DRINKING-WATER OFF-FLAVOR CAUSED BY THE FORMATION OF SHORT-CHAIN FATTY-ACIDS IN SLOW SAND FILTERS

A case study carried out at a municipal drinking water treatment plant in southern Sweden showed that the formation of short-chain fatty aci ds in slow sand filters can result in severe off-flavour problems. Whe n an extract of the headspace of the surface layer of a sand filter wa s subjected to gas chromatographic analysis with sensory detection (GC sniffing), several strong, rancid odours were detected. Mass spectrom etric analysis of the sane extract before and after methylation, showe d that substantial amounts of butyric acid, valeric acid and isovaleri c acid were present in the analysed sample. The off-flavour caused by these compounds was removed by repeated shock chlorination of the malf unctioning slow sand filter. Analysis of fatty acid esters may provide an early warning of the described off-flavour problem.