Use of the correct blank test in the determination of COD and AOX in bleached kraft mill D stage effluents

Abstract

A study of four types of blank, two of which (the placebo blank and the method blank) are amenable to direct measurements and the other two [the total Youden blank (TYB) and system blank] to extrapolation, revealed the need to use a correct blank test, the TYB, in order to eliminate the constant error component. The conclusions drawn here are demonstrated for the microcoulometric determination of adsorbable organic halogen (AOX), according to Scandinavian standard SCAN-W 9∶89, and in the spectrophotometric determination of chemical oxygen demand (COD) following a closed reflux spectrophotometric method. These environmental analytical parameters (AOX and COD) were determined in two different bleached kraft mill effluents: one from stage D (100% ClO₂) of the bleaching sequence AOD of the elemental chlorine-free type and the other for the chlorination step, the first in the conventional sequence (D₂₀C₈₀)(E₀)D₁D₂, applied to kraft pulp from Populus spp.