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Salts including NaCl are the most common food flavoring agents so they are often accumulated in food waste (FW) and have potential impact on anaerobic digestion (AD) of FW. In this study, the enhanced biogas production from two-stage anaerobic digestion (TSAD) of FW by microscale zero-valent iron (ZVI) under different salinity (3, 6, 9, and 15 g NaCl/L) was evaluated. Under salinity stress, ZVI becomes a continue-release electron donor due to the enhanced corrosion and dissolution effect and the slow-down surface passivation, further improving the performance of TSAD. Experimental results revealed that the biogas production including H 2 and CH 4 from TSAD with 10 g/L ZVI addition was promoted under salinity stress. The maximum H 2 and CH 4 yield (303.38 mL H 2 /g-VS and 253.84 mL CH 4 /g-VS) were observed at the salinity 9 g NaCl/L. Compared with that of zero salinity, they increased by 40.94% and 318.46%, respectively. Additionally, Sedimentibacter, an exoelectrogen that can participate in the direct interspecies electron transfer, also exhibited the highest relative abundance (34.96%) at the salinity 9 g NaCl/L. These findings obtained in this study might be of great importance for understanding the influence of salinity on the enhanced AD by ZVI., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

• The impact of S-mZVI on the anaerobic co-digestion of WAS and FW was evaluated. • The cumulative CH 4 yield within 15 days reached to 264.78 mL/g-VS at S-mZVI 10 g/L. • S-mZVI had significant influence on the methanogenesis stage of co-digestion. • The addition of S-mZVI improved the direct interspecies electron transfer (DIET). The enhancement of zerovalent iron (ZVI) on anaerobic digestion (AD) has been proved, but there are still some problems that constrain the large-scale application of ZVI, such as the destruction of cell membrane and the inhibition of methanogenesis led by rapid H 2 accumulation. Aiming at these problems, sulfidated microscale zerovalent iron (S-mZVI) was employed to evaluate its effect on anaerobic co-digestion (AcoD) of waste activated sludge (WAS) and food waste (FW). Experimental results showed that S-mZVI promoted the direct interspecies electron transfer (DIET) between specific bacteria and methanogens, resulting in higher methane yield. At S-mZVI 10 g/L, the cumulative methane yield and ETS activity reached 264.78 mL/g-VS and 24.62 mg INTF/(g-TS h), which was 1.33 and 1.83 times that of blank. Microbiological analysis demonstrated that the abundance of DIET-related microorganisms such as Syntrophomonas , Methanosarcina and Methanobacterium increased with the increasing dosage of S-mZVI. [ABSTRACT FROM AUTHOR]

• Nanoscale zero-valent iron immobilized activated carbon fiber material was prepared. • The nZVI/ACF plays a noble metal-free electrode for electrocatalytic BrO 3 − reduction. • The BrO 3 − reduction could be performed in a wide dissolved oxygen and pH range. • The possible mechanisms involved in the reaction process were explained. Bromate (BrO 3 −) is a disinfection by-product in drinking water and has been proven to be potentially carcinogenic to humans. Herein, electrocatalytic BrO 3 − reduction using a noble metal-free nanoscale zero-valent iron immobilized activated carbon fiber (nZVI/ACF) electrode was investigated. The operating conditions including Fe content, initial solution pH, applied current intensity, and initial Br 3 − concentration were optimized. 94.2% of BrO 3 − (1.22 μM) was removed and completely transformed into bromide (Br−) within 90 min by 3.0%-nZVI/ACF at the applied current intensity 10 mA. The electrocatalytic BrO 3 − reduction could be achieved under a wide dissolved oxygen (DO) (0.5–7.8 mg L−1) and pH (3.0–10.0), and the decreasing DO and pH was favorable to the electrocatalytic reaction. The mechanism study demonstrated that the electrocatalytic BrO 3 − reduction was accomplished via the direct reduction of nZVI (31.8%), electrocatalytic reduction by nZVI (41.9%) and ACF (26.3%). nZVI/ACF electrode could maintain its high electrocatalytic activity after five successive cycles. The experimental results suggested that nZVI/ACF could achieve the fast and effective removal of BrO 3 − and provide a new direction to the application of nZVI. [ABSTRACT FROM AUTHOR]