The increasing requirements in wastewater treatment have led to the development of new wastewater treatment processes based on the know-how and experience in reaction and process engineering of the chemical industry. Due to their compactness, closed operation and high flexibility, these. new processes show a large potential for process integration and significant cost reduction in particular for highly polluted industrial wastewaters, This paper discusses the HCR Gigh-performance compact reactor) -process, developed at the Mass Transfer Laboratory of the Technical University of Clausthal within the last decade. This process has been realized in more than 30 technical applications with a volume loading of up to 70 kg COD/m3 d and an energy consumption of about 0.4 kWh per kg COD,b.