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This work evaluates the nutrient (phosphorus and nitrogen) recovery from cow manure by hydrothermal carbonization (HTC). A series of experiments were conducted to evaluate the effects of reaction time (5, 30, and 120 min), temperature (170, 200, and 230 °C), and the addition of acids (citric acid and HCl) at several concentrations (0.1, 0.3, and 0.5 M) on the solubilization of phosphate and organic nitrogen to the aqueous phase. Statistical analysis of the experimental results revealed a significant effect of reaction temperature, acid addition, and acid concentration on phosphate extraction. Within the range of conditions studied, low HTC temperature and addition of either citric acid or HCl resulted in enhanced phosphate recovery in the aqueous phase. The maximum P solubilization (98% of the total P) in the aqueous phase occurred at 170 °C with the addition of citric acid. On the other hand, the results indicate only a minor effect of the experimental conditions with respect to N solubilization. The nitrogen mass balance showed that roughly 60% of the overall N was extracted into the aqueous phase.

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