Osmotically-induced Cleaning of Fouled Reverse Osmosis Membranes in Desalination

Abstract

To counteract the effects of fouling, desalination plant operators ultimately resort to chemical cleaning, which incurs system downtime, risk of membrane damage, and the generation of chemical waste. Driven by these limitations, chemical-free cleaning has emerged as a potential alternative. Recent works have demonstrated the viability of osmotically-induced cleaning (OIC), where a membrane effectively undergoes osmotic backwashing. In light of conflicting reports, however, a deeper analysis and understanding of the underlying mechanisms involved is necessary. In this work, the effectiveness of OIC is examined, underlying mechanisms are elucidated, and potential applicability in the presence of spacers is investigated. Sodium alginate is adopted as a model organic foulant and commercial RO membranes are operated to emulate fouling conditions in practice. Video footage is presented to document the cleaning procedure and refine our understanding, while important observations are noted. Experimental results demonstrate effective cleaning, demonstrating a flux recovery of 10- 30% depending on experimental conditions, while membrane integrity is preserved. To investigate the effect of OIC on biofilms, a real biofilm of Cobetia marina is exposed to solutions of higher salinity. The results indicate that while exposure to higher salinities does impact the biofilm spread and bacterial count, the method is far from completely eliminating the biofilm or preventing its regrowth once operation is resumed. Keywords: Reverse osmosis; Membrane fouling; Chemical-free cleaning; Osmotically-induced foulant