Based on the widely applied UASB system for anaerobic wastewater treatment a new generation of more advanced anaerobic reactor systems have recently been developed, according to the so-called expanded sludge bed concept. A successful version of this concept is the Internal Circulation (IC) reactor, characterized by the biogas separation in two stages within a reactor with a high height/diameter ratio and the gas-driven internal effluent circulation. The IC system can handle high upflow liquid and gas velocities, which makes treatment of low strength effluents at short hydraulic retention times, as well as treatment of high strength effluents at very high volumetric loading rates feasible. During the past years the IC technology has been successfully applied at full scale on a variety of industrial wastewaters. This article describes the design and operational results of three full scale anaerobic treatment plants with Internal Circulation reactors treating low, medium and high strength effluents from a dairy industry, food processing plant and brewery respectively.

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