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.
In anticipation of changing federal regulations, the Birmingham Water Works Board (BWWB) conducted a pilot plant study to evaluate the primary coagulant at its largest filter plant. This article discusses how the BWWB attempted to change the primary coagulant at its Shades Mountain Filter Plant (SMFP) from aluminum sulfate to ferric sulfate. However, the investigation was abandoned because of increased filter‐to‐waste for 46 gravity‐fed sand‐anthracite filters with a high rate of 2.8 gpm/ft2. Although the failed changeover left SMFP without improved total organic carbon (TOC) removal, the process provided valuable insights and prompted BWWB to purchase a mobile pilot plant. It was clear that any proposed changes to the treatment process required filter‐performance evaluation.
TreatmentDesiring a more versatile treatment option, an Alabama utility undertook a pilot-plant study to evaluate various coagulant doses to improve TOC removal, provide consistent floc formation, and reduce settled turbidity.
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