Water characterisation and fouling prediction tools for Seawater Reverse Osmosis Systems

RO is today the dominant technology in water desalination. However, some critical issues remain open: improvement of water quality, enhancement of the recovery factor, reduction of the unit water cost, minimizing the brine disposal impact. With the aim to solve these problems, an innovative approach based on the integration of different membrane operations in pre-treatment and post-treatment stages is proposed under the EU-MEDINA Project (Membrane Based Desalination – An Integrated Approach).

Fouling represents the major constraint to more cost-effective, and therefore expanded, application of membrane technology in drinking water, particularly for reverse osmosis systems. Indeed, spiral-wound membrane modules cannot be pneumatically backwashed on a regularly basis and only chemical cleanings can restore normal performance after fouling. Fouling can occur in several forms: Particle/colloidal fouling, Organic fouling, Biofouling, Scaling (inorganic fouling).

This research will focus on developing new, or modifying existing, water quality assessment tools to directly and/or indirectly predict the fouling potential of feed waters applied to seawater (SWRO) and brackish water (BWRO) reverse osmosis membranes. These tools will range from new methods to existing methods developed for freshwater feeds and adapted to seawater and brackish water feeds. Besides revealing fouling potential, these methods will provide insight into pre-treatment requirements and chemical cleaning protocols.

Various analytical protocols and surrogate bench-scale tests have been developed to assess feed water quality in terms of fouling potential with respect to (i) particulate/colloidal fouling, (ii) natural organic matter (NOM) fouling, (iii) biological fouling (biofouling), and (iv) inorganic fouling or scaling. Analytical protocols provide a direct measure of the amount, and ideally the character, of potential foulants in a feed stream, while surrogate tests provide an indirect indication of anticipated fouling trends, often in terms of a fouling index derived from a bench-scale test.

The emphasis of the proposed research is on seawater desalination and SWRO. However, some work is focused on brackish water and BWRO from two perspectives: (i) coastal estuarine/bay sources (i) inland brackish groundwater sources; while each has the attribute of lower salinities than seawater, estuarine/bay sources pose a greater challenge in pre-treatment and fouling while groundwater sources pose a challenge greater brine disposal.