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[Display omitted] • The series connection method of flow electrode ST-SC and MT-SC in multi-stage FCDI were proposed. • Flexible current control each level device to decrease ENRS. • MT-SC operating mode was more energy-efficient and efficient than traditional single stage devices. • The MT-SC operating mode could fully utilize the energy released during the desorption process. This article proposed a three-stage flow electrode capacitive deionization (FCDI) device, in which the flow electrodes were connected in series and circulated among the three stages. Four different methods of flow electrode series connection (ICC, SCC, ST-SC, and MT-SC) were investigated. The results showed that the MT-SC mode achieved the best desalination performance and saved 43.47 % of energy. To further reduce energy consumption, the current of the three-stage device was further optimized using flexible current, and the mode with gradually decreasing current (15 mA-10 mA-5 mA) was the most effective. Moreover, the effects of flow rate, influent salt concentration and current on the desalination performance of the three-stage FCDI device were studied. A fair comparison was made between the desalination performance of three-stage and single-stage FCDI devices, and the results showed that the multi-stage FCDI device with series flow electrodes can fully utilize the energy released during the short-circuit desorption process to reduce the energy consumption of desalination. Therefore, the multi-stage FCDI devices were more energy-efficient and economical than traditional single-stage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel E H 2 O 2 -MB-O 3 process was developed for antibiotics removal from wastewater. • More efficient CIP removal and mineralization were achieved in E H 2 O 2 -MB-O 3 process. • •OH oxidation was enhanced in E H 2 O 2 -MB-O 3 and contributed to CIP removal mainly. • Pyridone and piperazine ring in CIP molecule could be attacked by •OH more easily. Microbubble ozonation combined with electro-generated H 2 O 2 process (E H 2 O 2 -MB-O 3) was applied to degrade ciprofloxacin (CIP) as a typical antibiotic in wastewater in this study. The results showed that the performance of CIP degradation and mineralization in E H 2 O 2 -MB-O 3 process was more efficient than other related processes. Microbubble ozonation and electro-generated H 2 O 2 showed obvious synergistic effect on enhanced CIP removal in E H 2 O 2 -MB-O 3 process. The O 3 dosage, applied current and initial pH in E H 2 O 2 -MB-O 3 process were optimized as 12.5 mg/min, 50 mA and 7.0 (uncontrolled). Under the optimal conditions, CIP could be degraded completely within 60 min and the TOC removal efficiency of 28.85% could be achieved within 90 min in E H 2 O 2 -MB-O 3 process. The corresponding ozone utilization efficiency was close to 100%. More efficient ROS generation was observed in E H 2 O 2 -MB-O 3 process, especially •OH, compared with other related processes. The contribution rates of •OH, 1O 2 , O 3 and O 2.- to CIP removal were determined as 66.79%, 23.57%, 6.67% and 2.98% in E H 2 O 2 -MB-O 3 process, respectively. The electro-generated H 2 O 2 was clarified to contribute to not CIP removal but ROS generation. Three CIP degradation pathways were proposed according to identified degradation intermediates, which indicated that pyridone structure of quinoline and piperazine ring in CIP molecule could be destroyed more easily than benzene ring of quinoline, and the hydroxylation seemed to prevail in these CIP degradation pathways due to •OH electrophilic addition reaction probably. The removal of other antibiotics in E H 2 O 2 -MB-O 3 process also depended on not ozone direct oxidation but •OH oxidation mainly. [ABSTRACT FROM AUTHOR]