and TOC removal. Using liquid ferrate also resulted in a higher total ATP removal (>99%) and lower dissolved Fe concentration. The advanced coagulation reduced dry sludge production by 88%, resulting in a significant decrease in environmental impacts and operational costs.