Airborne bacteria associated with particulate matter from a highly urbanised metropolis: A potential risk to the population’s health

• The airborne bacteria of Mexico City are representative of urban environments. • Particle material<10 µm influenced the type and quantity of airborne bacteria. • The diversity and richness of bacteria were higher in the rainy season. • The emission & transport of airborne bacteria determine the atmosphere’s microbiome. • Bacterias as Kocuria, Paracoccus, and Staphylococcus were in the air of Mexico City. Bacteria in the air present patterns in space and time produced by different sources and environmental factors. Few studies have focused on the link between airborne pathogenic bacteria in densely populated cities, and the risk to the population’s health. Bacteria associated with particulate matter (PM) were monitored from the air of Mexico City (Mexico). We employed a metagenomic approach to characterise bacteria using the 16S rRNA gene. Airborne bacteria sampling was carried out in the north, centre, and south of Mexico City, with different urbanisation rates, during 2017. Bacteria added to the particles were sampled using high-volume PM₁₀ samplers. To ascertain significant differences in bacterial diversity between zones and seasons, the Kruskal-Wallis, Wilcoxon tests were done on alpha diversity parameters. Sixty-three air samples were collected, and DNA was sequenced using next-generation sequencing. The results indicated that the bacterial phyla in the north and south of the city were Firmicutes, Cyanobacteria, Proteobacteria, and Actinobacteria, while in the central zone there were more Actinobacteria. There were no differences in the alpha diversity indices between the sampled areas. According to the OTUs, the richness of bacteria was higher in the central zone. Alpha diversity was higher in the rainy season than in the dry season; the Shannon index and the OTUs observed were higher in the central zone in the dry season. Pathogenic bacteria such as Kocuria, Paracoccus, and Micrococcus predominated in both seasonal times, while Staphylococcus, Corynebacterium, and Nocardioides were found during the rainy season, with a presence in the central zone.     

Understand the local and regional contributions on air pollution from the view of human health impacts

• PM_2.5-related deaths were estimated to be 227 thousand in BTH & surrounding regions. • Local emissions contribute more to PM_2.5-related deaths than PM_2.5 concentration. • Local controls are underestimated if only considering its impacts on concentrations. • Rural residents suffer larger impacts of regional transport than urban residents. • Reducing regional transport benefits in mitigating environmental inequality. The source-receptor matrix of PM_2.5 concentration from local and regional sources in the Beijing-Tianjin-Hebei (BTH) and surrounding provinces has been created in previous studies. However, because the spatial distribution of concentration does not necessarily match with that of the population, such concentration-based source-receptor matrix may not fully reflect the importance of pollutant control effectiveness in reducing the PM_2.5-related health impacts. To demonstrate that, we study the source-receptor matrix of the PM_2.5-related deaths instead, with inclusion of the spatial correlations between the concentrations and the population. The advanced source apportionment numerical model combined with the integrated exposure–response functions is used for BTH and surrounding regions in 2017. We observed that the relative contribution to PM_2.5-related deaths of local emissions was 0.75% to 20.77% larger than that of PM_2.5 concentrations. Such results address the importance of local emissions control for reducing health impacts of PM_2.5 particularly for local residents. Contribution of regional transport to PM_2.5-related deaths in rural area was 22% larger than that in urban area due to the spatial pattern of regional transport which was more related to the rural population. This resulted in an environmental inequality in the sense that people staying in rural area with access to less educational resources are subjected to higher impacts from regional transport as compared with their more resourceful and knowledgeable urban compatriots. An unexpected benefit from the multi-regional joint controls is suggested for its effectiveness in reducing the regional transport of PM_2.5 pollution thus mitigating the associated environmental inequality.     

Characterization of bacterial communities during persistent fog and haze events in the Qingdao coastal region

• Light haze had little effect on bacterial communities. • Fog and heavy haze had significant effects on these communities. • Air pollution exerted a greater influence than particle size on bacterial community. Here, we report the characteristics of bacterial communities in aerosols with different particle sizes during two persistent fog and haze events in December of 2015 and 2016 in Qingdao, China. In the early stage of pollution, the accumulation of PM_2.5 led to the accumulation of microorganisms, thus increasing the bacterial richness and diversity of fine particle sizes. With the persistence and aggravation of pollution, the toxic effect was strengthened, and the bacterial richness and diversity of each particle size decreased. When the particle concentration was highest, the richness and diversity were low for each particle size. Light haze had little influence on bacterial communities. The occurrence of highly polluted humid weather and heavy haze resulted in significant changes in bacterial community diversity, composition and structure, and air pollution exerted a greater influence than particle size on bacterial community structure. During persistent fog and haze events, with the increase of pollutants, bacteria associated with each particle size may be extensively involved in aerosol chemistry, but the degree of participation varies, which requires further study.     

Distribution of antibiotic resistance genes and their association with bacteria and viruses in decentralized sewage treatment facilities

• Distribution of ARGs in decentralized sewage facilities were investigated. • Bacitracin-ARGs were most predominant ARGs in rural wastewater. • ARGs were identified in bacterial and viral community. • ARGs of rpoB, drfE, gyrA and parC were both correlated with bacteria and phages. • More attention should be paid to the risk of spreading ARG by phages. The distribution of antibiotic resistance genes (ARGs) has been intensively studied in large-scale wastewater treatment plants and livestock sources. However, small-scale decentralized sewage treatment facilities must also be explored due to their possible direct exposure to residents. In this study, six wastewater treatment facilities in developed rural areas in eastern China were investigated to understand their risks of spreading ARGs. Using metagenomics and network analysis tools, ARGs and bacterial and viral communities were identified in the influent (INF) and effluent (EFF) samples. The dominant ARGs belonged to the bacitracin class, which are different from most of municipal wastewater treatment plants (WWTPs). The dominant hosts of ARGs are Acidovorax in bacterial communities and Prymnesiovirus in viral communities. Furthermore, a positive relationship was found between ARGs and phages. The ARGs significantly correlated with phages were all hosted by specific genera of bacteria, indicating that phages had contributed to the ARG’s proliferation in sewage treatment facilities. Paying significant concern on the possible enhanced risks caused by bacteria, viruses and their related ARGs in decentralized sewage treatment facilities is necessary.     

Impact of anthropogenic heat emissions on meteorological parameters and air quality in Beijing using a high-resolution model simulation

• The Large scale Urban Consumption of energY model was updated and coupled with WRF. • Anthropogenic heat emissions altered the precipitation and its spatial distribution. • A reasonable AHE scheme could improve the performance of simulated PM_2.5. • AHE aggravated the O₃ pollution in urban areas. Anthropogenic heat emissions (AHE) play an important role in modulating the atmospheric thermodynamic and kinetic properties within the urban planetary boundary layer, particularly in densely populated megacities like Beijing. In this study, we estimate the AHE by using a Large-scale Urban Consumption of energY (LUCY) model and further couple LUCY with a high-resolution regional chemical transport model to evaluate the impact of AHE on atmospheric environment in Beijing. In areas with high AHE, the 2-m temperature (T₂) increased to varying degrees and showed distinct diurnal and seasonal variations with maxima in night and winter. The increase in 10-m wind speed (WS₁₀) and planetary boundary layer height (PBLH) exhibited slight diurnal variations but showed significant seasonal variations. Further, the systematic continuous precipitation increased by 2.1 mm due to the increase in PBLH and water vapor in upper air. In contrast, the precipitation in local thermal convective showers increased little because of the limited water vapor. Meanwhile, the PM_2.5 reduced in areas with high AHE because of the increase in WS₁₀ and PBLH and continued to reduce as the pollution levels increased. In contrast, in areas where prevailing wind direction was opposite to that of thermal circulation caused by AHE, the WS₁₀ reduced, leading to increased PM_2.5. The changes of PM_2.5 illustrated that a reasonable AHE scheme might be an effective means to improve the performance of PM_2.5 simulation. Besides, high AHE aggravated the O₃ pollution in urban areas due to the reduction in NO_x.     

Temporal variation of PM2.5-associated health effects in Shijiazhuang,Hebei

•Annual mean PM_2.5 in Shijiazhuang were 87, 95, and 82 µg/m³ in 2015–2017. •Health risk of cardiovascular system was higher than respiratory system. •Premature mortality attributed to PM_2.5 was 5088 people in 2017. •ΔMort and YLL reduced by 84.2% and 84.6% when PM_2.5 reduced to 10 µg/m³. •Health risks due to PM_2.5 were severe in Shijiazhuang in 2015–2017. Shijiazhuang is one of the cities in the North China Plain. In recent decades, this city has experienced high levels of fine particulate matter (PM_2.5), which have potentially significant effects on human health. In this study, the health effects of PM_2.5 exposure in Shijiazhuang were estimated by applying an integrated exposure-response model. Premature mortality, years of life lost (YLL), and the mortality benefits linked to reduced levels of PM_2.5 were quantified for the period 2015–2017. In 2015, 2016, and 2017, cerebrovascular diseases caused the highest premature mortality (2432, 2449, and 2483, respectively), followed by ischemic heart diseases (1391, 1479, and 1493, respectively), lung cancer (639,660, and 639, respectively), and chronic obstructive pulmonary diseases (533, 519, and 473, respectively). Notably, the total number of premature deaths caused by PM_2.5 exposure in Shijiazhuang in 2015, 2016, and 2017 were 4994, 5107, and 5088, respectively. Moreover, the YLL in the same years were 47001, 47880 and 47381, respectively. Interestingly, the YLL per 1000 females was lower than that per 1000 males. Finally, we noted that premature mortality and YLL decreased by 84.2% and 84.6% when the PM_2.5 levels diminished to 10 µg/m³. Overall, the results of this study improve our understanding of how high PM_2.5 concentrations affect human health and suggest the application of more stringent measures in Shijiazhuang to alleviate the associated health risks.     

Acid Orange 7 degradation using methane as the sole carbon source and electron donor

• AO7 degradation was coupled with anaerobic methane oxidation. • Higher concentration of AO7 inhibited the degradation. • The maximum removal rate of AO7 reached 280 mg/(L·d) in HfMBR. • ANME-2d dominated the microbial community in both batch reactor and HfMBR. • ANME-2d alone or synergistic with the partner bacteria played a significant role. Azo dyes are widely applied in the textile industry but are not entirely consumed during the dyeing process and can thus be discharged to the environment in wastewater. However, azo dyes can be degraded using various electron donors, and in this paper, Acid Orange 7 (AO7) degradation performance is investigated using methane (CH₄) as the sole electron donor. Methane has multiple sources and is readily available and inexpensive. Experiments using ¹³C-labeled isotopes showed that AO7 degradation was coupled with anaerobic oxidation of methane (AOM) and, subsequently, affected by the initial concentrations of AO7. Higher concentrations of AO7 could inhibit the activity of microorganisms, which was confirmed by the long-term performance of AO7 degradation, with maximum removal rates of 8.94 mg/(L·d) in a batch reactor and 280 mg/(L·d) in a hollow fiber membrane bioreactor (HfMBR). High-throughput sequencing using 16S rRNA genes showed that Candidatus Methanoperedens, affiliated to ANME-2d, dominated the microbial community in the batch reactor and HfMBR. Additionally, the relative abundance of Proteobacteria bacteria (Phenylobacterium, Pseudomonas, and Geothermobacter) improved after AO7 degradation. This outcome suggested that ANME-2d alone, or acting synergistically with partner bacteria, played a key role in the process of AO7 degradation coupled with AOM.     

Sulfur cycle as an electron mediator between carbon and nitrate in a constructed wetland microcosm

• Fe(III) accepted the most electrons from organics, followed by NO₃^‒, SO₄^2‒, and O₂. • The electrons accepted by SO₄^2‒ could be stored in the solid AVS, FeS₂-S, and S⁰. • The autotrophic denitrification driven by solid S had two-phase characteristics. • A conceptual model involving electron acceptance, storage, and donation was built. • S cycle transferred electrons between organics and NO₃^‒ with an efficiency of 15%. A constructed wetland microcosm was employed to investigate the sulfur cycle-mediated electron transfer between carbon and nitrate. Sulfate accepted electrons from organics at the average rate of 0.84 mol/(m³·d) through sulfate reduction, which accounted for 20.0% of the electron input rate. The remainder of the electrons derived from organics were accepted by dissolved oxygen (2.6%), nitrate (26.8%), and iron(III) (39.9%). The sulfide produced from sulfate reduction was transformed into acid-volatile sulfide, pyrite, and elemental sulfur, which were deposited in the substratum, storing electrons in the microcosm at the average rate of 0.52 mol/(m³·d). In the presence of nitrate, the acid-volatile and elemental sulfur were oxidized to sulfate, donating electrons at the average rate of 0.14 mol/(m³·d) and driving autotrophic denitrification at the average rate of 0.30 g N/(m³·d). The overall electron transfer efficiency of the sulfur cycle for autotrophic denitrification was 15.3%. A mass balance assessment indicated that approximately 50% of the input sulfur was discharged from the microcosm, and the remainder was removed through deposition (49%) and plant uptake (1%). Dominant sulfate-reducing (i.e., Desulfovirga, Desulforhopalus, Desulfatitalea, and Desulfatirhabdium) and sulfur-oxidizing bacteria (i.e., Thiohalobacter, Thiobacillus, Sulfuritalea, and Sulfurisoma), which jointly fulfilled a sustainable sulfur cycle, were identified. These results improved understanding of electron transfers among carbon, nitrogen, and sulfur cycles in constructed wetlands, and are of engineering significance.     

Fungal diversity and its mechanism of community shaping in the milieu of sanitary landfill

• Ascomycota was the predominant phylum in sanitary landfill fungal communities. • Saprophytic fungi may be of special importance in landfill ecology. • Both richness and diversity of fungal community were lower in leachate than refuse. • Physical habitat partly contributed to the geographic variance of fungal community. • NO₃⁻ was considered the most significant abiotic factor shaping fungal community. Land filling is the main method to dispose municipal solid waste in China. During the decomposition of organic waste in landfills, fungi play an important role in organic carbon degradation and nitrogen cycling. However, fungal composition and potential functions in landfill have not yet been characterized. In this study, refuse and leachate samples with different areas and depths were taken from a large sanitary landfill in Beijing to identify fungal communities in landfills. In high-throughput sequencing of ITS region, 474 operational taxonomic units (OTUs) were obtained from landfill samples with a cutoff level of 3% and a sequencing depth of 19962. The results indicates that Ascomycota, with the average relative abundance of 84.9%, was the predominant phylum in landfill fungal communities. At the genus level, Family Hypocreaceae unclassified (15.7%), Fusarium (9.9%) and Aspergillus (8.3%) were the most abundant fungi found in the landfill and most of them are of saprotrophic lifestyle, which plays a big role in nutrient cycling in ecosystem. Fungi existed both in landfilled refuse and leachate while both the richness and evenness of fungal communities were higher in the former. In addition, fungal communities in landfilled refuse presented geographic variances, which could be partly attributed to physical habitat properties (pH, dissolved organic carbon, volatile solid, NH₄⁺, NO₂⁻ and NO₃⁻), while NO₃⁻ was considered the most significant factor (p<0.05) in shaping fungal community.     

Partial anammox achieved in full scale biofilm process for typical domestic wastewater treatment

• A full scale biofilm process was developed for typical domestic wastewater treatment. • The HRT was 8 h and secondary sedimentation tank was omitted. • Candidatus Brocadia were enriched in the HBR with an abundance of 2.89%. • Anammox enabled a stable ammonium removal of ~15% in the anoxic zone. The slow initiation of anammox for treating typical domestic wastewater and the relatively high footprint of wastewater treatment infrastructures are major concerns for practical wastewater treatment systems. Herein, a 300 m³/d hybrid biofilm reactor (HBR) process was developed and operated with a short hydraulic retention time (HRT) of 8 h. The analysis of the bacterial community demonstrated that anammox were enriched in the anoxic zone of the HBR process. The percentage abundance of Candidatus Brocadia in the total bacterial community of the anoxic zone increased from 0 at Day 1 to 0.33% at Day 130 and then to 2.89% at Day 213. Based upon the activity of anammox bacteria, the removal of ammonia nitrogen (NH₄⁺-N) in the anoxic zone was approximately 15%. This showed that the nitrogen transformation pathway was enhanced in the HBR system through partial anammox process in the anoxic zone. The final effluent contained 12 mg/L chemical oxygen demand (COD), 0.662 mg/L NH₄⁺-N, 7.2 mg/L total nitrogen (TN), and 6 mg/L SS, indicating the effectiveness of the HBR process for treating real domestic wastewater.     

Deciphering the effect of sodium dodecylbenzene sulfonate on up-flow anaerobic sludge blanket treatment of synthetic sulfate-containing wastewater

• UASB reactor can work efficiently with high COD/SO₄^2- ratios when SDBS exists. • Outcome of the competition between SRB and MPA was affected by SDBS. • Presence of SDBS makes methanogens with H₂/CO₂ as a substrate dominant. • Microbial diversity decreases in the presence of SDBS. In this study, the effects of organic sulfur on anaerobic biological processes were investigated by operating two up-flow anaerobic sludge blanket (UASB) reactors with sodium dodecylbenzene sulfonate (SDBS) as a representative of organic sulfur. The results indicated that the specific methanogenic activity (SMA) and chemical oxygen demand (COD) removal efficiency of R2 (with SDBS added) were higher than those of R1 (without SDBS) when the COD/SO₄²⁻ ratio was above 5.0. However, when the COD/SO₄²⁻ ratio was lower than 5.0, the sulfate reduction efficiency of R2 was higher than that of R1. These results and the observed SDBS transformation efficiency in anaerobic reactors indicate that low concentrations of SDBS accelerate methane production and the continuous accumulation of SDBS does not weaken the reduction of sulfate. Similarly, the calculated electron flux for a COD/SO₄²⁻ ratio of 1.0 indicates that the utilization intensity of electrons by sulfate-reducing bacteria (SRB) in R2 was 36.48% higher than that of SRB in R1 and exceeded that of methane-producing archaea (MPA) under identical working conditions. Moreover, the addition of SDBS in R2 made sulfidogenesis the dominant reaction at low COD/SO₄²⁻, and Methanobacterium and Methanobrevibacter with H₂/CO₂ as the substrate and Desulfomicrobium were the dominant MPA and SRB, respectively. However, methanogenesis was still the dominant reaction in R1, and Methanosaeta with acetic acid as the substrate and Desulfovibrio were the dominant MPA and SRB, respectively.     

Particle-bound polycyclic aromatic hydrocarbons in typical urban of Yunnan-Guizhou Plateau: Characterization,sources and risk assessment

• The sampling was conducted in city on the Yunnan-Guizhou Plateau for one year. • The groups of PAHs revealed their different environmental fates and migration paths. • Seasonal biomass burning could affect the concentration by long-distance transport. • Industrial sources and traffic emissions were the main contributor of PAHs. • Living in industrial areas or winter had higher health risk by exposure PAHs in PM_2.5. Monthly particle-phase ambient samples collected at six sampling locations in Yuxi, a high-altitude city on the edge of Southeast Asia, were measured for particle-associated PAHs. As trace substances, polycyclic aromatic hydrocarbons (PAHs) are susceptible to the influences of meteorological conditions, emissions, and gas-particulate partitioning and it is challenging job to precise quantify the source and define the transmission path. The daily concentrations of total PM_2.5-bound PAHs ranged from 0.65 to 80.76 ng/m³, with an annual mean of 11.94 ng/m³. Here, we found that the concentration of PM_2.5-bound PAHs in winter was significantly higher than that in summer, which was mainly due to source and meteorology influence. The increase of fossil combustion and biomass burning in cold season became the main contributors of PAHs, while precipitation and low temperature exacerbated this difference. According to the concentration variation trend of PM_2.5-bound PAHs and their relationship with meteorological conditions, a new grouping of PAHs is applied, which suggested that PAHs have different environmental fates and migration paths. A combination of source analysis and trajectory model supported local sources from combustion of fossil fuel and vehicle exhaust contributed to the major portion on PAHs in particle, but on the Indochina Peninsula the large number of pollutants emitted by biomass burning during the fire season would affect the composition of PAHs through long-range transporting. Risk assessment in spatial and temporal variability suggested that citizens living in industrial areas were higher health risk caused by exposure the PM_2.5-bound PAHs than that in other regions, and the risk in winter was three times than in summer.     

The size distribution of airborne bacteria and human pathogenic bacteria in a commercial composting plant

•Bacterial concentrations from eight stages were 10⁴–10⁵copies/m³. •Diameter influenced clustering of bacterial and HPB lineages. •Dg of 8 HPB ranged from 2.42 to 5.09 μm in composting areas. •Dg of 8 HPB ranged from 3.70 to 8.96 μm in packaging areas. •HPB had high concentrations and small sizes in composting areas. Composting plants are regarded as one of the important sources of environmental bioaerosols. However, limitations in the size distribution of airborne bacteria have prevented our comprehensive understanding of their risk to human health and their dispersal behavior. In this study, different sizes of airborne bacteria were collected using an eight-stage impactor from a full-scale composting facility. Size-related abundance and communities of airborne bacteria as well as human pathogenic bacteria (HPB) were investigated using 16S rRNA gene sequencing coupled with droplet digital PCR. Our results indicate that the bacterial concentrations from the eight stages were approximately 10⁴–10⁵copies/m³. Although no statistical correlation was detected between the particle size and the Shannon index, the influence of size on bacterial lineages was observed in both composting and packaging areas. For airborne bacteria from different stages, the dominant phyla were Firmicutes, Proteobacteria, and Actinobacteria, and the dominant genera was Bacillus. Seven out of eight HPB with a small geometric mean aerodynamic diameter had a high concentration in composting areas. Based on diameters of 2.42 to 5.09 μm, most HPB in the composting areas were expected to be deposited on the bronchus and secondary bronchus. However, in the packaging areas, the deposition of HPB (diameters 3.70 to 8.96 μm) occurred in the upper part of the respiratory tract. Our results on the size distribution, abundance, and diversity of these bacteria offer important information for the systematic evaluation of bacterial pathogenicity and the potential health impacts on workers in composting plants and the surrounding residents.     

Removal of steroid hormones from mariculture system using seaweed Caulerpa lentillifera

•Steroid hormones could be removed efficiently from mariculture system using seaweed; • Caulerpa lentillifera was the most efficient seaweed for removal of steroid hormones; • More than 90% of E₂ or EE₂ were removed within 12 h using Caulerpa lentillifera; • The removal included the rapid biosorption and the slow bio-accumulation; •The hormones and nutrients in mariculture wastewater could be simultaneously removed. The removal of steroid hormones from the mariculture system using seaweeds (Caulerpa lentillifera, Ulva pertusa, Gracilaria lemaneiformis, and Codium fragile) was investigated. The results illustrated that both 17β-estradiol (E₂) and 17α-ethinylestradiol (EE₂) could be removed by the seaweeds at different levels, and the Caulerpa lentillifera was the most efficient one. More than 90% of E₂ or EE₂ at concentration of 10 μg/L was removed by Caulerpa lentillifera within 12 h. Processes including initial quick biosorption, the following slow accumulation, and biodegradation might explain the removal mechanisms of E₂/EE₂ by Caulerpa lentillifera. E₂/EE₂ removal was positively related to the nutrient level and the initial concentration of steroid hormone. A significant linear relationship for E₂ and EE₂ existed between the initial pollutant concentration and the average removal rate. The highest removal kinetic constant (k) value was obtained at 30°C as 0.34 /h for E₂ and at 20°C as 0.28 /h for EE₂, demonstrating the promising application potential of Caulerpa lentillifera in the water purification of the industrialized mariculture system with relatively high water temperature. Simultaneous and efficient removal of E₂ and EE₂ by Caulerpa lentillifera was still achieved after 3 cycles in the pilot-scale experiment. The steroid hormones and nutrients in mariculture wastewater could also be simultaneously removed using Caulerpa lentillifera. These findings demonstrated that Caulerpa lentillifera was the promising seaweed for the removal of steroid hormones in mariculture systems.     

Different response of bacterial community to the changes of nutrients and pollutants in sediments from an urban river network

• Bacterial community varied spatially in sediments from the urban river network. • Key environmental factors shaping bacterial community were detected by RDA. • Bacterial co-occurrence networks changed at different levels of nutrient and metal. • Potential indicator species were selected to predict pollution risk in sediment. Microbial communities in sediment are an important indicator linking to environmental pollution in urban river systems. However, how the diversity and structure of bacterial communities in sediments from an urban river network respond to different environmental factors has not been well studied. The goal of this study was to understand the patterns of bacterial communities in sediments from a highly dense urbanized river network in the lower Yangtze River Delta by Illumina MiSeq sequencing. The correlations between bacterial communities, the environmental gradient and geographical distance were analyzed by redundancy analysis (RDA) and network methods. The diversity and richness of bacterial community in sediments increased from upstream to downstream consistently with the accumulation of nutrient in the urban river network. Bacterial community composition and structure showed obvious spatial changes, leading to two distinct groups, which were significantly related to the characteristics of nutrient and heavy metal in sediments. Humic substance, available nitrogen, available phosphorus, Zn, Cu, Hg and As were selected as the key environmental factors shaping the bacterial community in sediments based on RDA. The co-occurrence patterns of bacterial networks showed that positive interaction between bacterial communities increased but the connectivity among bacterial genera and stability of sediment ecosystem reduced under a higher content of nutrient and heavy metal in average. The sensitive and ubiquitous taxa with an overproportional response to key environmental factors were detected as indicator species, which provided a novel method for the prediction of the pollution risk of sediment in an urban river network.     

Bacteriophages in water pollution control: Advantages and limitations

•Phages can be better indicators of enteric viruses than fecal indicator bacteria. •Multiple phages should be added to the microbial source tracking toolbox. •Engineered phage or phage cocktail can effectively target resistant bacteria. •In phage use, phage-mediated horizontal gene transfer cannot be ignored. •More schemes are needed to prevent phage concentration from decreasing. Wastewater is a breeding ground for many pathogens, which may pose a threat to human health through various water transmission pathways. Therefore, a simple and effective method is urgently required to monitor and treat wastewater. As bacterial viruses, bacteriophages (phages) are the most widely distributed and abundant organisms in the biosphere. Owing to their capacity to specifically infect bacterial hosts, they have recently been used as novel tools in water pollution control. The purpose of this review is to summarize and evaluate the roles of phages in monitoring pathogens, tracking pollution sources, treating pathogenic bacteria, infecting bloom-forming cyanobacteria, and controlling bulking sludge and biofilm pollution in wastewater treatment systems. We also discuss the limitations of phage usage in water pollution control, including phage-mediated horizontal gene transfer, the evolution of bacterial resistance, and phage concentration decrease. This review provides an integrated outlook on the use of phages in water pollution control.     

Research progress and prospects of complete ammonia oxidizing bacteria in wastewater treatment

• Comammox bacteria have unique physiological characteristics. • Comammox bacteria are widely distributed in natural and artificial systems. • Comammox bacteria have the potential to reduce N₂O emissions. • Coupling comammox bacteria with DEAMOX can be promoted in wastewater treatment. • Comammox bacteria have significant potential for enhancing total nitrogen removal. Complete ammonia oxidizing bacteria, or comammox bacteria (CAOB), can oxidize ammonium to nitrate on its own. Its discovery revolutionized our understanding of biological nitrification, and its distribution in both natural and artificial systems has enabled a reevaluation of the relative contribution of microorganisms to the nitrogen cycle. Its wide distribution, adaptation to oligotrophic medium, and diverse metabolic pathways, means extensive research on CAOB and its application in water treatment can be promoted. Furthermore, the energy-saving characteristics of high oxygen affinity and low sludge production may also become frontier directions for wastewater treatment. This paper provides an overview of the discovery and environmental distribution of CAOB, as well as the physiological characteristics of the microorganisms, such as nutrient medium, environmental factors, enzymes, and metabolism, focusing on future research and the application of CAOB in wastewater treatment. Further research should be carried out on the physiological characteristics of CAOB, to analyze its ecological niche and impact factors, and explore its application potential in wastewater treatment nitrogen cycle improvement.     

Potential shift of bacterial community structure and corrosion-related bacteria in drinking water distribution pipeline driven by water source switching

• Bacterial release from aged pipe sections under extreme conditions was quantified. • Released bacterial community structure exhibited large variation after transition. • Risks from transition reduced significantly with cleaner source. As a result of pollution in the present water sources, cities have been forced to utilize cleaner water sources. There are few reports regarding the potential shift of bacterial community structure driven by water source switching, especially that of corrosion-related bacteria. Three types of finished water were used for simulation, the polluted source water from the Qiantang and Dongtiaoxi Rivers (China) was replaced by cleaner water from Qiandao Lake (China). Here, we discussed the transition effects through three simulated reactors. The bacterial characteristics were identified using the high-throughput sequencing and heterotrophic plate count method. It was observed that the level of culturable bacteria declined by 2–3 orders of magnitude after water source switching. The bacterial community released from the pipeline reactor was significantly different under different finished water, and it exhibited large variation at the genus level. Porphyrobacter (58.2%) and Phreatobacter (14.5%) clearly replaced Novosphingobium, Aquabacterium, and Cupriavidus as new dominant genera in system A, which could be attributed to the lower carbon and nitrogen content of the new water source. Although corrosion-inhibiting bacteria decreased after switching, they still maintained dominant in three reactors (6.6%, 15.9%, and 19.7%). Furthermore, potential opportunistic pathogens such as Sphingomonas were detected. Our study shows that after transition to a high quality water source, the total culturable bacteria released was in a downtrend, which leads to a great reduction in the risk of bacterial leakage in the produced drinking water.     

Mechanism of dichloromethane disproportionation over mesoporous TiO2 under low temperature

• Mechanism of DCM disproportionation over mesoporous TiO₂ was studied. • DCM was completely eliminated at 350℃ under 1 vol.% humidity. • Anatase (001) was the key for disproportionation. • A competitive oxidation route co-existed with disproportionation. • Disproportionation was favored at low temperature. Mesoporous TiO₂ was synthesized via nonhydrolytic template-mediated sol-gel route. Catalytic degradation performance upon dichloromethane over as-prepared mesoporous TiO₂, pure anatase and rutile were investigated respectively. Disproportionation took place over as-made mesoporous TiO₂ and pure anatase under the presence of water. The mechanism of disproportionation was studied by in situ FTIR. The interaction between chloromethoxy species and bridge coordinated methylenes was the key step of disproportionation. Formate species and methoxy groups would be formed and further turned into carbon monoxide and methyl chloride. Anatase (001) played an important role for disproportionation in that water could be dissociated into surface hydroxyl groups on such structure. As a result, the consumed hydroxyl groups would be replenished. In addition, there was another competitive oxidation route governed by free hydroxyl radicals. In this route, chloromethoxy groups would be oxidized into formate species by hydroxyl radicals transfering from the surface of TiO₂. The latter route would be more favorable at higher temperature.     

Biotoxicity evaluation of zinc oxide nanoparticles on bacterial performance of activated sludge at COD,nitrogen, and phosphorus reduction

• ZnO-NP disrupted metabolic/catabolic balance of bacteria by affecting DHA activity. • ZnO-NPs toxicity was related to Zn²⁺ ion, interaction with cell and ROS generation. • Exposure to ZnO-NPs resulted in changed bacterial community structure at sludge. • The change in the EPS content was observed during exposure to ZnO-NPs. The unique properties and growing usage of zinc oxide nanoparticles increase their release in municipal wastewater treatment plants. Therefore, these nanoparticles, by interacting with microorganisms, can fail the suitable functioning of biological systems in treatment plants. For this reason, research into the toxicity of ZnO is urgent. In the present study, the toxicity mechanism of ZnO-NPs towards microbial communities central to granular activated sludge (GAS) performance was assessed over 120-day exposure. The results demonstrate that the biotoxicity of ZnO-NPs is dependent upon its dosage, exposure time, and the extent of reactive oxygen species (ROS) production. Furthermore, GAS performance and the extracellular polymeric substances (EPS) content were significantly reduced at 50 mg/L ZnO-NPs. This exposure led to decreases in the activity of ammonia monooxygenase (25.2%) and nitrate reductase (11.9%) activity. The Field emission scanning electron microscopy images confirmed that ZnO-NPs were able to disrupt the cell membrane integrity and lead to cell/bacterial death via intracellular ROS generation which was confirmed by the Confocal Laser Scanning Microscopy analysis. After exposure to the NPs, the bacterial community composition shifted to one dominated by Gram-positive bacteria. The results of this study could help to develop environmental standards and regulations for NPs applications and emissions.