Decentralized approach for resource recovery from human faeces and urine via hydrothermal carbonization: Effect of moisture content and potential for struvite production

Hydrothermal carbonization (HTC) can efficiently utilize human faeces and urine as the feedstock and convert them to carbon and nutrient-rich hydrochar and process water. This study investigated the influence of solid content (5, 10, 15, 20, 25, and 30 % of faecal matter, respectively) on the produced hydrochar and process water characteristics. The HTC of human faeces with urine as the reaction medium, at 200 °C for 2 h, resulted in a hydrochar yield of approximately 69.2 to 76.1 wt%, with a heating value ranging from 26.6 to 28.9 MJ/kg. The solubilization of carbon and nutrients in process water resulted in a total organic carbon (TOC) increase from 1.7 g/L in urine to 38.9 g/L in process water following the application of HTC. Furthermore, the morphology and weight % of elements analysed by SEM-EDS demonstrated that struvite was formed from produced process water at an optimum solid content of 10 %. Overall, the hydrochar and process water are rich in nutrients and energy, rendering them suitable for resource recovery.