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In this study, a hydrogen-based denitrification (HD) reactor was used to investigate the simultaneous treatment of nitrogen and decolorization in textile wastewater contaminated with organic matter. The reactor operated in two phases: without and with organic matter. Despite the short hydraulic retention time, the HD system successfully removed all pollutants, including nitrate, nitrite, reactive black-5 dye and chemical oxygen demand. The unhindered treatment efficiency for nitrogen and decolorization in the presence of organic pollutants was observed. With the addition of organic matter, the nitrogen removal efficiency increased slightly from 85% to 90–100%, and the decolorization rate doubled from 25% to 50–60%. Organic matter played a crucial role in stimulating heterotrophic bacteria during biological denitrification and acted as a carbon source facilitating biological denitrification and azo bond cleavage during dye degradation. Despite the generation of toxic byproducts and changes in the dominant microbial community, the treatment efficiency remained stable and improved. This approach offers a promising solution for enhancing treatment efficiency in textile wastewater, providing a cost-effective and environmentally friendly option for developing countries to treat wastewater before discharge. [ABSTRACT FROM AUTHOR]

Nitrite accumulation in hydrogen-based denitrification (HD) has been reported as a difficulty for achieving complete denitrification. Thauera sp. has been found as the dominant bacterial species in HD previously when using a plentiful amount of HCO3−. This present study was successful in isolating Pseudomonas sp., Dietzia sp., Pannonibacter sp., Halomonas sp., Bacillus sp., and Thauera sp. These isolated strains were selected for investigating the nitrogen removal performance under the plentiful HCO3− condition. Only Pseudomonas sp. and Thauera sp. were capable of removing NO2− where the specific NO2− removal rate of Thauera sp. (36.02 ± 5.66 mgN gVSS−1 day−1) was 9 times quicker than that of Pseudomonas sp. (3.94 ± 0.80 mgN gVSS−1 day−1). The Thauera sp. strain was then tested at different HCO3− amounts. As a result, Thauera sp. had no ability to function both NO3− and NO2− removals under HCO3− deficit condition. This study provided evidence on the role of Thauera sp. and the necessity of bicarbonate in the hydrogen-based denitrification process to enhance its efficiency and to simultaneously reduce the operational cost especially for hydrogen. [ABSTRACT FROM AUTHOR]