Breakthrough times for barrier systems at typical municipal solid waste landfills in China

Spatiotemporal distribution characteristics of physicochemical properties of waste plastics with different landfill age and depth

Plastics are widely used for their excellent properties, and the primary disposal method is sanitary landfilling. Waste plastics, persisting in landfills for long periods, change their surface physicochemical properties. However, research on the physicochemical changes of plastics after landfilling is scarce. This study analyzes the physicochemical characteristics of discarded plastics in landfills, focusing on depths (2-8 meters) and ages (0-30 years). The spatiotemporal distribution of waste plastics was studied using the 3D-Smoothe model. The results revealed that polypropylene (PP) and polyethylene (PE) were the predominant constituents of landfilled plastics. The carbonyl index (CI) and hydroxyl index (HI) accelerated with landfill age but increased and then decreased with landfill depth. Furthermore, the hydrophilicity of waste plastics increases with the landfill age, which is realized as 2 m > 5 m < 8 m in depth. The 3D model analysis indicates that PP displays a wavy downward trend in its spatiotemporal distribution, whereas PE exhibits a vortex-like downward trend. The toughness and strength of waste plastics rapidly decline in the early stages of landfilling and then stabilize. However, variations are noted at a depth of 5 m. The influence of landfill age on the mechanical properties of waste plastics is more significant than that of landfill depth by 3D model analysis. As the age and depth of landfills increase, there is a corresponding rise in the number of surface cracks and defects, a rise in surface roughness, and an increase in the abundance of surface elements. This study provides a scientific basis for understanding the environmental risks of landfilled waste plastics.

Experimental and modeled analysis of contaminant mobility in coal fly ash landfills under continuous rainfall regimes

In China, a significant amount of coal fly ash is stored or used for landfill reclamation. The contaminants in coal fly ash (CFA) leachate can cause regional soil and groundwater contamination during long-term storage. This paper focuses on a coal gangue comprehensive utilisation power plant in Fenyang City, Shanxi Province, China, where the leaching characteristics of CFA were investigated by leaching tests. Laboratory-scale long-term soil column leaching tests and long-term ash column leaching tests were conducted using compacted soil and compacted CFA, respectively, to simulate contaminant migration patterns from CFA during the early and later stages of landfill operation. Hydrus-1D simulation software was used to calculate contaminant transport from the CFA landfill. The test results indicate that the concentrations of six representative elements or compounds in the CFA leachate exceeded the Groundwater Standard Class III. Among these contaminants, Pb contamination was the worst, with concentrations 26.67 times above the standard. The flow rate of the leachate is lower when the degree of compaction of the Ma'lan loess and the CFA is higher, and it takes longer for the leachate to start flowing. The greatest release of the ions occurred at a Ma'lan loess compaction coefficient of 0.943 and a hydraulic conductivity of 6.031 × 10- 7. Under extreme rainfall conditions, the contaminants and heavy metals in the fly ash leachate migrate to a maximum depth of 56 cm in the compacted soil layer, with Pb reaching a depth of 28 cm, nickel 23 cm, cadmium 9 cm and hexavalent chromium 5 cm to meet Class III groundwater quality standards. These results indicate a potential risk of groundwater contamination in the vicinity of CFA deposits or land reclamation projects in long-term storage. To mitigate this risk, the Guofeng Power Plant may consider utilizing locally compacted Malan loess in combination with geosynthetic materials or implementing a liner much thicker than 1.5 m to enhance the impermeability of the fly ash landfill.

Simultaneous ammonia and organics degradation from municipal landfill leachate by electrochemical oxidation

The two primary issues for wide implementation of the electrochemical oxidation of wastewater are the significant cost of electrode and high energy consumption. On the other side, conventional biological processes and membrane technology have several drawbacks for recalcitrant landfill leachate (LL) treatment. To address these issues, graphite/PbO2 anode was used to treat medium to mature age (biodegradability index, 5-day biochemical oxygen demand/chemical oxygen demand: 0.25) LL. To reduce the cost of the oxidation process and maximize the efficiency, operating conditions were optimized. The optimum parameter values were obtained as 24.7 mA cm-2, 180 ± 3 rpm, and 1.9 cm of current density, stirring rate, and electrode gap, respectively. Dissolved organic carbon (DOC), chemical oxygen demand (COD), and ammonia-N removal efficiencies of 55 ± 1.4%, 81 ± 1.9%, and 56 ± 3% were obtained after 8 h of degradation at optimum conditions. The decrease in aromatic substances and ultraviolet (UV) quenching materials were evaluated by UV-Visible spectroscopy and Specific UV absorbance. The conversion of aromatic compounds into simpler molecule compounds was also verified by Fourier-transform infrared spectroscopy analysis. The lab-scale anode synthesis cost was evaluated as 0.42 USD.

Effects of Temperature, Ionic Strength and Humic Acid on the Transport of Graphene Oxide Nanoparticles in Geosynthetic Clay Liner

With the wide application of graphene oxide nanoparticles (GONPs), a great amount of GONP waste is discarded and concentrated in landfills. It has been proven that GONPs have strong toxicity and could gather toxic substances due to their high adsorption capacity. GONPs will seriously pollute the surrounding environment if they leak through the geosynthetic clay liner (GCL) in landfills. To investigate various factors (temperature, ionic strength (IS) and humic acid (HA)) on the transport and retention of GONPs in the GCL, a self-designed apparatus was created and column tests were carried out. The experimental results show that GONPs could be transported through the GCL. The mobility and sorption ratio of GONPs in GCL decreased with an increase in temperature and IS, and increased with an increase in HA. The temperature had little effect on the deposition ratio of GONPs in the GCL. The deposition ratio of GONPs in the GCL increased with IS, and decreased with an increase in HA. The transport of GONPs in GCL, glass beads and quartz sand was compared, and the results show that the retention ability of the GCL is much better than other porous materials. The experimental results could provide significant references for the pollution treatment in landfills.