The stress response of tetracycline resistance genes and bacterial communities under the existence of microplastics in typical leachate biological treatment system.

Landfill leachate is an important source of microplastics (MPs) and antibiotic-resistance genes (ARGs). Here, in the presence of polystyrene MPs (PS-MPs) and polyethylene MPs (PE-MPs), the nitrogen and phosphorus removal effect and sludge structure performance were affected in an anaerobic-anoxic-aerobic system, a typical biological leachate treatment process. The abundance of tetracycline-resistance genes (tet genes) in biofilms on the two types of MP was significantly higher than that in the leachate and sludge, and the load on PE-MPs was higher than that on PS-MPs because of the porous structure of PE-MPs. Aging of the MPs increased their surface roughness and abundance of oxygen-containing functional groups and shaped the profile of ARGs in the MP biofilms. The biofilm biomass and growth rate on the two types of MP increased with the incubation time in the first 30 days, and was affected by environmental factors. Structural equation models and co-occurrence network analysis demonstrated that the MPs indirectly affected the spectrum of ARGs by affecting biofilm formation, and, to a lesser extent, had a direct impact on the selective enrichment of ARGs. We discuss the mechanisms of the relationships between MPs and ARGs in the leachate treatment system, which will have guiding significance for future research. Our data on the colonization of microorganisms and tet genes in MPs biofilms provide new evidence concerning the accumulation and transmission of these ARGs, and are important for understanding the mechanisms of MPs in spreading pollution.

Mechanism of antibiotic resistance development in an activated sludge system under tetracycline pressure.

The mechanism of antibiotic resistance (AR) development in an activated sludge system under tetracycline (TC) pressure was discussed and analyzed. According to the variation of macro-factors, including TC, COD, TN, TP, NH3-N, pH, heavy metals, and reactor settings, the tet genes respond accordingly. Consequently, the enrichment sites of tet genes form an invisible AR selection zone, where AR microorganisms thrive, gather, reproduce, and spread. The efflux pump genes tetA and tetB prefer anaerobic environment, while ribosome protective protein genes tetM, tetO, tetQ, tetT, and tetW were more concentrated in aerobic situations. As a corresponding micro-effect, different types of tet genes selected the corresponding dominant bacteria such as Thauera and Arthrobacter, suggesting the intrinsic relationship between tet genes and potential hosts. In summary, the macro-response and micro-effect of tet genes constitute an interactive mechanism with tet genes as the core, which is the crucial cause for the continuous development of AR. This study provides an executable strategy to control the development of AR in actual wastewater treatment plants from the perspective of macro-factors and micro-effects.

Alteration of the migration trajectory of antibiotic resistance genes by microplastics in a leachate activated sludge system.

The environmental behavior of emerging contaminants of microplastics (MPs), antibiotics and antibiotic resistance genes (ARGs) in the leachate activated sludge system has been monitored and analyzed comprehensively. The results suggested that MPs could effectively alter the migration trajectory of tetracycline resistance genes (tet genes) in the leachate activated sludge system under intermittent and continuous influent conditions. After adding MPs, the total average abundance of tet genes in leachate increased from 0.74 ± 0.07 to 0.78 ± 0.07 (log10tet genes/log10 16S rRNA) and that in sludge increased from 0.65 ± 0.08 to 0.70 ± 0.06 (log10tet genes/log10 16S rRNA). Except for tetA, the abundance of tetB, tetO, tetM and tetQ on MPs increased with increasing TC concentration under both aerobic and anaerobic conditions. MPs not only significantly affect the abundance level and migration trajectory of ARGs in the leachate activated sludge system, but also remarkably improve the level of heavy metals in the ambient environment, indirectly promoting the selective effect of antibiotic-resistant bacteria (ARB) and promoting the development of antibiotic resistance (AR). In addition, MPs changed their physicochemical properties and released hazardous substances with aging to force tet genes to migrate from the leachate activated sludge system to the MPs, making AR more difficult to eliminate and persisted in wastewater treatment plants. Meanwhile, microorganisms played a driving role, making MPs serve as a niche for ARGs and ARB colonization. The co-occurrence network analysis indicated the specific distribution pattern of tet genes and microorganisms in different media, and the potential host was speculated. This study improves the understanding of the environmental behavior of emerging contaminants in leachate activated sludge system and lays a theoretical for protecting the ecological environment.

Performance, mechanism and stability of nitrogen-doped sewage sludge based activated carbon supported magnetite in anaerobic degradation of coal gasification wastewater.

In current study, the UASB reactor was enhanced by nitrogen-doped sewage sludge based activated carbon supported Fe3O4 (Fe3O4/N-SBAC) for coal gasification wastewater treatment. The results showed that COD removal efficiency was increased to 64.4% with Fe3O4/N-SBAC assistance and the corresponding methane production rate achieved up to 1093.6 mL/d. Fe3O4/N-SBAC promoted microbial growth and enzymatic activity, leading to high extracellular polymeric substances and coenzyme F420 concentrations. Fe3O4/N-SBAC also facilitated the sludge granulation process with high particle size, substantial interspecific signal molecules and low diffusible signal factor. Microbial community analysis revealed that Fe3O4/N-SBAC might support direct interspecies electron transfer process, in which the enriched Geobacter was likely to communicate with Methanothrix via electrical connection, improving anaerobic degradation of coal gasification wastewater. Total phenols shock and pH impact revealed that reactor stability was enhanced in the Fe3O4/N-SBAC-supplemented system.

Enhanced 2,4,6-trichlorophenol anaerobic degradation by Fe3O4 supported on water hyacinth biochar for triggering direct interspecies electron transfer and its use in coal gasification wastewater treatment.

Fe3O4 supported on water hyacinth biochar (Fe3O4/WHB) was successfully used in anaerobic degradation of 2,4,6-trichlorophenol and coal gasification wastewater (CGW). Chemical oxygen demand removal efficiency and methane production were significantly improved to 98.9% and 2.0 L with Fe3O4/WHB assisted. Fe3O4/WHB facilitated the conversion of CO2 to methane and reduce H2 production. A higher coenzyme F420 concentration of 1.32 µmol/(g-mixed liquor volatile suspended solids) was found with the presence of Fe3O4/WHB, which might result in a faster conversion of acetate to methane. More interspecific signal molecules, lower diffusible signal factor, and higher mean particle size indicated that Fe3O4/WHB accelerated the sludge granulation process. Microbial community analysis revealed that enriched bacteria Geobacter along with archaea Methanothrix and Methanosarcina may be involved in direct interspecies electron transfer by Fe3O4/WHB stimulation, enhancing the performance of 2,4,6-trichlorophenol fermentation. It is shown that use of Fe3O4/WHB is feasible for enhanced CGW treatment.