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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.

In a chloraminated drinking water distribution system, monochloramine decays due to chemical and microbiological reactions. For modeling and operational control purposes, it is necessary to know the relative contribution of each type of reaction, but there was no method to quantify these contributions separately. A simple method was developed to do so. It compares monochloramine decay rates of processed (0.2 microm filtered or microbiologically inhibited by adding 100 microg of silver/L as silver nitrate) and unprocessed samples under controlled temperature conditions. The term microbial decay factor (Fm) was defined and derived from this method, to characterize the relative contribution of microbiologically assisted monochloramine decay to the total monochloramine decay observed in bulk water. Fm is the ratio between microbiologically assisted monochloramine decay and chemical decay of a given water sample measured at 20 degrees C. One possible use of the method is illustrated, where a service reservoir's bulk and inlet waters were sampled twice and analyzed for both the traditional indicators and the microbial decay factor. The microbial decay factor values alone indicated that more microbiologically assisted monochloramine decay was occurring in one bulk water than the other. In contrast, traditional nitrification indicators failed to show any difference. Further analysis showed that the microbial decay factor is more sensitive and that it alone can provide an early warning.

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