Water Research 38 (2004) 972–982 Fate of wood extractives in wastewater treatment plants at kraft pulp mills and mechanical pulp mills A. Kostamo a , B. Holmbom b , J.V.K. Kukkonen a, * a Laboratory of Aquatic Ecology and Ecotoxicology, Department of Biology, University of Joensuu, PO Box 111, Joensuu 80101, Finland b Process Chemistry Group, ( Abo Akademi University, FIN-20500 Turku, Finland Received 13 May 2002; received in revised form 22 September 2003; accepted 29 October 2003 Abstract Extensive environmental effects of the forest industry led to implementation of activated sludge treatment of effluents in the 1980s. Although the existence of chlorinated compounds in the effluents has decreased, a discussion about the possible environmental effects of elemental-chlorine-free (ECF) and total-chlorine-free (TCF) bleached pulp mill effluents has arisen, and chronic effects on aquatic organisms have still been found. Recently, studies have mainly focussed on wood extractives and their role in the effects of effluents. Resin acids and unsaturated fatty acids are found to be toxic, and plant sterols are reported to have adverse endocrine effects on water organisms already at low concentrations. In this study, Finnish wastewater treatment plants of an ECF kraft pulp mill, a paper mill, and an integrated TCF kraft pulp and paper mill were sampled in order to ascertain how wastewater treatment plants, and especially activated sludge treatments, remove wood extractives. Concentrations of extractives in discharged wastewaters varied between 0.4 and 11g/t kraft or mechanical pulp, and the concentrations decreased over 95% during the treatment processes. Of the wood extractives, 1.1–64% were adsorbed to biosludge and 35–99% were degraded or transformed to other forms during the activated sludge treatment. A major part of these compounds were discharged in particles (74–99%). The removal of extractives was efficient even in the effluent treatment plant, which was highly loaded during the sampling period. r 2003 Elsevier Ltd. All rights reserved. Keywords: Wood extractives; Effluent; Activated sludge treatment; Pulp mill; Paper mill 1. Introduction In Finland, the extensive environmental effects of the pulp and paper industry led to implementation of activated sludge treatment of pulp and paper industry wastewaters in the 1980s. Biological wastewater treat- ment has reduced the COD load by 40–90% and the BOD load by over 90% [1]. The technical development of washing and bleaching methods and the regulation of water use followed by extended cooking have also substantially lowered the load from kraft pulp mills. Along with the replacement of conventional bleaching by elemental-chlorine-free (ECF) or total-chlorine-free (TCF) bleaching methods, the AOX load has decreased by 48–65% and the formation of chlorinated com- pounds has been lowered considerably [2]. Although the amounts of chlorinated compounds in the effluents have decreased significantly, discussion has arisen concerning the possible environmental effects of ECF and TCF bleached pulp mill effluents. Until now, the chronic toxicity and ecological effects of these effluents have been tested in a few studies, but the results have not been consistent [3–5]. Tana and Lehtinen [3] stated that the toxic effects are not dependent on which bleaching chemicals are used. ARTICLE IN PRESS *Corresponding author. Tel.: +358-13-251-3575; fax: +358- 13-251-3590. E-mail address: jussi.kukkonen@joensuu.fi (J.V.K. Kukkonen). 0043-1354/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2003.10.051