Anaerobic-Aerobic Treatment of Total Waste Effluent from a Pulp Mill Including Sludge Hydrolysis, 1994 Environmental Conference Proceedings

E. Dalentoft, M. Jonsson

A full scale anaerobic-aerobic biological treatment plant treating the total waste effluent from a pulp mill is in operation. All of the condensate and about half of the caustic extraction liquor generated in the sulphite pulping process are treated in the anaerobic process. The anaerobic plant is designed to treat 60,000 kg COD/d of which half comes from sulphite evaporator condensate, and half from caustic extraction liquor. The anaerobically treated water is led to the aerobic treatment stage, where it is treated with the rest of the extraction liquor and other effluent streams. The aerobic stage is designed for treatment of 102,000 kg COD/d and 37,000 kg BOD/d. The excess sludge from the aerobic treatment plant is further treated in an alkaline hydrolysis stage followed by an anaerobic digestion.

Results from operation of the aerobic stage with 70,000 kg COD/d and 30,000 kg BOD/d show good sludge characteristics and good treatment results; 65% COD-reduction and outlet concentrations of TSS < 50="" mg/l,="" tot-p="">< 1="" mg/l,="" and="" inorganic="" n="">< 6="" mg/l.="" in="" the="" sludge="" hydrolysis="" 70-75%="" of="" the="" suspended="" solids="" in="" the="" excess="" sludge="" are="" transformed="" into="" soluble="" form.="" about="" the="" same="" percentage="" of="" nutrients="" in="" the="" sludge="" is="" released="" and="" returned="" to="" the="" activated="" sludge="" plant="" via="" the="" reject="" water.="">