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% H 3 PO 4 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 m 2 /g) than that of HTS (43.8 m 2 /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 AlPO 4 , 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.

The presence of high fluoride concentration (> 1.5 mg/L) in water causes serious health problems such as fluorosis, infertility, brain damage, etc., which are endemic to many places in the world. This study has investigated the fluoride removal capacity of the novel activated biochar (BTS) and hydrochar (HTS) using Teff (Eragrostis tef) straw as a precursor. Activated biochar with mesoporous structures and large specific surface area of 627.7 m 2 /g were prepared via pyrolysis process. Low-cost carbonaceous hydrochar were also synthesized by an acid assisted hydrothermal carbonization process. Results obtained from both adsorbents show that the best local maximum fluoride removal was achieved at pH 2, contact time 120 min and agitation speed 200 rpm. The thermodynamic studies proved that the adsorption process was spontaneous and exothermic in nature. Both adsorbents equilibrium data fitted to Langmuir isotherm. However, Freundlich isotherm fitted best for BTS. The maximum fluoride loading capacity of BTS and HTS was found to be 212 and 88.7 mg/g, respectively. The variation could primarily be attributed to a relatively larger Surface area for BTS. Hence, to treat fluoride contaminated water, BTS can be promising as an effective adsorbent.

In this study, the adsorption behavior of fluoride has been investigated using the biomass derived activated hydrochar (AHC) prepared by a two-stage carbonization process. The adsorption process was spontaneous and exothermic in nature. The adsorption equilibrium data fitted to Langmuir isotherm. The maximum fluoride loading capacity (Qm) of AHC was found to be 88.7 mg/g. The adsorption process was spontaneous and exothermic in nature. Electrostatic interaction between the anion and the positive functional groups in the adsorbent was the main driving force for the adsorption of fluoride. Hence, activated hydrochar can be promising as an effective adsorbent to treat fluoride contaminated water.