AWWA WQTC57002

This paper demonstrates the applicability and performance of low-cost and relatively non-mechanical flocculation and rapid mix systems at the 40-year old South Fork Water Board conventional treatment plant (that serves the cities of Oregon City and West Linn, Oregon), whose mechanical systems were failing and in need of replacement and/or repair. Settled water quality and filter performance have remained the same or improved since implementation of these improvements. These improvements also resulted in long-term energy cost and O&M cost savings due to removal of mechanical systems. The selected hydraulic flocculation design incorporated the use of wooden baffle walls supported by concrete columns which were anchored with bases into the floor of the two flocculation basins. Three rows of baffle walls were created to force an "end around" flowpath with 3 main flocculation stages; each stage was provided with sequentially less headloss to create tapered flocculation to promote the formation of settleable floc when needed. Each stage was further divided into separate flocculation cells with full-depth openings to create the desired headloss. The opening sizes increased in each stage to reduce headloss. A diffuser wall at the end of the flocculation basin helps distribute flow evenly into the sedimentation basin across the width and depth.