Use of Iron-Modified Biochar Obtained from Rice Straw as an Adsorbent for Removal of Arsenic from Water

In Northern India, a large quantity of rice stubble is burned in situ in agricultural fields after the rice crop has been harvested, which releases harmful gases and particulate matter into the environment. This poses a threat to the environment and the health of living organisms. Stubble burning could be prevented by utilizing the rice straw directly or indirectly. In this study, efforts have been made to explore the use of biochar that is obtained from the pyrolysis of rice straw as an adsorbent for the removal of arsenic from water, because arsenic in groundwater is a worldwide problem. The rice straw was chemically modified and pyrolyzed to obtain iron-modified biochar. The iron-modified biochar was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) analysis. The adsorption optimization for the arsenic removal was carried out using response surface methodology for three adsorption parameters (e.g., contact time, adsorbent dosage, and initial arsenic concentration). The iron-modified biochar could remove 99% of the arsenic from water with 989 µg/L arsenic at an adsorbent dosage of 3.25 g/L. The leaching of iron from the iron-modified biochar was tested and was negligible. In addition, the disposal of exhausted adsorbent in municipal solid waste landfills was suggested following the toxicity characteristic leaching procedure.