Effect of DTPA and EDTA on Activated Sludge Reactors Treating Bleached Kraft Mill Effluent, 1999 Environmental Conference Proceedings

Belinda C. Larisch & Sheldon J.B. Duff

UBC Pulp and Paper Centre and Department of Chemical and Bio-Resource Engineering

University of British Columbia

To reduce the loss of hydrogen peroxide through metal-catalysed decomposition, modern bleaching sequences typically control the level of free metal ions through addition of chelants such as DTPA (diethylenetriaminepentaacetic acid) and EDTA (ethylenediaminetetraacetic acid)

at doses ranging from 2-5 kg/adt pulp. Metal ions are known to play a number of important roles in bacteria, including membrane/capsule stabilization and oxidative metabolism. Despite the wealth of studies on biodegradation of chelants, little work has examined the impact of such compounds on the microbial community in activated sludge treatment systems. In this study, we examined the impact of chelating agents on the microbial community in an activated sludge reactor treating effluent from a bleached kraft pulp mill.

Addition of doses of DTPA between 50-875 mg/L to continuous laboratory-scale reactors was found to produce a range of effects. After exposure to elevated (>600 mg/L) levels of DTPA, floc density was considerably reduced, and BOD removal efficiency was reduced by up to 39%. Further, a chelant dose-dependent decrease in substrate uptake kinetics for effluent and for methanol was observed. Exposure to chelants caused an increase in the amount of cellular solutes present in the medium by up to 150% indicating that DTPA and EDTA compromised the integrity of the microbial capsule and/or cell wall.