High quality hydro-char production through co-hydrothermal treatment of sewage sludge and wheat straw: novel properties

Co-hydrothermal carbonization (Co-HTC) of sewage sludge (SS) with wheat straw (WS) has emerged as a promising method for producing high quality biochar products through the utilization of low-cost biomass resources. The objective of this study was to investigate the physico-chemical properties of hydro-char derived from the Co-HTC treatment of the mixture of SS and WS at different Co-HTC temperatures (200, 240, and 280 degrees C). The research findings indicated that the inclusion of WS in the Co-HTC process positively influenced the properties of the hydro-char and higher Co-HTC temperatures enhanced this trend. It is revealed that the hydro-char produced at 280 degrees C exhibits the biggest surface area, abundance of micropore structures, and the highest electron accepting capacity (EAC = 0.4389 mol(-)/g(hydor-char)). Moreover, when increasing the Co-HTC temperature from 200 to 240 degrees C, the higher degree of aromatization (H/C = 1.1170 (atomic ratio)) can be achieved, which correlates with the electron donating capacity (EDC = 0.7358 mol(-)/g(hydor-char)). For the secondary dissolution of organic substances leaching from hydro-chars, the blending of SS and of WS can significantly enhance the content of aromatic protein II, with marginal impact on humic acid. Furthermore, the Co-HTC process proved effective in immobilizing heavy metals during the treatment. All of the improved properties facilitate the SW hydro-chars to be used as promoters in anerobic digestion system.