Study on the water retention curve of shredded municipal solid waste considering the compressibility of specimens based on the centrifuge method.

The water retention curve (WRC) of municipal solid waste (MSW) is the important hydraulic parameter for the study of unsaturated seepage analysis in landfills. Due to the compressibility and degradability of the waste, the search for a method to quickly and accurately test its water retention curve (WRC) is a current problem that needs to be solved. In this paper, considering the volume change of the waste specimens in test, the test principle of centrifuge testing of WRC is corrected to make it applicable to the testing of waste WRC. In addition, the WRCs of 20 MSW specimens with typical landfill compositions and porosities are measured using the corrected centrifuge test. The effects of compositions and porosities of waste specimens on WRC parameters were analyzed. The results are summarized as follows. Disregarding the height reduction of specimens resulted in overestimated matric suction values and underestimating volume water content values. By comparing uncorrected and corrected values, the maximum difference of the matric suction and volumetric water content reach 233 kPa and 11%, respectively. This study can provide a reference for accurately measuring the WRC of MSW using a centrifuge. For the waste specimen without kitchen and yard waste, composition had less of an effect on the WRC of waste compared to porosity. The effect of the content of the non-absorbable fraction on the residual volumetric water content θr and the parameter nv in the van Genuchten model was significant. The initial porosity n had a great effect on the parameter α.

A review of existing methods for predicting leachate production from municipal solid waste landfills.

Landfilling is one of the predominant methods of municipal solid waste (MSW) disposal worldwide, while the generation of leachate, a kind of toxic wastewater, is among the primary factors behind landfill instability and environmental contamination problems. Precise prediction of leachate production is crucial to landfill safety evaluation and design. This paper presents a comprehensive review of methods for predicting leachate production from MSW landfills. Firstly, compositional characteristics of MSW and leachate generation mechanism are analysed. Factors influencing leachate production are summarised based on the generation mechanism, including the components of MSW, climatic conditions, landfill structure, and environmental factors. Then, we classified the existing methods for predicting leachate production into four categories: water balance formula, water balance model, empirical formula, and artificial intelligence model methods. Advantages, disadvantages, and applicability of different leachate production prediction methods are compared and analysed. Furthermore, limitations in the existing leachate production prediction methods for MSW landfills and scope for future research are discussed.

Study of leachate recharge model and vertical well design method for bioreactor landfills.

Leachate recharging not only solves the leachate treatment problem but also has tremendous environmental and engineering benefits. In this study, a recharge model was developed based on consideration of the inhomogeneous characteristics of the pile and the degree of clogging of the leachate collection and removal system (LCRs), and a design diagram of the maximum injection pressure Ps and the minimum setback distance ds was given. The following conclusions are obtained: the rate of diffusion in the horizontal and burial depth directions depends on anisotropy coefficient A, and the rate of development of the blocked water level on the LCRs depends on the degree of blockage h1. The development rate of the region affected by the recharging is low at the beginning of the recharging and increases rapidly when the moment Tb is reached, which decreases with the injection pressure P, and the degree of blockage h1. The safety factor of slope Fs decreases at a slower rate when the anisotropy coefficient is 0 < A < 1 and 15 < A < 20, and at a faster rate when 1 < A < 15. When the LCRs is blocked, the injection pressure P and anisotropy coefficient A increase the degree of influence on the recharge efficiency and slope stability, and when the blocked water level h1 > 30 m, recharge is not recommended. This model and the vertical well design method can well simulate the recharging process and its effect on the slope stability and provide a reference for the design of vertical wells.

Atomistic insights into migration mechanism of graphene-based membranes on soil mineral phases.

Graphene-based membranes (GBM) will migrate in the soil and enter the groundwater system or plant roots, which will eventually pose potential risks to human beings. The migration mechanism of GBM depends on the interface behavior of complex soil components. Herein, we use molecular dynamics (MD) simulations to probe the interface behavior between GBM and three type minerals (quartz, calcite and kaolinite). Based on the investigation of binding energy, maximum pulling force and barrier energy, the order of the difficulty of GBM adsorption and desorption on the three minerals from small to large is roughly: quartz, calcite and kaolinite respectively. The graphene-oxide (GO), improves the binding energy and energy barrier, making GBM difficult to migrate in soil. Remarkably, a larger GBM sheet and high velocity external load improve GBM migration in soil to a certain extent. These investigations give the dynamic information on the GBM/mineral interaction and provide nanoscale insights into the migration mechanisms of GBM in soil.

Analysis of the existence form of landfill leachate water level and its development pattern under the condition of considering internal source water: a case study.

In this paper, we study the existence form and development pattern of leachate level in the pile through a case of high water level landfill. The innovation of this paper is to consider not only the infiltration of rainfall, but also the internal source water of waste as the source of leachate. There is one main water level and multiple layers of stagnant water levels in this study area. The main water level of the pile first appears along the base slope of the landfill, and the trend of development is to connect from the bottom pile upwards layer by layer. The connection point of each layer gradually moves from the upstream side to the downstream side with time, and the main water level is formed by the gradual connection of the stagnant water level in each layer of the pile. Piles filled with slope as the base surface, and the stagnant water level in the pile first develops on the slope. And piles that are filled with a gentle base surface, and stagnant water level in the pile is uniformly developed on the base surface. At least one layer of stagnant water level exists in each layer of the pile, and multiple saturated zones occur in landfills with gentle base surfaces, and the saturation zone of the upper and lower waste pile will be penetrated. Depending on the form of leachate water level present in the pile, the location can be reasonably chosen for engineered precipitation of the landfill, and based on the development trend of each water level in the pile, it can provide a reference for the site selection and design of the landfill.

Initial Relative Position Influencing Self-Assembly of a Black Phosphorus Ribbon on a CNT.

It is difficult to obtain a nanotube from phosphorus with a 3sp² electron configuration by chemical synthesis. However, a physical fabrication approach, such as self-assembly, is worth trying. In an experiment, when using a carbon nanotube (CNT) to trigger self-assembly of a black phosphorus (BP) ribbon, the final configuration of the BP component may be sensitive to the initial relative position of the CNT to the BP ribbon. For instance, using the same CNT with different initial relative positions to the BP ribbon, the BP ribbon may finally become a nanotube, or a scroll, or just wind upon the CNT, or escape from the CNT, etc. In this study, the sensitivity is investigated using molecular dynamics simulations. Numerical results illustrate some essentials for potential fabrication of a BP nanotube from ribbon.

Permeability test and slope stability analysis of municipal solid waste in Jiangcungou Landfill, Shaanxi, China.

UNLABELLED: With the rapid increase of city waste, landfills have become a major method to deals with municipal solid waste. Thus, the safety of landfills has become a valuable research topic. In this paper, Jiangcungou Landfill, located in Shaanxi, China, was investigated and its slope stability was analyzed. Laboratory tests were used to obtain permeability coefficients of municipal solid waste. Based on the results, the distribution of leachate and stability in the landfill was computed and analyzed. These results showed: the range of permeability coefficient was from 1.0 × 10(-7) cm sec(-1) to 6.0 × 10(-3) cm sec(-1) on basis of laboratory test and some parameters of similar landfills. Owing to the existence of intermediate cover layers in the landfill, the perched water level appeared in the landfill with heavy rain. Moreover, the waste was filled with leachate in the top layer, and the range of leachate level was from 2 m to 5 m in depth under the waste surface in other layers. The closer it gets to the surface of landfill, the higher the perched water level of leachate. It is indicated that the minimum safety factors were 1.516 and 0.958 for winter and summer, respectively. Additionally, the slope failure may occur in summer. IMPLICATIONS: The research of seepage and stability in landfills may provide a less costly way to reduce accidents. Landslides often occur in the Jiangcungou Landfill because of the high leachate level. Some measures should be implemented to reduce the leachate level. This paper investigated seepage and slope stability of landfills by numerical methods. These results may provide the basis for increasing stability of landfills.