A new process for integrated treatment of industrial wastewater at a municipal WWTP is presented. The process uses the ability of heterotrophic bacteria of rapid substrate uptake and storage. The excess sludge from the municipal treatment line is fed to a contact tank, which receives the industrial wastewater via a separate pipeline. The contact tank is aerated to such a degree that secures complete substrate uptake but minimises oxygen consumption due to instant substrate degradation. The sludge from the contact tank is mechanically pre-thickened and then fed to an anaerobic digester. Hence, the major portion of the incoming COD load of the industrial wastewater is transferred to the anaerobic digester, where it contributes to an increased biogas production. The back load of the industrial wastewater treatment process to the municipal treatment line is very low.