AWWA ACE63183

The goal of this research was to study the removal mechanisms of slow sand filtration (SSF) with special emphasis on the comparing of optimum summer conditions to more severe winter conditions as observed in the northern latitudes and mountainous regions. An effort was made to verify if the biological characteristics of the sand media are correlated to the microbial removal performance of the SSF at the different temperatures encountered in the New England area. The pilot filtration studies were conducted on the Narrows Pond surface water supply for the town of Winthrop, Maine. This site was chosen because according to the Winthrop Water Utilities the organic precursor content in the source water increased by roughly 10% from 2003 to 2004. Two pilot SSFs, Filter 1 (F1) and Filter 2 (F2), were operated simultaneously in the pipe gallery of the Winthrop, Maine water treatment facility. The first microbial challenge took place in July of 2004 and was followed by 8 more filter challenges with the most recent event taking place in March 2006. A final challenge is planned for July 2006. Each of the filter challenges was followed a week later by a filter coring event where sand samples were collected. This week between the microbial challenge event and the coring event was necessary due to the distance of the sampling site to the laboratory and also due to the amount of samples collected from those two events. Both filters operated continuously for the duration of the study for approximately 600 days and were only taken off-line for sand sample collection or cleaning/scouring purposes. A low amount of ozone was continuously pumped into F1 and resulted in longer filter runs in F1 than those on F2. Ozone residuals in F1 ranged from below detection limit to 1.10 mg O₃ mg/L. Includes 23 references, tables, figures.