Haixiang Li

The H₂-based membrane biofilm reactor (H₂-MBfR) has been acknowledged as a cost-effective microbial reduction technology for oxyanion removal from drinking water sources, but it remains unknown how the evolution of biofilm characteristics responds to the changing critical operating parameters of the H₂-MBfR for simultaneous bromate (BrO₃⁻) and nitrate (NO₃⁻) elimination. Therefore, an expanded multispecies model, applicable to mechanistically interpret the bromate-reducing bacteria (BRB)- and denitrifying bacteria (DNB)-dominated metabolic processes in the biofilm of the H₂-MBfR, was developed in this study. The model outputs indicate that (1) increased BrO₃⁻ loading facilitated the metabolism of BRB by increasing BRB fraction and BrO₃⁻ gradients in the biofilm, but had a marginal influence on NO₃⁻ reduction; (2) H₂ pressure of 0.04 MPa enabled the minimal loss of H₂ and the extension of the active region of BRB and DNB in the biofilm; (3) once the influent NO₃⁻ concentration was beyond 10 mg N/L, the fraction and activity of BRB significantly declined; (4) BRB was more tolerant than DNB for the acidic aquatic environment incurred by the CO₂ pressure over 0.02 MPa. The results corroborate that the degree of microbial competition for substrates and space in the biofilm was dependent on system operating parameters.

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.