Comparison of Bacteria and Archaea communities in municipal solid waste, individual refuse components, and leachate

Characterization of methanogens from landfill samples: implications for sustainable biogas production

This case study aimed to isolate and identify methanogenic bacteria from landfill soil, mud, and leachate samples to assess their role in anaerobic digestion and biogas production. Anaerobic digestion involves the breakdown of organic matter by a diverse group of bacteria under oxygen-free conditions, resulting in the production of methane and carbon dioxide. The collected samples from the landfill were cultured in a modified mineral salt medium (MSM). Microscopic observations revealed distinct coccus and bacillus morphologies of the isolated methanogenic bacteria. Gas production experiments and substrate utilization studies identified two types of methanogens. Methanosarcina sp., which utilized acetate and methanol for methane production, and Methanobacterium sp., utilizing hydrogen and carbon dioxide, as well as acetate. Scanning electron microscope (SEM) analysis confirmed the different morphotypes of the isolated methanogens. The study findings demonstrated the presence of diverse methanogens in the landfill environment, contributing to anaerobic digestion and biogas production.

Linking microbial population dynamics in anaerobic bioreactors to food waste type and decomposition stage

A key question in anaerobic microbial ecology is how microbial communities develop over different stages of waste decomposition and whether these changes are specific to waste types. We destructively sampled over time 26 replicate bioreactors cultivated on fruit/vegetable waste (FVW) and meat waste (MW) based on pre-defined waste components and composition. To characterize community shifts, we examined 16S rRNA genes from both the leachate and solid fractions of the waste. Waste decomposition occurred faster in FVW than MW, as accumulation of ammonia in MW reactors led to inhibition of methanogenesis. We identified population succession during different stages of waste decomposition and linked specific populations to different waste types. Community analyses revealed underrepresentation of methanogens in the leachate fractions, emphasizing the importance of consistent and representative sampling when characterizing microbial communities in solid waste.

Antibiotics inhibit methanogenesis during municipal solid waste decomposition

Municipal solid waste (MSW) landfills are significant sources of antibiotics. However, the effects of antibiotics on MSW decomposition process and methanogenesis during solid waste decomposition remain insufficiently characterized. This study investigated the effects of environmentally relevant concentrations (ERCs) of antibiotics (200 μg/kg for each antibiotic) on MSW decomposition and methanogenesis in bioreactors treated with and without eight antibiotics (three tetracyclines, three sulfonamides, and two macrolides). The key phases of MSW decomposition, namely the aerobic, anaerobic acid, and methanogenic phases, were determined by analyzing the key physiochemical parameters of the leachate, including pH, chemical oxygen demand, and biochemical oxygen demand. We assessed the bacterial and archaeal compositions, along with the abundance of the gene encoding the alpha subunit of methyl-coenzyme M reductase (mcrA), during MSW decomposition using high throughput 16S ribosomal RNA (rRNA) gene sequencing and quantitative polymerase chain reactions, respectively. Our results revealed that antibiotics significantly altered the compositions of bacteria and methanogens, leading to decreased mcrA abundance and methanogenesis. Specifically, antibiotics inhibited cellulose-degrading bacteria (Firmicutes) and archaea (E2) in the anaerobic acid phase and hydrolytic bacteria (Proteobacteria) in the methanogenic phase, resulting in lower degradation of biodegradable matter than that of the biodegradation without antibiotics treatment. However, the typical MSW decomposition process indicated by the key decomposition phases was successfully separated in both bioreactors, suggesting that antibiotics did not affect overall MSW decomposition process development or the associated individual decomposition phases establishment. These findings suggest that antibiotics at ERCs may inhibit methanogenesis during MSW decomposition, thereby providing fundamental information for methane management and climate change studies.

Transport of pollutants in groundwater of domestic waste landfills in karst regions and its engineering control technologies

Domestic waste produces leachate with a high concentration of pollutants in the landfill process due to biochemical degradation stages like compaction and fermentation. A large number of cases show that anti-seepage membranes widely used in refuse landfills tend to rupture under long-term tension and corrosion, causing leachate to enter the groundwater system and pollute the environment. To reveal the phenomenon of groundwater contamination in refuse landfills, typical domestic waste landfills in karst regions were examined, on the basis of a summary of hydrogeological conditions and hydrochemical characteristics, a three-dimensional groundwater flow model and solute transport model were constructed to analyze the pattern of pollutant diffusion, and its controlling factors, under the current conditions and massive rupture of anti-seepage membrane. The results show that with a minor rupture of the anti-seepage membrane, the area of the low pollution region increases first and then decreases while that of the slight pollution region continuously increases; When a massive rupture of the anti-seepage membrane appears, the ranges of heavy pollution region and total pollution regions continue to grow; Pollutant migrates along the same direction as the groundwater flow and diffuse from high concentration region to low concentration regions under the differential concentration effect. Based on the temporal-spatial distribution characteristics of groundwater pollutants, two engineering control schemes, namely, curtain grouting blocking and group well pumping, were established. A comparison of the two control schemes shows that group well pumping stably maintains water quality safety over the long term, pollutants overflow from both sides of the curtain after they have accumulated to a certain point of concentration, causing damage to the groundwater environment in the conservation area.

Microbial Mediation of Carbon, Nitrogen, and Sulfur Cycles During Solid Waste Decomposition

Landfills are a unique "terrestrial ecosystem" and serve as a significant carbon sink. Microorganisms convert biodegradable substances in municipal solid waste (MSW) to CH₄, CO₂, and microbial biomass, consisting of the carbon cycling in landfills. Microbial-mediated N and S cycles are also the important biogeochemical process during MSW decomposition, resulting in N₂O and H₂S emission, respectively. Meanwhile, microbial-mediated N and S cycles affect carbon cycling. How microbial community structure and function respond to C, N, and S cycling during solid waste decomposition, however, are not well-characterized. Here, we show the response of bacterial and archaeal community structure and functions to C, N, and S cycling during solid waste decomposition in a long-term (265 days) operation laboratory-scale bioreactor through 16S rRNA-based pyrosequencing and metagenomics analysis. Bacterial and archaeal community composition varied during solid waste decomposition. Aerobic respiration was the main pathway for CO₂ emission, while anaerobic C fixation was the main pathway in carbon fixation. Methanogenesis and denitrification increased during solid waste decomposition, suggesting increasing CH₄ and N₂O emission. In contract, fermentation decreased along solid waste decomposition. Interestingly, Clostridiales were abundant and showed potential for several pathways in C, N, and S cycling. Archaea were involved in many pathways of C and N cycles. There is a shift between bacteria and archaea involvement in N₂ fixation along solid waste decomposition that bacteria Clostridiales and Bacteroidales were initially dominant and then Methanosarcinales increased and became dominant in methanogenic phase. These results provide extensive microbial mediation of C, N, and S cycling profiles during solid waste decomposition.

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.

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.

Leachate microbiome profile reveals bacteria, archaea and eukaryote dynamics and methanogenic function during solid waste decomposition

Bacterial, archaeal, and eukaryotic community composition and dynamics in leachate during solid waste decomposition were investigated using Illumina MiSeq sequencing. The functional enzyme-encoding genes of methanogenic pathways were also predicted via PICRUSt. Succession of bacterial, archaeal, and eukaryotic community composition in aerobic phase (AP), anaerobic acid phase (ACP), and methanogenic phase (MP) was observed. The main representatives of microbial phyla, genera, and species significantly (p < 0.05) differed at least two phases. Protist Ciliophora occurred at ACP and was prevalent in MP, suggesting a short food chain establishment in the methanogenesis. Bacterial, archaeal, fungi and eukaryotic community structure were all pH and biochemical oxygen demand (BOD₅) dependent patter. Acetoclastic and hydrogenotrophic methanogenesis pathways with associated functional genes differed during solid waste decomposition and were inhibited in ACP.

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.

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.

A Review of Landfill Microbiology and Ecology: A Call for Modernization With 'Next Generation' Technology

Engineered and monitored sanitary landfills have been widespread in the United States since the passage of the Clean Water Act (1972) with additional controls under RCRA Subtitle D (1991) and the Clean Air Act Amendments (1996). Concurrently, many common perceptions regarding landfill biogeochemical and microbiological processes and estimated rates of gas production also date from 2 to 4 decades ago. Herein, we summarize the recent application of modern microbiological tools as well as recent metadata analysis using California, USEPA and international data to outline an evolving view of landfill biogeochemical/microbiological processes and rates. We focus on United States landfills because these are uniformly subject to stringent national and state requirements for design, operations, monitoring, and reporting. From a microbiological perspective, because anoxic conditions and methanogenesis are rapidly established after daily burial of waste and application of cover soil, the >1000 United States landfills with thicknesses up to >100 m form a large ubiquitous group of dispersed 'dark' ecosystems dominated by anaerobic microbial decomposition pathways for food, garden waste, and paper substrates. We review past findings of landfill ecosystem processes, and reflect on the potential impact that application of modern sequencing technologies (e.g., high throughput platforms) could have on this area of research. Moreover, due to the ever evolving composition of landfilled waste reflecting transient societal practices, we also consider unusual microbial processes known or suspected to occur in landfill settings, and posit areas of research that will be needed in coming decades. With growing concerns about greenhouse gas emissions and controls, the increase of chemicals of emerging concern in the waste stream, and the potential resource that waste streams represent, application of modernized molecular and microbiological methods to landfill ecosystem research is of paramount importance.

Prevalence of fluoroquinolone, macrolide and sulfonamide-related resistance genes in landfills from East China, mainly driven by MGEs

Landfills are one of the most important reservoirs of antibiotic resistance genes (ARGs), and ARG pollution in landfills has been well investigated. However, the various factors contributing to the widespread prevalence of ARGs in landfills have rarely been explored. Here, we quantified three classes of antibiotics, six kinds of heavy metals, eight types of ARGs, and five varieties of mobile genetic elements (MGEs) in refuse samples from 10 landfills in Zhejiang Province, China. Compared with sulfonamides and macrolides, fluoroquinolones were present at much higher concentrations in all refuse samples, reaching a concentration of 1406.85 μg/kg in the Jiaxing region. The relative abundances of qnrD, qnrS, mexF, ermA, ermB, mefA, sul1, and sul2 in most landfills were >10^-4 copies per 16S rRNA, suggesting the presence of highly contaminated ARGs. No significant correlations between most target antibiotics and their corresponding ARGs were found. Variation partitioning analysis indicated that MGEs could be the determining factor in the spread of ARGs in landfills. This research not only reveals high levels of ARGs and the ubiquitous presence of antibiotics in refuse, but also provides guidance for controlling the spread of ARGs in landfills.

Anaerobic/aerobic conditions determine antibiotic resistance genes removal patterns from leachate by affecting bacteria taxa-genes co-occurrence modules

Landfill treatment of municipal solid waste treatment produces a large amount of leachate, which has been an important hotspot of ARGs. This study aimed to investigate the ARGs removal potential, kinetics and mechanism from leachate in aerobic and anaerobic conditions. Simulated landfill reactors showed the efficacy in reducing ARGs, and the removal efficiencies depended on ARGs types and aerobic/anaerobic conditions. The ARGs tetQ and bla_CTX-M were more likely to attenuate with the log-removal efficiencies of 1.50-3 order of magnitude. The ARGs removal kinetic was well fitted by modified Collins-Selleck model, and aerobic condition showed better removal capacities and kinetics than anaerobic condition. Among the ARGs with great removal performance, sul2, aadA1and bla_CTX-M were eliminated from leachate and refuse simultaneously, but tetM, ermB, and mefA were removed from leachate but enriched in refuse. Aerobic/anaerobic states might drive the bacterial community shift of leachate and refuse, and topology property comparison of co-occurrence networks suggested that refuse had a closer non-random host relationship between ARGs and microbial taxa than leachate. Further module analyses revealed that ARGs removal efficiencies depended on the taxonomy of host bacteria in leachate, while the refuse taxa-ARGs correlation determined ARGs removal patterns. By selecting distinct bacteria cluster in different conditions, aerobic treatment benefited ARGs reduction in leachate and refuse, while anaerobic treatment enhanced the enrichment of ARGs in refuse. These findings can potentially foster the understanding of ARGs removal mechanism in biological treatment processes.

The case for examining fluid flow in municipal solid waste at the pore-scale - A review

In this paper, we discuss recent efforts from the last 20 years to describe transport in municipal solid waste (MSW). We first discuss emerging themes in the field to draw the reader's attention to a series of significant challenges. We then examine contributions regarding the modelling of leachate flow to study transport via mechanistic and stochastic approaches, at a variety of scales. Since MSW is a multiphase, biogeochemically active porous medium, and with the aim of providing a picture of transport phenomena in a wider context, we then discuss a selection of studies on leachate flow incorporating some of the complex landfill processes (e.g. biodegradation and settlement). It is clear from the literature survey that our understanding of transport phenomena exhibited by landfilled waste is far from complete. Attempts to model transport have largely consisted of applying representative elementary-scale models (the smallest volume which can be considered representative of the entire waste mass). Due to our limited understanding of fluid flow through landfilled waste, and the influence of simultaneously occurring biogeomechanical processes within the waste mass, elementary-scale models have been unable to fully describe the flow behaviour of MSW. Pore-scale modelling and experimental studies have proven to be a promising approach to study fluid flow through complex porous media. Here, we suggest that pore-scale modelling and experimental work may provide valuable insights into transport phenomena exhibited by MSW, which could then be used to revise elementary-scale models for improved representation of field-scale problems.

Intergovernmental panel on climate change's landfill methane protocol: Reviewing 20 years of application

The Intergovernmental Panel on Climate Change (IPCC) protocol for predicting national methane emission inventories from landfills was published 22 years ago in the 1996 Revised Guidelines. There currently exists a broad dataset to review landfill parameters and reported values and their appropriateness in use and application in a range of site-specific, regional, and national estimates. Degradable organic carbon (DOC) content was found to range from 0.0105 to 0.65 g C/g waste, with an average of 0.166 g C/g waste. The fraction of DOC that would anaerobically degrade (DOC _f) was reported to range from 50-83%, whereas higher and lower values have been experimentally determined for a variety of waste components, such as wood (0-50%) and food waste (50-75%). Where field validation occurred for the methane correction factor, values were substantially lower than defaults. The fraction of methane in anaerobic landfill gas ( F) default of 50% is almost universally applied and is appropriate for cellulosic wastes. The methane generation rate constant ( k) varied widely from 0.01 to 0.51 y^-1, representing half-lives from 1 to 69 years. Methane oxidation (OX) default values of 0 and 10% may be valid, but values greater than 30% have been reported for porous covers at managed sites. The IPCC protocol is a practical tool with uncertainties and limitations that must be addressed when used for purposes other than developing inventories.

Cellulose degradation potential of Paenibacillus lautus strain BHU3 and its whole genome sequence

The aim of this work was to study cellulose degradation and whole genome sequence of Paenibacillus lautus BHU3 isolate. The 16S rRNA gene sequence analysis revealed genetic relatedness (99%) of Iso 7 with Paenibacillus lautus, Iso 8 with Paenibacillus lactis, and Iso 9 with Bacillus amyloliquefaciens. Clear zone formation followed by CMCase and FPase assays exhibited cellulolytic potential in the order: P. lautus > P. lactis > B. amyloliquefaciens. The most potent isolate, Paenibacillus lautus strain BHU3 was subjected to whole genome analysis with reference to the genomic basis of cellulose degradation. Results showed that P. lautus strain BHU3 contains 6234 protein coding genes of which, 316 were associated with the carbohydrate metabolism. Further, genomic CAZymes analysis indicated that the P. lautus strain BHU3 comprising a range of glycoside hydrolase (GH) family genes (143), may play the vital role(s) in enhancing the cellulolytic attributes, and could be the useful tool for lignocellulosic biomass degradation and waste management.

Structure and diversity of bacterial communities in two large sanitary landfills in China as revealed by high-throughput sequencing (MiSeq)

Landfill disposal has been considered as a very economically viable management practice for municipal solid waste in mainland China. However, insufficient knowledge of the bacterial community structure and diversity in landfills hampers effectively landfill disposal. In this study, the structure and diversity of bacterial communities in two large sanitary landfills in northern and western parts of China were examined by high-throughput sequencing via a MiSeq platform. Nearly 1million effective sequences (981,575) were obtained from the 20 samples collected from four independent sites with different deposit depths (up to 18m). These sequences contained high amount of operational taxonomic units (OTUs), 2511-9955 OTUs at a cutoff level of 3% and a sequencing depth of 23,928. Firmicutes, Bacteroidetes and Proteobacteria were the most abundant phyla in the samples. Clear geographical differences between the sampling sites were revealed by nonmetric multidimensional scaling. Most of the samples from the same sampling site could be clustered together. Thus, the heterogeneity of the bacterial community structures was more significantly affected by the sampling site than by sampling depth. Redundancy analysis results suggested that seven physicochemical attributes, namely NH₄⁺-N, NO₂^--N, moisture, pH, dissolved organic carbon (DOC), SO₄^2- and total Cu element, significantly affected the bacterial community structures (P<0.001) based on variance inflation factor selection. Among these attributes, NH₄⁺-N, NO₂^--N, moisture, pH and DOC were the most important parameters influencing the bacterial community structures (P<0.05). This study elucidated the structure and diversity of bacterial communities in landfills and discerned the relationships between bacterial community structures and physicochemical attributes. To the best of our knowledge, this study is among the first to characterize bacterial community structures in landfills by using this novel high-throughput sequencing approach.

Sulfamethoxazole, tetracycline and oxytetracycline and related antibiotic resistance genes in a large-scale landfill, China

Landfills are likely to be important reservoirs of antibiotics and antibiotic resistant genes (ARGs) as they receive unused and unwanted antibiotics and ARGs in municipal solid waste (MSW). The distribution, transportation and dynamics of antibiotics and ARGs in landfills remain largely unknown. In the present study, 3 antibiotics - sulfamethoxazole (SMX), tetracycline (TC), and oxytetracycline (OTC) - and their related ARGs (sulI and tetO) were quantified in 51 refuse samples from different depths at 8 locations within a large-scale landfill in central China. The average concentration of OTC was the highest, up to 100.9±141.81μg/kg (dw, n=48), followed by TC (63.8±37.7μg/kg, n=40), and SMX (47.9±8.1μg/kg, n=30). Both sulI and tetO were detected in all samples. Of the ARGs, sul1 (-3.06±1.18, n=51, log10 ARGs/16SrDNA) was more abundant than tetO (-4.37±0.97) in all refuse samples (p<0.05). Both sulI and tetO negatively correlated to refuse age, suggesting they are attenuated during landfill stabilization. OTC and TC positively correlated to tetO (r=0.41, p<0.01) and sulI (r=0.29, p=0.04), respectively. Chemical conditions (e.g. moisture content and nitrate concentrations) within the refuse correlated to antibiotics and ARGs suggesting environmental factors impact the distribution of antibiotics and ARGs in landfill matrix. This study is the first comprehensive in situ landfill study to connect the concentrations of antibiotic residues to ARGs.

Nitrogen removal from raw landfill leachate by an algae-bacteria consortium

A remediation system for the removal of nitrogen from landfill leachate by a mixed algae-bacteria culture was investigated. This system was designed to treat leachate with minimal inputs and maintenance requirements, and was operated as an open semi-batch reactor in an urban greenhouse. The results of this study showed a maximum nitrogen removal rate of 9.18 mg N/(L·day) and maximum biomass density of 480 mg biomass/L. The ammonia removal rates of this culture increased with increasing initial ammonia concentration; maximum nitrogen removal occurred at an ammonia concentration of 80 mg N-NH3/L. At starting ammonia concentrations above 80 mg N-NH3/L a reduction in nitrogen removal was seen; this inhibition is hypothesized to be caused by ammonia toxicity. This inhibiting concentration is considerably higher than that of many other published studies.

Composition of bacterial and archaeal communities during landfill refuse decomposition processes

Little is known about the archaeal and the bacterial diversities in a landfill during different phases of decomposition. In this study, the archaeal and the bacterial diversities of Laogang landfill (Shanghai, China) at two different decomposition phases (i.e., initial methanogenic phase (IMP) and stable methanogenic phase (SMP)), were culture-independently examined using PCR-based 454 pyrosequencing. A total of 47,753 sequences of 16S rRNA genes were retrieved from 69,954 reads and analyzed to evaluate the diversities of the archaeal and bacterial communities. The most predominant types of archaea were hydrogenotrophic Methanomicrobiales, and of bacteria were Proteobacteria, Firmicutes, and Bacteroidetes. As might be expected, their abundances varied at decomposition phases. Archaea Methanomicrobiales accounts for 97.6% of total archaeal population abundance in IMP and about 57.6% in SMP. The abundance of archaeal genus Halobacteriale was 0.1% in IMP and was 20.3% in the SMP. The abundance of Firmicutes was 21.3% in IMP and was 4.3% in SMP. The abundance of Bacteroidetes represented 11.5% of total bacterial in IMP and was dominant (49.4%) in SMP. Both the IMP and SMP had unique cellulolytic bacteria compositions. IMP consisted of members of Bacillus, Fibrobacter, and Eubacterium, while SMP harbored groups of Microbacterium. Both phases had Clostridium with different abundance, 4-5 folds higher in SMP.

Archaeal community structure in leachate and solid waste is correlated to methane generation and volume reduction during biodegradation of municipal solid waste

Duplicate carefully-characterized municipal solid waste (MSW) specimens were reconstituted with waste constituents obtained from a MSW landfill and biodegraded in large-scale landfill simulators for about a year. Repeatability and relationships between changes in physical, chemical, and microbial characteristics taking place during the biodegradation process were evaluated. Parameters such as rate of change of soluble chemical oxygen demand in the leachate (rsCOD), rate of methane generation (rCH4), rate of specimen volume reduction (rVt), DNA concentration in the leachate, and archaeal community structures in the leachate and solid waste were monitored during operation. The DNA concentration in the leachate was correlated to rCH4 and rVt. The rCH4 was related to rsCOD and rVt when waste biodegradation was intensive. The structures of archaeal communities in the leachate and solid waste of both simulators were very similar and Methanobacteriaceae were the dominant archaeal family throughout the testing period. Monitoring the chemical and microbial characteristics of the leachate was informative of the biodegradation process and volume reduction in the simulators, suggesting that leachate monitoring could be informative of the extent of biodegradation in a full-scale landfill.

Microbial diversity and dynamics during methane production from municipal solid waste

The objectives of this study were to characterize development of bacterial and archaeal populations during biodegradation of municipal solid waste (MSW) and to link specific methanogens to methane generation. Experiments were conducted in three 0.61-m-diameter by 0.90-m-tall laboratory reactors to simulate MSW bioreactor landfills. Pyrosequencing of 16S rRNA genes was used to characterize microbial communities in both leachate and solid waste. Microbial assemblages in effluent leachate were similar between reactors during peak methane generation. Specific groups within the Bacteroidetes and Thermatogae phyla were present in all samples and were particularly abundant during peak methane generation. Microbial communities were not similar in leachate and solid fractions assayed at the end of reactor operation; solid waste contained a more abundant bacterial community of cellulose-degrading organisms (e.g., Firmicutes). Specific methanogen populations were assessed using quantitative polymerase chain reaction. Methanomicrobiales, Methanosarcinaceae, and Methanobacteriales were the predominant methanogens in all reactors, with Methanomicrobiales consistently the most abundant. Methanogen growth phases coincided with accelerated methane production, and cumulative methane yield increased with increasing total methanogen abundance. The difference in methanogen populations and corresponding methane yield is attributed to different initial cellulose and hemicellulose contents of the MSW. Higher initial cellulose and hemicellulose contents supported growth of larger methanogen populations that resulted in higher methane yield.

Microbial community signature of high-solid content methanogenic ecosystems

In this study, changes in bacterial and archaeal communities involved in anaerobic digestion processes operated with high solid contents were investigated. Batch tests were performed within a range of total solids (TS) of 10-35%. Between 10% and 25% TS, high methanogenic activity was observed and no overall specific structure of active bacterial communities was found. At 30% and 35%, methanogenesis was inhibited as a consequence of volatile fatty acids accumulation. Here, a specific bacterial signature was observed with three main dominant bacteria related to Clostridium sp., known for their ability to grow at low pH. Additionally, archaeal community was gradually impacted by TS content. Three archaeal community structures were observed with a gradual shift from Methanobacterium sp. to Methanosarcina sp., according to the TS content. Overall, several species were identified as biomarkers of methanogenesis inhibition, since bacterial and archaeal communities were highly specific at high TS contents.