Coupling biorefinery and biogas production from maize stover by enhancing the ensiling process: Role of the carbon/nitrogen ratio and buffer capacity

Compared with the traditional ensiling-biogas process, a novel ensiling-biorefinery-biogas process may increase the profit of straw biogas plants by mechanically recycling the value-added ensiling fermentation products. And it could be more profitable from enhanced ensiling fermentation products and specific methane yield via efficient ensiling regulation. This study investigated the role of the carbon/nitrogen (C/N) ratio and buffer capacity during the ensiling process for coupling biorefinery and biogas production, where maize stover was ensiled for 360 d at an initial C/N ratio of 25:1 by urea with a buffer capacity of 100–160 g lactic-acid/kg dry matter by CaCO3. In the ensiling process, the optimized C/N ratio enhanced lactic acid and acetic acid production, with an increased abundance of lactic-acid-producing bacteria (Lactobacillus). However, ∼50 g butyric acid/kg dry matter was produced with the assistance of CaCO3. Based on the role of synergetic regulation using urea and CaCO3, mechanically recovered raw biorefinery products were increased by 65–78%, and the silages’ specific methane yield was increased by ∼24%, which improved profits by up to 351 CNY/t stover by coupling biorefinery and biogas production, as compared with the profit increase during the traditional process of 36 CNY/t. Efficient ensiling enhancing and biorefinery product separation technologies are required for commercial application.