Leachate leakage enhances the microbial diversity and richness but decreases Proteobacteria and weakens stable microbial ecosystem in landfill groundwater.

Informal landfills pose potential threats to the environment and human health due to the lack of anti-seepage measures. However, little research has been conducted on the distribution of pollutants in informal landfill sites situated in arid climates, as well as the underlying interaction mechanisms between environmental factors and microbial structure. In this study, we sought to investigate the pollution characteristics and microbial community succession of the landfill in northern China. The results revealed that heavy metals in the landfill showed poor mobility and migration. The lower layers of the garbage samples had higher water-soluble contents of heavy metals compared to the upper layers. The landfill-derived dissolved organic matter (DOM) was found to originate from microbial production, and four fluorescent components were identified, including fulvic acid-like substances, humus-like substances, and protein-like components. Fluorescence intensity and humification degree increased with increasing depth. The microbial diversity and richness decreased with sampling depth. The most abundant phyla in the samples were Proteobacteria, unidentified_Bacteria, Bacteroidota, Firmicutes, Myxococcota, Gemmatimonadota, Actinobacteria, and Deinococcota. As the sampling depth increased, Proteobacteria decreased, while Bacteroidota and Firmicutes showed a remarkable increase, with little variation observed in the other phyla. The partial least-squares path model (PLS-PM) results indicated that pH had the most significant effect on microbial abundance and diversity (direct effect value = −5.560), while DOM and heavy metals had the opposite effect, with direct effects of 1.838 and 3.231, respectively. DOM was identified as the driving factor for the variation in other environmental factors. The redundancy analysis (RDA) showed that the dominant genera were greatly influenced by Cu, humic-like substances, and protein-like substances. Among them, Bacillus, Alcanivorax, Devosia, and Chryseolinea may play important roles in the remediation of landfills. Our study not only gains a deeper understanding of the pollution risk of informal landfills in arid climates, but also provides a scientific basis for the future treatment and restoration of contaminated sites associated with landfills. 

Pollution characteristics and microbial community succession of a rural informal landfill in an arid climate.

Landfills remain the predominant means of solid waste management worldwide. Widespread distribution and significant stockpiles of waste in landfills make them a significant source of methane emissions, exacerbating climate change. Anaerobic oxidation of methane (AOM) has been shown to play a critical role in mitigating methane emissions on a global scale. The rich methane and electron acceptor environment in landfills provide the necessary reaction conditions for AOM, making it a potentially low-cost and effective strategy for reducing methane emissions in landfills. However, compared to other anaerobic habitats, research on AOM in landfill environments is scarce, and there is a lack of analysis on the potential application of AOM in different zones of landfills. Therefore, this review summarizes the existing knowledge on AOM and its occurrence in landfills, analyzes the possibility of AOM occurrence in different zones of landfills, discusses its potential applications, and explores the challenges and future research directions for AOM in landfill management. The identification of research gaps and future directions outlined in this review encourages further investigation and advancement in the field of AOM, paving the way for more effective waste stabilization, greenhouse gas reduction, and pollutant mitigation strategies in landfills. 

Anaerobic oxidation of methane in landfill and adjacent groundwater environments: Occurrence, mechanisms, and potential applications.

Accumulation of plastic wastes in the environment forces industry to produce sustainable and biodegradable types of plastics. Our study was focused on evaluation of the landfill leachate as the environment for degradation of cassava-derived plastics (CAS). The metagenomic and ecotoxicological analysis of the landfill leachate was performed. The leachate exhibited a high ecotoxicity. A high throughput metagenomic analysis has revealed a dominant abundance of Proteobacteria (54.7 %), followed by Euryarchaeota (12.5 %). Biodegradation of CAS after the 30-day incubation in a 2 % leachate was higher in the set with agitation, as compared to static conditions, i.e., 49.9 % and 39.3 %, respectively. Regression analysis showed a high correlation between weight loss and reducing of a surface area during degradation process (R2 = 0.95). The results demonstrated a high potential of the landfill leachate with enormous microbial diversity for further optimization of the biodegradation process. 

Uncovering the potential of landfill leachate for biodegradation of cassava-derived plastics

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. 

Assessment of metal pollution and effects of physicochemical factors on soil microbial communities around a landfill.

Characteristic pollutants and microbial community in underlying soils for evaluating landfill leakage.

Landfills are the third largest source of anthropogenic CH4 emissions. Anaerobic oxidation of methane (AOM) activity and communities of methane-oxidizing bacteria were investigated in three informal landfills in this study, namely, BJ, CH and SZ landfills, among which BJ and CH represent traditional anaerobic landfills, while the SZ landfill was subjected to aeration to accelerate waste stabilization. The AOM rates of the investigated landfilled wastes ranged from 3.66 to 23.91 nmol g-1 h-1. Among the three landfills, the AOM rate was highest in the SZ-1-Top sample, which was closest to the aeration pipe. Among the possible electron acceptors for AOM, including NO3-, NO2-, SO42- and Fe3+, the NO2--N content was the only variable that was positively correlated with the AOM rate. Compared with α-Proteobacteria methanotrophs, γ-Proteobacteria methanotrophs were more abundant in the landfilled waste, especially Methylobacter, which was detected in nearly all samples. Members of the family Methylomirabilaceae, including Candidatus Methylomirabilis, were also detected in the SZ-1 and SZ-2-Bot samples. The relative abundance of the main methanotrophs in the families Methylomonadaceae, Methylococcaceae, Rokubacteriales and Methylomirabilaceae, the genus Methylocystis and the phylum NC10 were all positive correlations with the contents of NO2--N in the landfilled waste samples. Additionally, significantly positive correlations were observed between the AOM rates and the relative abundance of the main methanotrophs except for the family Methylococcaceae. This indicated that aeration could enhance the conversion of nitrogen compounds in the landfilled waste, in which the high contents of NO2--N could stimulate the growth of methanotrophs and increase AOM rate. These findings are helpful for understanding the mechanisms of CH4 oxidation in landfills and for taking effective measures to mitigate CH4 emissions from landfills. 

Characterization of anaerobic oxidation of methane and microbial community in landfills with aeration.

This paper estimates the impact of the carbon tax on oil and gas fiscal system. Carbon tax is regarded as the widely used mechanism for carbon policy. However, few studies analyzed the impacts of carbon tax on oil and gas fiscal system. This research addresses the gap by studying how the carbon tax affect the oil and gas industry and the risk of the carbon tax. In this paper, an integrated model considering the impact of the carbon tax in the oil and gas fiscal system and using the Monte-Carlo method to analyze the risk of the carbon tax is put forward. With the purpose of comparing the Royalty and Profit Sharing Contract, the distributions of the revenue are discussed. When the carbon price increases to US$100/ton, the contractor profit will drop to zero under Royalty fiscal system. When the carbon price increases to US$80/ton, the contractor profit will become negative under PSC. The result indicates that high carbon tax results in negative cash flow.

Impact of carbon tax on oil and gas fiscal system: an integrated evaluation model

Purpose: This study proposes to analyze the relationship between venture firms’ R&D investment and performance, furthermore to verify the moderating effect of industrial concentration in a row. Research design, data, and methodology: In order to test the hypotheses, this study was conducted with the panel data of 300 venture firms listed on the Korean KOSDAG market for the period from 2014 to 2020. Results: The main results of this study are summarized as follows. First, we confirm that R&D investment as an independent variable had a significantly positive(+) effect on technological performance measured by patent, and industrial concentration had a significantly positive(+) moderating effect on the relationship between R&D investment and technological performance. Second, positive correlation was found between R&D investment and return on equity (ROE), market value(Tobin’s Q). In addition, industrial concentration had a significantly positive(+) moderating effect on the relationship between R&D investment and ROE, whereas it had a significantly negative(-) moderating effect on the relationship between R&D investment and Tobin’s Q. Finally, although technological performance as an independent variable had no significant effect on ROE, meanwhile industrial concentration had a significantly positive(+) moderating effect on the relationship between technological performance and ROE. Implications: Higher R&D investment helps venture firms increase their technological performance, ROE, and Tobin’s Q. However, in non-competitive market, while R&D investment effect on technological performance and ROE is greater, R&D investment has a weaker effect on Tobin’s Q. Besides, although technological innovation has no direct correlation with ROE, non-competitive market helps venture firms improve ROE with technological innovation. Last but not least, firms can take advantage of their technological innovation to enhance Tobin’s Q, especially in non-competitive market. The findings reveal a more comprehensive picture about the Korean venture firms’ R&D investment efficiency and the effect of market structure on R&D investment efficiency, providing insightful implications for firms and government. 

Study on the Relationship Between R&D Activity and Performance of the Korean Venture Firms: Focusing on the Moderating Effect of Industrial Structure Characteristics

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Characteristic pollutants and microbial community in underlying soils for evaluating landfill leakage.

Characterization of anaerobic oxidation of methane and microbial community in landfills with aeration.

Impact of carbon tax on oil and gas fiscal system: an integrated evaluation model

Study on the Relationship Between R&D Activity and Performance of the Korean Venture Firms: Focusing on the Moderating Effect of Industrial Structure Characteristics