Particulate and organic matter fouling of seawater reverse osmosis systems: Characterization, modelling and applications

Particulate/colloidal and organic fouling in seawater reverse osmosis (SWRO) systems results in flux decline, higher energy costs, increased salt passage, increased cleaning frequency, and use of chemicals. In practice, indices like SDI and MFI are used to assess particulate fouling, but they are performed at very high initial flux (> 1500 L/m2-h) and do not take into account the deposition of particles/colloids in RO systems. In this study, the Modified Fouling Index with ultrafiltration membranes (MFI-UF) at constant flux was further developed by incorporating the effects of particle/ colloidal deposition and flux. The percentage of particle deposition in real RO plants was between 10-30 % for Mediterranean seawater and between 80-90 % for North seawater. The biopolymer fraction (~60 %) and humic substances (~10-40 %) were found more likely to deposit on RO membranes in full scale desalination plants. A new portable set-up was developed capable of working with membranes of various pore sizes (10-100 kDa) and flux ranges between 10-350 L/m2-h. A model equation to predict particulate fouling was further developed to incorporate the effects of particle/ colloid deposition and flux. Employing the new improved model, the rate of particulate/ colloidal fouling potential of pre-treated seawater was found to be close to that of full scale desalination plants (between 0.2-1 bar/month), using a 10 kDa membrane at similar flux rate to a real RO system. The new developments presented in this study will enable engineers, plant operators and scientists not only to design better plants, but also to improve operation and monitoring of organic and particulate/colloidal fouling in SWRO systems