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A novel iron-cycling process based on core-shell iron granules, which contained zero-valent iron (Fe 0 ) in the core and maghemite (γ-Fe 2 O 3 ) on the shell (Fe 0 @Fe III granules), was proposed to in-situ control hydrogen sulfide in the sediments of the polluted urban rivers. The Fe 0 @Fe III granules added in the top sediment layer removed 97% of sulfide generated by sulfate-reducing bacteria in the sediments, and the sulfide removal capacity of virgin granules was 163 mg S/g Fe (114 mg S/g granule). The Fe 0 @Fe III granules removed the formed sulfide through the abiotic sulfide oxidation and precipitation, and they also stimulated the microbial iron reduction, which competitively consumed wastewater-derived organics and partially inhibited the sulfate reduction in the sediments. The used Fe 0 @Fe III granules were easily regenerated through magnetic separation from sediments and air exposure for 12 h, which enhanced the sulfide removal capacities of the regenerated granules by 12%-22%, compared to the virgin granules. During the air exposure, ferrous products (i.e., iron sulfide and surface-associated Fe II ) on the granule shell were completely oxidized to poorly ordered Fe III hydroxides (γ-FeOOH and amorphous FeOOH) having larger specific surface areas and higher reactivity to sulfide than γ-Fe 2 O 3 on the virgin granules. Meanwhile, the Fe 0 in the core was also partially oxidized through the indirect electron transfer, which was facilitated by the electrically conductive iron oxide minerals (Fe 3 O 4 and Fe 2 O 3 ) and the microbial electron carriers (e.g., Geobacter). The oxidation of Fe 0 core contributed additional Fe III hydroxides to the sulfide control. The Fe 0 @Fe III granules were reused for four times in a 293-day trial, and their overall sulfide removal capacity was at least 920 mg S/g Fe. The proposed iron-cycling process can be a chemical-saving, energy-saving and cost-effective approach for the hydrogen sulfide control in the sediments of polluted urban rivers, as well as lakes, aquaculture ponds and marine., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Sulfidogenic process using sulfate-reducing bacteria (SRB) has been used to remove arsenite from the arsenic-contaminated waters through the precipitation of arsenite with sulfide. However, excessive sulfide production and significant pH increase induced by sulfate reduction result in the formation of the mobile thioarsenite by-products and the inefficiency and instability of arsenite removal, especially when the arsenite level fluctuates. In this study, we proposed a novel sulfidogenic process driven by sulfur reducing bacteria (S 0 RB) for the arsenite removal under acidic conditions. In a long term experiment, efficient sulfide production (0.42 ± 0.2 kg S/m 3 -d) was achieved without changing the acidic condition (pH around 4.3) in a sulfur reduction bio-reactor. With the acidic sulfide-containing effluents from the bio-reactor, over 99% of arsenite (10 mg As/L) in the arsenic-contaminated water was precipitated without the formation of soluble thioarsenite by-products, even in the presence of excessive sulfide. Maintaining the acidic condition (pH around 4.3) of the sulfide-containing effluent was essential to ensure the efficient arsenite precipitation and minimize the formation of thioarsenite by-products when the arsenite to sulfide molar ratios ranged from 0.1 to 0.46. An acid-tolerant S 0 RB, Desulfurella, was found to be responsible for the efficient dissimilatory sulfur reduction under acidic conditions without changing the solution pH significantly. The microbial sulfur reduction may proceed through the direct electron transfer between the S 0 RB and sulfur particles, and also through the indirect electron transport mediated by electron carriers. The findings of this study demonstrate that the proposed sulfidogenic process driven by S 0 RB working under acidic conditions can be a promising alternative to the SRB-based process for arsenite removal from the arsenic-contaminated waters., (Copyright © 2018 Elsevier Ltd. All rights reserved.)