An investigation into the efficiency of electrokinetic and electrokinetic coupled with calcium peroxide permeable reactive barriers techniques for soil remediation using a statistical analysis.

The current study emphasizes on the applicability of combining the electrokinetic (EK) and permeable reactive barriers (PRB) techniques compared to the simple EK technique. For this purpose, a statistical analysis is conducted using the Fractional Factorial Design statistical method. Also, General Linear Model and Two-sample T-Test analyzes are considered to clarify which type of soil remediation technique represents the highest efficiency. Calcium peroxide, an affordable material with easy capability for cultivation, is utilized in the PRB process to eliminate the soil from diesel contamination. The experiments were performed for 3 days and 10 days, according to which the initial contamination rates of 10 and 20% were selected, and the applied voltages were 20 V and 30 V. Using the innovative remediation technique, the experiments were conducted for 10 days with 20% initial pollution content and the applied voltage of 30 V, the initial gasoil content was about 190.5 mg/g, and after applying the proposed technique, the average final pollution content throughout soil reached approximately 37 mg/g. This experiment was also conducted for the approximately initial gasoil content of 185, 206, and 191 mg/g, which led to the removal efficiency of 79.59%, 78.93%, and 79.15%, respectively. The main novelty of this paper is attributed to the use of calcium peroxide in the EK-PRB technique and the statistical analysis conducted in this study that indicates the remarkable efficiency of the proposed approach. It was also revealed that the efficiency of the proposed technique is on par with the other state-of-art ones presented in the literature and even sometimes outperforms them.

A comparison between constitutive models for the municipal solid waste.

This paper compares the behavioural models of municipal solid waste (MSW) using the corresponding experimental data. To do so, the proposed models are first reviewed and, then, the algorithms and codes of different models are written. After obtaining each model's algorithm, the same experimental data are considered as input, and the strain-stress curve is plotted for each model. In the first method, the total strain in the waste is obtained based on the summation of the elastic, plastic, biological, and creep strains. Afterward, the equivalent stress is obtained. In this method, using biological changes over time, the age of the waste is calculated as an effective parameter in MSW behaviour. Moreover, the effect of creep on the waste is considered independently. In the second algorithm, MSW is considered as fibre and paste material, and the strain-stress curve is obtained. In this method, the waste is considered as a soil model, and the effect of different parameters are calculated. Due to the complexity of the MSW behaviour and considering various parameters, such as the age of the waste, E changes over time, creep, and biological changes, the Krase model has less error than the other models. Using the soil behaviour model for the waste has a significant error, indicating the difference between the results for the behaviours of the two substances.

Effects of anisotropy in correlation structure on reliability-based slope stability analysis of a landfill.

In this study, a reliability-based analysis of slope stability in a landfill considering the spatial variability of shear strength (c and φ) and unit weight (γ) of municipal solid waste was performed using the random finite difference method. The effect of the anisotropic correlation (AC) structure of random variables including c, φ, and γ on mean and coefficient of variation (CoV) of safety factor values was investigated using Monte Carlo simulation. Also, probability of failure was determined through probability distribution fitting to a series of safety factor data. The results showed that the AC of the random variables has a significant effect on the stochastic safety factor of landfill slope. In general, the mean of the stochastic safety factor decreases with increasing horizontal and vertical correlation lengths (CLs). Also, the CoV of the safety factor increased with increase in horizontal or vertical CLs or both. Moreover, it was found that failure probability increases with an increase in the horizontal and vertical CLs and assuming isotropic structure for the correlation of random variables leads to the underestimation of failure probability. Overall, the results indicate that assuming an AC structure results in different failure mechanisms in the landfill slope, which are different from the deterministic cases.

A laboratory study on the MSW mechanical behavior in triaxial apparatus.

Shear strength characterization of MSW materials is a mandatory task when performing analyses related to landfill design and landfill geometry improvements. Despite the considerable amount of research focusing on MSW mechanical behavior there remain certain aspects which are not completely understood and deserve attention in particular the case of the undrained behavior of MSW. This paper presents the results of a comprehensive laboratory testing program using a large-scale triaxial apparatus at the Federal University of Bahia, Salvador, Brazil. The effect of factors such as confining pressure, unit weight, fiber content, rate of loading and over-consolidation on the MSW mechanical response were investigated. Tested samples presented typical MSW shear/strain curves (concave upward) in all the tests, despite the pore water pressure reaching levels almost equal to the confining pressure. The obtained results show that increasing confining stress, unit weight, loading rate, fiber content and over-consolidation lead to an increase in the MSW shear strength. The importance of the fibrous components in the waste behavior is highlighted and graphs showing the variation of the MSW shear strength with fiber content in different drainage conditions are shown. The authors believe these results could be of interest to many companies, especially considering the new trend of plastic material recycling (prior landfilling) for energy recovery purposes.

Evaluation of the geotechnical properties of MSW in two Brazilian landfills.

The characteristics of municipal solid waste (MSW) play a key role in many aspects of waste disposal facilities and landfills. Because most of a landfill is made up of MSW, the overall stability of the landfill slopes are governed by the strength parameters and physical properties of the MSW. These parameters are also important in interactions involving the waste body and the landfill structures: cover liner, leachate and gas collection systems. On the other hand, the composition of the waste, which affects the geotechnical behavior of the MSW, is dependent on a variety of factors such as climate, disposal technology, the culture and habits of the local community. It is therefore essential that the design and stability evaluations of landfills in each region be performed based on the local conditions and the geotechnical characteristic of the MSW. The Bandeirantes Landfill, BL, in São Paulo and the Metropolitan Center Landfill, MCL, in Salvador, are among the biggest landfills in Brazil. These two disposal facilities have been used for the development of research involving waste mechanics in recent years. Considerable work has been made in the laboratory and in the field to evaluate parameters such as water and organic contents, composition, permeability, and shear strength. This paper shows and analyzes the results of tests performed on these two landfills. The authors believe that these results could be a good reference for certain aspects and geotechnical properties of MSW materials in countries with similar conditions.

Municipal solid waste effective stress analysis.

The mechanical behavior of municipal solid waste (MSW) has attracted the attention of many researchers in the field of geo-environmental engineering in recent years and several aspects of waste mechanical response under loading have been elucidated. However, the mechanical response of MSW materials under undrained conditions has not been described in detail to date. The knowledge of this aspect of the MSW mechanical response is very important in cases involving MSW with high water contents, seismic ground motion and in regions where landfills are built with poor operation conditions. This paper presents the results obtained from 26 large triaxial tests performed both in drained and undrained conditions. The results were analyzed taking into account the waste particles compressibility and the deformation anisotropy of the waste samples. The waste particles compressibility was used to modify the Terzaghi effective stress equation, using the Skempton (1961) proposition. It is shown that the use of the modified effective stress equation led to much more compatible shear strength values when comparing Consolidated-Drained (CD) and Consolidated-Undrained (CU), results, explaining the high shear strength values obtained in CU triaxial tests, even when the pore pressure is almost equal to the confining stress.