Automatic flow titrator based on a multicommutated unsegmented flow system for alkalinity monitoring in wastewaters

A full automatic flow system based on potentiometric titration for alkalinity monitoring in wastewater treating plants is presented. Titration to an end-point of pH 5.75 partial alkalinity CPA) and then to pH 4.3 intermediate alkalinity CIA) allows to distinguish the relative buffering contributions of both bicarbonate and volatile acids in anaerobic digesters and, thus, the attainment of a IA:PA ratio which is a sensitive parameter of digestion monitoring that increases rapidly with the process upset. The titration approach is based on a time-based sequential introduction of increasing titrant and decreasing titrand volumes into a mixing chamber The theoretical model for the titration process already presented and discussed was used to determine the titrand concentration without prior calibration. The interface between the analytical system and the anaerobic digester was also developed, allowing completely automated on-line monitoring of alkalinity. The results obtained were reproducible (R.S.D. lower than 2.4 and 5.1% for repeatability and reproducibility, respectively) and in good agreement with those given by the comparative method. (C) 2001 Elsevier Science B.V. All rights reserved.