Maximizing A Wastewater Treatment Plant's Capacity, 1990 Environmental Conference Proceedings

An expansion project at Boise Cascade’s mill in International Falls, Minnesota, included evaluation of the mill’s wastewater treatment plant capacity. The treatment plant consists of one primary sedimentation tank, two pure-oxygen activated sludge reactors, one secondary sedimentation tank, and one belt filter press. The preliminary evaluation showed that plant capacity was limited by the inability to remove sludge from the secondary clarifier adequately, inadequate dewatering capacity, and inadequate oxygen transfer in the first stage of the reactors. The preliminary evaluation also identified immediate improvements that would increase treatment capacity. The improvements included converting the clarifier’s sludge draw-off tubes to airlifts, installing additional sludge dewatering capacity, and making repairs in the reactors. Upon completion of the modifications, a full scale test of the plant was conducted. The full scale test indicated a significant increase in capacity.