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This study aimed to develop a multistage treatment system for highly toxic wastewater named reverse osmosis concentrates of landfill leachate. Therefore, a combination of the ammonia stripping process (ASP), catalytic ozone oxidation process (COP), and heterotrophic nitrification-aerobic denitrification process (HNADP) was proposed and the quality of effluent was evaluated for the concentration of chemical oxygen demand (COD), ammonia nitrogen (NH 4 + -N), and total nitrogen (TN). ASP had moderate removal efficiency of NH 4 + -N, and TN in the effluent. COP was catalyzed by cerium-supported-activated carbon achieved good performance in disposal of COD. The effluent of HNADP had the most significant removal efficiency of COD, NH 4 + -N, and TN. As a result, the effluent of combined process successfully met the discharge standards for NH 4 + -N and TN according to Table 1 of GB 16889-2008 in China. To investigate the microbial mechanism of pollutant removal in HNADP, 16S rRNA high-throughput sequencing was performed and the results suggested that the relative abundance and diversity of microorganisms fluctuated with the changes of COD/TN ratio in HNADP. Truepera and Halomonas were identified as the key genera involved in the simultaneous degradation of COD and nitrogen-containing pollutants, the functional genes (hao, amoA, nirS, and nirK) were predicted in nitrification and denitrification process. Overall, this study demonstrates a feasible multistage system for treatment of concentrates and propose that further explorations of combined techniques may lead to even more satisfactory removal efficiencies., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Bromate (BrO 3 - ) and ammonia nitrogen (NH 4 + ) are both typical environmental pollutants: BrO 3 - has been categorized as one of the Group 2B carcinogen by IARC; an excess of NH 4 + might result in the eutrophication of water. The existence of NH 4 + could inhibit the transformation of bromide (Br - ) to bromate (BrO 3 - ). However, the interaction of NH 4 + and BrO 3 - during the removal process is not clear. This study intends to disclose the mutual relationships of ammonia nitrogen and bromate ions under UV irradiation or UV/TiO 2 conditions. Without UV irradiation, BrO 3 - and NH 4 + were both stable even under the presentation of each other. Under UV irradiation or UV/TiO 2 conditions, BrO 3 - and NH 4 + promoted the degradation of each other, showing the synergistic degradation mechanism. In the neutral environment, both of BrO 3 - and NH 4 + could be transformed effectively. Furthermore, NH 4 + accelerated the transformation of BrO 3 - to Br - at the reaction beginning and the existence of BrO 3 - is beneficial for the transformation of NH 4 + to N 2 ., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)