Soil and Environmental Applications of Hydrochar.

Hydrothermally carbonizing surplus animal manures from concentrated animal feeding operations (CAFOs) may become a viable manure management alternative. Hydrothermal carbonization (HTC) not only provides environmentally acceptable manure treatment, but it may also bring potential income revenues to farmers from producing nutrient-rich hydrochar.  Emerging compounds, such as pharmaceuticals, personal care products, and endocrine disrupting compounds posing significant environmental concerns in animal wastes, landfills, and wastewater may be thermally degraded/transformed under autoclaving conditions of HTC. Although there exist numerous research studies in the literature on soil and environmental applications using plant-based biochar made from traditional dry pyrolysis (hereafter referred as pyrochar), a very few such studies exist for hydrochar made from hydrothermally carbonizing animal manures. The objective of this study is to investigate greenhouse gas emission and groundwater pollution potentials of the swine hydrochar when used as a soil amendment.

Swine hydrochar was prepared by hydrothermally carbonizing the swine solids at 250 ^oC for 20 h. Some of the hydrochars were washed with 200 mL acetone for 2 hours in order to remove labile compounds accumulated on the hydrochar surface. Hydrochar or pyrochar was mixed with a 50/50 mixture of Norfolk Ap and E horizon at a rate of 20 g kg^-1. Sufficient deionized H₂0 was added periodically so that each pot would be maintained at 10 % moisture content (w/w).  Triplicate pots containing soil without biochar served as controls.   During the incubation periods of 42 to 127 days, greenhouse gas (CO₂ and N₂O) emission fluxes were measured by nonlinearly regressing time-series headspace gas concentrations.  

Mehlich 1 extraction of the initial soils amended with hydrochar showed significant increase in nutrients such as K, P, Ca, Mg, Zn and Mn.  Surprisingly, the hyrochar-amended soils leached very little of these nutrients probably due to complex surface functionalities binding these nutrients. Addition of swine solid hydrochar increased soil CO₂ emission; however, N₂O emission was repressed.