Microbial community structures and metabolic profiles response differently to physiochemical properties between three landfill cover soils

Tracing residual patterns and microbial communities of pharmaceuticals and personal care products from 17 urban landfills leachate in China

Landfill leachate contributes significantly to the presence of pharmaceuticals and personal care products (PPCPs) in the environment, and is a crucial source of contamination. To examine the occurrence of PPCPs and microbial communities, this study comprehensively investigated the concentrations of PPCPs and the abundance of microorganisms in the leachate from 17 municipal landfills across China. Generally, Lidocaine, Linear alkylbenzene sulfonate-C11, and Triclocarban, which are closely associated with human activities, exhibited a detection frequency of 100 % in the leachate. Driven by consumer demand, analgesic and antipyretic drugs have emerged as the most prominent PPCPs in leachate (accounting for 39.9 %). Notably, the Ibuprofen peaked at 56.3 μg/L. Regarding spatial distribution, the contamination of PPCPs in leachates from the eastern regions of China was significantly higher than that in other regions, owing to the level of economic development and demographic factors. Furthermore, the 16S rRNA results revealed significant differences in microbial communities among the leachates from different areas. Although the impact of PPCPs on microbial communities may not be as significant as that of environmental factors, most positive correlations between PPCPs and microorganisms indicate their potential role in providing nutrients and creating favorable conditions for microbial growth. Overall, this research offers new perspectives on the residual features of PPCPs and the microbial community structure in leachates from various regions in China.

Landfill intermediate cover soil microbiomes and their potential for mitigating greenhouse gas emissions revealed through metagenomics

Landfills are a major source of anthropogenic methane emissions and have been found to produce nitrous oxide, an even more potent greenhouse gas than methane. Intermediate cover soil (ICS) plays a key role in reducing methane emissions but may also result in nitrous oxide production. To assess the potential for microbial methane oxidation and nitrous oxide production, long sequencing reads were generated from ICS microbiome DNA and reads were functionally annotated for 24 samples across ICS at a large landfill in New York. Further, incubation experiments were performed to assess methane consumption and nitrous oxide production with varying amounts of ammonia supplemented. Methane was readily consumed by microbes in the composite ICS and all incubations with methane produced small amounts of nitrous oxide even when ammonia was not supplemented. Incubations without methane produced significantly less nitrous oxide than those incubated with methane. In incubations with methane added, the observed specific rate of methane consumption was 0.776 +/- 0.055 μg CH4 g dry weight (DW) soil-1 h-1 and the specific rate of nitrous oxide production was 3.64 × 10-5 +/- 1.30 × 10-5 μg N2O g DW soil-1 h-1. The methanotrophs Methylobacter and an unclassified genus within the family Methlyococcaceae were present in the original ICS samples and the incubation samples, and their abundance increased during incubations with methane. Genes encoding particulate methane monooxygenase/ ammonia monooxygenase (pMMO) were much more abundant than genes encoding soluble methane monooxygenase (sMMO) across the landfill ICS. Genes encoding proteins that convert hydroxylamine to nitrous oxide were not highly abundant in the ICS or incubation metagenomes. In total, these results suggest that although ammonia oxidation via methanotrophs may result in low levels of nitrous oxide production, ICS microbial communities have the potential to greatly reduce the overall global warming potential of landfill emissions.

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.

Use of methanotrophically activated biochar in novel biogeochemical cover system for carbon sequestration: Microbial characterization

Biochar-amended soils have been explored to enhance microbial methane (CH₄) oxidation in landfill cover systems. Recently, research priorities have expanded to include the mitigation of other components of landfill gas such as carbon dioxide (CO₂) and hydrogen sulfide (H₂S) along with CH₄. In this study, column tests were performed to simulate the newly proposed biogeochemical cover systems, which incorporate biochar-amended soil for CH₄ oxidation and basic oxygen furnace (BOF) slag for CO₂ and H₂S mitigation, to evaluate the effect of cover configuration on microbial CH₄ oxidation and community composition. Biogeochemical covers included a biochar-amended soil (10% w/w), and methanotroph-enriched activated biochar amended soil (5% or 10% w/w) as a biocover layer or CH₄ oxidation layer. The primary outcome measures of interest were CH₄ oxidation rates and the structure and abundance of methane-oxidation bacteria in the covers. All column reactors were active in CH₄ oxidation, but columns containing activated biochar-amended soils had higher CH₄ oxidation rates (133 to 143 μg CH₄ g^-1 day^-1) than those containing non-activated biochar-amended soil (50 μg CH₄ g^-1 day^-1) and no-biochar soil or control soil (43 μg CH₄ g^-1 day^-1). All treatments showed significant increases in the relative abundance of methanotrophs from an average relative abundance of 5.6% before incubation to a maximum of 45% following incubation. In activated biochar, the abundance of Type II methanotrophs, primarily Methylocystis and Methylosinus, was greater than that of Type I methanotrophs (Methylobacter) due to which activated biochar-amended soils also showed higher abundance of Type II methanotrophs. Overall, biogeochemical cover profiles showed promising potential for CH₄ oxidation without any adverse effect on microbial community composition and methane oxidation. Biochar activation led to an alteration of the dominant methanotrophic communities and increased CH₄ oxidation.

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.

Bacteria Community Vertical Distribution and Its Response Characteristics to Waste Degradation Degree in a Closed Landfill

The diversity, community structure and vertical distribution characteristics of bacteria in the surface and subsurface soil and water samples of a closed landfill in Shanghai Jiading District were investigated to reveal the relationships between natural waste degradation degree and the succession of bacterial community composition. High-throughput sequencing of bacteria 16S rDNA genes was used to analyze the bacterial community structure and diversity. The results showed that the diversity of bacteria in the surface samples was higher than that in the deep samples. Proteobacteria was the dominant phylum in all the samples, and the percentage increased with depth. At the genus level, Thiobacillus, Pseudomonas, Aquabacterium, and Hydrogenophaga were the dominant genera in surface, medium, deep and ultra-deep soils, respectively. The Bray–Curtis dissimilarity of the soil bacterial communities in the same layer was small, indicating that the community composition of the samples in the same layer was similar. The RDA result showed that ammonium, nitrate, pH and C/N significantly influenced the community structure of soil bacteria. This is of great relevance to understand the effect of natural waste degradation on bacterial communities in closed landfills.

Effectiveness of chelating agent-assisted Fenton-like processes on remediation of glucocorticoid-contaminated soil using chemical and biological assessment: performance comparison of CaO2 and H2O2

Glucocorticoids (GCs) have drawn great concern due to widespread contamination in the environment and application in treating COVID-19. Most studies on GC removal mainly focused on aquatic environment, while GC behaviors in soil were less mentioned. In this study, degradation of three selected GCs in soil has been investigated using citric acid (CA)-modified Fenton-like processes (H₂O₂/Fe(III)/CA and CaO₂/Fe(III)/CA treatments). The results showed that GCs in soil can be removed by modified Fenton-like processes (removal efficiency gt; 70% for 24 h). CaO₂/Fe(III)/CA was more efficient than H₂O₂/Fe(III)/CA at low oxidant dosage (< 0.28-0.69 mmol/g) for long treatment time (> 4 h). Besides the chemical assessment with GC removal, effects of Fenton-like processes were also evaluated by biological assessments with bacteria and plants. CaO₂/Fe(III)/CA was less harmful to the richness and diversity of microorganisms in soil compared to H₂O₂/Fe(III)/CA. Weaker phytotoxic effects were observed on GC-contaminated soil treated by CaO₂/Fe(III)/CA than H₂O₂/Fe(III)/CA. This study, therefore, recommends CaO₂-based treatments to remediate GC-contaminated soils.

Effect of Different Substrates on Soil Microbial Community Structure and the Mechanisms of Reductive Soil Disinfestation

Reductive soil disinfestation (RSD) has recently attracted much attention owing to its effectiveness for controlling pathogens. In this study, we aimed to evaluate the effects of different C/N substrates on RSD and to explore the changes in microbial community structure during RSD treatment. The experimental set up included 10 groups, as follows: CK, without substrates; RSD treatments with alfalfa (Medicago sativa L.)[AL], maize (Zea mays Linn. Sp.) straw [MS], and rice (Oryza sativa L.) straw [RS], with three levels of addition (0.5% [L], 2% [M], and 5% [H]), yielding ALL, ALM, ALH, MSL, MSM, MSH, RSL, RSM, and RSH groups. Compared with CK, RSD treatments significantly increased the content of NH4+-N, and effectively eliminated the accumulated NO3--N in the soil. The relative abundances of organic acid producers, including Clostridium, Coprococcus, and Oxobacter, in all RSD groups were significantly higher than those in the CK by day 21. Moreover, on day 21, Aspergillus and Fusarium in all RSD groups were significantly lower than those in the CK. In summary, RSD treatments clearly increased the relative abundances of organic acid generators and effectively inhibited pathogens; however, when the C/N was too low and the amount of addition too high, ammonia poisoning and rapid growth of some microorganisms (e.g., Pseudallescheria and Arthrographis) may occur.

Linking nano-ZnO contamination to microbial community profiling in sanitary landfill simulations

Nanomaterials (NMs) commercially used for various activities mostly end up in landfills. Reduced biogas productions reported in landfill reactors create a need for more comprehensive research on these greatly-diverse microbial pools. In order to evaluate the impact of one of the most widely-used NMs, namely nano-zinc oxide (nano-ZnO), simulated bioreactor and conventional landfills were operated using real municipal solid waste (MSW) for 300 days with addition nano-ZnO. Leachate samples were taken at different phases and analyzed by 16S rRNA gene amplicon sequencing. The bacterial communities were distinctly characterized by Cloacamonaceae (phylum WWE1), Rhodocyclaceae (phylum Proteobacteria), Porphyromonadaceae (phylum Bacteroidetes), and Synergistaceae (phylum Synergistetes). The bacterial community in the bioreactors shifted at the end of the operation and was dominated by Rhodocyclaceae. There was not a major change in the bacterial community in the conventional reactors. The methanogenic archaeal diversity highly differed between the bioreactors and conventional reactors. The dominance of Methanomicrobiaceae was observed in the bioreactors during the peak methane-production period; however, their prominence shifted to WSA2 in the nano-ZnO-added bioreactor and to Methanocorpusculaceae in the control bioreactor towards the end. Methanocorpusculaceae was the most abundant family in both conventional control and nano-ZnO-containing reactors.

Odor removal by and microbial community in the enhanced landfill cover materials containing biochar-added sludge compost under different operating parameters

Odor problem has become a growing concern for municipal solid waste (MSW) operators and communities located close to landfill sites. In this study, nine laboratory-scale landfill reactors were used to simulate in-situ odor control by a novel landfill cover material consisting of biochar-added sludge compost under various operating parameters. Characterization of odor removal and microbial community in the cover layer under various operating parameters was conducted using gas chromatograph-mass spectrometry and 454 high-throughput pyrosequencing, respectively. Results showed that H₂S (76.9-86.0%) and volatile organic sulfur compounds (VOSCs) (12.3-21.7%) were dominant according to their theoretical generated odor concentrations. The total odor REs calculated using the theoretical odor concentrations in the landfill reactors were different than using the measured odor values, which were ranked from high to low as: R6 > R5 > R7 > R4 > R8 > R9 > R3 > R2 > R1, showing the largest discrepancy of 25.3%. The optimum combination of operating parameters based on the theoretical odor concentration was different with that based on the measured odor concentrations. Moreover, although Firmicutes (12.21-91.48%), Proteobacteria (3.55-51.03%), and Actinobacteria (4.01-47.39%) were in general the three major bacterial phyla found in the landfill covers, the detailed bacterial communities in the cover materials of the simulated reactors varied with various operating parameters. Alicyclobacillus and Tuberibacillus showed positive correlations with the removal efficiencies (REs) of chlorinated compounds, H₂S, aromatic compounds, volatile organic sulfur compounds (VOSCs), and organic acids. The correlations of Rhodanobacter, Gemmatimonas, Flavisolibacter and Sphingomonas were strongly positive with ammonia RE and relatively positive with REs of organic acids, VOSCs, and aromatic compounds. These findings are instrumental in understanding the relationship between the structure of microbial communities and odor removal performances, and in developing techniques for in-situ odor control at landfills.

Effects of copper on expression of methane monooxygenases, trichloroethylene degradation, and community structure in methanotrophic consortia

Copper plays a key role in regulating the expression of enzymes that promote biodegradation of contaminants in methanotrophic consortia (MC). Here, we utilized MC isolated from landfill cover to investigate cometabolic degradation of trichloroethylene (TCE) at nine different copper (Cu²⁺) concentrations. The results demonstrated that an increase in Cu²⁺ concentration from 0 to 15 μM altered the specific first-order rate constant k _1,TCE, the expression levels of methane monooxygenase (pmoA and mmoX) genes, and the specific activity of soluble methane monooxygenase (sMMO). High efficiency TCE degradation (95%) and the expression levels of methane monooxygenase (MMO) were detected at a Cu²⁺ concentration of 0.03 μM. Notably, sMMO-specific activity ranged from 74.41 nmol/(mg_cell h) in 15 μM Cu²⁺ to 654.99 nmol/(mg_cell h) in 0.03 μM Cu²⁺, which contrasts with cultures of pure methanotrophs in which sMMO activity is depressed at high Cu²⁺ concentrations, indicating a special regulatory role for Cu²⁺ in MC. The results of MiSeq pyrosequencing indicated that higher Cu²⁺ concentrations stimulated the growth of methanotrophic microorganisms in MC. These findings have important implications for the elucidation of copper-mediated regulatory mechanisms in MC.