Techno-economic Analysis for the Valorization of Palm Kernel Shell via Hydrothermal Carbonization and Anaerobic Digestion

This project addresses implementing a plant to produce adsorbents via hydrothermal carbonization (HTC) and anaerobic digestion (AD) of the spent liquors made after the HTC process. Since some of the organic compounds in the spent liquors can be transformed into biogas and fertilizer after biological treatment, the latter can also be commercialized. In 2022, Ecuador’s palm oil extraction industry produced 68,000 tons of palm kernel shells (PKSs). In most cases, PKS is disposed of in landfills, or even worse, it is involved in stubble burning, critically affecting air quality. In this context, a circular strategy for PKS valorization is proposed in this work. First, the aim is to evaluate the feasibility of producing a porous/functionalized adsorbent material (i.e., hydrochar) from the HTC process, including an annual production of 1259 tons. This hydrochar-based adsorbent is prepared for dye adsorption for textile wastewater treatment. On the other hand, yearly production values of 6233 and 25,803 tons are proposed for biogas and fertilizer, respectively. After the process design, including mass balance, equipment design and selection, and a simulation for the AD process, the plant was economically evaluated, resulting in a profitable project to be implemented at an industrial scale. Based on these findings, it can be suggested that the biorefinery concept represents a valuable approach for contributing to the circular economy toward agricultural waste valorization, not only in wastewater treatment using hydrochar but for soil amendment for the fertilizer case, and even better for renewable energies in the case of biogas production.