An analysis of a specific application of anaerobic wastewater treatment at a pulp and board mill, Stora Enso Skoghall, was carried out. A literature study was done and effluent wastewater from CTMP pulp production was analyzed. The analysis consisted of a broad constituent analysis and an anaerobic treatment trial. Results from these test where used to calculate the treatment effectiveness and resulting energy potential at the mill. The literature study and constituent analysis showed that toxicity of the water to be treated, due to wood extractives and sulphur content, was of concern. Detoxification chemicals targeting these constituents where used in the anaerobic treatment trial. The trial consisted of a two chamber upflow reactor and aerobic post treatment. The result of the trial is that the water of concern has about 50% anaerobically degradable content. A full scale implementation of anaerobic wastewater treatment would result in a methane production of 3,76 to 7,76 GWh/yr. An application of anaerobic wastewater treatment will also result in electricity savings, in aerated pond, and increase the capacity margin on current sludge handling techniques.