EFFECT OF H2O2 AND DTPA ON THE CHARACTERISTICS AND TREATMENT OF TCF (TOTALLY CHLORINE-FREE) AND ECF (ELEMENTALLY CHLORINE-FREE) KRAFT PULPING EFFLUENTS

Perceived negative environmental effects associated with chlorine blea ching have led to the development and implementation of pulp bleaching technologies which eliminate the use of elemental chlorine (ECF) or a ny chlorine containing compounds (TCF). Commercial implementation of t hese technologies has moved forward; however, the research necessary t o fully understand the impact of effluents from these new bleaching te chnologies on the environment and on existing biological treatment pro cesses has lagged behind, and is for many novel bleaching sequences, n on-existent. This study examined the impact of hydrogen peroxide (H2O2 ) and chelating agents on the characteristics and treatment of TCF and ECF kraft effluents. Effluent BOD was reduced approximately 25% by ad dition of H2O2 concentrations from 20-640 mg/L, however, effluent toxi city was not affected by hydrogen peroxide concentrations of up to 640 mg/L. Unacclimated activated sludge was inhibited by sudden exposure to shock doses of hydrogen peroxide. While the viability of the sludge (as measured by the rate of substrate metabolism) was profoundly affe cted, the effect was reversible, with full recovery of metabolic activ ity restored within approximately 10 hours of the shock In continuous trials, as the activated sludge reactor became acclimated to H2O2, the kinetics of degradation of hydrogen peroxide increased. Chelating age nts, particularly diethylene triamine pentaacetic acid (DTPA), were al so found to have a dramatic impact on sludge viability and reactor per formance. Batch tests indicated a DTPA dose-dependent decrease in oxyg en uptake rate. Introduction of DTPA at levels commonly found in TCF e ffluents to continuous reactors resulted in a disruption of flee struc ture and a 39% decrease in BOD removal efficiency. Removal of acute to xicity as measured by Microtox was maintained despite the poor BOD rem oval efficiency. (C) 1997 IAWQ.