Investigation of optimal blending of livestock manures to produce biocrude via hydrothermal liquefaction

Livestock manure is one of the most abundant agro-wastes worldwide. Most of the manures are landfilled or composted to produce fertilizers, which raises concerns associated with the possible pollution of air and contamination of groundwater. Meanwhile, Hydrothermal liquefaction (HTL) is attracting growing attention to valorise wet wastes as an alternative to anaerobic digestion to produce value-added energy products. Livestock manures differ in terms of their composition, availability, and cost; therefore, an optimal blending of multiple livestock manures for liquefaction is expected to yield biocrude with distinct properties and contribute to process efficiency improvement. As such, this study evaluates the effect of different blending ratios of five typical livestock manures on the yield of biocrude and biochar, as well as the process environmental burden in terms of water consumption and CO₂ emissions. Aspen Plus® software is used to simulate the liquefaction process and to develop a mathematical optimization model to determine the optimal blending scenarios that satisfy adopted technical and environmental preferences. A weighted normalised decision metric is then used to minimise the gap between the solutions for the multiple objectives. The model suggested the optimal manures blend to be (50%, 26%, 14%, 5%, 5%) for cattle, camel, horse, poultry, and sheep manures, respectively. This study provides an insight into enhancing HTL process efficiencies through a careful selection of feedstock blends.