Waste to Worth: A Case Study of the Biogas Circular Economy in Pennsylvania

Abstract

Highlights The case study farm produces 66% of its biogas from off-farm food waste sources, highlighting the potential to increase the circularity of food and agricultural systems when farms capture and recycle external waste sources. The farm can meet 78% of its crop nitrogen needs from waste products recycled in digestion, assuming a 37% nitrogen use efficiency (NUE). However, phosphorus in the imported food waste creates an excess relative to crop needs. The farm creates an excess of energy that is returned to the electric grid, providing broader off-farm benefits through a circular economy approach. Widespread commercial implementation of circular economy principles in the U.S. dairy sector requires more measured data about how farms successfully implement circularity within the constraints of market incentives and farm operations. Abstract. Coupling agricultural production with sustainable bioenergy systems may help us improve the circular economy of the food system and work within planetary boundaries for climate stabilization. However, leading sustainable dairies often do not have data to support that claim. As a result, practical case studies of circular economies with measured data from commercially operating farms are lacking in the literature, which is instead dominated by hypothetical and theoretical analyses. To grow and scale commercial implementation of circular economy and sustainability principles, it is important to understand how commercial farms implement these principles within the constraints of market incentives and actual farm operations. We conducted a case study of a commercial dairy farm in Pennsylvania, where a well-managed anaerobic digester system serves as the basis for a circular farm economy and allows the next generation to grow the farm business and expand the portfolio of revenue streams. The farm recycles food and agricultural waste into heat, renewable electricity, and fertilizer to heat and power the farm, amend the soil, and reduce farm costs. We also highlight the potential to scale the case study farm's circular economy approach in Pennsylvania using the state's projected 2030 manure, corn stover, winter double crops, switchgrass, and food waste resources to produce energy via biogas or renewable natural gas (RNG). We estimate the state could generate 40 million MJ annually from such integrated anaerobic digestion systems, meeting 3% of its electricity consumption. Circular economies like this case study can be designed in food and agricultural systems to operate within the constraints of an operating farm and recycle waste, produce nitrogen- and phosphorus-rich soil amendments and reduce imports of synthetic fertilizers, reduce and offset fossil energy consumption and greenhouse gas emissions associated with crop and livestock production, regenerate natural ecosystems, help ensure agricultural resilience and sustainability, and provide economic benefits. Keywords: Anaerobic digestion, Biogas, Circular economy, Digestate, Food waste.