Comparison of Chemical Composition and Toxicity of Wastewaters from Pulp Industry
Abstract : Wastewaters from different pulp-making processes contain various organic and inorganic compounds : wood-derived, process chemicals and compounds generated during the reactions between the chemicals and raw materials.
Carbohydrates and lignin-derived compounds constitute the main groups of components that cause oxygen demand in wastewater (COD), but they have rather low toxicity. Among all wood-derived compounds, resin acids (e.g. abietic acid, dehydroabietic acid) are generally recognised as the main source of acute toxicity in pulp and paper industry effluents. A review of studies on toxicity of resin acids has shown that the acute lethal concentration of individual acids for fish (rainbow trout and salmon) is around 0.4-1 mg/l. The lowest sublethal concentration of dehydroabietic acid (DHAA) has been reported to be between 5 and 20 mg/l (rainbow trout - inhibition of enzyme conjugation and bile acid uptake). Unsaturated fatty acids are also present in wastewaters but their contribution to toxicity is less than that of resin acids.
In this study the concentration of toxic compounds (resin and fatty acids, chlororesin acids, phenolic and chlorophenolic compounds) in wastewaters from pulping, recovery of chemicals and bleaching processes have been determined. The chemical composition of influents and effluents of biological treatment plants were also studied. Five microbiotests : Microtox, Spirotox, Protoxkit F™, Rotoxkit F™ and Thamnotoxkit F™ were used to assess the toxicity of the wastewater streams mentioned above. The Microtox test was the most sensitive microbiotest from the battery applied, but the toxicity values were not correlated with the concentrations of the pollutants analyzed. The other tests in turn had L(E)C50s which correlated better with the toxicity equivalency units (TEUs).