Integrating anaerobic digestion, hydrothermal liquefaction, and biomethanation within a power-to-gas framework for dairy waste management and grid decarbonization: a techno-economic assessment

Abstract

This study highlights the potential of combining energy and dairy waste management systems to maximize resource recovery and reduce dairy farming environmental impacts. A combined anaerobic digestion, hydrothermal liquefaction, and a biomethanation process system was used to generate Renewable Natural Gas (RNG). The biomethanation step is part of a Power-to-Gas (PtG) system incorporating an electrolyzer that generates hydrogen to react with carbon dioxide to produce additional RNG. A distributed system of biorefineries was utilized to evaluate the economic feasibility of producing renewable biomethane for gas pipeline injection in an effort to decarbonize New York's natural gas grid and lower environmental impacts. Considering the waste produced by 397 000 dairy cows in NY State, this distributed biorefinery system was shown to generate 22 million MJ of RNG per year. The RNG selling price, as defined by carbon credit pricing mechanisms, was found to be the most critical factor in determining economic viability. For example, using the Low Carbon Fuel Standard (LCFS) and the Renewable Fuel Standard (RFS) result in a $7 billion 20 year NPV and a competitive effective Levelized Cost of Energy (LCOE_e) of $10 per GJ.