Integrated production of hydrogen and methane in a dairy biorefinery using anaerobic digestion: Scale-up, economic and risk analyses

Abstract

Anaerobic digestion has emerged as the most appealing waste management strategy in biorefineries. Particularly, recent studies have highlighted the energy advantages of waste co-digestion in industrial biorefineries and the use of two-stage systems. However, there are some concerns about moving the system from laboratory testing to industrial scale. One of them is the high level of investment that is required. Therefore, this study carried out a techno-economic analysis (scale-up and energy production, economic and risk analysis, and factorial design) to assess the feasibility of single- and two-stage systems in the treatment of cheese whey and glycerin for the production of hydrogen and methane. Scenarios (S1 to S9) considered thermophilic and mesophilic single and two-stage systems with different applied organic loading rates (OLRA). The analyses of scale-up and energy production revealed that S3 (a thermophilic single-stage system operated at high OLRA 17.3 kg-COD.m−3.d−1) and S9 (a thermophilic-mesophilic two-stage system operated at high OLRA 134.8 kg-COD.m−3.d−1 and 20.5 kg-COD.m−3.d−1, respectively) were more compact and required lower initial investment compared to other scenarios. The risk analysis performed by a Monte Carlo simulation showed low investment risks (10 and 11%) for S3 and S9, respectively, being the electricity sales price, the key determining factor to define whether the project in the baseline scenario will result in profit or loss. Lastly, the factorial design revealed that while the net present value (NPV) is positively impacted by rising inflation and electricity sales price, it is negatively impacted by rising capitalization rate. Such assessments assist in making decisions regarding which system can be fully implemented, the best market circumstances for the investment, and how market changes may favorably or unfavorably affect the NPV and the internal rate of return (IRR).