This paper outlines the sustainable management of the whiskey distillery by-products, known as draff and pot ale, through anaerobic digestion (AD). The substrates were pre-treated using 0.6M NaOH and high shear homogenizer for 24 h. Substrate pre-treatment helped improve the digestabilility of lignocellulosic materials towards AD. In addition, the complex cellulose, hemicellulose and lignin contents are disintegrated. A continuous stirred tank reactor with a volume of 1766 m3 and organic loading rate of 4.04 kg COD/m3/day operating under mesophilic conditions for 30 days was designed to facilitate the complete digestion of the substrates. Compared with the conventional digesters, the proposed novel pre-treatment method achieved a 20% increase in methane yield. The energy recovery potential using a combined heat and power unit can cover 24 and 42.5% of the thermal and electrical demand of the distillery, respectively. The capital cost of the proposed facility was estimated as €3.6 million with a payback period of 9.60 years. In comparison, there is a payback period of 15.13 years without the pre-treatment. Additionally, this model decreases the distillery's carbon footprint by 33%. Although the proposed design applies to the distillery in Ireland, results could be used to design distillery plants in other countries.
Keywords: Anaerobic digestion; Circular economy; Cost-benefit analysis; Process design; Sustainable biofuel.
© 2022 The Author(s).