Nutrient-rich hydrothermal carbon production by exogenous nutrients combined with seaweed internal water

As a product of hydrothermal carbonization (HTC) technology, hydrothermal carbon has shown excellent application potential in soil improvement, greenhouse gas reduction and pollution remediation. Since a large amount of water and biomass are directly used as reaction media, hydrothermal carbon produced by traditional HTC possesses poor nutrient properties and accompanied by the generation of toxic and hazardous wastewater. Here, a versatile and easily scalable strategy has been demonstrated for the one-step production of industrial nutrient-rich hydrothermal carbon (NRHC) by combining the exogenous nutrients with seaweed internal water. During the reaction process, exogenous nutrients (NH₄H₂PO₃, KNO₃, CO(NH₂)₂) participated in the HTC reaction and were uniformly distributed on the surface of hydrothermal carbon through surface complexation precipitation, ion exchange, and electrostatic interactions. Simulations based on density functional theory revealed that NRHC produced in presence of exogenous nutrients possessed more active sites and surface charges. Moreover, the adsorbent and adsorbate were simultaneously affected by intermolecular forces, electrostatic forces, and internal energy of the system, and the thermodynamics of adsorption process was more stable. Compared with no exogenous nutrient involvement, NRHC produced by exogenous nutrients showed 2.12, 18.56, and 25.69 times increase in the N, P, and K content. The length of the seed germination root system increased by 4.3-5.9 times, which met the standards set for agricultural fertilizer. Due to increased yield per unit volume and reduced wastewater generation, the cost of NRHC production reduced by 47.83-58.23 per cent and profit enhanced by 1.56-1.68 times, as compared to traditional HTC. This low-cost streamlined process provides a new strategy for large-scale production and direct application of hydrothermal carbon.