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Pyrite (FeS 2 ) catalyzed conversion of H 2 O 2 into oxidants is increasingly recognized as a promising Fentonlike process for treating recalcitrant contaminants. However, the underlying mechanism remains unclear, especially for nano-pyrite. The present study explored the potential of a nano-pyrite Fenton system for p-nitrophenol oxidation using high energy ball milled nano-pyrite. The enhancement in cOH production, with 3 times faster p-nitrophenol degradation than the conventional Fenton system, is ascribed to the reduction of pyrite size to the nanoscale, which alters the Fe 2+ regeneration pathway, favoring faster and very efficient production of cOH during H 2 O 2 decomposition. The amount of H 2 O 2 required was reduced due to the increased conversion efficiency of H 2 O 2 to cOH from 13.90% (conventional Fenton) to 67.55%, in which surface S 2 2À species served as an electron source. An interpretation of the degradation intermediates and mineralization pathway of p-nitrophenol was then made using gas chromatography-mass spectrometry. This study bridges the knowledge gap between p-nitrophenol removal and the nano-pyrite catalyzed oxidant generation process.

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BACKGROUND: The potential effect of chromium on the denitrification process has drawn much attention recently. The efficient remediation of groundwater contaminated by both hexavalent chromate [Cr(VI)] and nitrate (NO 3 − ) was hampered due to the deficiency of denitrification in the presence of Cr(VI). The goal of this work was to understand the mechanisms of how Cr(VI) affected denitrification. RESULTS:To better understand the underlying nature, Cr(VI) effects on denitrification were investigated in batch. Negative effects of Cr(VI) exposure on denitrification were confirmed and ascribed to restriction of bacterial activities, by regulating functional genes expression and altering community composition. Stronger inhibition of the expression of denitrifying genes was observed with increased Cr(VI) loading (0-50 mg L −1 ). The critical inhibitory concentration and IC 50 of Cr(VI) on electron transport system activities were calculated to be 3.21 and 4.87 mg L −1 , respectively. Further amplicon analysis revealed that Betaproteobacteria were enriched, implying their potential key role in simultaneously removing nitrate and Cr(VI). The presence of Cr(VI) also upregulated the metabolic activities related to apoptosis. CONCLUSION: These findings shed light on the biogeochemical fates of Cr(VI) and NO 3− in aquifers, and may contribute in enhancing their practical application for bioremediation using microbial processes. ETSA assayElectron transport activity of the bacteria was measured by reducing 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium wileyonlinelibrary.com/jctb