Accelerated biodegradation of EDTA in a conventional activated sludge plant under alkaline conditions

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