Integration of CaO2/Fe2+ and ultrafiltration acts as multiple-workfunctions pretreatment for seawater desalination during harmful algal blooms

Abstract

This study employed calcium peroxide/ferrous iron (CaO2/Fe2+) as an innovative pretreatment strategy for seawater reverse osmosis (SWRO) operation during harmful algae blooms (HABs). CaO2/Fe2+ showed improved coagulation performance compared to conventional coagulation (Fe3+ coagulant). The dynamic dominance of foulants between micro-particles and algal organic matters (AOMs), due to the different dosages of CaO2/Fe2+, was found to be crucial in reducing ultrafiltration (UF) fouling. As a result, the optimal dosage of 0.05 mM/0.1 mM of CaO2/Fe2+ achieved a higher reduction of 71.6 % of modified fouling index (MFI) compared to conventional coagulation (38.1 % via 0.1 mM Fe3+). Specifically, CaO2/Fe2+ demonstrated a greater capacity to remove micro-particles across size ranges of 1–5 μm and various AOMs (i.e., biopolymer and humics) in algae-laden seawater compared to conventional coagulation. This resulted in reduced flux decline and less accumulation of algal cells, proteinaceous substances and humics on membrane surfaces, which were validated through Optical-Photothermal Infrared Spectromicroscopy (O-PTIR) with sub-micron resolution. Additionally, CaO2/Fe2+ reduced dissolved Fe3+ in UF permeate, and generated combined chlorine simultaneously with disinfection effects on marine algae (evidenced by O-PTIR and Raman spectroscopy). Thus, it would reduce fouling of subsequent SWRO membranes. Overall, CaO2/Fe2+ presents a multiple-workfunctions pretreatment method for HAB mitigation in seawater desalination plants.