Evaluating the environmental impact of hydrothermal cracking solid organic fertilizer: Carbon and nitrogen retention...

Hydrothermal cracking converts biomass waste into superior organic fertilizer by hydrolyzing it at temperatures of 180-220 °C and pressures of 1.5-2.45 MPa, enhancing treatment efficiency and nutritional value. Most of the research on hydrothermal cracking solid organic fertilizer (HCSOF) has been centered on its characterization and fertilizer properties; however, research is scarce regarding its greenhouse gas emissions and toxic metals (TMs). This study assesses the carbon and nitrogen retention rate and TMs of industrial HCSOF. Specifically, environmental impact was evaluated using indicators such as hazard quotient (HQ) and risk assessment code (RAC), with planting experiments conducted to assess TM's effect on soil and plants. The results indicate that industrial HCSOF has a high fixed carbon rate of up to 91.2 % and a fixed nitrogen rate of 98.40 %, manifesting the potential for reducing greenhouse gas emissions. Additionally, HCSOF contains high ecological safety of TMs such as Hg (HQ = 0.008, RAC = 0 %), As (HQ = 0.055, RAC = 37.08 %), Cd (HQ = 0.708, RAC = 1.76 %), Pb (HQ = 0.176, RAC = 0.87 %), and Cr (HQ = 0.853, RAC = 0.12 %). After being applied to sandy soil, 15,000 kg/ha of HCSOF can increase the organic matter and nutrients in both soil and maize straw, reducing TMs and their ecological risks. By obtaining a deeper understanding of the composition and practical application of industrial HCSOF, valuable insights can be offered to reduce greenhouse gas emissions and eliminate potential risks associated with TM pollution.