Synergies during hydrothermal liquefaction of cow manure and wheat straw

Abstract

Agribusiness crop and animal residues constitute some of the major waste streams worldwide. Among them, wheat straw and cow manure are large contributors to the quantities generated. Both materials can be converted using hydrothermal liquefaction (HTL) for recovery of biocrude and here we investigate how combined HTL processing can be of great interest to boost biocrude production and carbon recovery. This study presents batch HTL experiments using individual and blended feedstock mixtures to build predictive models for biocrude, carbon and energy recovery. These models are validated using a continuous HTL pilot plant. The combined approach led to the nitrogen-containing compounds present in cow manure to react with lignocellulosic-derived compounds from wheat straw and divert carbon into the oil phase, the reason for which biocrude, carbon and energy yields were drastically improved. Continuous HTL pilot plant campaigns successfully demonstrated increased carbon yields from 40% to 60% when using optimal feedstock ratios. Continuous data also shows the great benefits of increasing the organic matter concentration input with combined processing, resulting in total energy efficiencies larger than 50% and energy return over investment of 2.6, compared to 1.3–1.9 for individual feedstock processing.