Thermal hydrolysate is the liquid fraction (supernatant) of thermally treated wastewater sludge. Based on a literature study, a factorial design experiment was carried out in order to investigate important condition-variables in the thermal hydrolysis step. The objective of the study was to investigate the influence on composition and amount of produced thermal hydrolysate, as well as the influence on the quality of hydrolysate as carbon source for denitrification, from varying hydrolysis conditions. The thermal hydrolysis experiments demonstrated that carbohydrates are the organic fraction that is most easily decomposed, while proteins are most easily solubilized. A small increase in the content of VFA was found during thermal hydrolysis, while fat did not seem to be affected. The varying hydrolysis conditions resulted in varying content of the produced hydrolysate, but the quality of the hydrolysate as carbon source did not vary dramatically with varying hydrolysis conditions.

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