Techno-Economic Analysis of Onion Waste Biorefinery Framework

Abstract

Onion waste contains valuable nutrients but is often discarded, harming the environment. This study presents a techno-economic analysis of an onion-waste-integrated biorefinery framework using process simulation. Integrated system combining AD, HTL, CHP was simulated in Aspen Plus® v14.1 at a feed rate of 1000 kg h -1 with a water-to-onion ratio of 10:1. Under mesophilic (37 °C) and thermophilic (55 °C) AD conditions, the system generated 550 L kg -1 VS of biogas containing 95 % CH 4 with an energy content of 17.5 MJ kg -1 . HTL of digestate produced 23 wt% biocrude, 18 wt% biochar, and nutrient-rich process water, with the biofertilizer containing 4.1% N, 1.8% P, and 3.5% K. The integrated system achieved 85 % energy recovery and >90 % carbon utilization, with CHP supplying 80 % of process heat. Techno-economic analysis estimated CAPEX USD 2.86 M, OPEX USD 0.68 M, NPV USD 8.7 M, IRR 16.8 %, PI= 2.28 % and payback 6.1 yr. The MSP of biomethane was determined as 0.45 USD Nm -3 using a system-level break-even approach with co-product credits. This study demonstrates a sustainable, scalable strategy for onion waste management that supports circular bioeconomy principles and contributes to UN SDGs 7 (clean energy), 12 (responsible production), and 13 (climate action).