Hydrothermal co-carbonization of sewage sludge and pinewood sawdust for nutrient-rich hydrochar production: Synergistic effects and products characterization

The aim of this study is to explore the synergistic effects of hydrothermal co-carbonization of sewage sludge and pinewood sawdust on hydrochar production. Firstly, the effects of mixing ratios on hydrothermal carbonization were investigated, and then, the hydrochar was characterized by diverse analytical techniques. The mass balance results indicated that a significant synergistic enhancement occurred in terms of the increased hydrochar yield, organic and carbon retentions. By combining sewage sludge and pinewood sawdust at the mass ratio of 1:1, 58.11 ± 0.91% of hydrochar yield was obtained with high synergistic coefficients (8.41% for hydrochar yield, 13.09% for carbon retention, and 14.92% for organics retention). The hydrochar properties of nutrients, such as nitrogen and phosphorus, and surface functional groups were improved by hydrothermal co-carbonization approach. The FT-IR spectra, CP-MAS 13C NMR and SEM results further indicated that hydrothermal co-carbonization promoted the development of aromaticity and surface structure. Our findings suggested that hydrothermal co-carbonization is a promising strategy to tailor high-performance hydrochar for different applications.