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Four materials were prepared as carriers for immobilizing anaerobic ammonium-oxidizing sludge. Nitrogen removal performance by these immobilized gel bead groups was evaluated. The removal ratios of ammonium and nitrite by CMC anammox-immobilized beads were 100% and 95.3% in 48 hours, respectively. The removal efficiencies of ammonium and nitrite by SA, PVA-SA and PVA anammox-immobilized beads were lower than the CMC beads. Subsequently, the physical properties of the beads were studied. PVA-SA was found to be the best support material among the four by comparing the case of the immobilization procedure, nitrogen removal efficiencies, and the costs of materials. PVA-SA gel entrapment was optimized by an orthogonal experiment. The SEM micrographs displayed that the surface structure of PVA-SA immobilized beads is loose and finely porous, which facilitates diffusion of the nitrogen. The SEM micrographs also clearly showed that anammox bacteria existed in the gel beads. All results clearly demonstrate that immobilizing anammox sludge in gel carriers is feasible and exhibit good performance. This research provided a new route to maintain sufficient amount of anammox sludge in a practical anammox reactor.

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To provide a solution for pursuing high redox reactivity beyond the compromise between the numbers of sulfur vacancies and electron transfer ability, 2D‐2D architecture of MoS2/rGO composite was fabricated with 2D graphene‐like transition metal dichalcogenides and graphene. By employing this material as heterogeneous catalyst, imines, also known as Schiff base, was synthesized by direct aerobic oxidative coupling of amines. Taking advantage of few‐layered MoS2 nanosheets and graphene, catalytic performance was significantly enhanced, exhibiting both excellent conversion and remarkable selectivity. Due to the good oil‐absorbing capability of this open porous 2D‐2D architecture, the hydrolysis of NH‐imines by water was inhibited and thus aldehydes byproducts were diminished. A second order kinetic behavior was observed in the imines formation, indicating the bimolecular condensation might be the rate determining step in such coupling reaction.

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Anaerobic ammonium oxidation (anammox) has been proved to be a promising nitrogen removal method for treating ammonium-rich wastewater. However, because of the low-growth rate of anammox bacteria, maintenance of a sufficient amount of anammox biomass in reactor became a key factor in application. Gel immobilization is an efficient method to prevent biomass from being washed out and to promote hyper-concentrated cultures. This study focused on a nitrogen removal process by anammox enrichment culture immobilized in polyvinyl alcohol and sodium alginate (PVA-SA) gel beads. The rapid startup of reactor demonstrated that gel entrapment was supposed to be a highly effective technique for immobilizing anammox bacteria. The anammox bacteria present in the enrichment were identified to be Jettenia-like species (>98%). Moreover, the effect of hydraulic retention time (HRT), pH, and temperature on immobilized anammox processes were investigated. The effect of pH and temperature on the anammox process was evidently weakened in PVA-SA immobilized gel beads, however, the effect of HRT on the anammox reaction was enhanced. Therefore, a stable operated reactor could be obtained in an anaerobic sequencing batch reactor, which proved gel immobilization was an excellent method to maintain the biomass in anammox reactor for application.

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