In the dairy industry, large amounts of alkaline cleaning solutions are used at high temperatures, typically 80 degrees C. Discharge of used cleaning solutions causes significant environmental problems and the need for neutralization before discharge. The possibility of purifying such solutions by membrane separation technology was investigated. The basic idea was to remove milk compounds and thus make it possible to reuse the cleaning solutions for an extended period of time before discharge thus saving energy, water and chemicals. Flux and COD retention were investigated for various types of detergents and cleaning objects using ceramic membranes. High and stable fluxes could be obtained. In some cases, however, severe fouling was observed. The composition of spent solutions as well as the COD retention and the flux level varied greatly, also after cleaning of the same object. The concentration of organic pollutants had only a minor influence on the flux even at high volume reduction factors. No correlation was found between the COD content and the retention of organic compounds. No retention of sodium hydroxide was observed.