A 5 pH Point Titration Method for Determining the Carbonate and SCFA Weak Acid/Bases in Anaerobic Systems

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Abstract
A 5 pH point acid titration method is proposed to measure the short chain fatty acids, total carbonate species concentration and H2CO3*alkalinity in anaerobic systems. To test the method, aqueous solutions containing NaHCO3 (1990; 2488 mg/ℓ as CaCO3) and the short chain fatty acid (SCFA) acetic acid with concentrations ranging from 100 to 1000 mg/ℓ were titrated using the method; the H2CO3*alkalinity and SCFA estimates ranged around the expected values with an average standard deviation of 5 and 8 percent respectively. Estimates of the SCFA by the method and by Montgomery et al 9s wet chemical method on the effluents of UASB reactors treating brewery and wine distillery waste correlated closely (r = 0.98). Other tests demonstrated as predicted that the presence of ammonium has a negligible effect on the derived results. However, phosphates can have a significant effect on the H2CO3*alkalinity but not on the SCFA estimates. The phosphate effect is eliminated in the derived estimates if its concentration is known. The method also identifies errors in pH due to the residual liquid junction effect or poor calibration and corrects the estimates accordingly; deliberately imposed pH calibration errors were identified and their error effects on the H2CO3*alkalinity and SCFA estimates largely corrected.

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