Effect of fulvic acid on transparent exopolymer particle formation and membrane fouling

Transparent exopolymer particle (TEP) formation and its membrane fouling behavior have already been discussed in the presence of various cations. However, the effect of coexisting dissolved organic matters, such as ubiquitous humic substances, is still unknown. In this study, fulvic acid (FA) is used as the surrogate for dissolved humic substances. Its effects on the formation of TEPs derived from different alginate block fractions, namely, heteropolymeric blocks of β-d-mannuronic acids and α-l-guluronic acids (MG-blocks), homopolymeric blocks of α-l-guluronic acids (GG-blocks), and homopolymeric blocks of β-d-mannuronic acids (MM-blocks), and the resulting membrane fouling are investigated. The results showed that the presence of FA enhanced the interaction between alginate blocks and promoted the formation of TEPs. Alginate-associated membrane fouling was also aggravated in the presence of FA, which was positively correlated with the TEP concentration. Moreover, more severe irreversible fouling was detected after backwashing because FA strengthened the adhesive affinity between the membrane and TEPs. The GG-block was the most susceptible to the presence of FA. However, the differences between the three types of alginate block fractions were not significant as the FA concentration increased to 30 mg/L. This study provides insights into the TEP formation from alginate in the presence of FA, and helps to better understand the TEP-associated membrane fouling in complex solution conditions.