PH Buffer Capacity Based Monitoring of Algal Wastewater Treatment

Abstract

A pH buffer capacity based method for multivariate monitoring of tertiary algal wastewater treatment systems is presented. A pilot plant with algal biomass receiving the effluent of a carbon removing activated sludge municipal wastewater treatment plant was used for the experimental work. Two types of buffer capacity profiles are considered, first resulting from a titration from the actual pH to pH 2.5 (down titration), and second as a result of a titration from pH 2.5 to pH 11 (up titration). The experiments were conducted with a laboratory titrator and the buffer capacity profiles were processed by fitting mathematical models of buffer systems to them. This allowed quantification of the inorganic carbon (IC) buffer from the down titration profiles. IC is of major importance because it is the only carbon source used by algae. It is shown that the IC concentration derived from the buffer capacity profile gives different process information than a standard alkalinity measurement. The up titration profiles were successfully used for the quantification of NH4 − and o-PO4, although an exact comparison of the laboratory results and the buffer capacity based results is difficult, because of the filtration step preceding laboratory analyses and possible interferences caused by unmodeled buffer systems. No filter device was used, which makes it possible to implement this measurement method in a robust and field applicable sensor. The complete measurement cycle (down titration followed by up titration and data interpretation) can be performed in less than 1 hour, with little manipulation, and could easily be automated.