Microplastics (MPs) are found to be ubiquitous and serve as vectors for other contaminants, and the inevitable aging process changes MP properties and fates. However, whether the MPs in aging process affects the fates of antibiotic resistance gene (ARGs) in aquatic environments is poorly understood. Herein, the physicochemical property alteration of MPs being aged in landfill leachate, an important reservoir of MPs and ARGs, was investigated, and microbial community evolution and ARGs occurrence of MP surface during the aging process were analyzed. Aging process remarkably altered surface properties, including increasing specific surface areas, causing the formation of oxygen-containing groups, and changing surface morphology, which further increased the probability of microbial colonization. The bacterial assemblage on MPs showed higher biofilm-forming and pathogenic potential compared to leachate. ARGs quantification results suggested that MPs exhibited selective enrichment for ARGs in a ratio of 5.7–10³ folds, and the aging process enhanced the enrichment potential. Further co-occurrence networks suggested that the existence of non-random, closer and more stable ARGs-bacterial taxa relations on MP surface affected the ARG transmission. The study of ARG partitioning on MPs indicated that extracellular DNA was a nonnegligible reservoir of ARGs attached on MP surface, and that biofilm bacterial community influenced ARGs partitioning pattern during the aging process. This study confirmed that the aging process could enhance the potential of MPs as vectors for ARGs, which would promote the holistic understanding of MP behavior and risk in natural environments.

Subsurface wastewater infiltration systems (SWISs) have been widely used to treat rural domestic sewage. However, the low nitrogen removal and severe clogging problem always restrict the sustainability of SWISs for wastewater treatment. This study investigated the effects of aeration and biochar on the accumulation of nutrients and dissolved organic matter (DOM) in the substrate of loess soil-based SWISs for understanding the accumulation characteristics of DOM and the enhanced decontamination mechanism. The results showed that biochar addition could not improve the accumulation of nitrogen and phosphorus in the substrate, but could enhance denitrification (22%) via providing sufficient carbon for microorganisms. Moreover, the accumulation of organic matter in the substrate was also greatly affected. The DOM concentration of System D in the 40–60 cm layer reached 85.76 mg L⁻¹, which indicated that biochar could release abundant DOM. Substrate DOM mainly contained humic acid-like and tryptophan-like substances. Moreover, the refractory macromolecular DOM components with high aromaticity and humification were found in the substrate below 60 cm of systems with biochar addition. This may be related to the DOM released by biochar and the extracellular polymeric substance (EPS) produced by microorganisms. It may affect the sustainability of the substrate to a certain extent, but fortunately that intermittent aeration could reduce this adverse effect. This research could provide new insights for preventing clogging and useful guidance for improving wastewater treatment performance in SWISs.

Ecological floating beds (EFBs) have become a superior method for treating secondary effluent from wastewater treatment plant. However, insufficient electron donor limited its denitrification efficiency. Iron scraps from lathe cutting waste consist of more than 95% iron could be used as electron donors to enhance denitrification. In this study, EFBs with and without iron scraps supplementation (EFB-Fe and EFB, respectively) were conducted to explore the impacts of iron scraps addition on nitrogen removal, nitrous oxide (N₂O) emissions and microbial communities. Results showed the total nitrogen (TN) removal in EFB-Fe improved to 79% while that in EFB was 56%. N₂O emission was 0–6.20 mg m⁻² d⁻¹ (EFB-Fe) and 1.74–15.2 mg m⁻² d⁻¹ (EFB). Iron scraps could not only improve nitrogen removal efficiency, but also reduce N₂O emissions. In addition, high-throughput sequencing analysis revealed that adding iron scraps could improve the sum of denitrification related genera, among which Novosphingobium accounted for the highest proportion (6.75% of PFe1, 4.24% of PFe2, 3.18% of PFe3). Iron-oxidizing bacteria and iron-respiring bacteria associated with and nitrate reducing bacteria mainly concentrated on the surface of iron scraps. Principal co-ordinates analysis (PCoA) indicated that iron scraps were the key factor affecting microbial community composition. The mechanism of iron scraps enhanced nitrogen removal was realized by enhanced biological denitrification process. Iron release dynamic from iron scraps was detected in bench-scale experiment and the electron transfer mechanism was that Fe⁰ transferred electrons directly to NO₃⁻-N, and biological iron nitrogen cycle occurred in EFB-Fe without secondary pollution.

The effects of algae on the removal of contaminant by iron sulfide (FeS) are still unknown. Chlorella vulgaris (CV), a remarkable algal specie, was used to prepare the CV-supported FeS (CV-FeS) and to investigate the role that CV plays in the removal of a heavy metal (i.e., hexavalent chromium (Cr(VI)) by FeS. The stabilized effect from algal extracellular polymeric substance (EPS) enhanced the reactivity of FeS due to the decrease of FeS aggregation, thus increasing Cr(VI) removal rate from 0.21 min⁻¹ to 0.79 min⁻¹. Furthermore, the strong buffering induced by the algal functional groups could effectively prevent the solution pH from increasing, which improved Cr(VI) removal because acidic solution facilitated Cr(VI) reduction by FeS. However, the complexing capacity from algal EPS made Fe(II) unavailable for Cr(VI) reduction, which led to 35% decrease of Cr(VI) removal. The Fe(II) was oxidized to α-FeOOH by Cr(VI) in the absence of CV, while the unreacted Fe(II) was detected as in the form of Fe(OH)₂ in CV-FeS. Cr(VI) was reduced to Cr(III) and S(-II) was oxidized to elemental sulfur (S₈) regardless of the CV. This work showed the different roles of algae in the removal of Cr(VI) by FeS and provided value information for the application of FeS in the polluted algae-containing water system.

The valorization of municipal solid waste incineration bottom and fly ashes (IBA and IFA) as catalysts for thermochemical plastic treatment was investigated. As-received, calcined, and Ni-loaded ashes prepared via hydrothermal synthesis were used as low-cost waste-derived catalysts for in-line upgrading of volatile products from plastic pyrolysis. It was found that both IBA and air pollution control IFA (APC) promote selective production of BTEX compounds (i.e., benzene, toluene, ethylbenzene, and xylenes) without significantly affecting the formation of other gaseous and liquid species. There was insignificant change in the product distribution when electrostatic precipitator IFA (ESP) was used, probably due to the lack of active catalytic species. Calcined APC (C-APC) demonstrated further improvement in the BTEX yield that suggested the potential to enhance the catalytic properties of ashes through pre-treatment. By comparing with the leaching limit values stated in the European Council Decision, 2003/33/EC for the acceptance of hazardous waste at landfills, all the ashes applied remained in the same category after the calcination and pyrolysis processes, except the leaching of Cl⁻ from the ESP, which was around the borderline. Therefore, the use of ashes in catalytic reforming application do not significantly deteriorate their metal leaching behavior. Considering its superior catalytic activity towards BTEX formation, C-APC was loaded with Ni at 15 and 30 wt%. The Ni-loading favored an increase in overall oil yield, while reducing the gas yield when compared to the benchmark Ni loaded ZSM catalyst. However, Ni addition also caused the formation of more heavier hydrocarbons (C20–C35) that would require post-treatment to recover favorable products like BTEX.

Heavy metal pollution in ecosystem is a global threat. The associated toxicity and carcinogenic nature of heavy metals/metalloids such as mercury, cadmium, lead, and arsenic are imposing a severe risk to both ecological diversity and human lives. Harnessing the adaptive feature of microalgae for remediating toxic heavy metal has reached a milestone in past few decades. Transcriptomics analyses have provided mechanistic insights to map the dynamics of cellular events under heavy metal stress, thus deciphering the strategic responses of microalgae. Here, the present review comprehensively addresses the elicited molecular responses of microalgae to detoxify the heavy metal stress. The review highlights the intricate role of biochemical components and signaling networks mediating stress responsive transitions of microalgae at physiological level. Furthermore, the differential gene expression signifying the transporters involved in uptake, distribution/sequestration, and efflux of heavy metal has also been reviewed. In a nutshell, this study provided a comprehensive understanding of the molecular mechanisms adopted by microalgae at transcriptome level to nullify the oxidative stress while detoxifying the heavy metals.

The environment of a large-scale vegetable production area can be exposed to antibiotic residues and antibiotic-resistant bacteria (ARB) via animal manure and irrigation with contaminated water, which can facilitate the dissemination of ARB. However, the occurrence of ARB in plantation areas and their dissemination in this environment remain largely unexplored. In total, 382 samples including those from vegetable (n = 106), soil (n = 87), well water (n = 24), river water (n = 20), river sediments (n = 20), farmer feces (n = 58) and farmer hands (n = 67) were collected in 2019 from a large-scale cultivation area in Shandong, China. Selective agar plates were used to screen for carbapenem-resistant Enterobacteriaceae (CRE) and whole-genome sequencing and Southern blotting were used to characterise isolates and mobile genetic elements carrying carbapenem resistance determinants. A total of nine NDM-5-producing isolates of Escherichia coli, Klebsiella pneumoniae, and Citrobacter spp. were identified from environmental sources and human feces, all of which were multidrug-resistant. Single nucleotide polymorphism analysis suggested clonal transmission of carbapenem-resistant Citrobacter sedlakii within greenhouse soils in the area. Eight of the isolates carried closely related or identical IncX3 plasmids carrying blaNDM₋₅, which were shown to be conjugative via filter mating experiments, indicating the highly transmissible nature of this genetic element. Isolates of E. coli and Citrobacter freundii were detected in the feces of local farm workers and contained similar IncX3 plasmids with blaNDM₋₅ environmental isolates, suggesting a potential risk of CRE transfer from the work environment to the farm workers. Thus, further research is required to investigate the potential health risks associated with environmental exposure to CRE in vegetable cultivation areas.

The infrastructures of coal-fired power plants in China have changed significantly since 2010, but the magnitude and characteristics of polycyclic aromatic hydrocarbon (PAH) emissions remain to be updated. In the present study, a unit-based PAH emission inventory for coal-fired power plants between 2010 and 2017 was constructed for Anhui Province, China. Atmospheric PAH emissions from pulverized coal (PC) and circulating fluidized bed (CFB) units in 2017 were 8600 kg and 7800 kg, respectively. The emission rates and intensities for CFB units (7.2 kg ton⁻¹ and 2.1 kg MW⁻¹) were significantly higher than those for PC units (1.1 kg ton⁻¹ and 0.19 kg MW⁻¹), primarily because CFB boilers were operated at lower combustion temperatures and poor combustion conditions compared to PC boilers. The distribution patterns of PAH emissions across different age groups largely reflected the time periods for constructing coal-fired units in Anhui and for the transition of small units to large ones. The accomplishment of ultralow emission technologies and phase-out of outdated coal-fired units were responsible for the decreasing trend of PAH emissions between 2012 and 2017. The warmer summer in 2013 and 2017 and colder winter in 2011 compared to other years probably caused increased use of air conditioners, resulting in increased electricity consumption and PAH emissions. Future PAH emissions would decrease by 45–57% during 2017–2030, benefitting from power plant fleet optimization, i.e., phasing out outdated coal-fired units and replacing them with large ones. With the best available optimized power plant fleets and end-of-pipe control measures accomplished in Anhui’s CFPPs, PAH emissions in 2030 would potentially be reduced by 56–65%.

Owing to its physicochemical similarity to strontium (Sr), calcium (Ca) was tested as a key component of a soil washing solution for Sr-contaminated soil collected near a nuclear power plant. A four-factor, three-level Box–Behnken experimental design combined with response surface modeling was employed to determine the optimal Sr washing condition for Ca-based solution. The Ca concentration (0.1–1 M), liquid-to-soil ratio (5–20), washing time (0.5–2 h), and pH (2.0–7.0) were tested as the independent variables. From the Box–Behnken design, 27 sets of experimental conditions were selected, and a second-order polynomial regression equation was derived. The significance of the independent parameters and interactions was tested by analysis of variance. Ca concentration was found to be the most influential factor. To determine whether the four variables were independent, three-dimensional (3D) response surface plots were established. The optimal washing condition was determined to be as follows: 1 M Ca, L/S ratio of 20, 1 h washing, and pH = 2. Under this condition, the highest Sr removal efficiency (68.2%) was achieved on a soil contaminated with 90.1 mg/kg of Sr. Results from five-step sequential extraction before and after washing showed that 84.0% and 82.9% of exchangeable and carbonate-bound Sr were released, respectively. In addition, more tightly bound Sr, such as Fe/Mn oxides-bound and organic matter-bound Sr, were also removed (86.2% and 64.5% removal, respectively).