Measuring Alkalinity Accurately in Aqueous Systems Containing High Organic Acid Concentrations

Abstract

ABSTRACT Alkalinity is one of the most important parameters in biological waste management systems. It is a measurement of the chemical buffering capacity and its level therefore is an indication of the biological health of aqueous waste treatment processes. Alkalinity is based primarily on the carbonate-bicarbonate-carbonic acid complex as the major contributor. The measurement of alkalinity for years has been based on the fact that titration to a pH endpoint of 4.3 or 3.7 {Standard Methods, 1985, 1980) would measure all the carbonic acid system. While this is true, in waste management processes where organic acids are significant, titration to this pH also measures much of the organic acid complex. This is a false alkalinity since the pKa of most organic acid systems is below 4.75. Jenkins et al. (1983) first expressed concern about this phenomenon. Described here is a simple titrametric procedure for determining alkalinity in wastewater samples that is approximately 10 times more accurate than the Standard Methods (1985) procedure. The study used synthetic controlled chemical solutions. The levels of organic acid, true bicarbonate alkalinity and endpoint titration pH were closely controlled and their influence on the measured alkalinity was determined. The results show that titration to pH 4.3, when organic acids are present, can result in great error (ca. 600%) in measured alkalinity. Using the procedure proposed here, the error is much less (<45%).