Synergizing redox of zerovalent iron and singlet oxygen to remove aniline, chromium and antimony in printing and dyeing wastewater synchronously: Multifunctional effect of sludge derived biochar

Printing and dyeing wastewater (PDW) with complex water matrix generally contains ubiquitous organic pollutant (e.g., aniline) and heavy metals (e.g., Cr(VI) and Sb(III)), aggravating their environmental risks and remediation difficulty. To date, little is known about the synchronous removal of aniline, Cr(VI) and Sb(III) because ternary processes including oxidation, reduction and adsorption need to function synchronously. Herein, we proved multiple redox active centers (e.g., Fe-containing moieties, C-containing moieties and PFRs) present in sludge derived biochar (SDBC), which ensured synchronous degradation of aniline, reduction of Cr(VI) and oxidation of Sb(III) over a wide pH range. Results demonstrated that degradation of aniline was mainly attributed to singlet oxygen (1O2), originating from activating O2 to O2 center dot- and 1O2 by SDBC without any external oxidants. Cr(VI) was reduced to Cr(III) by reductive active species (i.e., O2 center dot- and Fe-containing moieties: zerovalent iron (Fe(0)) and Fe(II)), while Fe(0) triggered the dominant Cr(VI) reduction. The conversion of Sb(III) to Sb(V) was ascribed to Fe(III) and C = O moiety, and Fe(III) supported the major Sb(III) oxidation. The generated Cr(III) and Sb(V) could be further immobilized onto SDBC through electrostatic attraction, complexation and precipitation. Overall, this study provides a novel understanding on recycling sewage sludge to functional biochar accompanied by carbon-storage, while offering a promising strategy for the simultaneous removal of multicomponent contaminants in practical PDW.