Comparison study of carbon rich products under thermal carbonization and hydrothermal carbonization on their characteristics, greenhouse gas emission, and tomato growth.

Carbon-rich products from pyrolysis (pyrochars) and hydrothermal carbonization (HTC, hydrochars) have been proposed as soil amendments to mitigate greenhouse gas emissions and increase production. This research compared the amendment impact of two different types of biochars on GHG emissions in tomato production and their major functional characteristics. Fluxes of CO₂, CH₄, and N₂O were measured in the tomato growing pots using a manual static chamber method during the tomato growing season. The temperature and soil moisture were measured continuously using sensor pups, and the results were transferred to a data retriever. The collected gas samples were analyzed using a gas chromatograph (model 8610C, SRI Instruments). Nitrous oxide was detected with the electron capture detector (ECD) operated at 325°C, and CO₂ and CH₄ were measured with a mechanized interface with a îame ionization detector (FID). These results demonstrate that pyrochar application significantly decreased N₂O emission compared to the emission from the control treatment. We observed that two different soil amendments did not substantially improve tomato production. This study also focuses on comparing the occurrence of 16 PAHs regulated by the US EPA in 22 char samples. Results showed that the sum of the 16 EPA PAHs in all samples was well below the requirements in the two standards, except for a pyrochar produced at the farm scale. They ranged from 131 to 9358 µg·kg^-1 in the seven pyrochars and from not detected to 333 µg·kg^-1 for the fourteen hydrochars. Our findings indicate that hydrochar produced via hydrothermal methods exhibits much lower concentrations and toxicity of the 16 PAHs regulated by the US EPA than pyrochars, making them a potentially safer option for soil amendment and environmental applications.