Correlating phosphorus transformation with process water during hydrothermal carbonization of sewage sludge via experimental study and mathematical modelling

Abstract

Recently, hydrothermal carbonization (HTC) based phosphorus (P) recovery from sewage sludge (SS) has attracted considerable interests worldwide. However, they concentrated on P transformation in the hydrochars, while ignored that the variations of process water (PW) might influence P transformation, since it exposed to water thoroughly during HTC. In this study, correlation of P transformation with PW were examined via experimental study and mathematical modelling. The results showed that statistical significance (p < 0.05) of HTC temperature and feedwater pH on NH4+-N concentration in the PW was observed due to deamination and ring opening reactions of amino acids, confirming by their excellent correlation with R2 = 0.988. NH4+-N concentration dominated increasing PW pH, which stimulated the transformation of NAIP to AP. Associated model was developed with satisfactory R2 = 0.938. Although P transformation during HTC was significantly influenced by HTC temperature and feedwater pH, supporting by their strong correlation with R2 = 0.956, its transformation was PW pH dependent. Ultimately, detailed P transformation pathways during HTC was proposed with incorporation into the impact of PW. This work can provide new insights into HTC-based P transformation in the pristine SS.