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Carcinogenic bromate (BrO3−) can be present in drinking water as a result of its formation from bromide (Br−) during ozonation. A fixed bed column reactor filled with elementel sulfur and limestone was operated for about six months under autotrophic and mixotrophic (autotrophic + heterotrophic) conditions at 30°C. The reactor was operated at the hydraulic retention time (HRT) ranging from 16.5 to 10.1 h at autotrophic conditions. Under mixotrophic conditions, 45 mg/L NO3‐N was removed completely at C/N ratio (mg CH3OH/mg NO3‐N) between 0.55 and 1.66 at HRT of 10.1 h. The average effluent pH was 7.8 and the sulfate concentration was lower than the Environmental Protection Agency limits at the mixotrophic stages. Efficient simultaneous BrO3− and nitrate removal was achieved at feed concentrations of 100–500 µg/L BrO3− and 45 mg/L nitrate under autotrophic and mixotrophic conditions. Effluent Br− measurements indicated that BrO3− was completely reduced without accumulation of by‐products.

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The effects of various parameters on bromate reduction were tested using lab-scale batch reactors with sulfur based autotrophic and methanol based heterotrophic denitrification processes. The initial bromate (BrO3–) concentration of 100 and 500 μg/L was completely reduced and bromide (Br-) was produced stoichiometrically from bromate in all batch reactors. In all experiments, nitrate was completely reduced to below detection limit. Kinetic studies showed that the sulfur-based autotrophic nitrate reduction rate increased with increasing initial nitrate concentration. At stoichiometrically sufficient methanol concentration as an external carbon source, nitrate and bromate were reduced to below US EPA drinking water limits in heterotrophic denitrification conditions. The methanol was completely depleted at the end of the heterotrophic operation conditions.

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BACKGROUND Conductive materials have become the focus of recent studies to accelerate and stabilize the conversion of organic wastes to methane in anaerobic digestion processes. In this study, the effect of the addition of reduced graphene oxide (rGO) on biogas/biomethane production from municipal organic solid wastes in anaerobic batch reactors was investigated. In this context, the effect of loading ratios (0, 0.5, 1 and 2 gVS inoculum (gVS nutrient)−1) and rGO addition at different concentrations (0, 10, 20 and 30 mg L−1) was examined during a 45‐day study period. RESULTS The highest biogas production reached a level of 816 ± 14 mL (gVS)−1 when substrate/inoculum ratio was 1 and 20 mg L−1 rGO was added (50% more than the group without rGO added). Addition of 30 mg L−1 rGO resulted in 667 ± 12 mL (gVS)−1 corresponding to 23% higher biogas production compared to the control reactor without rGO. The highest cumulative biomethane production was observed to be 525 ± 20 mL (gVS)−1 in the reactor with 20 mg L−1 rGO added in which substrate/inoculum ratio was 1. In the reactors with 10 and 30 mg L−1 and without rGO addition biomethane productions were 448 ± 21, 401 ± 13 and 323 ± 23 mL (gVS)−1, respectively. CONCLUSIONS Results revealed that the addition of rGO increased biomethane production from municipal organic solid wastes. It is concluded that rGO addition has the potential to be applied for real‐scale facilities within the scope of renewable energy production and circular economy. © 2021 Society of Chemical Industry