Electrochemical reduction using a metal-based electrode is a novel method for wastewater containing Cr (VI) treatment. However, the removal efficiency with a metal-based electrode is limited by the low conductivity and specific surface area. In this study, a stainless steel (SS) electrode modified with graphene was fabricated and used to reduce Cr (VI) in an electrochemical system. Under the optimal conditions (i.e., the graphene loading of 1.50 mg·cm-2, -0.7 V, pH 1.5 and the electrolyte concentration (Na2SO4) of 10 g·L-1), this composite electrode removed 99.70 ± 0.00% of Cr (VI) with an initial concentration of 10 mg·L-1 in 80 min. Cr (VI) was removed by the following pathways: (1) under the additive electric field, Cr (VI) was mainly reduced into Cr (III) directly by accepting electrons, (2) Cr (VI) was reduced to Cr (III) by -OH of graphene, (3) -COOH on the surface of graphene underwent bonding with H+ thereby producing hydrogen bonding to adsorb Cr (VI). Meanwhile, COO- was produced via losing H+ to adsorb Cr (III).
Bioelectrochemical system is a novel method for controlling down nitrate pollution, yet the feasibility of using methane as the electron donors for denitrification in this system remains unknown. In this study, using the effluent from mother BESs as inocula, a denitrifying anaerobic methane oxidation bioelectrochemical system was successfully started up in 92 days. When operated with 50 mmol/L phosphate buffer solution at pH 7 and 30°C, the maximum methane consumption, nitrate, and total nitrogen removal load reached 0.23 ± 0.01 mmol/d, 551.0 ± 22.1 mg N/m3/d, and 64.0 ± 18.8 mg N/m3/d, respectively. Meanwhile, the peak voltage of 93 ± 4 mV, the anodic coulombic efficiency of 6.99 ± 0.20%, and the maximum power density of 219.86 mW/m3 were obtained. The metagenomics profiles revealed that the dominant denitrifying bacteria in the cathodic chamber reduced most nitrate to nitrite through denitrification and assimilatory reduction. In the anodic chamber, various archaea including methanotrophs and methanogens converted methane via reverse methanogenesis to form formate (or H2), acetate, and methyl compounds, which were than utilized by electroactive bacteria to generate electricity.Practitioner Points A denitrifying anaerobic methane oxidation BES was successfully started up in 92 d. Simultaneous removal of methane and nitrate was achieved in the DAMO‐BES. Functional genes related to AMO and denitrification were detected in the DAMO‐BES. Methylocystis can mediate AMO in the anode and denitrification in the cathode.
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