Design Algorithm for Vertically-Baffled Flocculators

To date, design guidance for hydraulic flocculators has been limited, with several articles focusing on the design of horizontally-baffled flocculators. In this article, a design algorithm for vertically-baffled flocculators is introduced based on physical principles governing baffled hydraulic flocculator performance. Vertically-baffled flocculators are more compact than their horizontally-baffled counterparts for design flow rates less than about 170 L/s (4 MGD). To accommodate narrow baffle spacings at the lowest flow rates, this work introduces the concept of obstacles, which are placed on baffles to enhance mixing to maintain the same mixing efficiency attainable in larger flocculators. Well-designed hydraulic flocculators have more uniform velocity gradients than conventional mechanical flocculators; approach plug-flow behavior, which has faster flocculation kinetics and less short-circuiting; and are less expensive to operate and maintain. Design algorithms based on theoretical and practical considerations are developed, after which two illustrative design examples are given. Afterward, a discussion of the range of applicability for vertically-baffled and horizontally-baffled flocculators is presented. Cost comparisons with horizontally-baffled flocculators and mechanical flocculators are then made and turbidity performance data are provided. This vertically-baffled flocculator design approach has been proven in Central America, where it has been used to design 17 flocculators that are currently in use and have demonstrated dependable performance and low-cost operation and maintenance.