Spatiotemporal and seasonal dynamics in the microbial communities of a landfill-leachate contaminated aquifer

Leachate derived humic-like substances drive the variation in microbial communities in landfill-affected groundwater

Landfills are commonly used for waste disposal in many countries, and pose a significant threat of groundwater contamination. Dissolved organic matter (DOM) plays a crucial role as a carbon and energy source, supporting the growth and activity of microorganisms. However, the changes in the DOM signature and microbial community composition in landfill-affected groundwater and their bidirectional relationships remain inadequately explored. Herein, we showed that DOM originating from more recent landfills mainly comprises microbially produced substances resembling tryptophan and tyrosine. Conversely, DOM originating from older landfills predominantly comprises fulvic-like and humic-like compounds. Leachate leakage increases microbial diversity and richness and facilitates the transfer of foreign bacteria from landfills to groundwater, thereby increasing the vulnerability of the microbial ecosystem in groundwater. Deterministic processes dominated the assembly of the groundwater microbial community, while stochastic processes accounted for an increased proportion of the microbial community in the old landfills. The dominant phyla observed in groundwater were Proteobacteria, Bacteroidota, and Actinobacteriota, and humic-like substances play a crucial role in driving the variation in microbial communities in landfill-affected groundwater. Predictions using PICRUSt2 suggested significant associations between various metabolic pathways and microbial communities, with the Kyoto Encyclopedia of Genes and Genomes pathway "Metabolism" being the most predominant. The findings contribute to advancing our understanding of the transformation of DOM and its interplay with microbial communities and can serve as a scientific reference for decision-making regarding groundwater pollution monitoring and remediation.

Environmental pitfalls and associated human health risks and ecological impacts from landfill leachate contaminants: Current evidence, recommended interventions and future directions

The improper management of solid waste, particularly the dumping of untreated municipal solid waste, poses a growing global challenge in both developed and developing nations. The generation of leachate is one of the significant issues that arise from this practice, and it can have harmful impacts on both the environment and public health. This paper presents an overview of the primary waste types that generate landfill leachate and their characteristics. This includes examining the distribution of waste types in landfills globally and how they have changed over time, which can provide valuable insights into potential pollutants in a given area and their trends. With a lack of specific regulations and growing concerns regarding environmental and health impacts, the paper also focuses on emerging contaminants. Furthermore, the environmental and ecological impacts of leachate, along with associated health risks, are analyzed. The potential applications of landfill leachate, suggested interventions and future directions are also discussed in the manuscript. Finally, this work addresses future research directions in landfill leachate studies, with attention, for the first time to the potentialities that artificial intelligence can offer for landfill leachate management, studies, and applications.

Leachate leakage enhances the microbial diversity and richness but decreases Proteobacteria and weakens stable microbial ecosystem in landfill groundwater

Sanitary landfill is the most prevalent and economic method for municipal solid waste disposal, and the resultant groundwater pollution has become an environmental problem due to leachate leakage. The pollution characteristics in groundwater near landfill sites have been extensively investigated, although the succession characteristics and driving mechanisms of microbial communities in leachate-contaminated groundwater and the sensitive microbial indicators for leachate leakage identification remain poorly studied. Herein, results showed that leachate leakage enhanced the microbial diversity and richness and transferred endemic bacteria from landfills into groundwater, producing an average decrease of 17.73% in the relative abundance of Proteobacteria. The key environmental factor driving the evolution of microbial communities in groundwater due to leachate pollution was organic matter, which can explain 16.13% of the changes in microbial community composition. The |βNTI| values of the bacterial communities in all six landfills were <2, and the assembly process of microbial communities was primarily dominated using stochastic processes. Leachate pollution changed the assembly mechanism, transforming the community assembly process from an undominated process to a dispersal limitation process. Leachate pollution reduced the efficiency and stability of microbial communities in groundwater, increasing the vulnerability of the stable microbial ecosystems in groundwater. Notably, microbial indicators are more sensitive to leachate leakage and could accurately identify landfills where leachate leakage occurred and other extraneous pollutants. The phylum Proteobacteria and mcrA could act as appropriate indicators for the identification of leachate leakage. These results provide a novel insight into the monitoring, identification of groundwater pollution and the scientific guidance for appropriate remediation strategies for leachate-contaminated groundwater.

Bioelectrochemical stability improvement by Ce-N modified carbon-based cathode in high-salt stress and mechanism research

Although microbial fuel cells (MFCs) have potential for high-salt wastewater treatment, their application is limited by poor salt tolerance, deactivation and unstable catalytic performance. This study designed Ce-C, N-C, and Ce-N modified activated carbon (Ce-N-C) based on the catalytic mechanism and salt tolerance performance of Ce and N elements to address these limitations. With activated carbon (AC) as the control, this study analyzed the stability of the four cathodes under different salinity environments using norfloxacin (NOR) as a probe to assess the effect of cathodes and salinity on MFC degradation performance. After three months, comparing with other three cathodes, the Ce-N-C cathode demonstrated superior and stable electrochemical and power generation performance. In particular, the advantages of Ce-N-C in high-salt (600 mM NaCl) environment is more significant than no-salt or low-salt. The potential of Ce-N-C-End at current density of 0 was 14.0% higher than AC-End, and the power density of the MFC with Ce-N-C cathode was 105.7 mW/m², which was 3.1 times higher than AC. Also, the stability of NOR removal under the function of Ce-N-C improved with the increase of NaCl concentration or operation time. The CeO₂(111) crystal form, N-Ce-O bond and pyridine N might be the key factors in improving the catalytic performance and salt tolerance of the Ce-N modified carbon-based cathode using XPS and XRD analysis.

A comparative analysis employing a gene- and genome-centric metagenomic approach reveals changes in composition, function, and activity in waterworks with different treatment processes and source water in Finland

The emergence and development of next-generation sequencing technologies (NGS) has made the analysis of the water microbiome in drinking water distribution systems (DWDSs) more accessible and opened new perspectives in microbial ecology studies. The current study focused on the characterization of the water microbiome employing a gene- and genome-centric metagenomic approach to five waterworks in Finland with different raw water sources, treatment methods, and disinfectant. The microbial communities exhibit a distribution pattern of a few dominant taxa and a large representation of low-abundance bacterial species. Changes in the community structure may correspond to the presence or absence and type of disinfectant residual which indicates that these conditions exert selective pressure on the microbial community. The Archaea domain represented a small fraction (up to 2.5%) and seemed to be effectively controlled by the disinfection of water. Their role particularly in non-disinfected DWDS may be more important than previously considered. In general, non-disinfected DWDSs harbor higher microbial richness and maintaining disinfectant residual is significantly important for ensuring low microbial numbers and diversity. Metagenomic binning recovered 139 (138 bacterial and 1 archaeal) metagenome-assembled genomes (MAGs) that had a >50% completeness and <10% contamination consisting of 20 class representatives in 12 phyla. The presence and occurrence of nitrite-oxidizing bacteria (NOB)-like microorganisms have significant implications for nitrogen biotransformation in drinking water systems. The metabolic and functional complexity of the microbiome is evident in DWDSs ecosystems. A comparative analysis found a set of differentially abundant taxonomic groups and functional traits in the active community. The broader set of transcribed genes may indicate an active and diverse community regardless of the treatment methods applied to water. The results indicate a highly dynamic and diverse microbial community and confirm that every DWDS is unique, and the community reflects the selection pressures exerted at the community structure, but also at the levels of functional properties and metabolic potential.

Microbial assembly and co-occurrence network in an aquifer under press perturbation

Purpose

Thousands of aquifers worldwide have been polluted by leachate from landfills and many more remained threatened. Microbial communities from these environments play a crucial role in mediating biodegradation and maintaining the biogeochemical cycles, but their co-occurrence and assembly mechanism have not been investigated.

Method

Here, we coupled network analysis with multivariate statistics to assess the relative importance of deterministic versus stochastic microbial assembly in an aquifer undergoing intrinsic remediation, using 16S metabarcoding data generated through Illumina MiSeq sequencing of the archaeal/bacterial V3–V4 hypervariable region.

Results

Results show that both the aquifer-wide and localised community co-occurrences deviate from expectations under null models, indicating the predominance of deterministic processes in shaping the microbial communities. Further, the amount of variation in the microbial community explained by the measured environmental variables was 55.3%, which illustrates the importance of causal factors in forming the structure of microbial communities in the aquifer. Based on the network topology, several putative keystone taxa were identified which varied remarkably among the wells in terms of their number and composition. They included Nitrospira, Nitrosomonadaceae, Patulibacter, Legionella, uncharacterised Chloroflexi, Vicinamibacteriales, Neisseriaceae, Gemmatimonadaceae, and Steroidobacteraceae. The putative keystone taxa may be providing crucial functions in the aquifer ranging from nitrogen cycling by Nitrospira, Nitrosomonadaceae, and Steroidobacteraceae, to phosphorous bioaccumulation by Gemmatimonadaceae.

Conclusion

Collectively, the findings provide answers to fundamental ecological questions which improve our understanding of the microbial ecology of landfill leachate plumes, an ecosystem that remains understudied.

Dissemination of antibiotic resistance genes from landfill leachate to groundwater

Landfill leachate, a highly concentrated organic wastewater containing diverse microorganisms and various heavy metals, has become an important reservoir of antibiotic resistance genes (ARGs). In this study, a total of 203 unique ARGs and 10 mobile genetic elements (MGEs) were identified from collected landfill leachate and groundwater. The number and abundance (normalized and absolute) of antibiotic resistome in effluent of leachate treatment plants decreased significantly compared to influent. The abundance of ARGs in groundwater increased as the distance from the leachate basin decreased. Fast expectation-maximization microbial source tracking (FEAST) showed that up to 96 % of ARGs in groundwater (GW3) may originate from nearby leachate, suggesting that ARGs in leachate can penetrate and spread into the groundwater environment. A significant correlation between ARGs and bacterial communities was identified. Together with network analysis showing the 12 bacterial taxa co-occurring with seven classes of antibiotic-associated ARGs, our results revealed the diverse potential microbial hosts of ARGs in water samples around the landfill sites. Heavy metals, bacterial community and MGEs were the driving factors shaping the ARGs patterns in the water samples, with their interactions explaining 57 % of ARGs variations. Our results provide an understanding of the distribution and dissemination of ARGs from landfill leachate to the nearby groundwater and suggest a comprehensive impact assessment of ARGs in aquatic environments of landfills.

Subsurface microbial communities as a tool for characterizing regional-scale groundwater flow

Subsurface microbial community distribution patterns are influenced by biogeochemical and groundwater fluxes and may inform hydraulic connections along groundwater-flow paths. This study examined the regional-scale microbial community of the Death Valley Regional Flow System and evaluated whether subsurface communities can be used to identify groundwater-flow paths between recharge and discharge areas. Samples were collected from 36 sites in three groundwater basins: Pahute Mesa-Oasis Valley (PMOV), Ash Meadows (AM), and Alkali Flat-Furnace Creek Ranch (AFFCR). Microbial diversity within and between communities varied by location, and communities were separated into two overall groups that affiliated with the AM and PMOV/AFFCR basins. Network analysis revealed patterns between clusters of common microbes that represented groundwaters with similar geochemical conditions and largely corroborated hydraulic connections between recharge and discharge areas. Null model analyses identified deterministic and stochastic ecological processes contributing to microbial community assemblages. Most communities were more different than expected and governed by dispersal limitation, geochemical differences, or undominating processes. However, certain communities from sites located within or near the Nevada National Security Site were more similar than expected and dominated by homogeneous dispersal or selection. Overall, the (dis)similarities between the microbial communities of DVRFS recharge and discharge areas supported previously documented hydraulic connections between: (1) Spring Mountains and Ash Meadows; (2) Frenchman and Yucca Flat and Amargosa Desert; and (3) Amargosa Desert and Death Valley. However, only a portion of the flow path between Pahute Mesa and Oasis Valley could be supported by microbial community analyses, likely due to well-associated artifacts in samples from the two Oasis Valley sites. This study demonstrates the utility of combining microbial data with hydrologic, geologic, and water-chemistry information to comprehensively characterize groundwater systems, highlighting both strengths and limitations of this approach.

Exploratory analysis of the microbial community profile of the municipal solid waste leachate treatment system: A case study

Studies on the degradation dynamics of landfill leachate indicate that the microbial community profile is a valuable and sensitive tool for landfill monitoring programs. Although knowledge about the microbial community can improve the efficiency of leachate treatment systems, little is known about the microbial profile changes that occur throughout the leachate attenuation process. In the present work, an exploratory analysis of the microbial community profile of the MSW leachate treatment system in the municipality of Osório (Brazil) was conducted. In this way, a comprehensive analysis of chemical parameters, isotopic signature and microbial profile data were applied to monitor the changes in the structure of the microbial community throughout the leachate attenuation process and to describe the relationship between the microbial community structure and the attenuation of chemical and isotopic parameters. From data analysis, it was possible to assess the microbial community structure and relate it to the attenuation of chemical and isotopic parameters. Based on massive parallel 16S rRNA gene sequencing, it was possible to observe that each leachate treatment unit has a specific microbial consortium, reflecting the adaptation of different microorganisms to changes in leachate characteristics throughout treatment. From our results, we concluded that the structure of the microbial community is sensitive to the leachate composition and can be applied to study the municipal solid waste management system.

A nature-based solution to a landfill-leachate contamination of a confined aquifer

Remediation of groundwater from landfill contamination presents a serious challenge due to the complex mixture of contaminants discharged from landfills. Here, we show the significance of a nature-based solution to a landfill-contaminated aquifer in southeast Norway. Groundwater physicochemical parameters monitored for twenty-eight years were used as a proxy to infer natural remediation. Results show that concentrations of the major chemical variables decreased with time and distance until they tailed off. An exception to this was sulphate, which showed an increase, but apparently, exhibits a stationary phase. The water types were found to be most similar between samples from active landfill and post-closure stages, while samples from the stabilised stage showed a different water type. All the chemical parameters of samples from the stabilised stage were found to be within the Norwegian drinking water standards, except iron and manganese, which were only marginally above the limits, an indication of a possible recovery of this aquifer. The findings highlight the significance of natural attenuation processes in remediating contaminated aquifers and have significant consequences for future contamination management, where natural remediation can be viewed as an alternative worth exploring. This is promising in the wake of calls for sustainable remediation management strategies.