Micro- and ultrafiltration of karstic spring water

Karstic springs are characterized by their unsteady behaviour of quantitative and qualitative parameters. The irregular and unpredictable increases of turbidity, natural organic matter (NOM), particles and solutes require a flexible and reliable treatment to ensure save drinking water quality at any time. In this study, results of a microfiltration (MF) and an ultrafiltration (UF) pilot plant are presented based on 15 and 12 months on-site experience. The investigations were focused on the optimization of the operation conditions of the membranes (maximum flux, dead-end mode, cross-flow mode) in order to guarantee drinking water production at any raw water quality. The results strongly support that MF performance is mainly influenced by submicron particles contained in the raw water suspension at higher turbidity peaks and that UF membrane permeability is affected by NOM during storm weather events. Additional quality problems in some springs caused by the presence of micropollutants (trichlorethene, tetrachlorethene, atrazine) gave rise to experimentally assess the combination of powdered activated carbon (PAC) with membrane filtration. The adsorption characteristics of the solutes on different PACs were tested in laboratory and pilot scale. In the on-site experiments, removal rates of 80–90% could be achieved by adopting the necessary contact time to the previously determined kinetic data. Additionally, NOM adsorption by PAC addition could substantially improve UF performance.