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

Spatiotemporal profiling and succession of microbial communities in landfills based on a cross-kingdom abundance quantification method

Landfill provides a unique niche for both prokaryotic and eukaryotic microorganisms, in which organic matter and physiochemical conditions continuously change with the landfill age and drive the succession of landfill microbiomes. Nonetheless, information on the spatiotemporal changes of landfill microbiomes, particularly the prokaryotic and eukaryotic communities and their interactions, remain scarce. In this study, a new cross-kingdom abundance quantification method was devised to obtain cell abundance of both prokaryotes and eukaryotes based on high-throughput sequencing, and employed to elucidate microbiomes of leachate samples collected from nationwide landfills in China. Results showed the clustering of landfills into two groups primarily based on microbial community compositions, being in line with the change in their landfill ages (i.e., Group-I, <10 years; Group-II, ≧10 years), and 1320.9 and 88.0 times of abundance difference between prokaryotes and eukaryotes in the Group-I and -II communities, respectively. Reducing equivalent was determined as a primary factor governing the landfill microbial abundance, assembly and interactions. In contrast to Group-I characterized by the extensive organic matter fermentation and multi-pathway methanogenesis driven by fermenters and methanogenic archaea, aerobic heterotrophs played a primary role in element cycling and archaea-mediated methanogenic activities were diminished in Group-II communities, in which heterotrophic bacteria and fungi might synergistically degrade recalcitrant organic matter. Interestingly, protozoa and metazoa as bacteria/fungi predators decreased the stability of Group-II communities in a top-down manner. Based on these observations, a scenario was proposed for the energy-driven succession of landfill microbiomes and mediated biogeochemical processes. Our study provided the first large-scale and comprehensive insight into the landfill microbiomes for their future sustainable management.

Uncovering rare earth and precious metal in landfill-mined soil-like-fractions: distribution prediction, ecological risk and resource potential

The introduction of rare earth elements (REEs) and precious metals (PMs) containing wastes in aged landfills leads to a significant pollutant and resource potential. Against this backdrop, the accumulation of REEs and PMs in soil-like-fractions (SLF) remains uncertain. This study pioneers a comprehensive analysis of the REE/PM speciation, ecological risks of REEs and economic potential of PMs in SLF. Concentrations of REEs and PMs varied from 146.14 to 464.28 mg/kg and 4.20 to 111.86 mg/kg, respectively, with a particular enrichment in the upper SLF. REEs and PMs were immobilized by SLF and stabilized into organic- and mineral-bound fractions. A dataset linking urban development and landfill conditions to REE/PM concentrations was created, and the Support Vector Regression (SVR) model was utilized to achieve high-precision prediction of REEs and PMs content (R2 > 0.9). The Shapley Additive Explanations (SHAP) algorithm revealed development of electronics industry as the primary driver of REE/PM enrichment, followed by organic matter content in SLF. The potential ecological risk index (PERI) showed limited risks of REEs, but the bioavailable REEs posed long-term accumulation and chronic toxicity in terrestrial organisms, emphasizing the detoxification before SLF reusage. The economic potential of PMs reached 871.82 USD per ton of SLF, higher than primary minerals. These findings provide new insights into valuable resources during landfill mining and suggest potential areas for applying modern techniques, such as machine learning, to landfill management.

Metagenomic insights into the functional potential of non-sanitary landfill microbiomes in the Indian Himalayan region, highlighting key plastic degrading genes

Solid waste management in the Indian Himalayan Region (IHR) is a growing challenge, intensified by increasing population and tourism, which strain non-sanitary landfills. This study investigates microbial diversity and functional capabilities within these landfills using a high-throughput shotgun metagenomic approach. Physicochemical analysis revealed that the Manali and Mandi landfill sites were under heavy metal contamination and thermal stress. Taxonomic annotation identified a dominance of bacterial phyla, including Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes, with genera like Pseudomonas and Bacillus prevalent. Squeezemeta analysis generated 9,216,983 open reading frames (ORFs) across the sampling sites, highlighting diverse metabolic potentials for heavy metal resistance and degrading organic, xenobiotics and plastic wastes. Hierarchical clustering and principal component analysis (PCA) identified distinct gene clusters in Manali and Mandi landfill sites, reflecting differences in pollution profiles. Functional redundancy of landfill microbiome was observed with notable xenobiotic and plastic degradation pathways. This is the first comprehensive metagenomic assessment of non-sanitary landfills in the IHR, providing valuable insights into the microbial roles in degrading persistent pollutants, plastic waste, and other contaminants in these stressed environments.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Impact of incineration slag co-disposed with municipal solid waste on methane production and methanogens ecology in landfills

Co-landfill of incineration slag and municipal solid waste (MSW) is a main method for disposal of slag, and it has the potential of promoting methane (CH₄) production and accelerating landfill stabilization. Four simulated MSW landfill columns loaded with different amount of slag (A, 0%; B, 5%; C, 10%; D, 20%) were established, and the CH₄ production characteristics and methanogenic mechanisms were investigated. The maximum CH₄ concentration in columns A, B, C and D was 10.8%, 23.3%, 36.3% and 34.3%, respectively. Leachate pH and refuse pH were positively correlated with CH₄ concentration. Methanosarcina was the dominant genus with abundance of 35.1%∼75.2% and it was positively correlated with CH₄ concentration. CO₂-reducing and acetoclastic methanogenesis were the main types of methanogenesis pathway, and the methanogenesis functional abundance increased with slag proportion during stable methanogenesis process. This research can help understanding the impact of slag on CH₄ production characteristics and microbiological mechanisms in landfills.