Hydrochar and pyrochar for sorption of pollutants in wastewater and exhaust gas: A critical review

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed. • Progress on biochar for pollutants sorption in wastewater and waste gas highlighted. • Sorption mechanism, behavior and ability of pyrochar and hydrochar compared. • Target pollutants include heavy metal, organics and exhaust gases. • Potential promotion for the two biochar-based adsorbents prospected. • Challenges and prospective of biochar for pollutants sorption addressed. This work provides new insights into sorption possible mechanism and ability of emerging hydrochar and pyrochar on the sorption of pollutants in wastewater and exhaust gases.