Biochar from waste biomass, its fundamentals, engineering aspects, and potential applications: an overview.

Environmental pollution control in the growing world is a challenging task for all the countries in order to keep the environmental sustainability. Biochar, a processed carbon material, draws a significant attention in the field of environmental remediation, as of its active functional groups that help remove environmental pollutants to a level insignificant to cause hazardous effects. As such, there is an increasing interest developed to promote highly productive biochar for exploring environmental engineering aspects. There is limited comprehensive literature available for understanding biochar science and its potential applications under an umbrella. This review was set to fill this knowledge gap by discussing key points related to biochar, its novel engineering aspects and potential environmental applications. Therefore, this overview tends to summarize and discuss biochar, its fundamentals, engineering aspects commonly used modifications and the potential applications of biochar in water treatment with an intention of addressing the importance of biochar for environmental remediation process. This overview will be useful for researchers, policy-makers and stakeholders to plan and review relevant scientific works in order to produce customized biochar for future environmental applications.

Adsorptive behavior of engineered biochar /hydrochar for tetracycline removal from synthetic wastewater.

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 π-π interaction, whereas cation exchange, mass diffusion, and π-π 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.

Lab-scale engineered hydrochar production and techno-economic scaling-up analysis.

Despite the extensive use of engineered hydrochar (EHC) for contaminants adsorption in water, little is known about the scaling-up of EHC production which has kept the technology at a low readiness level (TRL). Full-scale EHC production was simulated to help bridge this knowledge gap. A systematic analysis was performed where EHC was produced from rice straw using hydrothermal carbonization (HTC) at 200 °C with iron addition. A techno-economic evaluation model was employed to simulate the production process and to estimate energy requirements, configuration, and cost scenarios for the HTC process. The minimum selling price (MSP) analysis of the engineered hydrochar was found to be almost half compared to the market price for other similar sorbents ($ 76/t vs. $136/t) suggesting that EHC production is feasible for scaling up. Finally, as a trial, the resulting material was tested for its efficacy in the adsorption of an anionic organic contaminant (e.g., Congo Red, C32H22N6Na2O6S2) in water to identify its potential for water treatment. Experimental results showed that EHC adsorbed > 95% CR suggesting significant adsorption capability and feasibility for production scale-up.