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Effect of DTPA and hydrogen peroxide on activated sludge performance Larisch, Belinda Cornelia V.


This work explores the behaviour of a standard biological treatment system when exposed to two of the most common residuals from novel bleaching processes: hydrogen peroxide and the chelant DTPA. The potential problems for an activated sludge biological treatment unit, from the introduction of a chelating agent and hydrogen peroxide, were anticipated to stem from the sequestering of vital trace elements by the chelant, and the oxidation of biomass by the hydrogen peroxide. Typical residual quantities from TCF bleaching processes are 0.875 g DTPA / L and 0.2 g H2O2 / L, although the peroxide residual concentration is variable, up to approximately 1 g/L. The effects of running a typical biological treatment system on effluent from novel bleaching processes were also determined, in addition to the effects of switching influent sources between novel and conventional bleaching effluent. Activated sludge secondary treatment systems could successfully treat elementally chlorine free (ECF) and totally chlorine free (TCF) bleached kraft mill effluents by achieving > 90% BOD removal, > 40 % COD removal, and 100% acute toxicity removal. Influent feed changes between untreated chlorine free bleaching effluent and conventional effluent (from a 60% ClO2 bleaching sequence) resulted in immediate changes in treatment efficiency. Switching from TCF to conventional effluent decreased BOD removal, whereas switching from ECF to conventional effluent increased BOD removal. The addition of DTPA and hydrogen peroxide was found to have significant effects on activated sludge treatment. Continuous treatment of peroxide-containing wastewater reduced floe density at peroxide concentrations greater than 200 - 500 mg/L, although treatment efficiency was maintained. Continuous treatment of DTPA containing wastewater resulted in BOD removal efficiencies of 60% at DTPA concentrations greater than 600 mg/L. The addition of both DTPA and peroxide at typical TCF bleached kraft mill effluent (BKME) residual concentrations caused biological treatment to cease entirely. Individually, the effects of hydrogen peroxide and DTPA were: the reduction of biomass metabolic activity at concentrations of 100 mg/L H2O2, and 500 mg/L DTPA, the induction of catalase activity upon H2O2 addition, and the release of cellular material due to cell wall damage at DTPA concentrations greater than 50 mg/L. [Scientific formulae used in this abstract could not be reproduced.]

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