Valorization of solid digestate into activated carbon and its potential for CO2 capture

Anaerobic digestion of agricultural waste for producing biogas as a renewable energy source is an established and promising technological option, producing a huge quantity of solid digestate as residue waste. Valorization of solid digestate into high-value products is necessary to make the anaerobic digestion process more cost-effective and enhance environmental benefits. In this study, activated carbon was fabricated from solid digestate with phosphoric acid activation in the fixed bed reactor. The physicochemical properties of the activated carbons have been analyzed by elemental analysis, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and N2 adsorption and desorption isotherms. The effect of H3PO4/digestate char impregnation ratio on structural and morphological change of the produced activated carbon was tested, and the function of H3PO4 in the activation procedure was discussed. The results indicated that an appropriate H3PO4/digestate char ratio was useful for the creation of pore structure. The highest surface area of 201 m2/g was attained at H3PO4/char ratio of 2 and at 600 °C. The potential for the use of the prepared activated carbon for CO2 capture was also evaluated thermogravimetrically under dynamic conditions, indicating good cyclic stability. This study provides the feasibility of integrating anaerobic digestion for biogas with subsequent activated carbon production from solid digestate. •H3PO4/digestate impregnation ratio greatly affected textural and surface property of activated carbons.•The SiO2 in digestate char could react with P to form silicon diphosphate during H3PO4 activation.•Digestate-derived activated carbon has a good CO2 capture cyclic stability.