LIGHT-SCATTER PARTICLE COUNTING - IMPROVING FILTERED-WATER QUALITY

Forward-angle light-scatter (FALS) particle counting is investigated as a means to quantify and improve filtered-water quality in drinking-water treatment. In the laboratory, FALS particle counts are found to be precise and reproducible by multiple analysts when proper sample handling procedures are followed. In FALS counts of water samples with added Giardia cysts, FALS categorizes Giardia cysts as equivalent to spheres of 1-5-mu-m in diameter, demonstrating the importance of using a particle counter to size particles of interest prior to selecting size ranges for routing monitoring. In full-scale water-treatment plant trials, FALS particle counts are used to show that particles in filtered water are substantially reduced when filter operation is changed from intermittent, fixed rate, 60-hour filter runs to continuously operated, variable rate, with 48 hours between back-washes. Filtered-water quality is also higher in stage 2 of the Bearspaw Water Treatment Plant than in stage 1 under all operating conditions. Turbidity measurements follow trends in particle counts in most cases. Further improvements in filtered-water quality can likely be made by using FALS particle counting to optimize backwashing procedures and filter-ripening strategies.