Summary: | 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 (<0.5 %) of the adsorbable organic halides (AOX) in the leachates. The chlorinated
phenolic concentrations in the sludge leachates were low when compared to concentrations found
in treated effluents. Analysis of individual molecular fractions revealed the presence of low
molecular weight chlorinated phenolics and resin acids (<1000 Daltons) in the high molecular
(>1000 Daltons) weight fraction which indicated adsorption to these larger molecules.
Toxicity studies with the two bioassays revealed different sensitivities. Generally the
Microtox bioassay was more sensitive than the D.magna bioassay. The bioavailability of the
chlorinated compounds in the sludge leachates was confirmed by some high bioconcentration
factors in freshwater leeches. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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