Impacts of Water Quality, Membrane Material and Operating Conditions on the Performance and Cost of MF/UF Membranes in Water and Wastewater Treatment

Over the past two decades, membrane filtration has proliferated globally to become the gold standard for removing pathogens, suspended solids, emulsified oils and colloids from virtually every type of water source – traditional and non-traditional, fresh and saline. Hence, everywhere nanofiltration (NF) and reverse osmosis (RO) membranes are used – and – anywhere filtration or clarification is required microfiltration (MF) and ultrafiltration (UF) membranes are now frequently used as either treatment or NF/RO pre-treatment.

Globally, about 90% of membrane installations for municipal water and wastewater utilize polymeric hollow fiber membranes (with some exceptions, but) predominantly made from either poly(ethersulfone), PES, or poly(vinylidene fluoride), PVDF. Generally, ceramic modules cost 10-20X more per unit area of membrane than polymeric modules, and because ceramic system wetted parts are constructed from stainless or higher grade steel (pumps, vessels, header/footer pipes, valves, etc.) system costs are about 4-5X more than polymer membrane systems. However, ceramic membranes are more fouling tolerant, thermally and chemically stable, clean up easier and last longer than polymerics, so there are new scenarios emerging where overall life cycle costs may be comparable for polymerics and ceramics.

Generally, MF/UF membranes suffer from two key limitations – fouling and integrity. All MF/UF membranes foul and the rate at which fouling requires back-washing and cleaning dictates overall water recovery, energy demand, CapEx and OpEx. Membrane integrity issues are somewhat specific to hollow fiber filters in municipal applications, where fiber breakage can be a frequent occurrence and significant operating costs are incurred due to the labor, downtime and lost production associated with integrity testing and pinned fibers. This is exacerbated for high fouling feed waters where frequent backwashing and cleaning are required to combat flux decline, where the mechanical limits of hollow fibers are overextended during backwashing and cleaning. Over time, MF/UF plant throughput can drop off significantly due to irreversible fouling and fiber pinning.

This talk will begin with a review of state-of-the-art and emerging MF/UF technologies followed by presentation of performance data from two MF/UF pilot studies on: (1) municipal wastewater and (2) industrial wastewater. The presentation will conclude by tying together the impacts of influent water quality and membrane properties on water recovery, energy demand, capital costs and operating costs.