Correlation of chemically irreversible fouling with organic constituents of feed water during membrane filtration

Abstract

Nowadays, fouling remains a huge obstacle for the application of membrane technology. Chemically irreversible fouling (CIF) is not cancelled by chemical cleaning (CC) and can cause long-term permeability loss. However, the characteristics of CIF foulants have not been systematically investigated yet. In this work, a pilot-scale long-term microfiltration process for surface water treatment with periodic CC was carried out to identify the nature of CIF foulants. A chemically irreversible fouling index (CIFI) approach was proposed to quantify CIF potential, and Pearson correlation analysis was further adopted to correlate CIFI with the organic constituents of feed water in terms of hydrophilicity/ hydrophobicity, molecular weight (MW) distribution and fluorophores. It was found that CIFI was significantly correlated to neutral hydrophilic fractions (R2 = 0.728, p-value = 0.007) and MW<1 kDa components (R2 = 0.749, p-value = 0.006), whereas no reliable correlation could be established of CIFI with fluorescent substances (humic-like or protein-like substances). Further, we found polysaccharides (PS) had a strong linear correlation with CIFI (R2 = 0.939, p = 0.0008) and the result was also supported by the detection of Fourier transform infrared spectroscopy. To sum up, the organics consisting of low MW (<1 kDa) and neutral hydrophilic PS-like constituents were mainly responsible to CIF. For the first time, we systematically reported the nature of CIF foulants in a low-pressure membrane filtration process.