Fouling of Reverse Osmosis Membrane by Alginate and the Role of Calcium Ions in the Integrated Membrane System for Reclamation of Municipal Wastewater

Abstract

The objective of this study was to deepen the understanding on the fouling of reverse osmosis (RO) membranes by alginate and the role of calcium ions (Ca²⁺) in the integrated membrane system for the reclamation of municipal wastewater. When feed water was not pretreated with the microfiltration (MF) membrane, the fouling of the RO membrane was accelerated with an increase in Ca²⁺ concentration. This result is explained by the ability of Ca²⁺ to bind to alginate and the corresponding formation of calcium alginate gel, which has a higher water resistance than sodium alginate. It was also found that the ratio of β-D-mannuronate (M) to α-L-guluronate (G) of alginate is distributed, and GG and MG blocks with a higher affinity with Ca²⁺ than MM blocks were preferentially deposited on the RO membrane surface. On the other hand, when feed water was pretreated with the MF membrane, the fouling propensity of the RO membrane was significantly alleviated because the multimer of GG and MG blocks was effectively removed by the pretreatment. Additionally, contrary to the case where MF pretreatment was not performed, less fouling of the RO membrane occurred for higher Ca²⁺ concentrations because of the more effective formation of large alginate multimers.