Sulfate in effluent is a challenging issue for wastewater reuse around the world. In this study, sulfur (S) removal and transformation in five batch constructed wetlands (CWs) treating secondary effluent were investigated. The results showed that the presence of the plant cattail (Typha latifolia) had little effect on sulfate removal, while the carbon-rich litter it generated greatly improved sulfate removal, but with limited sulfide accumulation in the pore-water. After sulfate removal, most of the S was deposited with the valence states S (-II) and S (0) on the iron-rich gravel surface, and acid volatile sulfide was the main S sink in the litter-added CWs. High-throughput pyrosequencing revealed that sulfate-reducing bacteria (i.e. Desulfobacter) and sulfide-oxidizing bacteria (i.e. Thiobacillus) were dominant in the litter-added CWs, which led to a sustainable S cycle between sulfate and sulfide. Overall, this study suggests that recycling plant litter and iron-rich filling material in CWs gives an opportunity to utilize the S in the wastewater as both an electron acceptor for sulfate reduction and as an electron donor for nitrate reduction coupled with sulfide oxidation. This leads to the simultaneous removal of sulfate, nitrate, and organics without discharging toxic sulfide into the receiving water body.

Department of Applied Ecology Faculty of Environmental Sciences Czech University of Life Sciences Prague 16521 Czech Republic

Department of Environmental Biotechnology Helmholtz Centre for Environmental Research UFZ Permoserstr 15 Leipzig 04318 Germany

Institute of Environmental Science and Engineering Hangzhou Dianzi University Hangzhou 310018 PR China

Key Laboratory of Yangtze Water Environment of Ministry of the State Education College of Environmental Science and Engineering Tongji University Shanghai 200092 PR China

Key Laboratory of Yangtze Water Environment of Ministry of the State Education College of Environmental Science and Engineering Tongji University Shanghai 200092 PR China; Department of Applied Ecology Faculty of Environmental Sciences Czech University of Life Sciences Prague 16521 Czech Republic

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