Novel calcium hypochlorite/ferrous iron as an ultrafiltration membrane pretreatment process for purifying algae-laden water

Algal fouling has become one of the most critical factors hindering the large-scale development of membrane processes in algae-laden water treatment. Herein, novel calcium hypochlorite (Ca(ClO)2)/ferrous iron (Fe(II)) process was proposed as an ultrafiltration (UF) membrane pretreatment technology, and its effects on membrane fouling and water properties were systematically studied. Results showed that the terminal specific fluxes were significantly elevated to 0.925 and 0.933, with the maximum removal ratios of reversible resistance reaching 99.65% and 96.99% for algae-laden water and extracellular organic matter (EOM), respectively. The formation of cake filtration was dramatically delayed, accompanied by a significant reduction of the adhesion free energy, and the contaminants attached to the membrane surface were effectively decomposed. With respect to water quality, the removal ratios of OD685 and turbidity achieved 81.25-95.31% and 90.16-97.72%, individually. The maximum removal rates of DOC, UV254 and fluorescent organics in influent water reached 46.14%, 55.17% and 75.77%, respectively. Furthermore, the generated reactive species (e.g., center dot OH, Cl center dot, Cl2 center dot- and ClO center dot) could efficiently degrade EOM, which appreciably reduced the electrostatic repulsion between the algal foulants while ensuring the integrity of algal cells. At the Ca(ClO)2/Fe(II) dosage of 0.04/0.24 mM, the zeta potential changed from -32.9 mV to -10.8 mV, and a large range of aggregates was formed. The macromolecules in the algal solution were significantly removed, and the proportion of micromolecular organics was increased to some extent. Coagulation of in-situ formed Fe(III) dominated the membrane fouling mitigation, and the reactive species also contributed to the improvement of filtration performance. Overall, Ca(ClO)2/Fe(II) pretreatment has an exceptional prospect for efficient degradation of algal pollutants and enhancement of UF capability.

Automated summary

This study proposes a novel ultrafiltration membrane pretreatment technology using calcium hypochlorite and ferrous iron process for algae-laden water treatment. The results show that the technology significantly reduces membrane fouling, improves water quality, and has great potential in efficiently degrading algal pollutants and enhancing the ultrafiltration capability.