Techno-Economic Analysis of Enzyme Supplementation in Anaerobic Digestion : A Case Study of Dairy Cow Farm

Sammanfattning

This study investigates the effects of enzyme supplementation on the technical, economic, and environmental performance of a full-scale anaerobic digester operating on liquid dairy cow manure. Given the limited biogas yields caused by manure’s high lignocellulosic content, enzyme dosing presents a promising solution—though evidence under mono-digestion conditions remains scarce. To address this gap, a three-month enzyme trial is conducted, building on a two-year operational baseline. The study analyzed biogas production, parasitic energy use, and process stability, as well as techno-economic and environmental performance under combined heat and power and biogas upgrading scenarios. The study reveals that enzymes increased biogas production on average by approximately 13% without compromising digester stability or altering methane content. The potential impact on this improvement is proven with economic sensitivity analysis identifying the efficiency of converting feedstock into biogas as a key driver of economic viability, alongside capital expenditures and energy electricity and biomethane) sales prices, highlighting the potential of technologies such as enzyme dosing. Translating the observed biogas gains and enzyme costs into economic terms resulted in favorable cost-benefit ratios of 2.18 for the CHP pathway and 2.60 for biogas upgrading, indicating strong improvements in plant performance. Further, Monte Carlo simulations incorporating probabilistic distributions of biogas yields before and after enzyme supplementation confirmed robust performance gains: NPV increased by 13% (from 465.497€ to 524,354 €) in the CHP scenario and 15% (from 698,235 € to 804,678 €) in the upgrading scenario; IRR improved by 0.4 and 0.5 percentage points, respectively; LCOE decreased by 2.95% (from 0.1256 €/Kwh to 0.1219 €/kwh) and 3.1% (from 0.5193 €/Nm3 to 0.5032 €/Nm3 ); and Payback Periods shortened by 0.22 and 0.24 year. Environmentally, enzyme use led to additional greenhouse gas emission avoidance: +56.72 t CO2eq (+2.4%, CHP) and +75.56 t CO2eq (+3.1%, Upgrading). These results in a real case scenario offer valuable insights for farmers, technology developers, investors, and policymakers aiming to enhance the sustainability and profitability of biogas projects.