The methanogenic toxicity of wood resin constituents

The purpose of this study was to evaluate the inhibitory effect of representative wood resin compounds on the activity of methanogenic bacteria. Resin is by definition the mixture of wood components that are extractable with apolar solvents. Major resin constituents are long-chain fatty acids, terpenes, resin acids, lignans and apolar phenols. The methanogenic inhibition was determined at a temperature of 30°C in standardized toxicity assays utilizing anaerobic granular sludge. An apolar phenol, 4-hydroxystilbene, was the most toxic of the compounds studied, with a 50% inhibiting concentration of 20 mg/litre. Resin acids and volatile terpenes were also highly toxic to methanogenic activity. Concentrations causing 50% inhibition ranged from 43 to 330 mg/litre. In contrast, triterpenes were non-toxic at relatively high concentrations, 1000–1300 mg/litre. These results suggest that wood resin constituents play an important role in the anaerobic inhibition exerted by several forest industry wastewaters.