Fate of nutrients during hydrothermal carbonization of biogenic municipal waste

The biogenic fraction of municipal solid waste is rich in various inorganic nutrients along with the organic content and imposes environmental threats in the absence of proper disposal techniques. To valorize the highly wet biogenic municipal waste (BMW), hydrothermal carbonization (HTC) can be an effective low-temperature treatment method. The knowledge on the distribution of the nutrients in the product phases after HTC can improve processing of BMW for minimizing environmental impacts and enabling nutrient recovery. This study aims to investigate the segregation of the inorganic nutrients (i.e. nitrogen, phosphorus, potassium, calcium, and sodium) in the hydrochar and liquid product from HTC of BMW. Experiments were performed by varying reaction temperature (190, 220, and 250 °C) and reaction time (30, 60, and 90 min) at a constant feed-to-water ratio to observe the effects of reaction conditions. Majority of the sodium (> 93%) and potassium (> 96%) were transferred to the liquid after HTC irrespective of the reaction condition. Calcium (> 50%), phosphorus (> 91%), and nitrogen (> 26%) remained mainly in the hydrochar. Multivariate analysis on the variables under consideration showed that the fate of phosphorus and nitrogen was affected by the reaction conditions remarkably. The fate of potassium, sodium, and calcium was found to be less dependent on the reaction conditions. By optimizing the reaction conditions, both liquid phase and hydrochar obtained from HTC of BMW could be potential sources of plant nutrients.