Enhanced coagulation is proposed by the US Environmental Protection Agency as a best available technology to remove dissolved organic carbon (DOC). In this article, an improved model of DOC removal by enhanced coagulation is proposed based on Langmuir isotherm theory. For the purpose of the model, DOC is assumed to comprise three fractions: humic acid, nonpolar, and nonsorbable. The nonsorbable fraction is not removed. Removal of the humic acid fraction is dependent on pH, whereas that of the nonpolar fraction is not. This model, which includes five coefficients, was fitted to data from experiments on various Australian and US waters. It predicted the final DOC for a given metal coagulant and water within a standard deviation of the error of either 5.5% or 0.15 mg/L of DOC over the valid combinations of coagulant dose and pH. Generally at a given pH alum was found to remove more DOC at lower doses than ferric coagulant, whereas at higher doses, ferric coagulant removed more DOC than alum.
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