AWWA ACE63003

Filtration rate above 4 gpm/sf is still considered "high rate" by most regulators in the United States. The desire to achieve more cost effective filter capacity drives many water utilities to select a filtration rate of 6 gpm/sf or higher, which is typically implemented through up-rating existing filters. Regulatory pressures to provide low turbidity water, and the need to properly handle recycle or discharges of wastewater has placed filter operations under much more scrutiny than 10 or 20 years ago. The decision of high-rating existing filters should also take into consideration more than just effluent turbidity concentrations or particle counts as is commonly done for high rate approvals. The overall operation of the facility should also be considered. This paper reviews some of the key results of water plant high rate studies (in Michigan and North Carolina) for rate increases up to 6 gpm/sf on conventional sand and anthracite dual media filters, with media depths ranging from 24 to 48 inches. The studies showed that during normal operations, the plants were obvious candidates for higher rate filtration, however, from an operations standpoint; the plant(s) performed much differently under high production periods or problematic source (high algae or manganese) water periods. Filter runs, filter to waste periods, washwater handling volumes and facilities, unit filter run volumes (UFRV), and overall plant reliability was discussed in light of both regulatory limits and Partnership for Safe Water goals of 0.10 ntu. Recommendations for review of operational factors outside of simple filter effluent water quality were presented to allow for better assessment of higher filtration rates, and related facility improvements as part of future plant upgrades. Includes tables, figures.