Biochar technology in wastewater treatment: A critical review

Biochar is used for soil conditioning, remediation, carbon sequestration and water remediation. Biochar application to water and wastewater has never been reviewed previously. This review focuses on recent applications of biochars, produced from biomass pyrolysis (slow and fast), in water and wastewater treatment. Slow and fast pyrolysis biochar production is briefly discussed. The literature on sorption of organic and inorganic contaminants by biochars is surveyed and reviewed. Adsorption capacities for organic and inorganic contaminants by different biochars under different operating conditions are summarized and, where possible, compared. Mechanisms responsible for contaminant remediation are briefly discussed. Finally, a few recommendations for further research have been made in the area of biochar development for application to water filtration.

The forms of alkalis of the biochars produced from the straws of canola, corn, soybean and peanut at different temperatures (300, 500 and 700°C) were studied by means of oxygen-limited pyrolysis. The alkalinity and pH of the biochars increased with increased pyrolysis temperature. The X-ray diffraction spectra and the content of carbonates of the biochars suggested that carbonates were the major alkaline components in the biochars generated at the high temperature; they were also responsible for the strong buffer plateau-regions on the acid-base titration curves at 500 and 700°C. The data of FTIR-PAS and zeta potentials indicated that the functional groups such as -COO(-) (-COOH) and -O(-) (-OH) contained by the biochars contributed greatly to the alkalinity of the biochar samples tested, especially for those generated at the lower temperature. These functional groups were also responsible for the negative charges of the biochars. Copyright © 2010 Elsevier Ltd. All rights reserved.