Immersed ultrafiltration membranes for tertiary wastewater treatment and reuse
The long-term performance of an immersed hollow-fibre ultrafiltration (UF) pilot plant was evaluated using secondary effluent from a municipal wastewater treatment plant as a feed source. Operating parameters including sustainable flux, short- and long-term fouling rates and recovery cleaning intervals were assessed with and without the in-line addition of hydrolyzed metal coagulants (alum and ferric chloride) at varying doses as a feed pre-treatment. At optimised coagulant doses, removal of total phosphorus met or bettered the 0.30mg/L discharge limit soon to be implemented at the wastewater treatment plant. Pre-treatment also allowed for the UF pilot to consistently meet the water reuse standards currently in place in numerous jurisdictions, despite spikes in turbidity and suspended solids levels in the feed that greatly exceeded the membranes' design specifications. Furthermore, it was determined that coagulant pre-treatment led to greater stability in both short- and long-term membrane fouling, through an increase in the average particle size of organic carbon particles present in the feed stream.