Resistance of bound chloroguaiacols and AOX from pulp mill effluent to degradation by Trichoderma harzianum isolated from Lake Bonney, south-eastern South Australia

Abstract

Previous studies have shown that chlorophenolic compounds persisted in water and sediments of Lake Bonney, south-eastern South Australia, following discontinuation of chlorine bleaching at a sulfite pulp mill that discharged effluent into the lake. Although free and bound chlorophenolics were detected in the lake after discontinuation of chlorine bleaching, the predominant forms were found to be bound compounds. In assessing the persistence of chlorophenolics in the lake, fungi were isolated from the lake water and studied for their capacities to degrade these compounds. One fungus, Trichoderma harzianum, was found to be capable of reducing concentrations of spiked (free) 2,4,6-trichlorophenol, 4,5-dichloroguaiacol, 3,4,5-trichloroguaiacol and tetrachloroguaiacol in a mineral salts culture medium and concentrations of adsorbable halogenated organic compounds (AOX) attributable to the spiked compounds. This fungus was also found to be capable of dehalogenating free tetrachloroguaiacol in a mineral salts medium. Degradation of bound chloroguaiacols present in chlorination-stage effluent from the mill by Trichoderma harzianum was not detected in this study. The inability of this fungus to degrade bound chlorophenolics demonstrates the resistance of these compounds in bound form to biodegradation and may explain the persistence of some chlorophenolics in Lake Bonney.