Three years operational experience with ultrafiltration as SWRO pre-treatment during algal bloom

Abstract In the period 2009–2012 Evides conducted extensive research with an open intake UF-SWRO desalination demonstration plant in the Oosterschelde area, Netherlands. Major attention was devoted to the performance of ultrafiltration (UF) as pre-treatment. It was established that in the period from July to March, i.e. outside Spring, limited UF fouling occurred and the UF could be operated continuously without coagulation and at limited chemical consumption. However, during the period April–June, UF fouling rate (i.e. permeability decline) increased severely. This coincided with the occurrence of algal bloom, as manifested by peak levels of algal count, chlorophyll and transparent exopolymer particles (TEP, as measured by Unesco-IHE). During the algal bloom, implementation of inline coagulation by ferric chloride was required. In 2010, coagulation was conducted by dosing in the UF buffer tank. However, UF operation appeared unstable, requiring increased coagulant doses (1–4 mg Fe/L). In Spring 2011, the...