Hydrothermal carbonization of cow dung with human urine as a solvent for hydrochar: An experimental and kinetic study

Hydrothermal carbonization (HTC) is the most cost-effective, environmentally friendly, and efficient physico-chemical and biochemical process for converting biomass to products with added value. The objective and novelty of this work is to produce and investigate the qualities of hydrochar fuel (as a solid fuel) from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel (i.e., coal). HTC based studies were conducted in batch, at three different reaction temperatures (180 degrees C, 200 degrees C, and 220 degrees C) and two different reaction periods (2 and 4 h). For kinetic analysis and reaction mechanism of the combustion behavior of the produced hydrochar, the model free kinetic methods and the z-master plot were used. From the model free kinetics methods, it was observed that the resultant optimum average activation energy and pre-exponential factor for the produced hydrochar at 180 degrees C and 2 h reaction period (HTC 180 2) were-120 kJ/mol and similar to 5.59 x 10(25) sec(-1), respectively. In addition, the little variation between Delta E-alpha and Delta H-alpha (similar to 10 kJ/mol) suggests that the combustion of produced hydrochar (HTC_180_2) occurred with minimal energy use. Furthermore, the hydrochar exhibited its highest heating value at 200 degrees C for 4 h (HTC_200_4) which was 1.44 times higher than the raw dung (13.4 MJ/kg) due to the HTC process. The produced hydrochar demon-strated a significant improvement compared to the conventional solvent, i.e. water.

Automated summary

This study aimed to produce and investigate the qualities of hydrochar fuel from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel. The study found that the hydrochar produced at 180℃ and 2-hour reaction period had the lowest energy consumption during combustion. Additionally, the hydrochar produced at 200℃ and 4-hour reaction period had the highest heating value, 1.44 times higher than raw dung.