Accelerated degradation of EDTA in an activated sludge plant

Ethylenediaminetetraacetic acid (EDTA) is used in the pulp and paper industry in bleaching where EDTA forms catalytically inactive-complexes with transition metal ions preventing them from catalyzing the decomposition of hydrogen peroxide. EDTA complexes may have harmful effects on the environment and only a minor part of the complexes (about 10 %) are eliminated during bioprocessing of the mill waste waters under normal conditions (pH about 7). In this study, biodegradation of EDTA in an activated sludge plant of a paper mill was monitored under alkaline conditions (pH 8-9). An average EDTA reduction of about 50 % was obtained during a 7-week test period. The results also indicated that the pH adjustment to 8-9 with calcium oxide (CaO) did not interfere with the normal operation of the activated sludge plant.