Search Results (9)

With the growing severity of water pollution, conventional treatment technologies are increasingly unable to satisfy the demand for deep purification. Catalytic wastewater treatment has emerged as an effective strategy for degrading refractory pollutants because of its high efficiency, mild operating conditions, and environmentally friendly nature. This review systematically summarizes recent progress in catalytic materials for wastewater treatment, covering four major categories: metal-based materials, carbon-based materials, multicomponent composites, and photo/electrocatalytic systems. Particular attention is given to their design strategies, structural characteristics, and performance advantages. On this basis, the full mechanistic chain is discussed, from interfacial adsorption and activation to reactive-species generation, including both radical and non-radical pathways, intermediate transformation, and macroscopic reaction kinetics. The review also highlights representative applications in practical wastewater streams, including textile dyeing and pharmaceutical, chemical, landfill leachate, and municipal tailwater treatment, thereby demonstrating the engineering potential of catalytic technologies. At the same time, several critical challenges remain, including insufficient long-term material stability, incomplete mechanistic understanding in complex water matrices, limited adaptability to real wastewater, and the high cost of large-scale preparation. Future research should therefore focus on the development of highly stable, low-cost, and interference-resistant catalytic materials, deeper mechanistic elucidation through in situ characterization and theoretical calculations, stronger integration with membrane separation, biological treatment, photovoltaic or electrochemical processes, and the establishment of standardized evaluation protocols and life-cycle assessment frameworks. These efforts will accelerate the transition of catalytic wastewater treatment toward greener, smarter, and more practical engineering applications. Full article

The distribution of leachate in landfill systems significantly influences landfill stability, pollutant migration, and gas transport. However, existing methods for measuring leachate levels in landfills with multiple intermediate cover layers remain insufficient. This study introduces a novel in situ testing method to determine multi-layer leachate levels. Field experiments at a landfill site in northwestern China successfully quantified leachate levels on each intermediate cover layer. Seepage analysis simulated the leachate level recovery test method used in field investigations, enabling examination of the formation mechanisms and drainage characteristics of multi-layer leachate systems. Measurement results demonstrated that each intermediate cover layer retained a corresponding perched leachate level. Variations in perched water head across waste layers arise from differences in drainage capacity between waste strata. Differential settlement of the intermediate cover layers in localized areas generated adverse hydraulic gradients, contributing to spatial heterogeneity in perched leachate distribution. Back analysis yields an in situ saturated hydraulic conductivity ranging from 1 × 10⁻⁴ to 3.3 × 10⁻³ cm/s. Low-permeability intermediate cover layers were identified as the primary factors contributing to multi-layer leachate formation. The implementation of effective horizontal drainage can reduce perched leachate accumulation above intermediate layers. Full article

Traditional landfill cover materials have low strength and poor dry–wet durability. Municipal solid waste incineration fly ash (MSWI FA) can be used to partially replace cement solidification dredging sediment (DS). This article investigates the possibility of using MSWI FA and ordinary Portland cement (OPC) composite cured DS as a covering material. The mechanical properties, permeability, and wet–dry durability of the cured system were investigated under the conditions of MSWI FA content ranging from 0% to 60% and OPC content ranging from 10% to 15%. The microscopic mechanism was analyzed by scanning electron microscopy and X-ray diffraction. The results showed that when the OPC and MSWI FA contents were 15% and 20%, respectively, the comprehensive performance of the cured specimens was best after 28 days of natural curing. The unconfined compressive strength reached 1993.9 kPa, and the permeability coefficient decreased to below 1 × 10⁻⁷ cm/s, fully meeting the requirements for landfill coverage. C-S-H gel is the main strength source of the solidified body, while Friedel salt and ettringite enhance the compactness of the matrix. An excessive moisture environment promotes the water absorption of soluble salts produced by MSWI FA hydration, leading to sample expansion and reduced strength. MSWI FA and OPC cured DS exhibit good compression performance in the intermediate cover system of landfills, and can maintain good engineering performance under periodic dry–wet cycles. This dual strategic synergy solves the hazardous disposal problem of MSWI FA and the resource utilization demand of DS, demonstrating enormous application potential. Full article

This study addresses the environmental challenges posed by consumerism, evaluating the impact of Degradation-Resistant Organic Compounds (DROCs), such as fats and oils, on surface environments, the subsurface, groundwater, and aquifers. Climate variability has intensified the dispersion of these compounds, particularly in open landfills and poorly managed sites, making it urgent to identify affected areas to plan remediation efforts and mitigate their effects on ecosystems and human health. The objective was to analyze the dispersion of DROCs in an abandoned landfill in northwestern Mexico and develop strategies to characterize the decomposition stages of these compounds. In 2021 and 2022, a two-dimensional geoelectric tomography (GT) was conducted using a SARIS-Scintrex resistivimeter, recording variations in the apparent resistivity of subsoil. Using resistivity measures, the progressive and regressive numerical interpolation of Newton for finite differences, combined with the Lévy-type diffusion operator, classified the invasion areas into three principal ranges: high (recent invasions), intermediate (transition phase), and low (mature invasions).. These ranges indicated how pollutants migrate from the surface to the saturated zones of the aquifer. To validate the presence of fats and oils, a 24-m-deep well was drilled, revealing a positive correlation (R² = 0.863) between the areas covered by the tomograms and the detected contaminants. The results emphasize the need for improved waste management and the careful selection of disposal sites to reduce environmental degradation. The methodology proved effective and rapid, facilitating remediation planning and highlighting the importance of sustainable practices in final disposal to mitigate the impacts of DROCs, reduce greenhouse gas emissions, and protect public and environmental health. Full article

The capillary barrier is a type of soil cover system commonly used in various geotechnical applications, such as limiting infiltration for slopes or landfills or providing cover for solid waste. It serves to prevent the movement of water through the soil layers by utilizing contrasting particle sizes. This paper focuses on investigating the effect of the granular layer on the performance of a three-layer cover with a capillary barrier, integrating the granular layer within clayey sand. The investigation involved one-dimensional infiltration tests utilizing four uniform granular soils with varying grain sizes. These tests were instrumental in calibrating soil water characteristic curves and hydraulic conductivity curves via back analysis. Subsequently, numerical analyses were conducted using a 15 m long model for each of the four distinct cover types. The results indicated that the fine gravel significantly improved the barrier performance beyond one-dimensional tests, owing to its high permeability and the influence of the slope. After the capillary barrier failure, the intermediate layers transitioned into efficient drainage layers, particularly in the gravel layer with the highest lateral drainage capacity. Clayey sand at the bottom delayed percolation, thereby supporting the conversion of the intermediate layer into an effective drainage component. Overall, the multi-layer system showed superior percolation performance compared to the clayey sand cover lacking a granular layer. Full article

This paper examines the environmental impact of the use of compacted sewage sludge:red gypsum (SS:RG) mixture as intermediate landfill cover in terms of yield and quality of leachate as characterised by hydraulic conductivity and leaching behaviour. A series of column tests using the constant head method is carried out by percolating the synthetic leachate through samples that have been compacted at various degrees (60, 70, 75, 80 and 85%). The leachate quality is monitored at pre-determined days for pH, COD, Cu, Fe and Zn. In general, hydraulic conductivity decreases in three stages, in which the first stage is mainly attributed to the particle rearrangement and hydration of calcium silicate hydrate (CSH). The hydration of CSH increases the pH, which causes the heavy metal to precipitate and be entrapped within the matrices of CSH gel, thereby further reducing the porosity and hydraulic conductivity. A minimum of 75% compaction has shown favourable final porosity, hydraulic conductivity, and leachate quality, although a minimum of 80% compaction is recommended in order to achieve a satisfactory compressive strength of greater than 345 kPa for a landfill operation. Full article

Solidified municipal sludge is widely used as temporary covering soil in landfill. Due to the complex leachate of landfill, solidified municipal sludge has the problems of stagnant water and strength degradation. In order to investigate the influence of solidified municipal sludge on the stability of landfills, a landfill slope model with SEEP/W and SLPOE/W was established, using the actual infiltration as the boundary condition. Based on the changes in permeability and strength of the intermediate overburden layer, the migration law of leachate in a landfill under the condition of an intermediate overburden layer was analyzed. The relationship between landfill slope safety, climatic conditions and deterioration of the intermediate overburden layer was further explored. The results show that the permeability of the intermediate overburden layer affects the distribution of leachate and the height of stagnant water. During the rainstorm period, the safety factor of the landfill slope decreased rapidly from 1.4 to 1.0 or even lower. With the decrease in the shear strength of the intermediate overburden, the safety factor of the landfill slope was reduced to less than 1.0. Therefore, maintaining the permeability and strength of solidified municipal sludge at a certain level is required to ensure the safety and stability of landfill slopes. Full article

Incineration bottom ashes (IBA) are the main waste from municipal solid waste (MSW) incineration. In the Iberian countries (Portugal and Spain), MSW incineration with energy recovery (WtE) plays an important role in MSW management. IBA is highly produced and managed differently both between and within countries. This paper aims to provide a comprehensive overview of the management model of IBA using the Iberian Peninsula as a case study, addressing its properties, current management, incentives and difficulties in valorizing, and prospects. For this purpose, incineration plants of both countries were approached, and a broad literature review was conducted to gather information. About 10% and 41% of IBA have been landfilled in Portugal and Spain, respectively. Metals (mostly ferrous) from Portuguese (6% of IBA) and Spanish (9% of IBA) WtE plants are recycled. In Portugal, the remaining IBA (84%) has been temporarily stored (11%), applied to landfills as a substitute for soil in intermediate and final covers, construction of paths, accesses, and platforms (41%), or used in civil engineering work and road construction (48%). In Spain, the remaining IBA (50%) has been reused mainly as a secondary raw material in the construction and civil engineering fields (77%), while the rest has been temporarily stored (11%), applied in the conditioning of landfills (4%), alsoa secondary aggregate replacing natural materials. Both countries regulate IBA reuse outside landfills but consider different requirements and criteria. Nevertheless, there are both drivers and barriers to valorization. In the future, different IBA applications will likely continue to be developed, with the concern of protecting the environment. Growing confidence in IBA reuse following the publication of proper studies is expected. Globally, uniform legal frameworks among EU members with the same standards would likely lead to better IBA valorization. Full article

This paper explores the feasibility of employing drinking water treatment sludge (WTS) mixed with soils, lime, or rock powder in geotechnical applications, as well as discusses the sustainability of the approach based on experimental results, aiming at the beneficial reuse of waste and the preservation of natural geomaterials. The selected materials were two soils largely used in earthworks, two WTSs, a high purity calcium hydrated lime, and rock powder from a granitic–gneissic quarry, all occurring in São Paulo State, Brazil. The mixtures were chemically, mineralogically, and geotechnically characterized, and the geotechnical properties permeability, shear strength, and deformability were investigated. Soil-WTS mixtures showed hydraulic conductivity (10⁻¹⁰–10⁻⁶ m/s, depending on soil and WTS), effective cohesion (10–30 kPa), friction angle (34°–40°), undrained strength (>50 kPa), and compression index (0.1–0.4) compatible with those of soils usually employed in earthworks. Lime:WTS and rock powder:WTS mixtures achieved 50 kPa undrained strength for WTS contents lower than 24% and 8%, respectively, and could be used as daily and intermediate covers of waste landfills, as well as in other applications with low soliciting stresses. The possibility of WTS being pumped instead of transported by trucks was analyzed in the light of results from rheological tests. Full article