Anaerobic-aerobic pilot-scale treatment of a sulphite evaporator condensate

Sulphite mill evaporator condensate mixed with 10% of volume of waste water from production of modified cellulose, was treated in an anaerobic-aerobic pilot plant. Influent COD and BOD//7 concentrations were 10 to 15 kg multiplied by (times) m** minus **3 and 3 to 5 kg multiplied by (times) m** minus **3 respectively. To maintain a stable treatment, the waste water was supplied with ferric iron, calcium hydroxide, nitrogen and phosphorus. The liquid volume of the anaerobic tank was 21 m**3 and that of the aerobic 3. 5 m**3. The anaerobic stage was operated as a contact reactor at 35 to 37 degree C and the aerobic as an activated sludge plant. Aerobic excess sludge was digested in the anaerobic tank. 85 to 88% anaerobic BOD//7 reduction was obtained at an organic load of 4 kg COD multiplied by (times) m** minus **3 multiplied by (times) d** minus **1. The total BOD//7 reduction was 95 to 96%. Methane production amounted to 300 to 320 L (S. T. P. ) per kg of COD reduced and methane concentration was 48 to 57%. It was concluded that anaerobic-aerobic treatment would provide an efficient and cost-attractive way to reduce pollution problems associated with sulphite evaporator condensate.