Fungal Pretreatment of Willow Sawdust with Abortiporus biennis for Anaerobic Digestion: Impact of an External Nitrogen Source

In this study the effect of nitrogen (N) supplementation in the fungal pretreatment of willow sawdust (WSD) via the white rot fungus Abortiporus biennis (A. biennis) was studied in terms of the fractionation of lignocellulosic biomass and biochemical methane potential (BMP). Thus, different external nitrogen sources (yeast extract (YE), urea (UR), and ammonium nitrate (AN)) at different ratios (N/C of 1/250 and 1/50) were added and the effect of the above parameters on the chemical composition of WSD during solid-state fermentation (SSF) experiments with A. biennis was assessed and compared to the experiment of fungal pretreatment without N supplementation (N/C was 1/500, control experiment). The results indicated that the addition of an external nitrogen source did not facilitate delignification, regardless of the type of nitrogen source and the ratio of N/C used. On the other hand, enhanced cellulose uptake was observed. Samples of the 28th day of cultivation, with and without N supplementation, were used for BMP tests, where a reduction in methane yield was observed, compared to the control experiment. In addition, a combination of fungal with alkali (20% NaOH w/w dry mass) pretreatment was performed in order to assess the effect of combined pretreatment on the lignocellulosic content and the BMP.