Sustainable production of lignocellulosic bioethanol towards zero waste biorefinery

This study proposes a novel process design for lignocellulosic biomass to ethanol conversion with zero waste generation. In comparison to traditional bioethanol process, the proposed new process not only produces ethanol, but also converts waste streams into high value-added by-products by undergoing multi-stage refinery steps. The feasibility the proposed process design, especially the additional waste processing, has been carried out. The results showed that co-producing by-products could significantly contribute to the profitability by decreasing the ethanol minimum viable sales price from $2.24/gal to $1.78/gal, comparing with traditionally produced bioethanol. It was also found that ethanol minimum sale price is highly sensitive to the lignin price fluctuation. The water pollution can be avoided in the proposed process due to an additional water recycling step, however, there is a trade-off between reduced water pollution and increased CO ₂ emissions when fossil fuel is used as operation energy. The results showed that, to ensure proposed bioethanol plant have environmental advantage with traditional ethanol refinery plant, the CO ₂ emission per kWh for all kinds of electricity should not be over 0.11 kg/kWh. Thus, we suggest that the proposed concept of zero-waste bioethanol plants could be established in Countries with access of sufficient renewable electricity supply.