Wei Zhang

Greenhouse gas generated from wastewater treatment plants has attracted much attention as it has the potential to be recovered and used as an energy source. In this study, a membrane biofilm reactor was designed to simultaneously enhance nitrate removal and reduce methane (CH₄) emissions during methane oxidation coupled with the denitrification process. The enrichment of CH₄-driven denitrification microbes with a relatively short hydraulic retention time (HRT) and its effects on the stable operation of the reactor were studied within 250 d. With an increasing HRT from 8 to 20 h, a removal rate of up to approximately 0.51 mg/L·h⁻¹ was achieved, which also kept the effluent NO₂⁻-N below 0.5 mg/L. Microbial community analysis showed that the diversity and uniformity of microorganism communities decreased with the addition of CH₄ as a carbon source, and the microbial structure changed significantly. Compared with that of seed sludge at the phylum level, the relative abundance of Proteobacteria increased significantly, Alphaproteobacteria and Sphingobacteriia continued to become enriched, and the abundance of Methylocystis increased significantly. Neither denitrifying anaerobic methane oxidation (DAMO) archaea nor bacteria were found in the sequencing analysis. Methylocystis was the dominant CH₄ oxidizing bacteria, in synergy with the co-occurrence of autotrophic and heterotrophic denitrifying bacteria, which likely join up in nitrogen removal. Unlike the systems described in most methane-driven denitrification studies, our system achieved nitrate removal without detectable DAMO microbes.

Due to the unique chemical and physical properties, graphene-based nanomaterials are increasingly being introduced into various scientific fields. They all play very important roles in different fields and are widely used. Graphene oxide (GO) is one of the most popular and representative carbon nanomaterials; scientists have great research interest in it. When carbon nanomaterials such as GO are released into the aquatic environment, their physicochemical properties will be influenced by natural light, resulting in the potential change in toxic effects on aquatic organisms. Algae, as a typical aquatic organism, is extensively regarded as a model microorganism to assess the biotoxicity of nanomaterials. In this review, we overview the light-mediated impact of GO on algae. We summarize the photo-transformation of GO under different illumination conditions and the effect of illumination on the physicochemical properties of GO. Then, we combined metabolomics, genotoxicity, and proteomics with standard toxicity assays (cell division, membrane permeability, oxidative stress, photosynthesis, cellular ultrastructure, and so on) to compare native and environmentally transformed GO induction toxicological mechanisms. By correlating lights, physicochemical properties, and biotoxicity, this review is valuable for environmental fate assessments on graphene-based nanoparticles, providing a theoretical basis and support for evaluating the potential ecological health and environmental risks of graphene-based nanoparticles in real natural water environments.