Effect of H2O2 and DTPA on the Characteristics and Treatment of TCG and ECF Bleached Pulping Effluent, 1996 Environmental Conference Proceedings

Totally chlorine-free (TCF) bleaching technologies can result in high concentrations of residual hydrogen peroxide and chelating agents in combined mill effluent. This study was undertaken to determine the effect of hydrogen peroxide and a chelant (DTPA) on effluent characteristics (BOD5 , toxicity), MLVSS characteristics (OUR, catalase-equivalent activity) and the efficiency with which laboratory-scale activated sludge reactors treat TCF bleached pulp mill effluents. The addition of over 20 mg/L hydrogen peroxide to TCF combined mill effluent was found to decrease the BOD5 by up to 25%, but did not markedly reduce effluent toxicity. Addition of increasing concentrations of hydrogen peroxide (up to 1000 mg/L feed) to lab-scale activated sludge reactor while initially affecting floc architecture, did not influence treatment efficiency. MLVSS was found to become acclimated to the presence of peroxide, with tolerance to peroxide shock loading, and catalase-equivalent activity increasing in proportion to influent H2 02 concentration. Chelating agents, particularly DTPA, were also found to have a dramatic impact on MLVSS viability and reactor performance. Batch tests indicated a DTPA dose-dependent decrease in OUR. Introduction of DTPA, at levels commonly found in TCF effluents, to continuous reactors resulted in a disruption of floc structure and a 39% decrease in BOD5 removal efficiency. Removal of acute toxicity as measured by Microtox was maintained despite the poor BOD5 removal efficiency.