Treatment of kraft black liquor using basidiomycete and ascomycete fungi

Abstract

The Kraft Black Liquor effluent generated by the pulp and paper industry is a highly alkaline solution with high chemical oxygen demand (COD), phenolic content, toxicity, and low biodegradability. Currently, it is usually concentrated and used as combustible in cogeneration systems. However, the profitability of this management depends on the unstable energy prices. As a possible alternative, in this work, different fungi have been used to treat this polluting wastewater. Tests were carried out at 25 ºC and 150 rpm for 10 days in a batch reactor. Two fungi capable of releasing suitable enzymes have been tested, i.e., Aspergillus uvarum and Phanerochaete chrysosporium. The effluent was treated with and without solids and with and without pH control. In all cases, the evolution of COD, biological oxygen demand (BOD5), colour index, and the concentration of reducing sugars and phenolic compounds were analysed. Besides, the enzymatic activities manganese peroxidase (MnP), lignin peroxidase (LiP), and laccase (Lac) were measured. Results showed that the presence or absence of solid did not affect the biodegradation process, achieving similar efficiencies. Bioremediation with P. chrysosporium allowed to obtain removals of COD, colour and phenolic compounds of 65 %, 37 % and 56 %, respectively, while A. uvarum achieved 61 %, 81 % and 67 %, for the best conditions tested. These results give good perspectives for application of both fungi for problematic industrial wastewaters, such as black liquor. It is especially interesting the good results obtained with A. uvarum, which has not been previously tested for the treatment of effluents from the paper industry.