Abstract:
In this research, engineered biochar and hydrochar derived from paddy husk were compared for the
adsorption tetracycline (TC) in water effluents. Biochar was produced at three different pyrolysis
temperatures (e.g., 250 °C, 300 °C and 350 °C) while hydrochar was produced using three different HTC
temperatures (e.g., 180 °C, 200 °C and 220 °C). The adsorptive experiments were performed for both
biochar and hydrochar using well-defined experimental conditions: pH (3); initial TC concentration (10
mg/L); adsorbent dosage (1 g/L); and temperature (27 °C) to study their adsorptive performances (qe in
mg/g). After selecting the best qe values for both biochar and hydrochar, both materials were modified
using 20% H3PO4. A comprehensive scientific evaluation of both engineered biochar (EBC 350) and
hydrochar (EHC 220) was performed using adsorption isotherm, adsorption kinetics, rate-limiting, and
thermodynamics tests along with their characterization using FTIR and point of zero charge (pzc). The
effects of temperature, dosage, and initial TC concentration on the adsorption process were studied for
both EBC 350 and EHC 220. Acid activation improved the adsorptive performance of EHC 220 almost
four times (from 1.9 to 7.5 mg/g), whereas adsorptive performance of EBC 350 improved 2.4 times from
3.8 to 9.1 mg/g. The best pH for TC adsorption onto EHC 220 was 5, whereas it was 3 for EBC 350. EBC
350 exhibited a good fit with the Freundlich model, whereas EHC 220 followed the Langmuir model. At
100 mg/L TC concentration, EHC 220 exhibited higher qe value (46.9 mg/g) compared to EBC 350 (41.7
mg/g). The Pseudo-first order kinetic model was the best fit for EHC 220 adsorption, whereas Pseudo-
second order model was most suitable for EBC 350. The adsorption mechanisms involved in TC
adsorption by EHC 220 included hydrogen bonding, hydrophobic effect, and interaction, whereas cation
exchange, mass diffusion, and interaction were involved for EBC 350. The results of this study will
facilitate the development of cost-effective filters with the incorporation of engineered biochar/engineered
hydrochar for the active removal of emerging contaminants, like tetracycline, from wastewater so as to
increase its reusable potential.
