(248av) Removal of recalcitrant aromatic organic compounds from wastewater using fungi

Humic substances (HS) are known as a product of degradation of lignin [1].   They are extremely resistant to biodegradation and their half-decay time (t1/2) can amount to thousands of years [2]. In pulp and paper industry, HS, which are being formed during the treatment of wood, cause membrane blockage and reduce the filtration flux [3]–[5]. Also HS and HS-like compounds constitute the main organic waste and aromatic content in the pulp and paper mill effluent. Therefore the discharge of these effluent can make problems to the receiving waters and environment [3], [6], [7].

White rot fungi (WRF) constitute a physiological group comprising mostly of basidiomycetous, and to a lesser extent, litter-decomposing fungi. WRF are the most abundant wood degraders in nature, which possess the unique ability of efficiently degrading lignin to CO2 [8], [9]. Thanks to WRF non-specific enzymes, they can degrade lignin and other recalcitrant compounds with molecular structure similar to lignin, like azo dyes, poly aromatic hydrocarbons, some aromatic pharmaceuticals, and humics [10], [11].

A total of 13 strains of 6 different species of White rot fungi were tested for their ability to grow on agar media containing humic acids (Fig 1). In next step, the selected strains from pre-screening in agar media, were tested in liquid phase to remove humic acid from water (Fig 2). Results showed that under sterile conditions, Phanerochaete chrysosporium, Pleurotus ostreatus and Trametes versicolor could remove 45-65% of the humics after 3 days and more than 95% after 15 days. Size exclusion chromatography and spectrophotometry measurements revealed about 85% humic removal after 17 days by Trametes versicolor. Furthermore, the absorption of HA to fungal mycelia was studied by recovering the portion of humics that has been absorbed to the fungal mycelia. Results showed between 25% to 55% recovery of humic acid, suggesting that removal mechanism of HA from water by WRF is a combination of degradation and absorption.  

Keywords: White rot fungi; Humic acid; recalcitrant organic compounds; wastewater treatment

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