Low C/N wastewater results from a wide range of factors that significantly harm the environment. They include insufficient carbon sources, low denitrification efficiency, and ${\mathrm{NH}}_4^{+}$-N concentrations in low C/N wastewater that are too high to be treated. In this research, the membrane biofilm reactor and hydrogen-based membrane biofilm reactor (MBR-MBfR) were optimized and regulated under different operating parameters: the simulated domestic sewage with low C/N was domesticated and the domestic sewage was then denitrified. The results of the MBR-MBfR experiments indicated that a C/N ratio of two was suitable for ${\mathrm{NH}}_4^{+}$-N, ${\mathrm{NO}}_2^{-}$-N, ${\mathrm{NO}}_3^{-}$-N, and chemical oxygen demand (COD) removal in partial nitrification-denitrification (PN-D) and hydrogen autotrophic denitrification for further treatment. The steady state for domestic wastewater was reached when the MBR-MBfR in the experimental conditions of HRT = 15 h, SRT = 20 d, 0.04 Mpa for H₂ pressure in MBfR, 0.4–0.8 mg/L DO in MBR, MLSS = 2500 mg/L(MBR) and 2800 mg/L(MBfR), and effluent concentrations of ${\mathrm{NH}}_4^{+}$-N, ${\mathrm{NO}}_3^{-}$-N, and ${\mathrm{NO}}_2^{-}$-N were 4.3 ± 0.5, 1.95 ± 0.04, and 2.05 ± 0.15 mg/L, respectively. High-throughput sequencing results revealed the following: (1) The genus Nitrosomonas as the ammonia oxidizing bacteria (AOB) and Denitratisoma as potential denitrifiers were simultaneously enriched in the MBR; (2) at the genus level, Meiothermus,Lentimicrobium, Thauera,Hydrogenophaga, and Desulfotomaculum played a dominant role in leading to ${\mathrm{NO}}_3^{-}$-N and ${\mathrm{NO}}_2^{-}$-N removal in the MBfR.

The hydrogen-based membrane biofilm reactor (MBfR) has been widely applied in nitrate removal from wastewater, while the erratic fluctuation of treatment efficiency is in consequence of unstable operation parameters. In this study, hydrogen pressure, pH, and biofilm thickness were optimized as the key controlling parameters to operate MBfR. The results of 653.31 μm in biofilm thickness, 0.05 MPa in hydrogen pressure and pH in 7.78 suggesting high-efficiency NO3−−N removal and the NO3−−N removal flux was 1.15 g·m⁻² d⁻¹. 16S rRNA gene analysis revealed that Pseudomonas, Methyloversatilis, Thauera, Nitrospira, and Hydrogenophaga were the five most abundant bacterial genera in MBfRs after optimization. Moreover, significant increases of Pseudomonas relative abundances from 0.36 to 9.77% suggested that optimization could effectively remove nitrogen from MBfRs. Membrane pores and surfaces exhibited varying degrees of calcification during stable operation, as evinced by Ca²⁺ precipitation adhering to MBfR membrane surfaces based on scanning electron microscopy (SEM), atomic force microscopy (AFM) analyses. Scanning electron microscopy–energy dispersive spectrometer (SEM–EDS) analyses also confirmed that the primary elemental composition of polyvinyl chloride (PVC) membrane surfaces after response surface methodology (RSM) optimization comprised Ca, O, C, P, and Fe. Further, X-ray diffraction (XRD) analyses indicated the formation of Ca₅F(PO₄)₃ geometry during the stable operation phase.

Medical waste is a kind of special waste with great harm. Since the 1950s, the treatment of medical waste has attracted widespread attention from all over the world. At present, scholars at home and abroad are increasingly rich in research on medical waste treatment technology and have achieved certain research results. This article comprehensively compares and analyzes the technical influencing parameters, advantages and disadvantages of incineration treatment, pressure steam sterilization treatment, chemical treatment, microwave treatment, plasma treatment and other medical waste treatment methods, and emphasizes that high-temperature pyrolysis incineration treatment technology has reduced weight and is harmless. This is the current direction of domestic medical waste treatment research and development.

The back-diffusion of inactive gases severely inhibits the hydrogen (H₂) delivery rate of the close-end operated hydrogen-based membrane biofilm reactor (H₂-based MBfR). Nevertheless, less is known about the response of microbial communities in H₂-based MBfR to the impact of the gases’ back-diffusion. In this research, the denitrification performance and microbial dynamics were studied in a H₂-based MBfR operated at close-end mode with a fixed H₂ pressure of 0.04 MPa and fed with nitrate (NO₃⁻) containing influent. Results of single-factor and microsensor measurement experiments indicate that the H₂ availability was the decisive factor that limits NO₃⁻ removal at the influent NO₃⁻ concentration of 30 mg N/L. High-throughput sequencing results revealed that (1) the increase of NO₃⁻ loading from 10 to 20–30 mg N/L resulted in the shift of dominant functional bacteria from Dechloromonas to Hydrogenophaga in the biofilm; (2) excessive NO₃⁻ loading led to the declined relative abundance of Hydrogenophaga and basic metabolic pathways as well as counts of most denitrifying enzyme genes; and (3) in most cases, the decreased quantity of N metabolism-related functional bacteria and genes with increasing distance from the H₂ supply end corroborates that the microbial community structure in H₂-based MBfR was significantly impacted by the gases’ back-diffusion.