Co-hydrothermal carbonization of swine manure and lignocellulosic waste: A new strategy for the integral valorization of biomass wastes

Abstract

Co-hydrothermal carbonization (co-HTC) is a promising strategy to improve hydrothermal carbonization (HTC) of low-quality wastes. HTC of swine manure (SM), with high N (2.9 wt%), S (0.7 wt%) and ash (22.6 wt%) contents, as well as low C (35.6 wt%) and higher heating value (HHV; 14.3 MJ kg−1), resulted in a hydrochar with unsuitable characteristics as a solid fuel. Co-HTC of SM and garden and park waste (GPW) improved hydrochar properties (C content (43 – 48 wt%) and HHV (18 – 20 MJ kg−1), and decreased N (∼2 wt%), S (<0.3 wt%) and ash (<15 wt%) content. A high GPW ratio (>50 wt%) during co-HTC resulted in a hydrochar similar to that obtained from GPW. The co-HTC increased nutrient migration to the process water, which allowed the precipitation of salt with high P (7.8 wt%) and negligible heavy metal content. Anaerobic digestion of co-HTC process water allowed high organic matter removal (up to 65%), and methane production (315 – 325 mL CH4 g-1CODadded). Gross energy recovery by HTC and anaerobic digestion was 5 – 6-fold higher than anaerobic treatment of feedstocks. Therefore, co-HTC of SM and GPW with a ratio > 50% GPW proved to be a suitable approach to valorize and manage SM and obtain value-added products (hydrochar, mineral fertilizer and methane).