Molecular phylogenetic analysis of dominant microbial populations in aged refuse

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.

Assessment and analysis of aged refuse as ammonium-removal media for the treatment of landfill leachate

This is the first attempt to explore the sustainability of aged refuse as ammonium-removal media. Batch experiments combined with the aged-refuse-based reactor were performed to examine how the adsorption and desorption processes are involved in the ammonia removal via aged refuse media in this research. The results showed that the adsorption of ammonium by aged refuse occurred instantly and the adsorbed ammonium was stable and less exchangeable. The adsorption data fit the Freundlich isotherms well and the n value of 0.1-0.5 indicated that the adsorption of ammonium occurred easily. The maximum adsorbed ammonium occupied less than 10% of the cation exchange capacity in aged-refuse-based reactors owing to the high solid/liquid ratios (50:1-120:1). The synergistic transformations of ammonium within the aged-refuse-based reactor indicated that the cation exchange sites only provide temporary storage of ammonium, and the subsequent nitrification process can be considered the predominant restoration pathway of ammonium adsorption capacity of the reactor. It seems reasonable to assume that there is no expiry for the aged-refuse-based reactor in terms of ammonium removal owing to its bioregeneration via nitrification.

Novel hydrolytic extremely halotolerant alkaliphiles from mature landfill leachate with key involvement in maturation process

Mature landfill leachate is a heavily-polluted wastewater due to its recalcitrant nature of organic matter, and high ammonia and salt content. Despite the moderate saline and alkaline nature of this habitat, no attention has been paid to the isolation and functional role of extremophiles in such environment. In this work, a total of 73 and 29 bacterial strains were isolated by using alkaline and saline media, respectively, while bacteria from mature landfill leachate growing in these media were enumerated as 1.5 ± 0.1 (×10⁸) and 5.8 ± 0.9 (×10⁸) cfu/L. Based on their pH and salt ranges and optima for growth, all bacterial isolates were halotolerant alkaliphiles (either facultative or obligate), with the majority of them being extremely halotolerant bacteria. These halotolerant alkaliphiles were classified into 14 operational taxonomic units (OTUs). Of these, 12 are placed within known halophilic and alkaliphilic species of the genera Dietzia, Glycocaulis, Halomonas, Marinobacter, Piscibacillus and Rhodobacter, while the remaining OTUs represented two novel phylogenetic linkages among the families Cyclobacteriaceae and Rhodobacteraceae. Examination of their hydrolytic ability through the performance of lipase, protease and β-glucosidase assays using landfill leachate as the growth substrate revealed that all halotolerant alkaliphiles isolated exhibited extremely high lipolytic activities (up to 78,800 U g^-1 protein), indicating a key involvement of extremophilic microbiota at the late landfill maturation stage. The wide extremely lipolytic halotolerant alkaliphilic community identified also makes mature landfill leachate an ideal microbial pool for the isolation of novel extremophiles of biotechnological interest.

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

Landfills are always the most important part of solid waste management and bear diverse metabolic activities involved in element biogeochemical cycling. There is an increasing interest in understanding the microbial community and activities in landfill cover soils. To improve our knowledge of landfill ecosystems, we determined the microbial physiological profiles and communities in three landfill cover soils (Ninghai: NH, Xiangshan: XS, and Fenghua: FH) of different ages using the MicroResp(TM), phospholipid fatty acid (PLFA), and high-throughput sequencing techniques. Both total PLFAs and glucose-induced respiration suggested more active microorganisms occurred in intermediate cover soils. Microorganisms in all landfill cover soils favored L-malic acid, ketoglutarate, and citric acid. Gram-negative bacterial PLFAs predominated in all samples with the representation of 16:1ω7, 18:1ω7, and cy19:0 in XS and NH sites. Proteobacteria dominated soil microbial phyla across different sites, soil layers, and season samples. Canonical correspondence analysis showed soil pH, dissolved organic C (DOC), As, and total nitrogen (TN) contents significantly influenced the microbial community but TN affected the microbial physiological activities in both summer and winter landfill cover soils.