mschock Posted March 19, 2021 Share Posted March 19, 2021 We have a situation with having a need to derive the total carbonate concentration in a closed system from laboratory analytical input parameters. The measurement we often have is total alkalinity, as defined by strong acid titration to the carbonic acid equivalence point. In drinking water context, there often are other dissociated weak acids, like phosphoric acid, hypochlorite ion, NH3, silicic acid, present in solution, which are titratable. We cannot analytically separate carbonate alkalinity from total alkalinity, in the absence of a direct coulometric or other analysis of total inorganic carbon in the water (which is only sometimes available). With solution pH and the rest of the major constituent water analysis, for example, total concentrations of Ca, Na, Mg, SO4, PO4, SiO2, free chlorine residual (hypochlorous acid/hypochlorite ion), total NH3, etc. we can get ionic strength, ion pairing and the other weak acids that would be caught in the total alkalinity measurement. This issue is described nicely in the documentation of the original USGS WATEQ series of computer programs, as well as in many other water chemistry texts. Is it possible to implement this calculation in GWB, particularly in the GSS spreadsheet and SPECE8? Assuming carbonate alkalinity = total alkalinity is very often a good approximation. But in waters of low carbonate concentration (less than 5 mg/L as C), typical water treatment practice results in concentrations of other weak acids and bases that are significant relative to the carbonate alkalinity. Quote Link to comment Share on other sites More sharing options...
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