pH buffer capacity based monitoring of algal wastewater treatment

A pH buffer capacity based method for multivariate monitoring of tertiary a lgal wastewater treatment systems is presented. A pilot plant with algal bi omass receiving the effluent of a carbon removing activated sludge municipa l wastewater treatment plant was used for the experimental work. Two types of buffer capacity profiles are considered, first resulting from a titratio n 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 condu cted with a laboratory titrator and the buffer capacity profiles were proce ssed 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 u sed by algae. It is shown that the IC concentration derived from the buffer capacity profile gives different process information than a standard alkal inity measurement. The up titration profiles were successfully used for the quantification of NH4- and o-PO4, although an exact comparison of the labo ratory results and the buffer capacity based results is difficult, because of the filtration step preceding laboratory analyses and possible interfere nces caused by unmodeled buffer systems. No filter device was used, which m akes 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 h our, with little manipulation, and could easily be automated.