Preparation, characterization and cost analysis of activated biochar and hydrochar derived from agricultural waste: a comparative study

Utilization of low-cost, abundant and biomaterials is highly recommended for sustainable environment protection. This study presents a comparative analysis on the preparation, characterization and cost analysis of the novel activated biochar (BTS) and activated hydrochar (HTS). Teff (Eragrostis tef) straw was used as a precursor for producing BTS and HTS through pyrolysis and hydrothermal carbonization process, respectively. Both chars were further activated using 30 wt% H3PO4 for 3 h activation time. The physicochemical properties of both chars were compared by different characterization techniques including BET, FTIR, XRD, SEM, and TGA. Briefly, BTS exhibited heterogeneous surface structures and comparatively larger specific surface area (627.7 m2/g) than that of HTS (43.8 m2/g) with the smooth coalesced carbon layer and dull surface edges. The XRD analysis revealed the amorphous character of HTS which is dominantly composed of AlPO4, whilst indicating BTS to be the crystalline structure with the very trivial amount of impurities. The oxygen-containing functional groups increased for HTS in comparison to BTS. Thermogravimetric analysis showed that HTS exhibited better thermal behaviors. Estimated costs incurred in the production of the HTS were found to be cheaper than compared to BTS. Overall, the experiment result suggested that Teff straw could have the potential for producing a low cost activated chars.