Biochar-activated persulfate oxidation of arsenic(III): Nonnegligible roles of environmentally persistent free radicals

The water ecosystem and public health are often threatened by Arsenic (As). The primary type of As in paddy field and ground water is As(III), which is more toxic and mobile than As(V). In this research, biochar prepared from sewage sludge (SBC) through hydrothermal technique was used to activate persulfate (PS) to oxidate As(III), making it less toxic As(V). The developed SBC/PS system could oxidate As(III) effectively in the wide pH values (2−10). Excluding the influence of specific surface area and functional groups, the concentration of environmental persistent free radicals (EPFRs) had a good linear relationship with the oxidation of As(III), reaching above 0.96. According to a mechanism analysis, EPFRs on SBC could transfer electrons to directly activate PS to produce SO 4 − ·, ·OH, O 2 − ·, and 1 O 2 to improve the oxidation of As(III). These results not only indicated that the biochar/PS system’s application scope can be successfully increased by adjusting the preparation conditions, but also revealed the invaluable role of EPFRs in As(III) oxidation process.