Effect of hydrothermal carbonization temperature and time on characteristics of bio-chars from chicken manure

Abstract: Hydrothermal carbonization is a thermochemical process for converting organic compounds into carbon-rich products, in water. It has attracted much attention as a promising large scale application, due to increasing demand for efficient biomass conversion technologies. Meanwhile, the bio-chars can be used as innovative nanometer material, adsorbent, solid fuel source and soil conditioner. The research data in literatures showed that the bio-chars as soil amendment affect soil physical, chemical, biological properties, crop production, and soil carbon sequestration. The tested feedstocks for manufacturing bio-char include poplar wood, olive residues, water hyacinth, digested maize silage, sugar beet and so on, but there has been little research on chicken manure. The main property of bio-char largely depends on the temperature and duration of hydrothermal carbonization treatment. Furthermore, bio-char properties primarily decide its application and benefits to soil, plant and environment. It is thus fundamental and necessary to investigate the bio-char characteristics prior to its application as a soil amendment. In this study, the fresh chicken manure was hydrothermally treated at 190 ℃ and 260 ℃ for 1, 6 and 12 h, respectively. The collected solid products were determined for the physical and chemical properties. The aim was to investigate the changes of properties with reaction temperature and duration. The results showed that the hydrothermal carbonization treatment led to the increases of C and P contents by more than 5% and 59%, respectively. But the process decreased of H, O, N and K contents by 9%-18%, 26%-65%, 19%-37% and 92%-97%, respectively. Both the amount of surface charge and its correlation with pH values in the medium were reduced after hydrothermal carbonization treatment. As a result, the effective cation exchange capacity was decreased by 50%-90%. Meanwhile, the hydrothermal carbonization facilitated the 1 and 100 μm pore structure development with a decrease in 1-5 μm pore volume. Overall, the higher reaction temperature and longer residence time caused greater changes in above indexes and higher degree of carbonization of bio-chars. The temperature had the larger impact on properties of bio-chars than reaction duration. In this paper, we also discussed the potential value of chicken manure bio-char as a soil conditioner. Our research result from this study can provide basic data for the application of chicken manure bio-char in improving soil fertility.