|Jackson, Michael - Mike|
|Compton, David - Dave|
|BERGE, NICOLE - University Of South Carolina|
Submitted to: Sustainability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2022
Publication Date: 4/22/2022
Citation: Ro, K.S., Jackson, M.A., Szogi, A.A., Compton, D.L., Moser, B.R., Berge, N.D. 2022. Sub- and near-critical hydrothermal carbonization of animal manures. Sustainability. 14(9), 5052. https://doi.org/10.3390/su14095052.
Interpretive Summary: Hydrothermal carbonization (HTC) is a process that uses water as the reaction medium to convert wet organic residues and wastes to a carbon-rich solid product called hydrochar. The hydrochar is used as a fossil coal alternative, soil amendment to improve soil quality, and increase soil carbon. It can also be used as adsorbents to remove pollutants from water or gases. When applied as a soil amendment, hydrochar is relatively unstable in soil for carbon sequestration because of its high content of volatile matter. To produce hydrochar with less volatile matter (VM) and more fixed carbon (FC) capacity, this study compared the hydrothermal carbonization of hen (HM) and swine (SM) manures at a typical HTC temperature of 210 oC to that of the slightly supercritical temperature (i.e., temperature > 374 degree Celsius, °C) of 400 °C. Physico-chemical properties of hydrochar, gaseous and liquid products were evaluated. As expected, both VM and yield decreased with temperature. The HTC reactions were exothermic. The fixed carbon (FC) increased almost twice. At the same time, the volatile matter (VM) significantly decreased, suggesting the high potential of producing more stable hydrochar at 400 °C. Additional work is still needed before recommendations on carbonization temperatures can be made.
Technical Abstract: Animal-manure-derived hydrochars improve soil fertility by providing abundant nutrients and reducing water polluting potential from nutrient leaching. However, hydrochars are relatively unstable in soils, reducing their carbon sequestration potential compared to pyrochar made from dry pyrolysis. To produce hydrochar with less volatile matter (VM) and more fixed carbon (FC) to increase its stability, this study compared the hydrothermal carbonization (HTC) of hen (HM) and swine (SM) manures at typical HTC sub-critical temperature of 210 degree Celsius (°C) and slightly super-critical temperature of 400 °C. Physico-chemical properties such as proximate, ultimate, Brunauer-Emmett-Teller (BET) surface area, higher heating value (HHV), chemical oxygen demand (COD), and inorganic nutrients of hydrochar, gaseous and liquid products were determined. As expected, both VM and yield decreased with temperature. The heats of HTC reactions were estimated to be exothermic, ranging from -5.7 to -8.6 MJ/kg. The FC approximately doubled while VM significantly decreased with a yield of 42.7 %, suggesting the high potential of producing more stable hydrochar via near-critical HTC (NCHTC) treatment of SM. Additional work is needed before recommendations on carbonization temperatures can be made. Specifically, there is a need to experimentally investigate how the chars produced from each carbonization condition influences plant growth and soil emissions.