Design Optimization for Biological Filter Models

Four different models are used: the Eckenfelder, the Galler-Gotaas, the National Research Council (NRC), and the Upper Mississippi and Great Lakes Board. Filter depth has the greatest influence on the most economical design with the Galler-Gotaas model, some influence in the Eckenfelder and the NRC models, and no influence in the Upper Mississippi and Great Lakes model. The most economical design is achieved when the depth is maximum to permit adequate filter ventilation, after which recirculation is economical up to about four recirculations. The radius of the filter must then be increased to provide greater volume to achieve the required BOD removal. Design curves are shown for the four models. Because more variables are included in the Galler-Gotaas model, it appears to provide the best fit to treatment observations for different types of wastes. If pumping to the filters is necessary regardless of the filter depth, deeper filters with forced ventilation are more economical than shallower filters.