Assessment of ultrafiltration as a pretreatment of reverse osmosis membranes for surface seawater desalination

Abstract

Pre-treatment of seawater feeding reverse osmosis (RO) membranes is a key step in designing desalination plants, especially when treating surface seawater with highly variable quality. The objective of the study was to assess the potential of ultrafiltration (UF) pre-treatment prior to RO for desalting seawater with high-fouling tendency. A UF pilot plant equipped with an Aquasource membrane was directly operated on Gibraltar surface seawater in dead-end mode. The competitiveness of UF pre-treatment towards conventional pre-treatment was assessed by looking at the impact on RO hydraulic performances. The study showed that UF provided permeate water with higher quality than with a conventional pre-treatment. The main seawater compounds responsible for UF fouling were organic matter released by phytoplanktonic organisms. The combination of UF with a pre-coagulation at low dose helped in controlling this fouling and providing water in steady state conditions. The performance of RO membranes downstream of UF exceeded the usual operating conditions encountered in seawater desalination. The combined effect of higher recovery and higher flux rate promises to significantly reduce the RO plant costs.

Reverse osmosis pretreatment technologies and future trends: A comprehensive review

“…This increasing trend in research and real time installations in RO plants is due to the various shortcomings associated with conventional pretreatment techniques, as discussed in section 2.1.7. More often, colloids and suspended particles pass through the conventional filters and contribute to RO membrane damage [128]. Therefore, the use of large pore size membranes in MF (0.1-0.35µm), UF (0.01-0.05µm) and NF (1-2nm) to pretreat RO water becomes essential [4].…”

Water treatment by reverse and forward osmosis

“…Membrane processes have rapidly developed since the 1960s (D'souza & Mawson, 2005;Loeb & Sourirajan, 1963) and now surpass thermal processes in new plant installations (75% of new production capacity). Currently, RO membranes are made so that these can reject more than 99% salts (Brehant, Bonnelye, & Perez, 2003;Reverberi & Gorenflo, 2007). RO membrane technology has been developed for both brackish and seawater applications.…”

“…A new trend in pretreatment has been the movement toward using larger pore-size membranes (microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF)) to use RO as a pretreatment to feed water that avoids the passage of colloids and suspended particles contributing to RO membrane fouling (Brehant et al, 2003). The membranes act as a defined barrier between the RO system and any suspended particles.…”

“…The membranes act as a defined barrier between the RO system and any suspended particles. Typical final permeate fluxes for a UF-RO system were reported to be in the range of 15e24 L/m 2 h (Kamp, Kruithof, & Folmer, 2000), whereas the permeate flux exiting the UF pretreatment stage was within 60e150 L/m 2 h (Brehant et al, 2003). MF membranes are an appropriate choice for the removal of larger particulate matter, whereas NF membranes are used to remove dissolved contaminants as well as particulate and colloidal material.…”

Study on performance of ultrafiltration membrane-based pretreatment for application to seawater reverse osmosis desalination

“…Few recent works have also been published on coagulation/UF performed on seawater. Brehant et al (2003) studied the combination of UF with a pre-coagulation with ferric chloride at low dose (1 mg/L). They showed that coagulation helped in controlling membrane fouling.…”