Toxicity of Conventional, Elemental Chlorine–free, and Totally Chlorine–free Kraft-Pulp Bleaching Effluents Assessed by Short-Term Lethal and Sublethal Bioassays

Abstract

Abstract-The toxicity of nine effluents from Swedish kraft-pulp mills using conventional, elemental chlorine-free (ECF) and totally chlorine-free (TCF) bleaching processes was studied. Effluents represented six different processes: conventional-softwood 30% ClO 2 ; ECF-softwood; TCF-hardwood, for which all the samples were taken before and after secondary treatment; conventionalsoftwood 8% ClO 2 ; TCF-softwood O 3 /H 2 O 2 ; and TCF-softwood H 2 O 2 . Comparison of effluents, which had not undergone secondary treatment, suggested that those from mills using conventional bleached pulp were the most toxic, with toxic emission factors (TEF) ഠ 1,000 according to the Microtox test (AZUR Environmental, Carlsbad, CA, USA). In the acute Nitocra spinipes test, the conventional-softwood 8% ClO 2 and the ECF-softwood effluents before secondary treatment were the most toxic, with TEF ഠ 700. In the reproduction test, N. spinipes was two to three times more sensitive than in the lethal test. The species most sensitive to the effluents investigated was the macroalga Ceramium strictum, with TEF values up to 3,000. The conventional effluent using a substitution of 8% ClO 2 was the most toxic, and the TCF effluents were the least toxic. Degradation treatment of the ECF and TCF effluents for 28 d in the laboratory did not eliminate acute lethal effects on N. spinipes and the Microtox bacterium.

Comparison of a test battery for assessing the toxicity of a bleached-kraft pulp mill effluent before and after secondary treatment implementation

“…Reductions in the toxicity of pulp and paper mill effluents through the introduction of secondary treatment have been observed in previous studies (Tarkpea et al 1999;Environment Canada 2003;Hewitt et al 2006;Parrott et al 2006). Such toxicity reductions are mainly due to decreases in the levels of critical chemical sum parameters, as was observed in the present study with regard to the TSS, COD, BOD, and AOX values, as well as to declines in the concentrations of chemical constituents (e.g., fatty and resin acids; Hall et al 1991;Kovacs et al 1994).…”

“…To circumvent this difficulty, the evaluation of the potential effects of pulp and paper mill effluents toward the environment is frequently based on chemical sum parameters and not on determinations of individual compounds (Oanh and Bengtsson 1995;Tarkpea et al 1999;Ferreira et al 2002). In this regard and with the purpose of achieving a high level of protection of the environment, the European Commission issued a Council Directive on integrated pollution prevention and control, requiring the implementation of the best available techniques to achieve environmental improvements, and establishing maximum discharge limits for key chemical parameters, namely chemical oxygen demand (COD), biological oxygen demand (BOD), adsorbable organic halogens (AOX), total suspended solids (TSS), and total phosphorus and nitrogen (EC 1991).…”

“…These changes have been particularly concerned with effluents from bleaching processes (brightening of the pulp fibers) which may contain one class of compounds of major environmental concern: chlorinated organic compounds. Efforts have focused on the replacement of elemental chlorine by chlorine dioxide (elemental chlorine-free bleaching; ECF) or by oxygen-containing compounds, such as ozone and hydrogen peroxide (totally chlorinefree bleaching; TCF; Tarkpea et al 1999;Latorre et al 2005). Also, the installation or the improvement of secondary effluent treatment plants aims at reducing AOX values, together with the levels of other parameters like BOD, COD, and TSS (Hall et al 1991;Kovacs et al 1994;Kostamo et al 2004).…”

“…Despite all the technological changes implemented to reduce toxicity, pulp and paper mill effluents continue often to present toxicity to various groups of aquatic organisms, namely bacteria (Tarkpea et al 1999), algae (Kovacs et al 1994), planktonic and benthic invertebrates (Dubé and Culp 1996;O'Connor et al 2003), and fish (Kovacs et al 2007). Moreover, a relationship between the levels of effluent parameters (e.g., AOX) and the degree of environmental impact is occasionally absent (Robinson et al 1994;Hewitt et al 2006;Latorre et al 2007).…”

“…Recent studies pointed out that further attention should be given to other compounds resulting from pulping operations, many of which are probably not yet identified (e.g., wood derivatives, additives, and their degradation products; Kostamo et al 2004;Kovacs et al 2006). Tests with a battery of organisms continue, therefore, to be a valuable tool to evaluate the toxicity of these effluents (Oanh and Bengtsson 1995;Bailey and Young 1997;Tarkpea et al 1999).…”