Silt density index as a fouling propensity parameter of various membrane materials using dissolved organic matter

Abstract

Silt density index (SDI) is the most widely used parameter for predicting fouling potential that occurs during reverse osmosis (RO) processes to assess and reduce fouling; however, this index cannot accurately predict fouling, particularly, organic fouling. Therefore, this study analyzed the application of five different membranes (i.e., mixed cellulose nitrate and cellulose acetate (MCE), cellulose nitrate (CN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polycarbonate (PC)) for measuring SDI and discerning the characteristics of organic foulants. The properties of the organic foulants on the membranes used to measure the SDI value were compared to those on the RO membrane. The quantitative fouling of the MCE, CN, PVDF, PC, and PTFE membranes in terms of the total organic carbon were 6.01 ± 0.03, 6.30 ± 0.14, 10.27 ± 0.10, 2.26 ± 0.12, and 3.08 ± 0.06 mg/L, respectively. In addition, liquid chromatography–organic carbon detection revealed that the MCE and CN were effective in predicting the fouling caused by building blocks and low-molecular-weight substances, respectively. The PVDF was effective in predicting fouling caused by biopolymers. The contaminants compositions on the PTFE and PC were similar; however, the PTFE was more effecting in detecting fouling caused by humic and low-molecular-weight substances. The composition of foulants on the PC was similar to that on the RO membrane, indicating that it can successfully predict the organic fouling of RO membrane. These results indicate that it is important to standardize the SDI value for PC membranes to make SDI a reliable index in the municipal wastewater reuse.