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Heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria are essential for aquaculture wastewater treatment to ensure product quality and environmental sustainability. Klebsiella aerogenes strain B23 was isolated from shrimp farm wastewater and identified based on phenotypic and phylogenetic characteristics. The strain demonstrated high removal efficiency and the maximum removal rates for ammonia (96.48%; 6.18 mg/L/h), nitrate (93.48%; 4.45 mg/L/h), and nitrite (90.92%; 2.38 mg/L/h). In wastewater from a shrimp farm, B23 reached a nitrate removal efficiency of 92.18% after 36 h. The expression of denitrifying genes (norV, norW, narJ, and narR) confirmed the HN-AD ability of strain B23. Single-factor experiments revealed that the optimal conditions for nitrate removal were a nitrate concentration of 5 mg/L, sucrose as a carbon source, temperature of 30 °C, pH of 7.5, rotation rate of 120 rpm, and salinity of 5‰. These findings demonstrate that strain B23 is a candidate for nitrogen removal in aquaculture wastewater treatment. [ABSTRACT FROM AUTHOR]

Nitrogen oxide emissions have attracted much attention due to their impact on the atmospheric environment and human health. Combined with NO removal in the cement production process, coal gasification slag was used to prepare denitrification materials to decompose NO in cement kilns without the addition of reducing agents. Denitrification materials were synthesized by a chemical precipitation method at different pH. The denitrification mechanism was proposed in this study. The results indicated that the denitrification material prepared at a pH of 7 exhibited the best denitrification performance. The NO decomposition rate first increased and then decreased below 400°C, and then increased as the temperature increased, reaching over 97% above 700°C. In the low-temperature range, Fe(II) was assumed to be active species, and the absorbed NO on the Fe(II) site obtained an electron, which promoted the decomposition of NO. In the high-temperature range, besides the active element Fe, the residual carbon in the coal gasification slag was prone to oxidation-reduction reactions, reducing nitric oxide to nitrogen. A new waste-to-value concept is introduced in this study, which promotes green technology for sustainable development. [ABSTRACT FROM AUTHOR]

NOx emission from the cement industry have received much attention. In order to reduce the NOx emission in cement kilns, nickel slag was used to prepare the non-ammonia denitrification material, and a denitrification mechanism was proposed in this study. The results showed that the denitrification material prepared at pH 7 exhibited the best denitrification performance. At low temperature, the highest denitrification performance was achieved between 200 and 300 °C with a NO decomposition rate of approximately 40%. Then, the NO decomposition rate increased as the temperature increased, reaching over 95% above 700 °C. The physicochemical characteristics showed that the material had the highest specific surface area and the highest relative Fe content, which benefited the denitrification performance. The divalent iron of the denitrification material was considered the active site for the reaction, and trivalent iron was not conducive to denitrification performance at a low temperature range. After the denitrification reaction, the Fe3+/Fe2+ increased from 0.89 to 1.31. The proposed denitrification mechanism was the redox process between divalent iron and trivalent iron. This study not only recycles industrial waste to reduce solid waste pollution but also efficiently removes nitrogen oxides from cement kilns without ammonia. [ABSTRACT FROM AUTHOR]