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The internal Fe2+/Fe3+ cycle is important for peroxymonosulfate (PMS) activation by iron-based materials to produce the reactive oxidative species (ROS) for the breakdown of organic contaminants. Previous studies have focused on the contribution of heterogeneous sulfur species to the Fe2+/Fe3+ cycle such as lattice S(-II) and surface SO32– of iron sulfides. In this study, we found that the dissolved S(-II) from mackinawite (FeS) had a substantial contribution to the Fe2+/Fe3+ cycle. Furthermore, the oxidation intermediates of the dissolved S(-II) such as S2O32− and SO32− ions could convert Fe3+ to Fe2+ in solution. The elimination of target organic pollutant bisphenol A (BPA) derived from PMS activation triggered by the dissolved Fe2+ might be enhanced by the equivalent dissolved S(-II) in the FeS/PMS system. These results revealed that previous studies underestimated the significance of PMS activation by dissolved Fe2+ of iron sulfides to organic pollutant degradation. Moreover, SO4•- and •OH were more likely to be the main ROS for BPA degradation in the FeS/PMS system compared with FeO2+. Considering that the metal sulfides have been widely used to activate PMS, H2O2 and peroxydisulfate, this study offers a new perspective on the function of sulfur in these advanced oxidation processes.

Allicin as an active component in allium species being widely present in food waste (FW) and waste activated sludge (WAS). Recently, allicin has been found to inhibit the anaerobic co-digestion. However, few literatures were available related to its impacting on organic matter release and microbial community in anaerobic co-digestion system of FW and WAS. Thus, this work aimed to fill that gap through use a series of batch test under conditions of pH 7 and 35 ± 1 °C. Experimental results showed that the anaerobic co-digestion system almost could not measure methane accumulation before day 20, when allicin dosage was 2.0 μg/L. However, the amount of intracellular material released from FW and WAS to substrate liquid was raised, including organic matter, PO43−-P and NH4+-N. Analysis of microbial community based on high throughput sequencing showed that microbial diversity increased at initial phase of anaerobic co-digestion from FW and WAS, meanwhile, community abundance of Candidatus_Methanofastidiosum raised significantly with co-digestion time. Whereas, methanosaeta abundance was only 19.74% in the allicin test reactor that it was the highest abundance in blank group.