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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]

Textile wastewater (TW) contains toxic pollutants that pose both environmental and human health risks. Reportedly, some of these pollutants, including NO3−, NO2− and reactive black 5 (RB-5) dye, can be removed via hydrogen-based denitrification (HD); however, it is still unclear how different factors affect their simultaneous removal. This study aimed to investigate the effect of H2 flow rate, the sparging cycle of air and H2, and initial dye concentration on the TW treatment process. Thus, two reactors, an anaerobic HD reactor and a combined aerobic/anaerobic HD reactor, were used to investigate the treatment performance. The results obtained that increasing the H2 flow rate in the anaerobic HD reactor increased nitrogen removal and decolorization removal rates. Further, increasing the time for anaerobic treatment significantly enhanced the pollutant removal rate in the combined reactor. Furthermore, an increase in initial dye concentration resulted in lower nitrogen removal rates. Additionally, some of the dye was decolorized during the HD process via bacterial degradation, and increasing the initial dye concentration resulted in a decrease in the decolorization rate. Bacterial communities, including Xanthomonadaceae, Rhodocyclaceae, and Thauera spp., are presented as the microbial species that play a key role in the mechanisms related to nitrogen removal and RB-5 decolorization under both HD conditions. However, both reactors showed similar treatment efficiencies; hence, based on these results, the use of a combined aerobic/anaerobic HD system should be used to reduce organic/inorganic pollutant contents in real textile wastewater before discharging is recommended. [ABSTRACT FROM AUTHOR]