A compost biofilter enriched in earthworms was adapted to treat cheese whey produced by a dairy in a mountainous area of the French pre-Alps. Until now, this type of installation has only been developed in mountain pasture areas and therefore only functions during the months of mountain pasture grazing, from May to September. The main goal of this study was to follow up pollutant removal performance after more than one year of operation. During the experiment, cheese whey loading varied from a few litres to 40 L m(-2) d(-1). Despite variations in the physical properties of the support media after 460 days of operation, whey removal performance was good. For COD and BOD, 80-88% of the loading mass and 70-80% of nitrogen and phosphorus was removed. In this experiment, the treated effluent could not meet the standards for discharge into rivers, but was a very effective and simple pretreatment. This study confirms the observations of previous experiments in mountain pastures both in France and Switzerland: a cheese whey volume of 20 L m(-2) d(-1) could be a basis for design, although the process can treat up to 40 L m(-2) d(-1) for seven days according to our results.