Over 20 years after independence of Kyrgyzstan, basic infrastructure has been continuously deteriorating because of inefficient management, lack of preventive maintenance and reduced capital investments. The waste water treatment plant in Osh was designed in 1969 based on a conventional activated sludge process. The treatment efficiency of the WWTP was poor because the mechanical treatment was only partially in operation condition and the activated sludge treatment was not operated properly. With the rehabilitation of the mechanical treatment the effluent efficiency is improved and the pre-condition for the rehabilitation of the biological treatment is set.