Critical evaluation of solid waste sample processing for DNA-based microbial community analysis

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.

Microbial diversity and potential health risks of household municipal solid waste in China: A case study in winter during outbreak of COVID-19

Microbial (bacteria and fungi) community structures and their distributions in urban household municipal solid waste (HMSW) were characterized in a sampling campaign in 38 cities of China covering 5 climatic zones. All samples were collected from garbage containers in residential communities during the Winter of 2022, from January 11 to 26. A total of 247 bacterial genera belonging to 22 phyla were identified among the samples. Firmicutes (44.3 %), Bacteroidetes (33.77 %) and Proteobacteria (21.54 %) were the top 3 dominant phyla, and Arcicella (33.11 %) and Leuconostoc (21.87 %) were the dominant genera. Meanwhile, 124 fungal genera from 7 fungal phyla were detected. Ascomycota was the most dominant phylum, with an average relative abundance of 77.31 %. Hanseniaspora (24.03 %), Debaryomyces (13.47 %), Candida (12.18) were the top 3 dominant fungal genera. Alpha-diversity analysis showed that the species richness and diversity of bacterial and fungal communities of HMSW samples belonging to different climatic zones did not differ significantly. Nonmetric multidimensional scaling (NMDS) analysis confirmed that climatic had an effect on microbial communities but did not show a significant correlation. In addition, the distribution of microbial community in different samples from the same climate zone varied considerably, suggesting the HMSW source play important role in shaping microbial community composition. Considering that residential HMSW is relatively fresh, we speculates that the original microorganisms residing in different components of HMSW are key influencing factor for the community, while the reshaping force driven by environmental conditions are relatively weak. In addition, the study identified 13 bacterial and 16 fungal pathogens with Pseudomonas putida (0.25 %) and Sclerotinia sclerotiorum (2.12 %) as the most abundant potential pathogenic bacteria and fungi, respectively. These findings provide valuable information for characterizing microbial features and potential risks of HMSW in its management system.

Substrate-restricted methanogenesis and limited volatile organic compound degradation in highly diverse and heterogeneous municipal landfill microbial communities

Microbial communities in landfills transform waste and generate methane in an environment unique from other built and natural environments. Landfill microbial diversity has predominantly been observed at the phylum level, without examining the extent of shared organismal diversity across space or time. We used 16S rRNA gene amplicon and shotgun metagenomic sequencing to examine the taxonomic and functional diversity of the microbial communities inhabiting a Southern Ontario landfill. The microbial capacity for volatile organic compound degradation in leachate and groundwater samples was correlated with geochemical conditions. Across the landfill, 25 bacterial and archaeal phyla were present at >1% relative abundance within at least one landfill sample, with Patescibacteria, Bacteroidota, Firmicutes, and Proteobacteria dominating. Methanogens were neither numerous nor particularly abundant, and were predominantly constrained to either acetoclastic or methylotrophic methanogenesis. The landfill microbial community was highly heterogeneous, with 90.7% of organisms present at only one or two sites within this interconnected system. Based on diversity measures, the landfill is a microbial system undergoing a constant state of disturbance and change, driving the extreme heterogeneity observed. Significant differences in geochemistry occurred across the leachate and groundwater wells sampled, with calcium, iron, magnesium, boron, meta and para xylenes, ortho xylenes, and ethylbenzene concentrations contributing most strongly to observed site differences. Predicted microbial degradation capacities indicated a heterogeneous community response to contaminants, including identification of novel proteins implicated in anaerobic degradation of key volatile organic compounds.

Effect of green waste and lime amendments on biostabilisation, physical-chemical and microbial properties of the composted fine fraction of residual municipal solid waste

Implementation of guidelines to reduce the amount of biodegradable municipal waste (BMW) sent to landfill has created a need in the waste-management industry to investigate possible methods of accelerating biostabilisation of residual BMW. The effect of commercially feasible manipulations (lime and green waste (GW)) on the rate of biostabilisation of the fine (<20 mm) fraction of residual BMW was investigated. The physical and chemical attributes of the composted wastes were measured, and their bacterial communities profiled using traditional culture-based methods. In addition, ammonia-oxidising microbes were monitored during the biostabilisation process using molecular profiling methods. Addition of GW accelerated biostabilisation, reduced conductivity and increased the levels of ammonia-oxidising bacterial (AOB) and archaeal (AOA) genes. The best stability was noted in the dual (Lime + GW) treatment, which was under the limit of 13 mmol O₂ kg DM^-1 h^-1 recommended by the Irish compost standard. Biostabilised wastes met recommendations for source-segregated compost for pH (6-8) and pathogens (E. coli and Salmonella), but not heavy metals, indicating their unsuitability for uses other than landfill cover. Levels of AOA genes (log 3-6 g^-1 DM) were higher than AOB (log 1-6 g^-1 DM, indicating AOA may contribute more to potential ammonia oxidation in residual BMW composting.

Evidence of thermophilic waste decomposition at a landfill exhibiting elevated temperature regions

There have been several reports of landfills exhibiting temperatures as high as 80 to 100 °C. This observation has motivated researchers to understand the causes of the elevated temperatures and to develop predictive models of landfill temperature. The objective of this research was to characterize the methanogenic activity of microbial communities that were derived from landfill samples excavated from a section of a landfill exhibiting gas well temperatures above 55 °C. Specific objectives were to: (1) determine the upper temperature limit for methane production; (2) evaluate the kinetics of methane generation when landfill-derived microcosms are incubated above and below their excavation temperature and derive a temperature inhibition function; and (3) evaluate microbial community shifts in response to temperature perturbations. Landfill microcosms were derived from 57 excavated landfill samples and incubated within ±2.5 °C of their excavation temperature between 42.5 °C and 87.5 °C. Results showed an optimum temperature for methane generation of ~57 °C and a 95% reduction in methane yield at ~72 °C. When select cultures were perturbed between 5 °C below and 15 °C above their in-situ temperature, both the rate and maximum methane production decreased as incubation temperature increased. Microbial community characterization using 16S rRNA amplicon sequencing suggests that thermophilic methanogenic activity can be attributed to methanogens of the genus Methanothermobacter. This study demonstrated that from a microbiological standpoint, landfills may maintain active methanogenic processes while experiencing temperatures in the thermophilic regime (<72 °C).

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.

Assessment of the environmental impact of sanitary and unsanitary parts of a municipal solid waste landfill

Only seven regional MSWLF in Serbia are considered sanitary, while about 3500 landfills operate without proper pollution control. This paper presents a unique opportunity to evaluate the impact of a closed landfill, and a new sanitary landfill, which are located next to each other. The following methodologies for the landfill impact assessment were applied, based on data from 2012 to 2017: Landfill water pollution index (LWPI) and Nemerow index (PI_GW) for groundwater, and the geo-accumulation (I_geo) and ecological risk (ERⁱ) indices and several PAH ratios for soil. The performance of the leachate control system was evaluated using two adapted pollution indices: LPI and the Nemerow index (PI_L). According to the obtained LWPI and PI_GW values, the quality of groundwater at the new landfill is improving (LWPI = 1.05-2.62; PI_GW = 0.52-1.29), while no significant changes were observed for the old landfill (LWPI = 3.06-5.13; PI_GW = 2.03-4.78). High concentrations of ammonia nitrogen (1.01-22.74 mg/l), Fe (0.76-57.11 mg/l), Ni (5.80-230.09 μg/l), Pb (4.2-202.4 μg/l) and ∑PAH₁₆ (150.93-189.55 ng/l) show the strong influence of the landfill on the groundwater quality at the old landfill, indicating the need for additional remediation action. High concentrations of Ni (21.9-133.0 mg/kg) and Cr (8.5-277.0 mg/kg) in the analyzed soil compared to other studies, as well as moderate I_geo values (I_geoNi = 0.36-1.88; I_geoCr = -1.20-1.52), raise concern and suggest the need for further monitoring. The high ERⁱ (158.6-295.0) and I_geo values (0.91-2.30) of Hg show significant potential ecological risk. LPI and PI_L values for early methanogenic phase leachate demonstrates the need to improve the leachate treatment system. The monitoring data and applied pollution indices indicate that Cr and As should be added to the EU Watch List of emerging substances, at least regarding EU potential candidate countries.

Increased loading stress leads to convergence of microbial communities and high methane yields in adapted anaerobic co-digesters

Enhancing biogas production, while avoiding inhibition of methanogenesis during co-digestion of grease interceptor waste (GIW), can help water resource recovery facilities reduce their carbon footprint. Here we used pre-adapted and non-adapted digesters to link microbial community structure to digester function. Before disturbance, the pre-adapted and non-adapted digesters showed similar methane production and microbial community diversity but dissimilar community composition. When exposed to an identical disturbance, the pre-adapted digester achieved better performance, while the non-adapted digester was inhibited. When re-exposed to disturbance after recovery, communities and performance of both digesters converged, regardless of the temporal variations. Co-digestion of up to 75% GIW added on a volatile solids (VS) basis was achieved, increasing methane yield by 336% from 0.180 to 0.785 l-methane/g-VS-added, the highest methane yield reported to date for lipid-rich waste. Progressive perturbation substantially enriched fatty acid-degrading Syntrophomonas from less than 1% to 24.6% of total 16S rRNA gene sequences, acetoclastic Methanosaeta from 2.3% to 11.9%, and hydrogenotrophic Methanospirillum from less than 1% to 6.6% in the pre-adapted digester. Specific hydrolytic and fermentative populations also increased. These ecological insights demonstrated how progressive perturbation can be strategically used to influence methanogenic microbiomes and improve co-digestion of GIW.

Biomineralisation performance of bacteria isolated from a landfill in China

We report an investigation of microbially induced carbonate precipitation by seven indigenous bacteria isolated from a landfill in China. Bacterial strains were cultured in a medium supplemented with 25 mmol/L calcium chloride and 333 mmol/L urea. The experiments were carried out at 30 °C for 7 days with agitation by a shaking table at 130 r/min. Scanning electron microscopic and X-ray diffraction analyses showed variations in calcium carbonate polymorphs and mineral composition induced by all bacterial strains. The amount of carbonate precipitation was quantified by titration. The amount of carbonate precipitated in the medium varied among isolates, with the lowest being Bacillus aerius rawirorabr15 (LC092833) precipitating around 1.5 times more carbonate per unit volume than the abiotic (blank) solution. Pseudomonas nitroreducens szh_asesj15 (LC090854) was found to be the most efficient, precipitating 3.2 times more carbonate than the abiotic solution. Our results indicate that bacterial carbonate precipitation occurred through ureolysis and suggest that variations in carbonate crystal polymorphs and rates of precipitation were driven by strain-specific differences in urease expression and response to the alkaline environment. These results and the method applied provide benchmarking and screening data for assessing the bioremediation potential of indigenous bacteria for containment of contaminants in landfills.

Next-generation sequencing showing potential leachate influence on bacterial communities around a landfill in China

The impact of contaminated leachate on groundwater from landfills is well known, but the specific effects on bacterial consortia are less well-studied. Bacterial communities in a landfill and an urban site located in Suzhou, China, were studied using Illumina high-throughput sequencing. A total of 153 944 good-quality reads were produced and sequences assigned to 6388 operational taxonomic units. Bacterial consortia consisted of up to 16 phyla, including Proteobacteria (31.9%-94.9% at landfill, 25.1%-43.3% at urban sites), Actinobacteria (0%-28.7% at landfill, 9.9%-34.3% at urban sites), Bacteroidetes (1.4%-25.6% at landfill, 5.6%-7.8% at urban sites), Chloroflexi (0.4%-26.5% at urban sites only), and unclassified bacteria. Pseudomonas was the dominant (67%-93%) genus in landfill leachate. Arsenic concentrations in landfill raw leachate (RL) (1.11 × 10³ μg/L) and fresh leachate (FL2) (1.78 × 10³ μg/L) and mercury concentrations in RL (10.9 μg/L) and FL2 (7.37 μg/L) exceeded Chinese State Environmental Protection Administration standards for leachate in landfills. The Shannon diversity index and Chao1 richness estimate showed RL and FL2 lacked richness and diversity when compared with other samples. This is consistent with stresses imposed by elevated arsenic and mercury and has implications for ecological site remediation by bioremediation or natural attenuation.

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.

Transport behavior of surrogate biological warfare agents in a simulated landfill: effect of leachate recirculation and water infiltration

An understanding of the transport behavior of biological warfare (BW) agents in landfills is required to evaluate the suitability of landfills for the disposal of building decontamination residue (BDR) following a bioterrorist attack on a building. Surrogate BW agents, Bacillus atrophaeus spores and Serratia marcescens, were spiked into simulated landfill reactors that were filled with synthetic building debris (SBD) and operated for 4 months with leachate recirculation or water infiltration. Quantitative polymerase chain reaction (Q-PCR) was used to monitor surrogate transport. In the leachate recirculation reactors, <10% of spiked surrogates were eluted in leachate over 4 months. In contrast, 45% and 31% of spiked S. marcescens and B. atrophaeus spores were eluted in leachate in the water infiltration reactors. At the termination of the experiment, the number of retained cells and spores in SBD was measured over the depth of the reactor. Less than 3% of the total spiked S. marcescens cells and no B. atrophaeus spores were detected in SBD. These results suggest that significant fractions of the spiked surrogates were strongly attached to SBD.