Biochar as sustainable adsorbents for chromium ion removal from aqueous environment: a review

The heavy metal pollution in the aqueous environment increases day by day due to the tremendous growth of industries and population. They are non-biodegradable and persistent in the aqueous environment for a long time and threaten the environment. The chromium exists in the aqueous environment as Cr(III) and Cr(VI), out of which Cr(VI) is the most hazardous oxidation state. Exceeding the level of the chromium ions in the drinking water greater than the permissible limit leads to various chronic health risks for both flora and fauna. The current scenario is that the remediation of the chromium ion from the aqueous environment has become the thirst of the universe. There are various remediation approaches applied for the extraction of chromium ions from the aqueous environment. Adsorption is the most optimized approach for the extraction of chromium ions from the aqueous environment because of the lower operational cost, easy operation, and produce less harmful by-products. Conventionally, ample adsorbents have been employed for the extraction of the chromium ion from the aqueous environment, but they are suffering from several limitations such as lower efficiency, higher cost, and poor selectivity. Biochar is a promising adsorbent for the removal of chromium ions from the aqueous environment. In this review, recent advancement in the biochar employed as the adsorbent for the extraction of chromium has been discussed.