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Characterization and toxicity of pulp and paper mill sludge leachates Perera, Dharshini Marian

Abstract

The main objective of this study was to investigate the characteristics of pulp and paper mill sludge leachates and to assess their toxicity. Sludges from three mills in British Columbia were subjected to aqueous leaching in laboratory columns at different pH levels to evaluate the relationship between leachability of the contaminants and pH. Leachates were fractionated by ultrafiltration into different molecular size fractions and the leachable contaminants were characterized for carbon content, colour and fluorescence properties, chlorinated phenolics, resin acids, metals and AOX content. The toxicity of the leachates was assessed by conducting laboratory bioassays on Daphnia magna and using the Microtox bioassay. The bioconcentration potential of the chlorinated phenolic compounds was measured using fresh water leeches. Leachates were also collected from sludge previously applied to a test site and analyzed for characteristics and toxicity to investigate the feasibility of applying pulp and paper mill sludge to forest land as an organic fertilizer. Leachability of carbon varied considerably between sludge leachates from different mills. The soluble carbon content of subsamples of the same sludge leachate varied between one to another, indicating the highly variable nature of these sludge leachates. Leachates of different molecular size fractions had different colour and fluorescence properties. No consistent relationship was found between the carbon distribution in the fractions and colour or fluorescence suggesting that colour or fluorescence cannot be used as an estimate of the total dissolved carbon or the predominance of any molecular size fraction in a sludge leachate. Leachability of contaminants was affected by pH. Generally the total concentration of chlorinated phenolics and resin acids increased with increasing pH for sludge leachates for all the mills. At higher pH’s, there was a tendency for the chlorinated phenolics with the lower chlorination number to leach out more. The identifiable chlorinated phenolics were a very small percentage (

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