Sludge bulking in the activated sludge system at Boise Cascade’s Rumfort Mill caused noncompliance with suspended solids (SS) and, occasionally, biochemical oxygen demand (BOD) discharge requirements. The cause of bulking was linked to the outgrowth of filamentous organisms caused by dissolved oxygen (DO) conditions. Return activated sludge (RAS) chlorination was found to be an excellent means of controlling sludge bulking and reducing SS discharges. The mill has utilized sludge chlorination as a power-saving feature in an expansion of its treatment plant aeration system.