Baffle Installation and Surface Aerator Placement Improve ASB Treatment Performance, 2003 Environmental Conference

High effluent concentrations of both total suspended solids (TSS) and 5-day biochemical oxygen demand (BOD5) has prompted Boise Paper’s Wallula, Washington, mill to look for methods to improve suboptimal aerated stabilization basin (ASB) treatment system performance to lower these parameters. An engineering study was conducted to determine a cost-effective means of substantially improving the treatment performance of the 2-stage ASB secondary treatment system.

The engineering study specifically focused on improving TSS settleability and maximizing existing surface aeration efficiency in the 5-day retention second-stage aeration basin, using a computer model to determine optimum placement of baffles and location of aerators. The volume of the aeration basin liquid column and the spatial distribution and volume of the sludge deposited on the bottom of the basin were determined using sonar mapping technology.

Following completion of the baffle installation and aerator relocation, a significant drop in the TSS and BOD5 discharge was observed, allowing aeration optimization to significantly save energy. Sludge deposit mapping has tracked both the spatial movement and accumulation rate of second-stage aeration basin sludge inventory.

The paper discusses application of the computer model and resulting data interpretation to determine placement of the baffles and aerators. In addition, an analysis comparing treatment system performance before and after the ASB upgrade is presented. Biological treatment kinetics were determined and compared to historical values using a computer model previously developed and calibrated for the Wallula mill secondary treatment system.