(587n) A Model-Based Approach for Sustainability Assessment of Biomethane from Anaerobic Digestion of Food Waste and Manure Mixtures

Anaerobic digestion (AD) is a process involving a series of biological reactions (Hydrolysis, acetogenesis, acidogenesis and methanogenesis), which converts the biodegradable organic materials into biogas comprised mostly of CH₄ and CO₂. As an earlier study on lifecycle assessment of Bio-CH₄ has shown (Ankathi et al. 2017) ¹, disposal of the food waste in landfills and conventional animal manure management has significant methane emissions contributing 20% to the U.S. national total. When these wastes are managed by AD, avoiding the landfilling and conventional manure management emissions, it is estimated that life cycle greenhouse gas emissions are -3.5 kg CO₂ eq./kg Bio-CH₄. The major advantage of AD on converting the food waste and manure into Bio-CH₄ is the displacement of fossil natural gas. On full-scale application of U.S. food waste / manure, AD saves 0.74 % of current annual natural gas consumption through large-scale Bio-CH₄ production.

A model-based approach involving AD modelling and Aspen process simulation for sustainability assessment is proposed based on an existing model by Batstone et al 2002 (ADM1) ². Aspen simulation includes different unit operations for Bio-CH₄ production; mixing, heating, anaerobic digestion, membrane separations, and gas compression. This kind of approach helps to study the effect of heat integration in the process and to predict the variations in the output concentrations of AD gases based on input compositions of food waste and manure. Through this approach, the economic costs and profits and environmental impacts will be analyzed and optimized.

 References

1. Ankathi Sharath K., James S. Potter, David R. Shonnard, “Carbon footprint and energy analysis of Bio-CH₄ from a mixture of food waste and dairy manure in Denver, Colorado.” The manuscript is currently under review in Environmental Progress and Sustainable Energy. The manuscript number is EP-17-129.
2. Batstone, D. J., et al. (2002). "The IWA anaerobic digestion model no 1 (ADM1)." Water Science and Technology 45(10): 65-73.