Migration and transformation of organic carbon and nutrients in rice straw during hydrothermal cracking

The sustainable utilization of straw supports the United Nations' Sustainable Development Goals. The effects of varying reaction temperatures and duration on the hydrothermal cracking process of rice straw were evaluated, focusing on the transfer of organic carbon and nutrients from rice straw. The results indicated that the hydrothermal cracking of rice straw was a thermochemical transformation primarily driven by dehydration reactions, with temperature serving as the key factor affecting the properties of the resulting products. Over 50 % of the organic carbon was retained in the solid-phase. A moderate reaction temperature of 180 °C promoted the preservation of easily oxidized organic carbon within the solid phase, accounting for approximately 98 %, with the retention of numerous hydroxyl groups. Elevated temperature accelerated the dehydration of rice straw and enhanced the aromaticity and hydrophobicity of the solid products. Three-dimensional fluorescence analysis indicated that higher temperatures facilitated the formation of humus-like substances in the liquid phase. Over 50 % of nitrogen and 70 % of potassium were transferred into the liquid phase, while move over 80 % of phosphorus was still retained in the solid phase. Liquid-phase nitrogen was predominantly nitrous nitrogen (∼60 %). It was important to note that when the temperature exceeded 200 °C, phosphorus was released in significant quantities into the liquid phase over time. This research offers valuable insights into production practices involving various raw materials, emphasizing the importance of precisely controlling reaction temperatures to effectively tailor solid and liquid fertilizers to meet specific production objectives.