Surface water treatment: current issues

Magazine article, 2006

Waterworks in Sweden that apply conventional surface water treatment are facing several challenges, including changes in raw water quality and demands for improved particle removal. Studies were conducted to evaluate conventional treatment and alternative process combinations with ultrafiltration, nanofiltration, and biological pre-filtration. In pilot-scale experiments, the removal of natural organic matter (NOM), particles, taste and odour compounds, were studied; so were the biofilm formation potential and the microbial barrier function. In this publication, we attempt to briefly summarise the results, relate them to current knowledge, and discuss possible implications for surface water treatment in Sweden. Conventional treatment was a mediocre barrier for biological particles in bacterial and protozoan size, and did not sufficiently remove dissolved taste and odour compounds. Ultrafiltration may replace or complement rapid media filters and was a powerful and robust barrier for suspended particles and microorganisms, including viruses; it had no effect on NOM. Nanofilters removed most of the NOM, but require either relatively pure feed water to avoid fouling problems, or need to be operated at a low hydraulic load. Biofiltration equalized peak loads of particles, removed taste and odour compounds and decreased NF fouling by reducing biofilm formation, and the concentrations of organic and inorganic compounds