Secondary Clarifier Baffling Exceeds Performance Expectations, 1999 Environmental Conference Proceedings

Steven E. Woodard & James D. Ekedahl

Woodard & Curran

Raymond Pepin

S.D. Warren Company

Steve Woodard

Woodard & Curran

The S.D. Warren Westbrook Mill is an integrated bleached kraft pulp and paper mill located in Westbrook, Maine. The mill currently treats an average wastewater flow of 68 MLD using primary sedimentation and an activated sludge process with pedestal-mounted, surface aerators. In the Spring of 1996, Woodard & Curran began a project with S.D. Warren to develop an improved method of reducing TSS levels in the treatment plant effluent. The first step in the process was to evaluate the hydraulic efficiency of the secondary clarifiers, to see how effective, if at all, the installation of baffles would be. Both slug and continuous dye tests were performed in each of the two clarifiers. Visual observation revealed the presence of significant floc carry-over.

The results of the dye testing were revealing. The slug dye test results demonstrated that the two identical clarifiers suffered from significant short circuiting currents, which were impairing TSS removal efficiency. The continuous dye test was used to pinpoint the location of the currents. Based on these results, it was decided that peripheral (Stamford) baffles would be the most effective method of mitigating the currents. The baffles were installed in one of the two clarifiers in October 1997, allowing side-by-side comparison of two clarifiers, one with baffles and one without. There were noticeable visual differences regarding floc carry-over between the two clarifiers. The results were impressive, as the baffled clarifier averaged 25% lower effluent TSS levels than the non-baffled clarifier. Peripheral Baffles were installed in the second clarifier in October 1998. Since baffle installation, effluent TSS and BOD loadings to the Presumpscot River have decreased by 49% and 37%, respectively. An added benefit is that polymer addition is no longer necessary, which has resulted in considerable cost savings.