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ABSTRACT: Most North American pulp and paper mills now biologically treat (biotreat) their liquid effluent. However, treated water still contains effluent-derived recalcitrant organic material (EROM), measured as chemical oxygen demand (COD), for which emission limits exist in Europe and are being considered in the U.S. Production of microbially resistant, dissolved natural organic material (NOM) typically found in Canadian stream and lake waters occurs slowly under gentle conditions, while mill EROM is generated from lignocellulosics by faster and harsher processes. Similarity of the environmental effects of NOM and pulp and paper mill EROM are examined. Changes occurring over 4 months in biologically treated effluent from two modern Canadian mills and lake NOM when sealed in gas- and light-permeable bags and placed in a pristine Quebec lake are reported. Addition of microbial co-metabolites significantly improved the dark mineralization of organochlorines surviving mill biological treatment. Mill EROM was light sensitive, nonacutely toxic in the Microtox assay, and similar to NOM in the surrounding lake in most bulk properties. There was no evidence to suggest that placing specific limits on mill EROM (COD) emissions would be environmentally beneficial. Water Environ. Res., 70, 1314 (1998).
KEYWORDS: chlorolignins, adsorbable organic halogens, chemical oxygen demand, kraft mills, newsprint mills, recalcitrant organic compounds.
Objective
In recent years, environmental concerns and increasingly stringent governmental regulations have prompted Canadian mills to greatly improve the environmental compatibility of their effluent. These improvements are the result of a variety of in-- mill process and equipment changes, especially in kraft bleachery (Annergren et al., 1987; Berry et al., 1991, Liebergott et al., 1993; and Luthe et al., 1992) and from installation of secondary (biological) effluent treatment at most mills in Canada. Secondary biological treatment typically removes all acute effluent toxicity, more than 90% of the 5-day biochemical oxygen demand (BOD^sub 5^) and 30 to 60% of the total adsorbable organic halogen (AOX). With the exception of bulk biologically treated AOX (Fisher et al., 1996), all of the effluent characteristics presently regulated, (total suspended solids [TSS], BOD^sub 5^, acute toxicity, chlorophenols, furans and dioxins, fixed nitrogen and phosphorus, and chlorate ions and chloroform) have been shown to have negative effects on receiving water communities or particular organisms; that is, there are sound scientific rationales for their regulation.
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