Characteristics and control of organic foulants on RO membranes during wastewater reuse

Abstract

Wastewater reuse has been proposed as a solution against water scarcity. Among state-of-art technologies for water reuse, the reverse osmosis (RO) process is being widely applied to get a higher water quality. In this study, strategies to mitigate organic fouling on the RO membrane surface have been proposed by analyzing the properties of organic foulants. In chapter 3, analytical methods including molecular weight distribution connected with fluorescent spectroscopy, parallel factor analysis (PARAFAC) of an excitation-emission matrix, and pyrolysis-GC/MS were applied and standardized to provide characteristics of organic foulants. Analytical results obtained from the autopsy of fouled RO membranes showed that the hydrophobic, highly aromatic, high molecular-weight, and microbial-oriented organic matters were commonly accounted for the major organic foulants. In chapter 4, the selective adsorption and oxidative transformation of microbial-oriented organic matter (MOOM) were investigated as strategies to mitigate organic fouling. Membrane fouling was dramatically reduced with the selective adsorption of high molecular weight of microbial-oriented organic matters by carbon-based nanomaterials such as expanded graphite and multi-walled carbon nanotubes. In the case of the ozone oxidation, the transformation of hydrophobic and high molecular weight MOOM was successfully achieved and led to a decrease in RO membrane fouling. In chapter 5, The effectiveness of fouling mitigation strategies suggested in chapter 4 was evaluated using real Ro concentrates. The accelerated RO test results showed that the pretreatment with the adsorption by carbon-based nanomaterials and ozone oxidation exhibited less than 50 % of flux decline compared to raw RO concentrates. In conclusion, the control of hydrophobic and high molecular-weight microbial-oriented organic matter was critical to mitigate organic fouling of the RO membrane, and the development of economic and efficient pretreatment technology is a need.