Microbial community structure and diversity in a municipal solid waste landfill

Vadose-zone characteristic pollutants distribution, microbial community structure and functionality changes in response to long-term leachate pollution of an informal landfill site

The study embarked on a comprehensive examination of the evolution and diversity of microorganisms within long-term leachate pollution environments, with a focus on varying depths and levels of contamination, and its linkage to soil characteristics and the presence of heavy metals. It was observed that microbial diversity presented distinct cross-depth trend, where archaeal communities were found to be particularly sensitive to alterations in soil depth. Noteworthily, Euryarchaeota increased by 4.82 %, 7.64 % and 9.87 % compared with topsoil. The abundance of Tahumarchaeota was successively reduced by 5.79 %, 9.58 %, and 12.66 %. The bacterial community became more sensitive to leachate pollution, and the abundance of Protebacteria in contaminated soil decreased by 10.27 %, while the abundance of Firmicutes increased by 7.46 %. The bacterial genus Gemmobacter, Chitinophaga and Rheinheimera; the archaeal genus Methanomassiliicoccus and Nitrosopumilus; along with the fungal genus Goffeauzyma, Gibberella, and Setophaeosphaeria emerged as pivotal biological markers for their respective domains, underpinning the biogeochemical dynamics of these environments. Furthermore, the study highlighted that geochemical factors, specifically nitrate (NO₃--N) levels and humic acid (HA) fractions, played crucial roles in modulating the composition and metabolic potential of these communities. Predictive analyses of functional potentials suggested that the N functional change of archaea was more pronounced, with anaerobic ammonia oxidation and nitrification decreased by 15.78 % and 14.62 %, respectively. Overall, soil characteristics alone explained 57.9 % of the total variation in the bacterial community structure. For fungal communities within contaminated soil, HMs were the primary contributors, explaining 46.9 % of the variability, while soil depth accounting for 6.4 % of the archaeal variation. This research enriches the understanding of the complex interrelations between heavy metal pollution, soil attributes, and microbial communities, paving the way for informed strategies in managing informal landfill sites effectively.

Exposure to resorcinol bis (diphenyl phosphate) induces colonization of alien microorganisms with potential impacts on the gut microbiota and metabolic disruption in male zebrafish

Organophosphate esters (OPEs) have been demonstrated to induce various forms of toxicity in aquatic organisms. However, a scarcity of evidence impedes the conclusive determination of whether OPEs manifest sex-dependent toxic effects. Here, we investigated the effects of tris (1-chloro-2-propyl) phosphate (TCPP) and resorcinol bis (diphenyl phosphate) (RDP) on the intestines of both female and male zebrafish. The results indicated that, in comparison to TCPP, RDP induced more pronounced intestinal microstructural damage and oxidative stress, particularly in male zebrafish. 16S rRNA sequencing and metabolomics revealed significant alterations in the species richness and oxidative stress-related metabolites in the intestinal microbiota of zebrafish under exposure to both TCPP and RDP, manifesting gender-specific effects. Based on differential species analysis, we defined invasive species and applied invasion theory to analyze the reasons for changes in the male fish intestinal community. Correlation analysis demonstrated that alien species may have potential effects on metabolism. Overall, this study reveals a pronounced gender-dependent impact on both the intestinal microbiota and metabolic disruptions of zebrafish due to OPEs exposure and offers a novel perspective on the influence of pollutants on intestinal microbial communities and metabolism.

Biochar dose-dependent impacts on soil bacterial and fungal diversity across the globe

Biochar, a widely used material for soil amendment, has been found to offer numerous advantages in improving soil properties and the habitats for soil microorganisms. However, there is still a lack of global perspectives on the influence of various levels of biochar addition on soil microbial diversity and primary components. Thus, in our study, we performed a global meta-analysis of studies to determine how different doses of biochar affect soil total carbon (C), nitrogen (N), pH, alpha- and beta-diversity, and the major phyla of both bacterial and fungal communities. Our results revealed that biochar significantly increased soil pH by 4 %, soil total C and N by 68 % and 22 %, respectively, in which the positive effects increased with biochar doses. Moreover, biochar promoted soil bacterial richness and evenness by 3-8 % at the biochar concentrations of 1-5 % (w/w), while dramatically shifting bacterial beta-diversity at the doses of >2 % (w/w). Specifically, biochar exhibited significantly positive effects on bacterial phyla of Acidobacteria, Bacteroidetes, Gemmatimonadetes, and Proteobacteria, especially Deltaproteobacteria and Gammaproteobacteria, by 4-10 % depending on the concentrations. On the contrary, the bacterial phylum of Verrucomicrobia and fungal phylum of Basidiomycota showed significant negative responses to biochar by -8 % and -24 %, respectively. Therefore, our meta-analysis provides theoretical support for the development of optimized agricultural management practices by emphasizing biochar application dosing.

Assessment of metal pollution and effects of physicochemical factors on soil microbial communities around a landfill

The physicochemical properties, chemical fractions of six metals (Cu, Zn, Pb, Cd, Cr, and Mn), and microbial communities of soil around a typical sanitary landfill were analyzed. The results indicate that soils around the landfill were from neutral to weak alkalinity. The contents of organic matter (OM), total nitrogen (TN), total phosphorous (TP), and activities of catalase, cellulase, and urease were significantly higher in landfill soils than those in background soils. Negative correlations were found between pH and metals. Cr was the dominant metal. Cu, Pb, Cr, and Mn were accumulated in the nearby farmland soils. Cd had the highest percentage of exchangeable fraction (33.7%-51.8%) in landfill and farmland soils, suggesting a high bioavailability to the soil environment affected by the landfill. Pb, Cr, and Mn existed mostly in oxidable fraction, and Cu and Zn were dominant in residual fraction. There was a low risk of soil metals around the landfill based on the RI values, while according to RAC classification, Cd had high to very high environmental risk. The MisSeq sequencing results showed that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla of bacteria, and the most abundant phylum of fungi was Ascomycota. The NMDS analysis revealed that the landfill could influence soil fungal communities more intensely than bacterial communities. TN, cellulase, and bioavailable metals (Pb-Bio and Cr-Bio) were identified to have main influences on microbial communities. Pb-Bio was the most dominant driving factor for bacterial community structures. For fungi, Pb-Bio was significantly negatively related to Olpidiomycota and Cr-Bio had a significantly negative correlation with Ascomycota. It manifests that bioavailable metals play important roles in assessing environmental risks and microbial community structures of soil around landfill.

The semen microbiome of miniature pony stallions

CONTEXT

Little is known about the microbial composition of stallion semen.

AIMS

To describe the microbiota detected in equine semen of healthy miniature pony stallions.

METHODS

Semen specimens were collected using a Missouri artificial vagina at a single time point. PacBio (Pacific Biosciences) genomic DNA sequencing of the 16S rRNA gene was performed on these specimens, following which next-generation microbiome bioinformatics platform QIIME2 was used to process fastq files and analyse the amplicon data. The data were categorised into genus, family, class, order and phylum.

KEY RESULTS

Firmicutes and Bacteroidetes phyla predominated (76%), followed by Proteobacteria (15%). Bacteroidales, Clostridiales and Cardiobacteriales predominated the microbial rank of order (86%). Class was mainly composed of Bacteroidia, Clostridia and Gammaproteobacteria (87%), while family was mainly composed of Porphyromonadaceae , Family_XI and Cardiobacteriaceae (62%). At the level of genus, 80% of the abundance was composed of seven genera, namely Porphyromonas, Suttonella, Peptoniphilus, Fastidiosipila, Ezakiella, Petrimonas and an unknown taxon.

CONCLUSIONS

The findings indicate that specific microbiota may be characteristic of healthy miniature pony stallions' semen with some inter-individual variations observed.

IMPLICATIONS

Larger equine studies involving fertile and infertile subjects could be informed by this study and could explore the relationship of the semen microbiome to male fertility.

Application of flow cytometry for rapid, high-throughput, multiparametric analysis of environmental microbiomes

Quantification of the abundance and understanding of the dynamics of the microbial communities is essential to establish a basis for microbiome characterization. The conventional techniques used for the quantification of microbes are complicated and time-consuming. With scientific advancement, many techniques evolved and came into account. Among them, flow cytometry is a robust, high-throughput technique through which microbial dynamics, morphology, microbial distribution, physiological characteristics, and many more attributes can be studied in a high-throughput manner with comparatively less time and resources. Flow cytometry, when combined with other omics-based methods, offers a rapid and efficient platform to analyze and understand the composition of microbiome at the cellular level. The microbial diversity observed through flow cytometry will not be equivalent to that obtained by sequencing methods, but this integrated approach holds great potential for high throughput characterization of microbiomes. Flow cytometry is regarded as an established characterization tool in haematology, oncology, immunology, and medical microbiology research; however, its application in environmental microbiology is yet to be explored. This comprehensive review aims to delve into the diverse environmental applications of flow cytometry across various domains, including but not limited to bioremediation, landfills, anaerobic digestion, industrial bioprocesses, water quality regulation, and soil quality regulation. By conducting an in-depth analysis, this article seeks to shed light on the potential benefits and challenges associated with the utilization of flow cytometry in addressing environmental concerns.

Quantitative analysis of TCE biodegradation pathway in landfill cover utilizing continuous monitoring, droplet digital PCR and multi-omics sequencing technology

The remediation of volatile chlorinated hydrocarbons in the quasi-vadose zone has become a significant challenge. We applied an integrated approach to assess the biodegradability of trichloroethylene to identify the biotransformation mechanism. The formation of the functional zone biochemical layer was assessed by analyzing the distribution of landfill gas, physical and chemical properties of cover soil, spatial-temporal variations of micro-ecology, biodegradability of landfill cover soil and distributional difference metabolic pathway. Real-time online monitoring showed that trichloroethylene continuously undergoes anaerobic dichlorination and simultaneous aerobic/anaerobic conversion-aerobic co-metabolic degradation on the vertical gradient of the landfill cover system and reduction in trans-1,2-dichloroethylene in the anoxic zone but not 1,1-dichloroethylene. PCR and diversity sequencing revealed the abundance and spatial distribution of known dichlorination-related genes within the landfill cover, with 6.61 ± 0.25 × 104-6.78 ± 0.09 × 106 and 1.17 ± 0.78 × 103-7.82 ± 0.07 × 105 copies per g/soil of pmoA and tceA, respectively. In addition, dominant bacteria and diversity were significantly linked with physicochemical factors, and Mesorhizobium, Pseudoxanthomonas and Gemmatimonas were responsible for biodegradation in the aerobic, anoxic and anaerobic zones. Metagenome sequencing identified 6 degradation pathways of trichloroethylene that may occur in the landfill cover; the main pathway was incomplete dechlorination accompanied by cometabolic degradation. These results indicate that the anoxic zone is important for trichloroethylene degradation.

Full life cycle and sustainability transitions of phthalates in landfill: A review

Phthalates (PAEs) are added to various products as a plasticizer. As these products age and are disposed of, plastic waste containing PAEs enters the landfill. The landfill environment is complicated and can be regarded as a "black box". Also, PAEs do not bind with the polymer matrix. Therefore, when a series of physical chemistry and biological reactions occur during the stabilization of landfills, PAEs leach from waste and migrate to the surrounding environmental media, thereby contaminating the surrounding soil, water ecosystems, and atmosphere. Although research on PAEs has achieved progress over the years, they are mainly concentrated on a particular aspect of PAEs in the landfill; there are fewer inquiries on the life cycle of PAEs. In this study, we review the presence of PAEs in the landfill in the following aspects: (1) the main source of PAEs in landfills; (2) the impact of the landfill environment on PAE migration and conversion; (3) distribution and transmedia migration of PAEs in aquatic ecosystems, soils, and atmosphere; and (4) PAE management and control in the landfill and future research direction. The purpose is to track the life cycle of PAEs in landfills, provide scientific basis for in-depth understanding of the migration and transformation of PAEs and environmental pollution control in landfills, and new ideas for the sustainable utilization of landfills.

Landfill: An eclectic review on structure, reactions and remediation approach

Since the enactment of the Clean Water Act (1972), which was supplemented by increased accountability under Resource Conservation and Recovery Act (RCRA) Subtitle D (1991) and the Clean Air Act Amendments (1996), landfills have indeed been widely used all around the world for treating various wastes. The landfill's biological and biogeochemical processes are believed to be originated about 2 to 4 decades ago. Scopus and web of Science based bibliometric study reveals that there are few papers available in scientific domain. Further, till today not a single paper demonstrated the detailed landfills heterogenicity, chemistry and microbiological processes and their associated dynamics in a combined approach. Accordingly, the paper addresses the recent applications of cutting-edge biogeochemical and biological methods adopted by different countries to sketch an emerging perspective of landfill biological and biogeochemical reactions and dynamics. Additionally, the significance of several regulatory factors controlling the landfill's biogeochemical and biological processes is highlighted. Finally, this article emphasizes the future opportunities for integrating advanced techniques to explain landfill chemistry explicitly. In conclusion, this paper will provide a comprehensive vision of the diverse dimensions of landfill biological and biogeochemical reactions and dynamics to the scientific world and policymakers.

Effects of capping on microbial populations and contaminant immobilization in an old unlined landfill

This research aimed at evaluating the effects of capping on the mitigation of impacts generated by a closed unlined landfill in São Carlos, SP, Brazil. Physicochemical and microbiological analyses (16S rRNA sequencing) of buried solid waste samples were performed, in capped and uncapped areas. Even though leachate pockets could still be encountered in capped areas, the capping construction reduced oxygen availability and created more reducing conditions, propitiating the development of sulfate-reducing bacteria and possibly contributing to the precipitation of the metals Pb, Cd, Ni, Co, As, and Zn as metal sulfides, causing their immobilization. The microbial populations adapted to the anaerobic conditions created under capped zones belonged to the phyla Firmicutes, Chloroflexi, and Euryarchaeota and the genera Methanosaeta, Hydrogenispora, Smithella, and Gelria. Differently, the phyla Acidobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria were more abundant in samples from the uncapped zones, in which the abundance of different genera varied homogeneously. Methanogenic activity was not impaired by the intervention measure, as assessed by the specific methanogenic activity (SMA). Capping of old unlined landfills brings benefits to the immobilization of metals and does not impair microbial degradation, being effective for the mitigation of impacts on soils and water resources.

A landfill serves as a critical source of microplastic pollution and harbors diverse plastic biodegradation microbial species and enzymes: Study in large-scale landfills, China

Microplastics (MPs) are emerging pollutants. Landfills store up to 42% of worldwide plastic waste and serve as an important source of MPs. However, the study of MPs distribution and the plastic biodegradation potential in landfills is limited. In this study, the distribution of abundance, size, morphology and polymer type of MPs and plastics biodegradation species in refuse samples along landfill depths were extensively investigated within a large-scale landfill in Shenzhen, China. In addition, plastics biodegradation enzymes were evaluated in seven Chinese large-scale landfills leachate. MPs distribution pattern was investigated in all refuse samples. The abundance of MPs in refuse samples varied between 81 and 133 items/g. The size of MPs in all samples varied between 0.03 and 5 mm, and the average sizes were 1.2 mm ± 0.1 mm. The main morphology and polymer type were fragments and cellophane, respectively. Landfill depth was significantly negatively correlated with the relative abundance of MPs size 1-5 mm (p < 0.05) and was positively correlated with the relative abundance of MPs size < 0.2 mm (p < 0.05), suggesting that plastics were broken down during municipal solid waste decomposition. The multiple regression on matrices analysis further showed the landfill depths and plastic morphology significantly impact the MPs distribution. The strains, Lysinibacillus massiliensis (with relative abundance of 1.8%) for low-density polyethylene and polystyrene biodegradation, and Pseudomonas stutzeri (0.1%) for low density polythene and polypropylene biodegradation, were detected on the plastic surface with high relative abundance. Furthermore, 75 plastic degradation species and their associated 31 enzymes (breakdown 24 plastics) were discovered in seven landfills leachate samples.

Urban mining of municipal solid waste incineration (MSWI) residues with emphasis on bioleaching technologies: a critical review

Metals are essential in our daily lives and have a finite supply, being simultaneously contaminants of concern. The current carbon emissions and environmental impact of mining are untenable. We need to reclaim metals sustainably from secondary resources, like waste. Biotechnology can be applied in metal recovery from waste streams like fly ashes and bottom ashes of municipal solid waste incineration (MSWI). They represent substantial substance flows, with roughly 46 million tons of MSWI ashes produced annually globally, equivalent in elemental richness to low-grade ores for metal recovery. Next-generation methods for resource recovery, as in particular bioleaching, give the opportunity to recover critical materials and metals, appropriately purified for noble applications, in waste treatment chains inspired by circular economy thinking. In this critical review, we can identify three main lines of discussion: (1) MSWI material characterization and related environmental issues; (2) currently available processes for recycling and metal recovery; and (3) microbially assisted processes for potential recycling and metal recovery. Research trends are chiefly oriented to the potential exploitation of bioprocesses in the industry. Biotechnology for resource recovery shows increasing effectiveness especially downstream the production chains, i.e., in the waste management sector. Therefore, this critical discussion will help assessing the industrial potential of biotechnology for urban mining of municipal, post-combustion waste.

Tricks and tracks in waste management with a special focus on municipal landfill leachate: Leads and obstacles

Landfilling is the most widely used disposal method for municipal solid waste around the world. The main disadvantage of this strategy is formation of leachate, among other aspects. Landfill leachate contains highly toxic and bio-refractory substances that are detrimental to the environment and human health. Hence, the risk(s) of discharging potentially harmful landfill leachate into the environment need to be assessed and measured in order to make effective choices about landfill leachate management and treatment. In view of this, the present review aims to investigate (a) how landfill leachate is perceived as an emerging concern, and (b) the stakeholders' mid- to long-term policy priorities for implementing technological and integrative solutions to reduce the harmful effects of landfill leachate. Because traditional methods alone have been reported ineffective, and in response to emerging contaminants and stringent regulations, new effective and integrated leachate treatments have been developed. This study gives a forward-thinking of the accomplishments and challenges in landfill leachate treatment during the last decade. It also provides a comprehensive compilation of the formation and characterization of landfill leachate, the geo-environmental challenges that it raises, as well as the resource recovery and industrial linkage associated with it in order to provide an insight into its sustainable management.

Insights into leachate reduction in landfill with different ventilation Rates: Balance of Water, waste physicochemical Properties, and microbial community

Ventilation is an efficient approach employed for accelerating stabilization and reducing aftercare of landfill, but its effect on leachate reduction is still elusive. To fill this knowledge gap, five lab-scale landfill reactors with different ventilation rates were established in this study. Suitable ventilation (e.g. 0.25-0.5 L·min^-1·kg^-1 dry solid of waste (DS)) was beneficial to promoting the stabilization of landfill, which effectively accelerated the degradation of organic matter and reduced water content of landfilled waste. Based on the mass balance of water, the dominant input water was initial water of landfilled waste (more than 94 %), which was partially converted to leachate and evaporated water. Ventilation enhanced the intensity of biochemical reactions heat to increase evaporated water content from 0 to 0.29 t/t DS while reducing the leachate generation significantly from 0.69 to 0.49 t/t DS with the increase of ventilation rate. Besides, the hydrophilic substances, such as humic acid-like substances, in landfilled waste increased, and the surface of the landfilled waste converted from smooth to rough. The reduction of the bound water content has a significant correlation with the degradation of organic matter content (p less than 0.05), which reduced the water-holding capacity of waste. Actinobacteriota and Firmicutes were the key bacterial phyla in the degradation of organic matter to promote bio-heat and evaporation of water, thus reducing leachate production under suitable ventilation conditions. Carbohydrates and amino acids were the main energy metabolism sources of bacteria during the landfill process. This study deepens our understanding of the leachate reduction mechanism in the micro-aerobic landfill.

Dynamic processes in conjunction with microbial response to unveil the attenuation mechanisms of tris (2-chloroethyl) phosphate (TCEP) in non-sanitary landfill soils

Although the environmental and health risks of chlorinated organophosphate esters (OPEs-Cl) have drawn much attention, its environmental behaviors have been insufficiently characterized. As a notable sink of this emerging contaminant, non-sanitary landfills, which may decompose/accumulate OPEs-Cl, is of particular concern. In the present study, the dynamic processes of the typical OPEs-Cl, tris(2-chloroethyl) phosphate (TCEP), in non-sanitary landfill soils were analyzed under anaerobic condition, and the microbial taxa involved in these processes were explored. Our results showed that TCEP could be simultaneously reduced by abiotic and biotic processes, as it was reduced by 73.9% and 65.5% over the 120-day experiment in landfill humus and subsoil, respectively. Notably, the degradation of TCEP was significantly (p < 0.05) enhanced under the stress of a high TCEP concentration (10 μg g^-1), while its ecological consequences were found insignificant regarding the microbial diversity and community structure and the typical soil redox processes, including Fe(III)/SO₄^2- reduction and methanogenesis, in both soils. The microbial diversity of subsoil was significantly lower, and acetate was an important factor in changing microbial communities in landfill soils. The microbes in the family Nocardioidaceae and genus Pseudomonas might contribute to in the degradation of TCEP in landfill humus and subsoil, respectively. The metabolism related to sulfur and sulfate respiration were significantly (p < 0.05) correlated with TCEP reduction, and Desulfosporosinus were found as a potentially functional microbial taxon in TCEP degradation in both soils. The results could advance our understanding of the environmental behavior of OPEs-Cl in landfill-like complex environments.

Characteristic pollutants and microbial community in underlying soils for evaluating landfill leakage

Leachate leakage poses a serious environmental risk to the safety of surrounding soils and groundwater. A much faster approach to reflect landfill leakage is the premise to mitigate the ecological risk of landfills. In this study, two landfills (BJ and WZ) were selected to investigate the leaching characteristics of various pollutants along the vadose soil depths. The physiochemical properties of underlying soils including NO₃^--N, NO₂^--N, NH₄⁺-N, OM, TN, EC and Cl^- exhibited a typical leaching dynamic along the depths. Among them, TN, NH₄⁺-N, OM, NO₃^--N, and EC might be used as characteristic pollutants to evaluate the leachate leakage issues in landfilled sites. The genera Thiopseudomonas, Acinetobacter, Pseudomonas, and Hydrogenispora dominated in underlying soils. Compared to BJ samples, a more diverse and active microbiome capable of carbon and nitrogen cycles was observed in WZ samples, which was mainly ascribed to nutrients and elements contained in different types of soils. Among the environmental factors, nitrogenous compounds, SO₄^2-, pH and EC had significant effects on the microbial community structures in the underlying soils. The relative abundances of Hydrogenispora and Caldicoprobacter might be used as characteristic microorganisms to evaluate the leachate leakage issues in landfilled sites. These results provided a deep insight into effects of leachate leakage in underlying soils, especially the pollutants vertical distribution and the corresponding microbial community structures.

Distinct Bacterial and Fungal Communities Colonizing Waste Plastic Films Buried for More Than 20 Years in Four Landfill Sites in Korea

Plastic pollution has been recognized as a serious environmental problem, and microbial degradation of plastics is a potential, environmentally friendly solution to this. Here, we analyzed and compared microbial communities on waste plastic films (WPFs) buried for long periods at four landfill sites with those in nearby soils to identify microbes with the potential to degrade plastics. Fourier-transform infrared spectroscopy spectra of these WPFs showed that most were polyethylene and had signs of oxidation, such as carbon-carbon double bonds, carbon-oxygen single bonds, or hydrogen-oxygen single bonds, but the presence of carbonyl groups was rare. The species richness and diversity of the bacterial and fungal communities on the films were generally lower than those in nearby soils. Principal coordinate analysis of the bacterial and fungal communities showed that their overall structures were determined by their geographical locations; however, the microbial communities on the films were generally different from those in the soils. For the pulled data from the four landfill sites, the relative abundances of Bradyrhizobiaceae, Pseudarthrobacter, Myxococcales, Sphingomonas, and Spartobacteria were higher on films than in soils at the bacterial genus level. At the species level, operational taxonomic units classified as Bradyrhizobiaceae and Pseudarthrobacter in bacteria and Mortierella in fungi were enriched on the films. PICRUSt analysis showed that the predicted functions related to amino acid and carbohydrate metabolism and xenobiotic degradation were more abundant on films than in soils. These results suggest that specific microbial groups were enriched on the WPFs and may be involved in plastic degradation.

Antibiotic resistance genes in landfill leachates from seven municipal solid waste landfills: Seasonal variations, hosts, and risk assessment

Landfills are reservoir of antibiotics and antibiotic resistance. Antibiotic resistance would transport to the environment through landfill leachate, posing threaten to the environment. However, long term monitoring on antibiotic resistance genes in landfill leachate transportation is limited. Furthermore, antibiotic resistance gene hosts and their risk assessment are lacking. In this study, we investigated the seasonal variation of ARGs sulI, tetO and tetW in seven Chinese municipal solid waste landfill leachates over two years (2017-2018) by quantitative polymerase chain reaction. We also evaluated the associated bacterial hosts and their risk levels based on metagenomics and omics-based framework for assessing the health risk of antimicrobial resistance genes, respectively. Because sulI, tetO and tetW are abundant and the most frequently detected ARGs in global landfill system, they are selected as target ARGs. Results showed that the relative content of target ARGs in 2017 was 100 times higher than that in 2018, suggesting ARGs attenuation. The hosts of sulI were phyla of Lentisphaerae and Proteobacteria, whereas the hosts of tetO and tetW were Bacteroidetes and Firmicutes. Remarkably, the host species include pathogenic bacterium (Salmonella enterica, Labilibaculum filiforme, Bacteroidales bacterium, Anaeromassilibacillus senegalensis, and Pseudochrobactrum sp. B5). ARGs tetO and tetW belong to the Rank II level with characters of enrichment in the human-associated environment and gene mobility, and sulI ranked as Rank VI. In addition, among 1210 known ARGs in the landfill leachate, 78 ARGs belonged to risk Rank I (enrichment in human-associated environment, gene mobility and pathogenicity), demonstrating high health risk of landfill system. These results demonstrate that antibiotic resistance in landfill and landfill leachate have high health risk and the kind of ARGs with high abundance in human-associated environment, gene mobility and pathogenicity should be paid more attention.

Characterization of anaerobic oxidation of methane and microbial community in landfills with aeration

Landfills are the third largest source of anthropogenic CH₄ emissions. Anaerobic oxidation of methane (AOM) activity and communities of methane-oxidizing bacteria were investigated in three informal landfills in this study, namely, BJ, CH and SZ landfills, among which BJ and CH represent traditional anaerobic landfills, while the SZ landfill was subjected to aeration to accelerate waste stabilization. The AOM rates of the investigated landfilled wastes ranged from 3.66 to 23.91 nmol g^-1 h^-1. Among the three landfills, the AOM rate was highest in the SZ-1-Top sample, which was closest to the aeration pipe. Among the possible electron acceptors for AOM, including NO₃^-, NO₂^-, SO₄^2- and Fe³⁺, the NO₂^--N content was the only variable that was positively correlated with the AOM rate. Compared with α-Proteobacteria methanotrophs, γ-Proteobacteria methanotrophs were more abundant in the landfilled waste, especially Methylobacter, which was detected in nearly all samples. Members of the family Methylomirabilaceae, including Candidatus Methylomirabilis, were also detected in the SZ-1 and SZ-2-Bot samples. The relative abundance of the main methanotrophs in the families Methylomonadaceae, Methylococcaceae, Rokubacteriales and Methylomirabilaceae, the genus Methylocystis and the phylum NC10 were all positive correlations with the contents of NO₂^--N in the landfilled waste samples. Additionally, significantly positive correlations were observed between the AOM rates and the relative abundance of the main methanotrophs except for the family Methylococcaceae. This indicated that aeration could enhance the conversion of nitrogen compounds in the landfilled waste, in which the high contents of NO₂^--N could stimulate the growth of methanotrophs and increase AOM rate. These findings are helpful for understanding the mechanisms of CH₄ oxidation in landfills and for taking effective measures to mitigate CH₄ emissions from landfills.

Physicochemical and microbiological characteristics of waste foundry sand used in landfills

Biodegradation of solid waste is a process that depends on the characteristics of waste and soil, and these characteristics may create a waterproof barrier in the landfill, changing its performance. Some residues, such as waste foundry sand (WFS), whose final destination is the sanitary landfill, can create waterproofing and alter the performance of the landfill. This study was carried out to test this hypothesis by evaluating two prototypes composed of layers of organic residues, one covered by a mixture of 30% clay soil + 70% WFS and the other covered only with clay soil, monitored for 24 months. The generated leachate was analyzed regarding the parameters of chemical oxygen demand (COD), pH and electrical conductivity. In addition, after the monitoring period, semi-undeformed samples were collected for quantification of microorganisms and physical-chemical analysis (pH, electrical conductivity, moisture content and images with scanning electron microscopy). In the soil prototype, there was the formation of a waterproofing barrier in its deepest layer (soil₃). Factors such as the clay-mineral portion, moisture content (33,18%) and amount of microorganisms influenced this formation (650.000 and 15.000 CFU/g bacterial and fungal biomass, respectively), showing that WFS avoids the formation of this waterproofing barrier, as indicated for covering organic waste in landfills.

Diversity of microbial community structure and their association with phthalic acid esters and physicochemical parameters in informal landfills

Informal landfill is a common waste treatment method employed in rural areas of China, and phthalic acid esters (PAEs) are one of the typical pollutants in landfill leachate. However, there is no corresponding theoretical basis for whether microbial treatment technology can be used to reduce environmental risk of PAEs in informal landfills. Thus, a typical informal landfill site in northern China was selected and approximately 1,133,023 effective sequences were obtained from 21 samples collected from three layers (different deposit depths) of the landfill. This research explored the correlation between PAEs and the composition and distribution of microbial community in specific environments of informal landfill sites. Here we found that dis(2-ethylhexyl) phthalate (DEHP), di-n-octyl phthalate (DOP), and diethyl phthalate (DEP) were positively and significantly correlated with Bhargavaea, Planococcus, Virgibacillus, and Oceanobacillus, respectively. The redundancy analysis demonstrated that moisture content, pH, NO2--N, and SUVA254 among the seven physicochemical factors (pH, TN, NO3--N,NO2--N,NH4+-N, SUVA254, and moisture content) significantly affected bacterial communities. The research conclusion can provide theoretical basis for the degradation technology of PAEs by microorganism and research basis for the treatment of informal landfill sites.

Delineating the Drivers and Functionality of Methanogenic Niches within an Arid Landfill

Microbial communities mediate the transformation of organic matter within landfills into methane (CH₄). Yet their ecological role in CH₄ production is rarely evaluated. To characterize the microbiome associated with this biotransformation, the overall community and methanogenic Archaea were surveyed in an arid landfill using leachate collected from distinctly aged landfill cells (i.e., younger, intermediate, and older). We hypothesized that distinct methanogenic niches exist within an arid landfill, driven by geochemical gradients that developed under extended and age-dependent waste biodegradation stages. Using 16S rRNA and mcrA gene amplicon sequencing, we identified putative methanogenic niches as follows. The order Methanomicrobiales was the most abundant order in leachate from younger cells, where leachate temperature and propionate concentrations were measured at 41.8°C ± 1.7°C and 57.1 ± 10.7 mg L⁻¹. In intermediate-aged cells, the family Methanocellaceae was identified as a putative specialist family under intermediate-temperature and -total dissolved solid (TDS) conditions, wherein samples had a higher alpha diversity index and near CH₄ concentrations. In older-aged cells, accumulating metals and TDS supported Methanocorpusculaceae, “Candidatus Bathyarchaeota,” and “Candidatus Verstraetearchaeota” operational taxonomic units (OTUs). Consistent with the mcrA data, we assayed methanogenic activity across the age gradient through stable isotopic measurements of δ¹³C of CH₄ and δ¹³C of CO₂. The majority (80%) of the samples’ carbon fractionation was consistent with hydrogenotrophic methanogenesis. Together, we report age-dependent geochemical gradients detected through leachate in an arid landfill seemingly influencing CH₄ production, niche partitioning, and methanogenic activity.

IMPORTANCE Microbiome analysis is becoming common in select municipal and service ecosystems, including wastewater treatment and anaerobic digestion, but its potential as a microbial-status-informative tool to promote or mitigate CH₄ production has not yet been evaluated in landfills. Methanogenesis mediated by Archaea is highly active in solid-waste microbiomes but is commonly neglected in studies employing next-generation sequencing techniques. Identifying methanogenic niches within a landfill offers detail into operations that positively or negatively impact the commercial production of methane known as biomethanation. We provide evidence that the geochemistry of leachate and its microbiome can be a variable accounting for ecosystem-level (coarse) variation of CH₄ production, where we demonstrate through independent assessments of leachate and gas collection that the functional variability of an arid landfill is linked to the composition of methanogenic Archaea.

Eukaryotic community composition and dynamics during solid waste decomposition

Consortia of microbial community are involved in organic waste decomposition in municipal solid waste (MSW) landfill via competition, syntropy, and predation. Bacterial and archaeal community structure and function have been extensively studied in this process, whereas the eukaryotic community structure and function are largely unidentified. This gap stands for one of the fundamental researches of microbial ecology, that is, "what is the importance of variation in eukaryotic community structure and function to solid waste decomposition? The main idea of this work is to characterize changes in eukaryotic community composition and the associated driver during solid waste decomposition. Using high throughput sequencing targeting 18S rRNA genes, community composition and dynamics of eukaryotic during solid wasted decomposition were studied, as well as the differences with solid waste and leachate physiochemical parameters. Concomitant to the expected changes in physiochemical factors, eukaryotic community composition and diversity changed along solid waste decomposition indicated by aerobic phase (AP), anaerobic acid phase (ACP), and methanogenic phase (MP) and the structure was shaped by the nutrients (BOD₅, total phosphorus, and nitrate) in leachate. Ascomycota, the predominant eukaryote, showed significant (p < 0.05) different structure among AP, ACP, and MP in phylum, genera, and species levels. Abundant Freshwater Opisthokonta was present in MP, suggesting a methane carbon cycling via grazing methane oxidation microorganism. Amoebozoa, Alveolata, Rhizaria, and Stramenopiles showed successional pattern during solid waste decomposition, indicating a short food chain establishment. Characterization on eukaryotic community composition and dynamics during solid waste decomposition are crucial for understanding of microbial consortia ecological function on solid waste decomposition and are also helpful for MSW management.Key points• Abundant Ascomycota significantly differed at AP, ACP, and MP.• Eukaryotic succession indicated a short food chain establishment.• Entire eukaryotic community structure was associated to nutrients in leachate.

Genome-centric metagenomics provides new insights into the microbial community and metabolic potential of landfill leachate microbiota

Landfills are important sources of microorganisms associated with anaerobic digestion. However, the knowledge on microbiota along with their functional potential in this special habitat are still lacking. In this study, we recovered 1168 non-redundant metagenome-assembled genomes (MAGs) from nine landfill leachate samples collected from eight cities across China, spanning 42 phyla, 73 classes, 114 orders, 189 families, and 267 genera. Totally, 74.1% of 1168 MAGs could not be classified to any known species and 5.9% of these MAGs belonged to microbial dark matter phyla. Two putative novel classes were discovered from landfill leachate samples. The identification of thousands of novel carbohydrate-active enzymes showed similar richness level compared to the cow rumen microbiota. The methylotrophic methanogenic pathway was speculated to contribute significantly to methane production in the landfill leachate because of its co-occurrence with the acetoclastic and hydrogenotrophic methanogenic pathways. The genetic potential of dissimilatory nitrate reduction to ammonium (DNRA) was observed, implying DNRA may play a role in ammonium generation in landfill leachate. These findings implied that landfill leachate might be a valuable microbial resource repository and filled the previous understanding gaps for both methanogenesis and nitrogen cycling in landfill leachate microbiota. Our study provides a comprehensive genomic catalog and substantially provides unprecedented taxonomic and functional profiles of the landfill leachate microbiota.

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.

Bacterial Community Structure and Predicted Metabolic Function of Landfilled Municipal Solid Waste in China

The biodegradation behavior of municipal solid waste (MSW) depends on the diversity and metabolic function of bacterial communities, which are affected by environmental factors. However, the diversity of the bacterial communities and metabolic functions in MSW, as well as their influencing factors, remain unclear. In deep-aged MSW, the abovementioned deficiencies are more significant, and will effectively hamper landfill disposal. In this study, high-throughput sequencing was performed to examine the bacterial community structure and metabolic function from depths of 10 m to 40 m, of two large MSW landfills on the southeast coast of China. Thermotogota (1.6–32.0%), Firmicutes (44.2–77.1%), and Bacteroidota (4.0–34.3%) were the three dominant phyla among the 39 bacterial phyla identified in aged MSW samples. Bacterial genera associated with the degradation of many macromolecules, e.g., Defluviitoga, Hydrogenispora, and Lentimicrobium were abundantly detected in MSW samples, even in aged MSW. Redundancy analysis (RDA) showed that bacterial diversity in the landfills was most strongly correlated with electrical conductivity, age, and moisture content of the MSW. Tax4fun2 analysis predicted that there were abundant metabolism functions in aged MSW, especially functional enzymes (e.g., glycine dehydrogenase and cellulase) related to amino acids and cellulose degradation. This study increases our understanding of the bacterial diversity and functional characteristics in landfilled MSW.

Microbes drive changes in arsenic species distribution during the landfill process

Landfills are considered an anthropogenic source of arsenic (As). The As species mediated by microbes in landfills vary significantly in toxicity. Based on random matrix theory, 16S rRNA genes were used to construct four microbial networks associated with different stages over 12 years of landfill ages. The results indicated that network size and microbial structure varied with landfill age. According to the network scores, about 208 taxa were identified as putative keystones for the whole landfill; the majority of them were Firmicutes, which accounted for 66.8% of all specialists. Random Forest analysis was performed to predict the keystone taxa most responsible for As species distribution under different landfill conditions; 17, 10 and 14 keystone taxa were identified as drivers affecting As species distribution at early, middle, and later landfill stages, respectively.

Processes and prospects on valorizing solid waste for the production of valuable products employing bio-routes: A systematic review

Humanity is struggling against a major problem for a proper management of generated municipal solid waste. The collected waste causes natural issues like uncontrollable emission of greenhouse gases and others. Even though, escalation of waste results in minimizing the areas accessible for disposing the waste. Creating awareness in the society to use organic products like biofuels, biofertilizers and biogas is a need of an hour. Biochemical processes such as composting, vermicomposting, anaerobic digestion, and landfilling play important role in valorizing biomass and solid waste for production of biofuels, biosurfactants and biopolymer. This paper covers the details of biomass and solid waste characteristics and its composition. It is also focused to provide updated information about reutilization of biomass for value creation. Technologies and products obtained through bio-routes are discussed in current review paper together with the integrated system of solid waste management. It also covers challenges, innovations and perspectives in this field.

Diversity, abundance and expression of the antibiotic resistance genes in a Chinese landfill: Effect of deposit age

Landfills are the hotspots for the occurrence of antibiotic resistance genes (ARGs) in the environment. However, limited information is available on the profile of ARGs in response to the varying age of refuse in landfills. In this study, the diversity, abundance and expression of ARGs in a Chinese landfill were assessed by high-throughput quantitative PCR. A total of 154 ARGs were detected and 66% of them were transcriptionally active. The total abundance of ARG transcripts was one magnitude lower than that of ARGs. The ermT-01, tetX, sul2, aadA-02 and aadA2-03 genes were found to be the most abundant ARGs (ARG transcripts) and their sum abundance showed a linear relation with the total abundance of ARGs (ARG transcripts). The total abundance of ARGs (ARG transcripts) in young refuse was significantly higher than that in old refuse (p < 0.01) and the profile of ARGs (ARG transcripts) between the old and young refuse was distinct as revealed by the principal coordinates analysis. The variation partitioning analysis showed heavy metals (mainly Cr and Zn) were the major drivers that affect the profile of ARGs (ARG transcripts). These findings provided new insights into the ARGs in landfills and indicated their potential threats should not be neglected.

Landfill microbiome harbour plastic degrading genes: A metagenomic study of solid waste dumping site of Gujarat, India

Globally, environmental pollution by plastic waste has become a severe ecological and social problem worldwide. The present study aimed to analyse the bacterial community structure and functional potential of the landfill site using high throughput shotgun metagenomic approach to understand plastic degrading capabilities present in the municipal solid waste (MSW) dumping site. In this study, soil, leachate and compost samples were collected from various locations (height and depth) of the Pirana landfill site in Ahmedabad city Gujarat, India. In total 30 phyla, 58 class, 125 order, 278 families, 793 genera, and 2468 species were predicted. The most dominant phyla detected were Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria in the soil and compost samples. Whereas, in leachate samples, the predominant phyla belonged to Firmicutes (54.24%) followed by Actinobacteria (43.67%) and Proteobacteria (1.02%). The functional profiling revealed the presence of enzymatic groups and pathways involved in biodegradation of xenobiotics. The results also demonstrated the presence of potential genes that is associated with the biodegradation of different types of plastics such as polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS). Present study extablishes the relationship between microbial community structure and rich sources of gene pool, which are actively involved in biodegradation of plastic waste in landfill sites.

Biogas production in a tropical landfill: Long-term monitoring results and analysis of variables of influence

The use of landfill gas for power production is a very attractive option in tropical sanitary landfills mainly in developing countries, where the waste composition, water content, and the climate conditions are favorable to a fast depletion of waste organic matter and a robust short term biogas production response. In this paper, the results of long-term monitoring and methane extraction activities in a tropical landfill are presented, and the obtained results are analyzed taking into account the structure of the prokaryotic communities and the fugitive emissions through the temporary covers. It is shown that waste depletion by aerobic processes and fugitive emissions are probable related to the drop in the efficiency of the extraction system verified in the field and that the performance of the temporary covers is of paramount importance when implementing good practices of waste management in sanitary landfills. The fugitive emissions through temporary covers was estimated at about 12% of the methane production in the field, and the distance from drains and sampling depth were confirmed as having an influence on the environmental conditions for waste depletion and on the relative abundance of the bacterial communities.

Bacterial Diversity and Community Structure of a Municipal Solid Waste Landfill: A Source of Lignocellulolytic Potential

Omics have given rise to research on sparsely studied microbial communities such as the landfill, lignocellulolytic microorganisms and enzymes. The bacterial diversity of Municipal Solid Waste sediments was determined using the illumina MiSeq system after DNA extraction and Polymerase chain reactions. Data analysis was used to determine the community's richness, diversity, and correlation with environmental factors. Physicochemical studies revealed sites with mesophilic and thermophilic temperature ranges and a mixture of acidic and alkaline pH values. Temperature and moisture content showed the highest correlation with the bacteria community. The bacterial analysis of the community DNA revealed 357,030 effective sequences and 1891 operational taxonomic units (OTUs) assigned. Forty phyla were found, with the dominant phyla Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidota, while Aerococcus, Stenotrophomonas, and Sporosarcina were the dominant species. PICRUSt provided insight on community's metabolic function, which was narrowed down to search for lignocellulolytic enzymes' function. Cellulase, xylanase, esterase, and peroxidase were gene functions inferred from the data. This article reports on the first phylogenetic analysis of the Pulau Burung landfill bacterial community. These results will help to improve the understanding of organisms dominant in the landfill and the corresponding enzymes that contribute to lignocellulose breakdown.

Prediction, enrichment and isolation identify a responsive, competitive community of cellulolytic microorganisms from a municipal landfill

Landfills are engineered, heterogeneously contaminated sites containing large reservoirs of paper waste. Cellulose degradation is an important process within landfill microbial ecology, and these anoxic, saturated environments are prime locations for discovery of cellulases that may offer improvements on industrial cellulose degradation efforts. We sampled leachate from three locations within a municipal landfill, a leachate collection cistern, and groundwater from an adjacent aquifer to identify cellulolytic populations and their associated cellulases. Metagenomic sequencing identified wide-spread and taxonomically diverse cellulolytic potential, with a notable scarcity of predicted exocellulases. 16S rRNA amplicon sequencing detected nine landfill microorganisms enriched in a customized leachate medium amended with microcrystalline cellulose or common paper stocks. Paper-enrichment cultures showed competition dynamics in response to the specific composition (lignin: hemi-cellulose: cellulose) of the different paper stocks. From leachate biomass, four novel cellulolytic bacteria were isolated, including two with the capacity for cellulolysis at industrially relevant temperatures. None of the isolates demonstrated exocellulase activity, consistent with the metagenome-based predictions. However, there was very little overlap between metagenome-derived predicted cellulolytic organisms, organisms enriched on paper sources, or the isolates, suggesting the landfill cellulolytic community is at low abundance but able to rapidly respond to introduced substrates.

Metagenomics Analysis Reveals the Microbial Communities, Antimicrobial Resistance Gene Diversity and Potential Pathogen Transmission Risk of Two Different Landfills in China

In this study, we used a metagenomic approach to analyze microbial communities, antibiotic resistance gene diversity, and human pathogenic bacterium composition in two typical landfills in China. Results showed that the phyla Proteobacteria, Bacteroidetes, and Actinobacteria were predominant in the two landfills, and archaea and fungi were also detected. The genera Methanoculleus, Lysobacter, and Pseudomonas were predominantly present in all samples. sul2, sul1, tetX, and adeF were the four most abundant antibiotic resistance genes. Sixty-nine bacterial pathogens were identified from the two landfills, with Klebsiella pneumoniae, Bordetella pertussis, Pseudomonas aeruginosa, and Bacillus cereus as the major pathogenic microorganisms, indicating the existence of potential environmental risk in landfills. In addition, KEGG pathway analysis indicated the presence of antibiotic resistance genes typically associated with human antibiotic resistance bacterial strains. These results provide insights into the risk of pathogens in landfills, which is important for controlling the potential secondary transmission of pathogens and reducing workers’ health risk during landfill excavation.

Insights into the stabilization of landfill by assessing the diversity and dynamic succession of bacterial community and its associated bio-metabolic process

The distribution of bacterial community in an actual landfill was analyzed and the bioprocess involved in refuse degradation was clarified. The results showed that the degradation degree of refuse showed great differences with the landfill age, in which the contents of organic matter (OM) and total Kjeldahl nitrogen (TKN) in refuse as well as the chemical oxygen demand (COD) in leachate presented decreasing trends with increasing landfill age. The diversity of bacterial community increased first and then decreased with increasing landfill age. The main bacterial phyla involved in refuse degradation were Proteobacteria, Firmicutes and Bacteroidetes, among which, Proteobacteria had an absolute advantage with a relative abundance ranging of 66-78%. With increasing landfill age, the abundance of Firmicutes decreased gradually, while that of Bacteroidetes increased. Pseudomonas, Thiopseudomonas, Psychrobacter and Desemzia were the main genera. The distribution of bacterial community in samples with landfill ages of 0-1 and 1-3 years were greatly influenced by TKN and pH, respectively. Amino acid and carbohydrate metabolism were the main biological pathways according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and the biodegradation of xenobiotics as well as terpenoids and polyketides also accounted relatively high frequencies in the landfill. These results provide a better understanding of landfill microbiology and bioprocesses for landfill stabilization.

Microbial community composition and metabolic functions in landfill leachate from different landfills of China

Landfill leachate usually harbors complex microbial communities responsible for the decomposition of municipal solid waste. However, the diversity and metabolic functions of the microbial communities in landfill leachate as well as the factors that influence them are still not well understood. In this study, Illumina MiSeq high-throughput sequencing was used to investigate the microbial community composition and metabolic functions in landfill leachate from 11 cities in China. The microbial diversity and structure of different leachate samples exhibited obvious differences. In general, Bacteroidetes, Firmicutes and Proteobacteria were the three dominant microbial communities among the 26 bacterial phyla identified in landfill leachate, regardless of the geographical locations. Diverse bacterial genera associated with various functions such as cellulolytic bacteria (e.g., Sphaerochaeta and Defluviitoga), acidifying bacteria (e.g., Prevotella and Trichococcus) and sulfate-reducing bacteria (e.g., Desulfuromonas and Desulfobacterium) were detected abundantly in the landfill leachate. Moreover, the archaeal community in all leachate samples was dominated by the orders Methanomicrobiales and Methanosarcinales belonging to the Euryarchaeota phylum. Notably, the archaea-specific primer pair covered more diverse archaeal communities than the universal bacteria-archaea primer pair. Seventeen archaeal genera belonging to acetoclastic, hydrogenotrophic, and methylotrophic methanogens were identified, and the composition of the dominant genera in these samples varied greatly. The canonical correlation analysis indicated that landfill age, electrical conductivity, ammonia nitrogen, and total nitrogen were significantly correlated with the microbial community structure. Based on PICRUSt2, a total of 41 metabolic pathways belonging to six metabolic pathway groups were predicted, and the KEGG pathway Metabolism was the most abundant group across all leachate samples. This study provides an important insight into the composition and functional characteristics of the microbial communities in landfill leachate.

Potential Environmental and Human Health Risks Caused by Antibiotic-Resistant Bacteria (ARB), Antibiotic Resistance Genes (ARGs) and Emerging Contaminants (ECs) from Municipal Solid Waste (MSW) Landfill

The disposal of municipal solid waste (MSW) directly at landfills or open dump areas, without segregation and treatment, is a significant concern due to its hazardous contents of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs), and metal resistance genes (MGEs). The released leachate from landfills greatly effects the soil physicochemical, biological, and groundwater properties associated with agricultural activity and human health. The abundance of ARB, ARGs, and MGEs have been reported worldwide, including MSW landfill sites, animal husbandry, wastewater, groundwater, soil, and aerosol. This review elucidates the occurrence and abundance of ARB, ARGs, and MRGs, which are regarded as emerging contaminants (ECs). Recently, ECs have received global attention because of their prevalence in leachate as a substantial threat to environmental and public health, including an economic burden for developing nations. The present review exclusively discusses the demands to develop a novel eco-friendly management strategy to combat these global issues. This review also gives an intrinsic discussion about the insights of different aspects of environmental and public health concerns caused due to massive leachate generation, the abundance of antibiotics resistance (AR), and the effects of released leachate on the various environmental reservoirs and human health. Furthermore, the current review throws light on the source and fate of different ECs of landfill leachate and their possible impact on the nearby environments (groundwater, surface water, and soil) affecting human health. The present review strongly suggests the demand for future research focuses on the advancement of the removal efficiency of contaminants with the improvement of relevant landfill management to reduce the potential effects of disposable waste. We propose the necessity of the identification and monitoring of potential environmental and human health risks associated with landfill leachate contaminants.

Deciphering acyl-homoserine lactones-mediated quorum sensing on geotextile bio-clogging in municipal solid waste and bottom ash co-disposal landfills

Bottom ash co-disposed in landfills accelerates geotextile clogging and decreases landfill stability. As the main contributor to clogging, bio-clogging may be associated with quorum sensing (QS) in microbial communities. This study investigated the potential roles of acyl-homoserine lactones (AHLs)-mediated QS in geotextile bio-clogging under different landfill conditions, including municipal solid waste landfill and bottom ash co-disposal landfill. The unit area of geotextile bio-clogging mass in the municipal solid waste landfill (MSW_G) ranged from 5.2 × 10^-3 to 8.2 × 10^-3 g/cm²_, while it was in the range of 8.4 × 10^-3 to 1.2 × 10^-2 g/cm² in the bottom ash co-disposal landfill (BA_G). Two types of AHLs were detected and the total AHLs content in the MSW_G (1,616.9 ± 103.8 ng/g VSS) was half of that in the BA_G (3,233.0 ± 646.8 ng/g VSS). High contents of the AHLs could increase bio-clogging. The bio-clogging was also attributed to QS genes and extracellular polymeric substances (EPS). EPS aggregation was stimulated due to the higher Ca²⁺ and Mg²⁺ in the BA_G. These results suggested that the co-disposal of bottom ash could increase the AHLs content, resulting in accelerated bio-clogging.

Livestock Manure Type Affects Microbial Community Composition and Assembly During Composting

Composting is an environmentally friendly way to turn plant and animal wastes into organic fertilizers. However, it is unclear to what extent the source of animal waste products (such as manure) affects the physicochemical and microbiological properties of compost. Here, we experimentally tested how the type of livestock manure of herbivores (sheep and cattle) and omnivores (pig and chicken) influences the bacterial and fungal communities and physicochemical properties of compost. Higher pH, NO₃-N, Total carbon (TC) content and C/N were found in sheep and cattle manure composts, while higher EC, NH₄-N, Total nitrogen (TN) and total phosphorus (TP) content were measured in pig and chicken manure composts. Paired clustering between herbivore and omnivore manure compost metataxonomy composition was also observed at both initial and final phases of composting. Despite this clear clustering, all communities changed drastically during the composting leading to reduced bacterial and fungal diversity and large shifts in community composition and species dominance. While Proteobacteria and Chloroflexi were the major phyla in sheep and cattle manure composts, Firmicutes dominated in pig and chicken manure composts. Together, our results indicate that feeding habits of livestock can determine the biochemical and biological properties of manures, having predictable effects on microbial community composition and assembly during composting. Manure metataxonomy profiles could thus potentially be used to steer and manage composting processes.

Bioaerosols in the landfill environment: an overview of microbial diversity and potential health hazards

Landfilling is one of the indispensable parts of solid waste management in various countries. Solid waste disposed of in landfill sites provides nutrients for the proliferation of pathogenic microbes which are aerosolized into the atmosphere due to the local meteorology and various waste disposal activities. Bioaerosols released from landfill sites can create health issues for employees and adjoining public. The present study offers an overview of the microbial diversity reported in the air samples collected from various landfill sites worldwide. This paper also discusses other aspects, including effect of meteorological conditions on the bioaerosol concentrations, sampling techniques, bioaerosol exposure and potential health impacts. Analysis of literature concluded that landfill air is dominated by microbial dust or various pathogenic microbes like Enterobacteriaceae, Staphylococcus aureus, Clostridium perfringens, Acinetobacter calcoaceticus and Aspergillus fumigatus. The bioaerosols present in the landfill environment are of respirable sizes and can penetrate deep into lower respiratory systems and trigger respiratory symptoms and chronic pulmonary diseases. Most studies reported higher bioaerosol concentrations in spring and summer as higher temperature and relative humidity provide a favourable environment for survival and multiplication of microbes. Landfill workers involved in solid waste disposal activities are at the highest risk of exposure to these bioaerosols due to their proximity to solid waste and as they practise minimum personal safety and hygiene measures during working hours. Workers are recommended to use personal protective equipment and practise hygiene to reduce the impact of occupational exposure to bioaerosols.

Evaluation of the Phytotoxicity of Leachate from a Municipal Solid Waste Landfill: The Case Study of Bukov Landfill

Municipal solid waste landfilling, landfilling process and landfill reclamation result in leachate, which may be dangerous to the environment. Municipal solid waste leachate phytotoxicity tests were performed using the toxicity test and a subchronic toxicity pot experiment by direct application of leachate to reference soil in 5, 25, and 50% concentration for a period of 28 days. White mustard (Sinapis alba L.) seeds were exposed to different leachate dilution. Leachate were collected monthly in 2018 in the period from April to September. Furthermore, pH, conductivity, and dissolved oxygen were measured. The inhibition results on Sinapis alba L. seeds in the tested leachate samples ranged from −18.02 to 39.03%. Lower concentration of leachate showed a stimulating effect (only for Sample 1 and Sample 2 at 5% concentration). It was found out that leachate taken at the landfill is phytotoxic. The results of measurements are based on rainfall which affects the quantity and quality of the leachate. The values of germinated seeds/growing plants from the subchronic toxicity pot experiment ranged from 80 to 104%; therefore, the leachate is considered phytotoxic. However, it was confirmed that leachate may be used for landfill irrigation.

Community diversity metrics, interactions, and metabolic functions of bacteria associated with municipal solid waste landfills at different maturation stages

Municipal landfills are hot spots of dynamic bioprocesses facilitated by complex interactions of a multifaceted microbiome, whose functioning in municipal landfills at different maturing stages is poorly understood. This study determined bacterial community composition, interaction conetworks, metabolic functions, and controlling physicochemical properties in two landfills aged 14 and 36 years. High throughput sequencing revealed a similar distribution of bacterial diversity, evenness, and richness in the 14‐ and 36‐year‐old landfills in the 0–90 cm depth. At deeper layers (120–150 cm), the 14‐year‐old landfill had significantly greater bacterial diversity and richness indicating that it is a more active microcosm than the 36‐year‐old landfill, where phylum Epsilonbacteraeota was overwhelmingly dominant. The taxonomic and functional diversity in the 14‐year‐old landfill was further reflected by the abundant presence of indicator genera Pseudomonas,Lutispora,Hydrogenspora, and Sulfurimonas coupled with the presence of biomarker enzymes associated with carbon (C), nitrogen (N), and sulfur (S) metabolism. Furthermore, canonical correspondence analysis revealed that bacteria in the 14‐year‐old landfill were positively correlated with high C, N, S, and phosphorus resulting in positive cooccurrence interactions. In the 36‐year‐old landfill, negative coexclusion interactions populated by members of N fixing Rhizobiales were dominant, with metabolic functions and biomarker enzymes predicting significant N fixation that, as indicated by interaction network, potentially inhibited ammonia‐intolerant bacteria. Overall, our findings show that diverse bacterial community in the 14‐year‐old landfill was dominated by copiotrophs associated with positive conetworks, whereas the 36‐year‐old landfill was dominated by lithotrophs linked to coexclusion interactions that greatly reduced bacterial diversity and richness.

Effect of substrate concentrations on aerobic biotransformation of 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate

Biotransformation of 6:2 fluorotelomer sulfonate (FTS) results in the formation of short-chain (C4 - C6) perfluorocarboxylic acids (PFCAs) in landfill leachate. Although leachate substrate concentrations (i.e., organic carbon, ammonia) vary widely, their effects on 6:2 FTS biotransformation and PFCAs formation are unknown. This study investigated the effect of organic carbon and ammonia concentration in 6:2 FTS aerobic biotransformation and PFCA formation in leachate. Biotransformation experiments were conducted with sediment collected from a landfill leachate ditch, to which deionized (DI) water and various amounts of leachate were added. Microbial community analysis using 16S rRNA indicated that while phylum Proteobacteria dominated the bacterial composition throughout the 60 days, Actinobacteria increased with time. Many genera from Proteobacteria and Actinobacteria can synthesize a wide array of enzymes, indicating that these phyla are likely to play an important role in 6:2 FTS biotransformation. Higher biotransformation of 6:2 FTS was observed in leachate-added microcosms (∼21%), compared to DI water microcosm (∼14%), likely reflecting the substrate dependency of 6:2 FTS biotransformation. Substrate limiting conditions in DI water microcosm resulted in slightly greater formation of ∑(C4 - C6) PFCAs (∼14 mol%), compared with leachate added microcosms (10-13 mol%). The findings suggest that dilution of landfill leachate, (e.g., during wet seasons), likely results in reduced 6:2 FTS biotransformation and increased PFCAs formation compared to dry conditions. Observed formation of C7 - C8 PFCAs in the live microcosms suggested that landfills act as secondary sources of legacy PFCAs (e.g., perfluorooctanoic acid) in the environment.

Tracing bacterial and fungal necromass dynamics of municipal sludge in landfill bioreactors using biomarker amino sugars

The dynamics of microbial necromass of municipal solid waste over long-term landfill remain unknown. This study presents the first investigation on the dynamics of bacterial and fungal necromass of municipal sludge in non-aeration versus alternating aeration landfill bioreactors by using amino sugar biomarkers. Results showed that under non-aeration treatment, the decomposition rate of muramic acid derived from bacteria is higher than that of fungal-derived glucosamine. The relative change in glucosamine and muramic acid in the early period of landfills under the alternating aeration treatment is consistent with that under non-aeration treatment. However, with the increase in alternating aeration cycles, bacterial necromass muramic acid exerts a lower decomposition rate than fungal necromass glucosamine. Throughout the entire landfill period, galactosamine is the amino sugar with the slowest decomposition rate under non-aeration mode but the amino sugar with the fastest decomposition rate under alternating aeration mode. The present work fills the knowledge gap of microbial necromass dynamics of municipal solid waste in landfills.

Microbial Communities and Sulfate-Reducing Microorganisms Abundance and Diversity in Municipal Anaerobic Sewage Sludge Digesters from a Wastewater Treatment Plant (Marrakech, Morocco)

Both molecular analyses and culture-dependent isolation were combined to investigate the diversity of sulfate-reducing prokaryotes and explore their role in sulfides production in full-scale anaerobic digesters (Marrakech, Morocco). At global scale, using 16S rRNA gene sequencing, Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Synergistetes, and Euryarchaeota were the most dominant phyla. The abundance of Archaea (3.1–5.7%) was linked with temperature. The mcrA gene ranged from 2.18 × 105 to 1.47 × 107 gene copies.g−1 of sludge. The sulfate-reducing prokaryotes, representing 5% of total sequences, involved in sulfides production were Peptococcaceae, Syntrophaceae, Desulfobulbaceae, Desulfovibrionaceae, Syntrophobacteraceae, Desulfurellaceae, and Desulfobacteraceae. Furthermore, dsrB gene ranged from 2.18 × 105 to 1.92 × 107 gene copies.g−1 of sludge. The results revealed that exploration of diversity and function of sulfate-reducing bacteria may play a key role in decreasing sulfide production, an undesirable by-product, during anaerobic digestion.

Extracellular enzyme and microbial activity in MSW landfills with different gas collection and leachate management practices

The performance of simulated municipal solid waste (MSW) landfills with two different biogas collection practices - (1) upward and upward-downward biogas flow collection (L_T-TB) in sequence and (2) simultaneous upward-downward biogas flow collection (L_TB) from the beginning of the anaerobic degradation process - was investigated in terms of landfill gas and leachate, enzyme activity, and microbial community structure associated with MSW compression and leachate recirculation. The cumulative methane volume in L_TB was 1.5 times higher than that in L_T-TB. With MSW compression and leachate recirculation, amylase and lipase activity were enhanced in L_TB. In L_T-TB, the activities gradually decreased after reaching a peak with compression. The two biogas collection strategies influenced the community structure and activity of bacteria and archaea. The upward and downward gas collection flow with waste compression and leachate recirculation improved the environment for enriching bacterial phyla Firmicutes, Proteobacteria, and Synergistetes and genus Methanosarcina in Archaea.

NGS-based characterization of microbial diversity and functional profiling of solid tannery waste metagenomes

Tanneries pose a serious threat to the environment by generating large amount of solid tannery waste (STW). Two metagenomes representing tannery waste dumpsites Jajmau (JJK) and Unnao (UNK) were sequenced using Illumina HiSeq platform. Microbial diversity analysis revealed domination of Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, and Planctomycetes in both metagenomes. Presence of pollutant degrading microbes such as Bacillus, Clostridium, Halanaerobium and Pseudomonas strongly indicated their bioremediation ability. KEGG and SEED annotated main functional categories included carbohydrate metabolism, amino acids metabolism, and protein metabolism. KEGG displayed 5848 and 9633 proteases encoding ORFs compared to 5159 and 8044 ORFs displayed by SEED classification in JJK and UNK metagenomes, respectively. Abundantly present serine- and metallo-proteases belonging to Bacillaceae, Clostridiaceae, Xanthomonadaceae, Flavobacteriaceae and Chitinophagaceae families exhibited proteinaceous waste degrading ability of these metagenomes. Further structural and functional analysis of metagenome encoded enzymes may facilitate the discovery of novel proteases useful in bioremediation of STW.