Granular activated carbon (GAC) media for filtration of drinking water can be used to remove microscopic substances at extremely effective rates though a process of adsorption. Two major problems with GAC are the high start-up costs and the short effective removal timeline before GAC replacement or reactivation. Three years ago, the Birmingham Water Works Board (BWWB), undertook a project sponsored by the Water Research Foundation (WRF) to evaluate GAC for removal of organics, pharmaceuticals, and pesticides. These results were published in December 2010. A primary coagulant change at the plant occurred shortly after the initial study and a spin-off study commenced. The GAC filters are continuously monitored for any significant changes in performance. Grab samples including total organic carbon (TOC), heterotrophic plate counts, and nitrates are collected and sent for analysis. Initial results show there is still significant reduction in TOC through the filters. This is important because previous research suggests the media has an adsorption timeline of approximately six months after which GAC media was determined to be biologically active. If GAC is effective at removing organics several years after installation through biofiltration which doesn't require reactivation, it may be a cost effective alternative to current procedures enabling BWWB to meet future regulations on drinking water.
Raw water quality, specifically total organic carbon (TOC) and chlorine demand, are of particular concern to the treatment process due to upcoming tightening regulations. To address this, the Birmingham Water Works Board developed the following study in an effort to further improve finished water quality. This year a survey was performed at Shades Mountain Filter Plant (SMFP) to monitor the influent water quality to the plant. The objective was to evaluate the difference in chlorine demand and TOC for the two primary source waters, Cahaba River and Lake Purdy. Initially sampling was performed at the following locations throughout the SMFP system: Upstream Cahaba River, Cahaba Pump Station, Lake Purdy, Bottom of Lake Purdy dam, Bridge located downstream from Lake Purdy, SMFP receiving basin, SMFP flume or rapid mix. These sites were chosen for their ability to provide information on each water source independently as well as information pertaining to their combination at SMFP. Sampling occurred during and/or after several weather events to capture all weather variations. Initial results suggested that Lake Purdy had higher TOC than the Cahaba River. Consequently, the Little Cahaba site was added approximately two miles downstream of Lake Purdy just before the junction of the two source waters. It will provide crucial information as to what the water quality of Lake Purdy is just before it is combined with the Cahaba River and sent to the plant as a blend. Evaluation of the water quality at this new site downstream from the lake is important because it will help determine if additional pre-treatment or reservoir treatment will be beneficial.
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