AWWA JAW64706

The turbidity spike that occurs during filter ripening can be minimized without additional equipment or chemicals, simply by optimizing backwash steps. However, filter-to-waste (FTW) is still needed to achieve aggressive filter effluent turbidity targets. A study was undertaken at the Central Lake County Joint Action Water Agency in Lake Bluff, Illinois, to minimize water consumption and maximize filter service life. Filtration and water use were optimized using existing equipment and a method called extended terminal subfluidization wash, demonstrating that 10-year-old biologically active granular activated carbon is still viable. The FTW peak following backwash was reduced from an average of 0.13 to 0.08 ntu. In addition, results suggest that FTW is not required in 96% of filter backwashes. Therefore, automatic FTW following backwash should be discontinued and, instead, FTW should only be used as needed. Includes 54 references, tables, figures.