Hydrothermal carbonisation of anaerobic digestate for hydro-char production and nutrient recovery

This study investigates the potential of hydrothermal carbonisation (HTC) for fractionating anaerobic digestate sewage sludge into carbon-rich hydrochar and nutrient-rich aqueous phase (AP). AP is subsequently used to supplement cultures alkali halophilic microalgae D. tertiolecta (CCAP 19/30), convert sodium bicarbonate carbonate solution as part an integrated biogas purification system. HTC at 200 °C gave highest yields (78%) solid carbon retentions (75%), indicating high capture potential. In contrast, essential growth nutrients nitrogen, phosphorus sulphur were partially solubilised, resulting in HTC-AP concentrations between 11 times (S) 50 (P) higher than those artificial medium. Trace nutrient 10–80 compared medium, with minimal heavy metal solubilisation. Dunaliella grew successfully without inhibition up 2% (produced °C). AP-supplemented achieved cell (up 10.0 ×106 cells mL−1), biomass content (maximum 1.14 ± 0.06 g L−1) bicarbonate-to-carbonate conversion (83% 80%, 1% HTC-AP) control cultures. Therefore, appears be a suitable medium substitute cultivating alkali-halophilic regenerate produce algae biomass, providing added-value product.