Enhancing anaerobic oxidation of methane in municipal solid waste landfill cover soil

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

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.

Effects of Hydrophobic Biochar-Modified Landfill Soil Cover on Methane Oxidation

Landfill cover soils play an important role in mitigating landfill methane (CH4) emissions. Incorporating biochar into the soil has proven effective in reducing CH4 emissions. However, the role of hydrophobic biochar in this context remains underexplored. This study investigated the CH4 removal efficiency of a biochar-modified landfill soil cover column (RB) and hydrophobic biochar-modified landfill soil cover column (RH) under varying CH4 influx gas concentrations (25 and 35%), simulated CH4 inflow rates (10, 15, and 20 ml/min), and temperatures (20, 25, 30, 35, and 40 °C). RH consistently outperformed RB in terms of CH4 removal efficiency under these experimental conditions. The optimal conditions for CH4 degradation by both RB and RH were observed at a CH4 influx gas concentration of 35%, a simulated CH4 inflow rate of 10 ml/min, and a temperature of ~30 °C. RH achieved a CH4 removal rate of up to 99.96%. In summary, the addition of hydrophobic biochar enhanced the air permeability and hydrophobicity of landfill cover soils, providing a promising alternative to conventional cover soils for reducing CH4 emissions from landfills.

Development of sand-plastic composites as floor tiles using silica sand and recycled thermoplastics: a sustainable approach for cleaner production

Strict environmental concerns, depleting natural recourses, and rising demand for building construction materials have promoted scientific research toward alternative building materials. This research supports the idea of sustainability and a circular economy via the utilization of waste to produce value-added products. The research explored the potential of waste plastics and silica sand for developing thermoplastic composite as floor tiles. The samples were characterized by water absorption, compressive strength, flexural strength, and sliding wear. The morphological analysis of the sand-plastic interfaces was covered under the umbrella of this study. The maximum compressive and flexural strength were found to be 46.20 N/mm² and 6.24 N/mm², respectively, with the minimum water absorption and sliding wear rate of 0.039% and 0.143 × 10^-8 kg/m, respectively. The study suggests the workability of the developed floor tiles in non-traffic areas of public places. Thus, the study provides a green building material through recycling waste plastics for sustainable development.

Gas transport in landfill cover system: A critical appraisal

Landfill gas (LFG) emission is gaining more attention from the scientific fraternity and policymakers recently due to its threat to the atmosphere and human health of the populace living in surrounding premises. Though landfill cover (LFC) (viz., daily, intermittent and final cover) is widely used by landfill operators to mitigate or reduce these emissions, their overall performance is still under question. A critical analysis of available literature, primarily pertaining to (i) the composition of the landfill gases and their migration in the LFC system, (ii) experimental and mathematical investigations of the transport mechanism of gas and (iii) the impact of additives to cover soils on transport and fate of gas, has been conducted and presented in this manuscript. Investigation of the efficiency of modified soil was mainly focused on laboratory test. More field tests and application of amended cover soils should be conducted and promoted further. Studies on nitrous oxide and emerging pollutants, including poly-fluoroalkyl substances transport in landfill cover system are limited and need further research. The transport mechanisms of these unconventional contaminants should be considered regarding the selection of LFC materials including geomembrane and geosynthetic clay liners. The existing analytical and numerical models can provide a basic understanding of LFG transport mechanisms and are able to predict the migration behaviour of LFG; however, there are still knowledge gaps concerning the interaction between different species of the gas molecule when modeling multi-component gas transport. Gas transport through fractured cover should also be considered when evaluating LFG emission in the future. Simplified design method for landfill cover system regarding LFG emission based on analytical models should be proposed. Overall, mathematical models combined with experiments can facilitate more visualized and intensive insights, which would be instrumental in devising climate adaptive landfill covers.

First evidence for anaerobic oxidation of methane process in landfill cover soils: Activity and responsible microorganisms

Landfill cover soils (LCS) play important roles in mitigating methane emissions from landfills. Anaerobic oxidation of methane (AOM) has been demonstrated as a potential methane removal process in aquatic ecosystems. However, whether AOM could occur in LCS is largely unknown. Here, microcosm incubations with ¹³CH₄ were applied to track the potential activities of AOM and quantitative PCR was used to identify the responsible microorganisms. AOM was found to be active in the bottom and middle layers of LCS. In the bottom layer, sulfate-AOM was the most active process, mainly dominated by ANME archaea (without ANME-2d). Meanwhile, in the middle layer, nitrate and nitrite were the major electron acceptors involved in AOM with high abundances of ANME-2d archaea and NC10 bacteria. Our results implied a spatial segregation of methane oxidizing microbes in LCS and might be helpful for future control of methane emissions by the enhancement of AOM.

Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover

A landfill biocover system optimizes environmental conditions for biotic methane (CH4) consumption that controls the fugitive and residual emissions from landfills. Research shows that wasted compost material has more (CH4) oxidation potential than other materials. Thus, in this study, the authors investigate the engineering properties of compacted compost to test its suitability for CH4 oxidation capacity. Different laboratory and analytical approaches are employed to attain the set objectives. The biochemical tests show that the studied material indicates the presence of methanotrophs with sufficient organic contents. The compacted compost also shows adequate diffusivity potential to free air space for a wide range of water content. The data also imply that compacting compost to low hydraulic conductivity can be accomplished for a wide range of water content, according to the suggested values for a landfill hydraulic barrier. Furthermore, the low thermal properties of compost as compared to other mineral materials seem more beneficial, as specifically, during the winter season, when the atmospheric temperature is low, low thermal conductivity enables it to sustain a stable temperature for the activities of the microbial organisms, which therefore extends the CH4 oxidation process right through a long period in the winter.

Insight into SO4(-II)- dependent anaerobic methane oxidation in landfill: Dual-substrates dynamics model, microbial community, function and metabolic pathway

In anaerobic landfill, SO42- could serve as electron receptor for methane oxidation. In theory, concentrations of both methane and SO42- should be related to methane oxidation rate. However, the dynamics process has yet to be discovered, and the understanding of metabolic pathways of the sulfate-dependent anaerobic methane oxidation (S-DAMO) process in landfill remains limited. In this study, S-DAMO dynamics was investigated by observing the CH4 oxidation rates under different CH4/ SO42-counter-gradients. The CH4-SO42- dual-substrate model based on MichaeliseMenten equation was got (maximum substrate degradation rate Vmax [22.9 ± 1.31] µmol/[kg·d], half-saturation constants [Formula: see text] , and [Formula: see text] ). High-throughput sequencing analysis indicated Methanobacterials, Methanosarcinales, and Soil Crenarchaeotic were the main functional microorganisms for S-DAMO in landfill. The metabolic pathway of S-DAMO was speculated as the reverse methanogenesis pathway through Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUST) analysis, while methanogenesis was the methyl nutrition way based on methanol. The enzymes related to the carbon and sulfur cycles and their relative abundances in the microcosms were analyzed to graph the methane metabolic pathway and the sulfur metabolic pathway. The findings provide important parameters for CH4 mitigation in landfills, and give a new insight for understanding S-DAMO metabolic pathway in landfill.

Surface Hydrophobic Modification of Biochar by Silane Coupling Agent KH-570

Biochar-amended soil cover (BSC) in landfills can improve the oxidation of methane. However, adding biochar can cause a larger amount of rainwater to enter the soil cover and landfill because it increases the permeability of the soil cover, which increases leachate production. Improving the hydrophobicity and waterproof ability of BSC is expected to reduce rainwater that goes into landfills. Silane coupling agent KH-570 is used to modify biochar to improve its hydrophobicity and waterproof ability after being added to the soil cover. The waterproofness of hydrophobic biochar-amended soil cover (HBSC) was studied by conducting a precipitation simulation test. Results showed that the optimum hydrophobicity of the surface-modified biochar was obtained when the mass fraction of KH-570 was 7%, the biochar dosage was 7 g, and the modification temperature was 60 °C. In these conditions, the contact angle was 143.99° and the moisture absorption rate was 0.10%. The analysis results of thermogravimetric, X-ray diffractometer and scanning electron microscopy before and after the biochar modification showed that KH-570 formed a hydrophobic organic coating layer on the biochar surface, indicating that the surface hydrophobic modification of biochar was successfully carried out by silane coupling agent. The waterproof ability of HBSC was significantly better than that of BSC in the simulated precipitation test.

Atmospheric methane and nitrous oxide: challenges alongthe path to Net Zero

The causes of methane's renewed rise since 2007, accelerated growth from 2014 and record rise in 2020, concurrent with an isotopic shift to values more depleted in ¹³C, remain poorly understood. This rise is the dominant departure from greenhouse gas scenarios that limit global heating to less than 2°C. Thus a comprehensive understanding of methane sources and sinks, their trends and inter-annual variations are becoming more urgent. Efforts to quantify both sources and sinks and understand latitudinal and seasonal variations will improve our understanding of the methane cycle and its anthropogenic component. Nationally declared emissions inventories under the UN Framework Convention on Climate Change (UNFCCC) and promised contributions to emissions reductions under the UNFCCC Paris Agreement need to be verified independently by top-down observation. Furthermore, indirect effects on natural emissions, such as changes in aquatic ecosystems, also need to be quantified. Nitrous oxide is even more poorly understood. Despite this, options for mitigating methane and nitrous oxide emissions are improving rapidly, both in cutting emissions from gas, oil and coal extraction and use, and also from agricultural and waste sources. Reductions in methane and nitrous oxide emission are arguably among the most attractive immediate options for climate action. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

Alternative rapeseed based oil fluid for hydraulic systems of tractors

The paper analyzes the main applications of alternative fuels and lubricants in automotive vehicles, considers the possibility of using vegetable oils as a working fluid for hydraulic systems of agricultural machinery. Based on the laboratory findings, it states the ways to improve a lubrication formula based on rapeseed oil. The formula is proven to be optimal if it includes 88.9% rapeseed oil + 3.7% D-11 + 3.2% EFO + 4.197% graphite + 0.003% MS-200A, which is superior in tribological properties to MGE-46V hydraulic oil, and can be recommended for use in hydraulic systems of agricultural machinery as an alternative to mineral oils.