The Effects of Domestic Septage Derived Hydrochar on Brassica oleracea and SoilGreenhouse Gas Responses

In the United States, a majority of the nutrients applied to crops come from unsustainablesources that have human and environmental health consequences. Alternative sources ofnutrients that are more sustainable with fewer negative impacts are needed to improvecurrent food systems. Hydrothermal carbonization is a technology that could be used totransform organic wastes into agriculturally useful materials. Hydrochar, the end productof hydrothermal carbonization, is a nutrient rich product that has the potential to be aslow-release fertilizer. The purpose of this study is to investigate the effects of septagederived hydrochar fertilization on soil responses, plant responses, and soil GHGresponses and to evaluate the potential nutrient availability in wastes for Ohio. A potstudy was completed to evaluate the response of kale to hydrochar fertilization at twodifferent application rates (10g N-eq hydrochar m-2 (H10), 20 g N-eq hydrochar m-2 (H20)) compared to synthetic fertilizer with N and P (dosage equivalent to the 10g N-eqhydrochar m-2 group) sourced from urea and triple super phosphate in two different soiltypes. Soil responses were evaluated at the end of the growing period. A soil incubationexperiment was done over six months to evaluate the changes in soil GHG responses overtime after hydrochar additions (10g N-eq of hydrochar applied) in three soil types. Kalebiomass significantly increased with increasing hydrochar doses, with the highest percentdifferences being 96% and 84% in the H10 and H20 groups respectively of the field soiltype. All plant and soil responses were positively impacted by hydrochar or hydrocharhad no significant effect. Soil GHG responses were not different from the control bymonth three of the incubation, and only CO2 emissions were ever significantly differentfrom the control. The nutrients in waste inventory revealed that 17% of Ohio’sagricultural N demand and 24% of Ohio’s agricultural P demand could be met from justnutrients found in sewage sludge if all nutrients were utilized and processed viahydrothermal carbonization. Additionally, the GHG emissions from producing nutrientsfrom hydrochar instead of sourcing nutrients from synthetic fertilizers reduced GHGemissions by an estimated 84.7% for N production and 77.6% for P production. Wastesturned to hydrochar is a potential avenue for utilizing currently unused nutrients to meet aportion of agricultural nutrient needs in the United States.