Alkalinity is a measure of a solution's ability to neutralize acids to the equivalence point of carbonate or bicarbonate ions. Alkalinity plays a key role in the overall treatability of raw water because it determines the waters ability to chemically react. H. Y. Carson Filter Plant (CFP), operated by the Birmingham Water Works Board (BWWB), receives its raw water primarily from Inland Lake. Inland Lake has very low alkalinity, < 30 mg/L; low total organic carbon (TOC), 2.0-2.5 mg/L; and low turbidity, < 2ntu. This combination of water quality parameters creates an interesting dilemma when attempting to improve TOC reduction through enhanced coagulation.Almost two years ago Shades Mountain Filter Plant (SMFP), also owned by the BWWB, underwent a successful coagulant changeover from aluminum sulfate to ferric sulfate to improve their TOC reduction. Upon this success, the BWWB decided that a pilot study at CFP was needed to determine if a coagulant change would be as beneficial there. Although there are many differences between SMFP and CFP, one of the most significant is that SMFP receives raw water that is high in alkalinity, approximately 100 mg/L. This major difference in alkalinity between the two treatment plants played a major role in determining what the most effective coagulant and optimal dose would be at CFP.
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.
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