Technoeconomic analysis of an integrated camelina straw-based pellet and ethanol production system†

This study proposes an innovative biorefinery concept, integrating microbial pretreatment (MBP), wet storage (WS), and mushroom cultivation to transform herbaceous biomass into high-value products, including biofuel pellets, Turkey tail mushrooms, and ethanol. This environmentally friendly approach reduces pretreatment times, economically delignifies lignocellulosic structures, and improves the durability and enzymatic digestibility of densified pellets. The biorefinery model includes five pellet-mushroom production facilities (Pellet Plant A) and one ethanol plant (Ethanol Plant A), strategically located approximately 140 km south of Saskatoon (50°53′16.1′′N, 106°42′15.5′′W) in the province of Saskatchewan, Canada, to minimize pellet transport distances. Pellet Plant A, with a capacity of 250 000 t per year, incurs unit production costs (UPC) of US$201–242 per t, primarily driven by the cost of fungal liquid inoculum preparation. These costs exceed those of conventional steam-explosion pellet plants, such as natural gas-fired (US$181 per t) and biomass-fired systems (US$166 per t). Consequently, ethanol produced at Ethanol Plant A, using these pellets, costs US$1.32 per L, compared to US$0.89 per L for centralized MBP straw bales-to-ethanol plants and US$0.57 per L for conventional dilute acid pretreatment plants. The economic viability of this biorefinery concept requires a minimum ethanol selling price (MESP) of US$1.03 per L and at least 50% farmer participation to achieve a positive net present value (NPV) without mushroom credits. However, integrating revenue from Turkey tail mushroom production significantly enhances financial outcomes, increasing Pellet Plant A's NPV by up to US$10 billion. This enables a reduction in pellet selling prices, lowering the MESP to US$0.77 per L with a pellet purchasing cost of US$100 per t. These findings demonstrate the economic feasibility and sustainability of this innovative biorefinery model, emphasizing the potential of combining microbial pretreatment technologies with diversified revenue streams.