Batch and continuous anaerobic toxicity of resin acids from chemithermomechanical pulp wastewater

Abstract

Chemithermomechanical pulp (CTMP) wastewaters are being treated anaerobically, in full scale operations, in spite of the presence of inhibitory compounds. These compounds are neither well identified nor are they placed in an order of priority in terms of inhibition to anaerobic bacteria. In this study batch anaerobic toxicity assays were used to quantify the relative toxicity of resin acids to the total toxicity in hydrogen peroxide bleached CTMP (BCTMP) wastewater. Resin acids are partitioned between the soluble wastewater and the insoluble fiber fractions. Therefore fiber toxicity was also compared to raw BCTMP wastewater toxicity. Resin acids were found to be toxic to anaerobic bacteria but were not found to be responsible for all the toxicity in BCTMP effluents. Toxicity associated with the fiber was soluble in methanol. The bulk of the fiber which was not methanol soluble exhibited no toxicity to the anaerobic cultures used. Batch results were compared to continuous toxicity assays using an upflow anaerobic sludge blanket reactor. The continuous reactor was relatively unaffected by short term or long term exposure to resin acids at concentrations that invoked inhibition in batch tests. Inferences from these tests indicated that batch results may be unreliable when applied to continuous systems.