Differences in behaviour of three biopolymer constituents in coagulation with polyaluminium chloride: Implications for the optimisation of a coagulation–membrane filtration process. (15th April 2018)

• Record Type: Journal Article
• Authors: Ding, Qing; Yamamura, Hiroshi; Yonekawa, Hitoshi; Aoki, Nobuhiro; Murata, Naoki; Hafuka, Akira; Watanabe, Yoshimasa
• Is Part Of: Water research. Volume 133(2018)
• Page Start: 255
• Page End: 263
• Publication Date: 2018-04-15
• Subjects: Biopolymers -- Membrane fouling -- EEM-PARAFAC -- Pre-coagulation -- Low-pressure membrane filtration -- Polyaluminium chloride; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2018.01.034
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Coagulation is often applied as a pre-treatment for membrane processes to reduce dissolved organic matter and to prevent membrane fouling. Biopolymers (BPs) have repeatedly been reported as major organic foulants, and coagulation conditions such as pH or dose have been optimised to minimise the remaining BPs. Optimisation however remains problematic because of the complex and heterogenetic nature of BP. In this study, the behaviour of several BP fractions in a coagulation process was investigated by excitation–emission matrix-parallel factor analysis (EEM-PARAFAC) following liquid chromatography (LC)-fractionation. Using a series of jar tests, we found that BP removal depends on the type of source water, reflecting differences in charge neutralisation conditions in three samples of natural water despite nearly identical processes for removing humic substances. This result demonstrates the complexity of optimisation for BP coagulation. Fractionation of EEM-PARAFAC to BP by LC showed that at least three organic component groups (C1, C2 and C3) constitute BP. C1 is tryptophan-like organic matter that is often found in wastewater effluent, C2 is tyrosine-like organic matter that has a phenolic chemical structure, and C3 is a humic-like substance. C1 was removed thoroughly at acidic pH but not at neutral pH, while the removal of C2 was inefficient even with a significant change in pH or dose, indicating similar difficulties in a coagulation process. The difference in components C1 and C2 may partly explain the difference in efficiencies of removal of BP in water from different sources. Our investigation suggests that the optimisation or selection of appropriate pre-treatment processes for membrane systems should be substantially based on the composition of BPs (e.g., C1 and C2 components). Graphical abstract: Image 1 Highlights: Trends of biopolymer (BP) removal efficiency in coagulation depended on raw water. Difference in charge neutralisation conditions also reflected the complexity of BP. The fluorescent components of BP contained three components (eg, C1, C2 and C3). Removal of C1 was strongly affected by coagulation pH but that of C2 was not. Composition of BP should be paid attention to when selecting treatment processes.