Biological Post-Treatment of Anaerobically-Treated Black Liquor Spills from Kraft Pulp-Mill

Previous research has shown that anaerobic treatment in biological fluidized bed reactors of kraft black liquor spills effluents (DL) is an effective alternative. However, important concentrations of recalcitrant organic matter and color still remain in the anaerobic effluent (AnE). Aerobic bacterial post-treatment was ineffective, while adsorption onto activated carbon removed both color and organic matter, but at potentially unfeasible costs.

The purpose of this work was to evaluate the post-treatment of the AnE by the application of selected ligninolytic fungi strains under a variety of experimental conditions. A factorial experiment 2³×3 with repetition was planned, the factors being: fungal strain (2 levels, Lentinus edodes, L.e., and Trametes versicolor, and T.v.); effluent concentration (2 levels, 50% and 100% v/v); carbon source supplementation (2 levels, 0.0 and 0.5 g/L glucose), and fungus immobilization (none, alginate, and activated carbon). The experimental responses were the net specific removals of color (1/mg biomass) and ligninoid substances (g lignin/mg biomass) discounted for adsorptive removal.

It was found that L.e. effected significantly higher color and ligninoid removals (0.008 1/mg and 0.012 g lg/mg biomass) than T.v. Interestingly, whole AnE (100% concentration) resulted in higher responses (approximately 0.011 1/mg and 0.011 g lg/mg biomass) than dilute effluent (50%). Glucose supplementation at 0.5 g did not have a conclusive effect: supplemented flasks showed a slightly higher ligninoid reduction than the nonsupplemented, but the color removal was significantly lower than the corresponding to nonsupplemented flasks. Fungi immobilization on alginate showed the highest pollutant removals (0.012 1/mg and 0.012 g lg/mg biomass). Free mycelium was second, while immobilization on activated carbon was last. Overall, the best color and recalcitrant organic matter removals were obtained for Lentinus edodes, whole AnE, no carbon-source supplementation, and fungus immobilizaton on alginate.