Simultaneous removal of Cr and organic matters via coupling Cr-Fenton-like reaction with Cr flocculation: The key role of Cr flocs on coupling effect

Abstract

Cr contamination is frequently combined with organic pollution. Cr flocculation using flocculants results in difficulty in Cr recovery and increase of salinity. Moreover, the fates of coexisted organic pollutants are rarely attended. In this study, the Fenton-like reaction based on Cr redox reaction (Cr-Fenton-like reaction) coupled with Cr flocculation was established using H2O2 as additives, which gave the opportunity to realize simultaneous removal of Cr and organic matters sustainably. In the coupling system, Cr-Fenton-like reaction generated more OH− for Cr flocculation via the H2O2 decomposition, meanwhile, Cr flocculation provided heterogeneous catalytic regions for Cr-Fenton-like reaction. The formation of Cr flocs was the key to the coupling effect. They created partially alkaline regions, therefore Cr-Fenton-like reaction (reaction condition: pH > 5) and Cr flocculation (reaction condition: pH > 8) occurred in these heterogeneous regions, although the pH of the solutions was below 5. Besides, the Cr flocs in the coupling system tended to adsorb Cr(III) which also contributed to the coupling effect. Although Cr-Fenton-like reaction generated Cr(VI) inevitably, the dissolved Cr(VI) didn't accumulate due to the persistent acidic condition and the heterogeneous catalysis of Cr flocs in the coupling system. When the coupling effect was applied to a stimulated tannery wastewater with Cr and organic co-pollution, the simultaneous removal rates for Cr and total organic carbon were 81.2% and 41.34% respectively after an 8-h running. This study gives deep insights into the coupling effect and provides a sustainable and eco-friendly strategy for the remediation of wastewater with Cr and organic co-pollution.