Biotransformation and Partitioning of Resin Acids Within and Aerated Stabilisation Basin, 1996 Environmental Conference Proceedings

Resin acid biodegradation and biotransformation processes have been investigated in a New Zealand bleached kraft softwood pulp and paper mill aerated stabilisation basin. Influent resin acid concentrations averaged approximately 13 mg/L. Unexpectedly, treated wastewater concentrations of resin acids weren found to increase by over 150%. The major compound in the treated effluent was dehydroabietic acid. Over 40% of the total resin acid consituents were composed of a range of decarboxylated resin acid hydrocarbons, partially and fully-saturated resin acids, and oxygenated resin acids. Most of the biotransformation occurred very rapidly (within hours) in a highly active anaerobic zone at the entrance of the basin. A significant portion of the transformed resin acids were associated with suspended solids material which appeared to have been resuspended from contaminated sediments via methanogenesis. Substantial levels of resin acid derived compounds were found in basin sediments. Concentrations were in the range 5300 - 68 000 mg/kg dry weight and 24 000 - 190 000 mg/kg dry weight for neutral and acidic compounds respectively. The major sediment compounds were dehydroabietin, tetrahydroretene, pimarenic acid, isopimarenic acid, and abietanic acid. Analysis of deeper sediment cores indicated that total resin acid concentrations in aged sediments had decreased by only 53% in 30 years. Significant increases in the highly lipophilic and persistant compounds, fichtelite and retene, were observed in the older sediments.