Landfill Age Research Articles

Ozone Plasma Nanobubble (OPN) Reactor Combined with Coagulation-Flocculation Process: A Promising Technology for Leachate Treatment

According to World Bank data, approximately 2.01 billion tons of urban waste is produced annually, with approximately 33% of waste being improperly managed, leading to concentrated and toxic leachate. This poses a global challenge due to its varied characteristics influenced by climate, landfill age, and waste composition, resulting in groundwater and surface water pollution with severe impacts on human health, ecosystems, and biodiversity, necessitating stringent treatment measures. To address this, a study integrated coagulation-flocculation and advanced oxidation processes (AOPs) using a dielectric barrier discharge (DBD) ozone plasma nanobubble (OPN) reactor to degrade leachate. Gas flow rate, plasma voltage, and gas sources are variated. This research uses O2 or air as a gas source that produces plasma. The leachate is fed into the DBD reactor, so the bubble will burst and produce further ROS. Optimal results were observed after 60 min, with oxygen gas feed reducing total suspended solids (TSS), chemical oxygen demand (COD), and biological oxygen demand (BOD) by 100, 93.93, and 74.12%, respectively, alongside a decrease in pH. This study indicates the promising potential of this technology for leachate treatment and demonstrates the potential for nitrate production using both types of gas feed.

Statistical investigation of climate and landfill age impacts on Kupferberg landfill leachate composition: one-way ANOVA analysis

This study investigated seasonal variations in the physico-chemical properties of leachate from the Kupferberg landfill site, examining the influence of landfill age and climatic factors. Data provided by the Windhoek Municipality during the years 2017 to 2022 facilitated the exploration of critical concerns related to groundwater protection and human health. Guided by two research questions and anchored in hypotheses tested at a 95% confidence level, the study employed Statistical Packages for Social Scientists (SPSS) for analysis.Significant temperature variations were observed across years [F (5, 21) = 4.493, p < 0.05], indicating a substantial relationship between landfill age and seasonal variations in leachate physico-chemical properties. Further ANOVA tests revealed temperature trends impacting leachate parameters, such as organic content and pH. While COD displayed a declining trend with landfill age, inorganic components like Cl- and alkalinity exhibited no distinct age-related pattern.Wet seasons demonstrated higher EC and Cl--mean values than dry seasons, correlating with elevated COD levels. The study underscored the incremental rise in parameter values over time and during the rainy season, attributed to solid waste degradation and rainwater percolation. Notably, climatic conditions significantly influenced seasonal variations in leachate physico-chemical properties (p < 0.05). Based on this outcome, null hypothesis 1 was rejected. The second null hypothesis was also rejected because climatic conditions do influence the seasonal variations in physico-chemical properties. These findings are crucial for emphasizing the need for effective leachate management strategies and providing valuable insights for arid regions. Future research can expand on a national scale, employing one-way ANOVA tests on other landfills in Namibia, and engaging local communities for comprehensive data collection on cross-contamination.

Compressibility characteristics of municipal solid waste considering multiple factors.

Borehole samples were collected from a municipal solid waste (MSW) landfill in Xi'an, China, and subjected to a series of basic geotechnical and compression tests. This study aims to investigate the influence of composition, dry unit weight, moisture content, organic content, and landfill age on the compressibility of MSW. The results show that with increasing landfill age, the compressible components and organic content exhibit a decreasing trend while the dry unit weight increases. The moisture content does not vary significantly. There is also a linear trend between the logarithm of the primary compression strain and vertical stress. In addition, with an increase in compressible components content, moisture content, and organic content, the modified primary compression index (Cc') shows an increasing trend, whereas with an increase in dry unit weight and landfill age, Cc' shows a decreasing trend. Furthermore, regarding the 34 sets of data, authors only selected five data points for a detailed comparative analysis, this decision was made on the basis that these data points are representative. A modified primary compression index prediction model that considers the dry unit weight, moisture content, and landfill age of the MSW as influencing factors results in a fitting coefficient of 0.797. The Cc' values in this study are within the range of 0.12 to 0.36. These findings provide a reference for the vertical expansion design of existing landfills.

Corrosion characteristics of concrete by landfill leachates of different ages

Landfill leachate is a highly corrosive pollutant, and the composition of landfill leachate varies greatly between landfill ages. Landfill leachates of different ages pose a corrosive danger to concrete structures. In this study, four landfill leachates of different ages were selected for concrete immersion corrosion tests to elucidate the corrosion characteristics of concrete. Measurements of concrete mechanical property indices were combined with microscopic analysis methods, such as X-ray diffraction and scanning electron microscopy. The effects of the compositional differences of the landfill leachate of different ages and contact times on the concrete were analyzed and evaluated. The test results showed that the young landfill leachate slowed down the hydration process of concrete and promoted the generation of expansive corrosive crystals such as gypsum and calcium sulfate, which changed the internal microstructure of the concrete and caused irreversible damage. Exposure to leachates caused a decrease of the concrete quality, compressive strength, and dynamic elastic modulus to below their initial values. The participation of intermediate and mature landfill leachate in the hydration process of concrete promoted the hydration reaction in the short term. However, with the prolongation of the test period, this enhancement gradually weakened, and at the same time, the sulfate in the landfill leachate and the hydration products generated ettringite, which produced expansion stress on the internal structure of the concrete, destroying the structure and decreasing its strength. The experimental results of this study provide theoretical support for the treatment of different ages of landfill leachates and the design and protection of landfill concrete structures.

Can on-site leachate treatment facilities effectively address the issue of perfluoroalkyl acids (PFAAs) in leachate?

In recent decades, the presence of perfluoroalkyl acids (PFAAs) in municipal solid waste leachate has emerged as a growing concern. Research has focused on PFAA release and occurrence characteristics in landfill and waste-to-energy leachate, highlighting their significant impact when released into wastewater treatment plants. Given the extremely high loading rate faced by current on-site leachate treatment plants (LTPs), the objective of this study is to assess whether the current “anaerobic/aerobic (A/O) + membrane bioreactor (MBR) + nanofiltration (NF) + reverse osmosis (RO)” configuration is effective in PFAAs removal. Concentrations of raw and treated leachate in 10 on-site LTPs with same treatment configuration and varying landfill ages were measured, and a comprehensive mass flow analysis of each treatment process was conducted. The results indicate that A/O treatment has limited capacity for PFAA removal, while NF and RO processes reached 77.44 % and 94.30 % removal rates of ∑PFAAs concentration, respectively. Short-chain PFAAs (> 80 % detected frequency) primarily influenced the distribution and variations of PFAAs in leachate and tend to disperse in the water phase. Correlation analysis revealed the current on-site LTPs exhibit a more efficient removal capacity for long-chain PFAAs.

Characterization and differentiation of dissolved organic matter in leachate derived from an old Japanese landfill site through Orbitrap mass spectrometry

Elucidating the characteristics of dissolved organic matter (DOM) is crucial to assessing its impact on the bioavailability and mobility of pollutants in landfill leachate. This study reports a comprehensive 5–month investigation into the characteristics of DOM in leachate from an old Japanese landfill, collected at six different sampling points. The molecular composition, chemical properties, and structural characteristics of DOM were assessed using Orbitrap mass spectrometry and spectral analysis. The leachate DOM mainly consisted of CHO-containing molecules (58.5–88.9%), low-oxygen unsaturated phenolic compounds (40.5–54.0%), and aliphatic compounds (19.4–47.3%), with slight variation among sampling points. A significant portion of the nominal oxidation state of carbon was in the reduced zone (76.2–95.4%). The results underscore the distinct molecular composition of DOM in mature Japanese landfill leachate compared to young and mature leachates from other countries. Two of six sampling points, with notable differences in molecular characteristics, were compared and elucidated. The composition of landfill waste, rather than landfill age, was the main factor affecting the characteristics and differentiation of leachate DOM.

Assessing the impacts and contamination potentials of landfill leachate on adjacent groundwater systems

Landfilling is a globally prevalent method for managing municipal solid waste disposal. Nonetheless, the potential for serious contamination and the significant regional disparities in the leachate produced pose varying degrees of risks to groundwater quality. Previous studies have focused on a single landfill or the same geo-climatic conditions, with a limited number of samples having resulted in a narrow distribution of landfill age and scale, which prevents the description of the pattern of change in landfill age and scale. As well as the effect of this change on the contaminants in the landfill leachate and surrounding groundwater is still unclear. Therefore, we sampled and analyzed leachate and surrounding groundwater from 62 landfills with different landfill ages, scales, and operating conditions in a region with dense and varied topography and climate. Aim to explore the effects of different landfill ages, scales, and operating conditions on contaminants in leachate and surrounding groundwater. Findings indicate that pollutant profiles in different media are influenced by the age, scale, and operational status of the landfill, and the impact of leachate on pollutant types and concentrations in groundwater is limited. A significant correlation exists between the concentration of contaminants in the groundwater affected by leaching from the impermeable layer and the age and scale of the landfill when compared to the leachate. The contamination potentials posed by different pollutants vary across environmental media. Total dissolved solids and NH4+-N in leachate presented high contamination potentials, whereas elemental metalloids (Mn, Al, Ba, and Fe) in the surrounding groundwater posed high environmental concerns. These insights furnish new avenues for monitoring, identification, and safeguarding against pollutants in landfills and proximate groundwater, which is imperative for the sustainable management of municipal waste.

Waste-to-energy power plants: Multi-objective analysis and optimization of landfill heat and methane gas by recirculation of leachate

Elevated thermal energy trapped in landfill voids is a potential threat to humans since, fires might get ignited, eventually releasing poisonous gases, contaminated fluids (leachate), and abnormal quantity of heat. This study explores the practical potential of landfills to produce heat and methane gas through a leachate recirculation process, which involves returning nutrient-rich fluids to landfills to maximize electricity generation. This paper presents an experimental investigation of the physio-chemical properties of landfills by recirculating leachate to achieve sustainable performance characteristics of landfill models. Five input parameters i.e. waste particle size (WPS in mm), waste addition (WA in Ktoe), inorganic matter content (IO in %), leachate recirculation rate (LRR in liters/day), and age of landfill (LA in years) each at five levels is considered. The investigation is accomplished on the central composite rotating design (CCRD) matrix with a 5-level factor. The results reveal that WPS at D10, WA at 52.32 Ktoe, IO at 2%, LRR at 300 l/day, and LA at 4.07 year is the optimal setting of the input parameters that produce optimum values of the output responses considered simultaneously. An innovative method is studied for simultaneously lowering the internal temperature of landfills to ideal levels while also enhancing the rate of methane production. Energy transfer to the ORC system is 2.3 GJ in winters while 1.5 GJ in summers. Landfills equipped with leachate recirculation facilities provide 2.2 times more energy with stabilization occurring in 4th year with an energy content of 950 MJ/m3 of waste.

Effect of geomembrane liner on landfill stability under long-term loading: interfacial shear test and numerical simulation.

Clay liners have been widely used in landfill engineering. However, large-scale clay excavation causes secondary environmental damage. This study investigates the feasibility of replacing clay liners with high-density polyethylene (HDPE) geomembranes with different specifications and parameters. Laboratory interface shear tests between municipal solid waste (MSW) samples of different ages and geomembranes were conducted to study the influence of landfill age on interface shear strength. Finite element method was adopted to compare the long-term stability of landfills with HDPE geomembrane versus clay as intermediate liner. The interfacial shear test results show that the cohesion of MSW increases in a short term and then decreases with landfill age. The internal friction angle exhibits an increasing trend with advancing age, however, the rate of its increment declines withage.The rough accuracy of the film surface can increase the interfacial shear strength between MSW. The simulation results show that, unlike clay-lined landfills, the sliding surface of geomembrane-lined landfills is discontinuous at the lining interface, which can delay the penetration of slip surfaces and block the formation of slip zone in the landfill. In addition, the maximum displacement of landfills with geomembrane is 10% lower than that with clay, and the absolute displacement of slope toe decreases with the increase of roughness at the interface of geomembrane. Compared with clay-lined landfills, the overall stability safety factor increased by 18.5-30%. This study provides references for landfill design and on-site stability evaluation, contributing to enhanced long-term stability.

Landfill leachate treatment by direct contact membrane distillation: Impacts of landfill age on contaminant removal performance, membrane fouling and scaling

The imperative for sustainable urban development necessitates the proper treatment of landfill leachate (LFL), driven by its high level of contaminants. Although membrane distillation (MD) effectively captures non-volatile contaminants, impediments persist in practical implementation in LFL, notably membrane fouling and scaling induced by organic and inorganic substances. These challenges are particularly salient in treating LFL with varying contaminant concentrations contingent upon its age. This study comprehensively investigated the treatment efficiency of direct contact membrane distillation (DCMD) for both young landfill leachate (YLFL) and aged landfill leachate (ALFL), along with an examination of the associated membrane fouling and scaling conditions over a 15-d period. The results demonstrated that chemical oxygen demand (COD) and metal ions in both YLFL and ALFL were effectively retained by DCMD, with rejection rates exceeding 99 %. Nevertheless, escalating membrane fouling led to diminished distillate fluxes, with reductions of 26 %–32 % for YLFL and 63 %–86 % for ALFL. The fouling mechanisms differed between YLFL and ALFL treatments. YLFL primarily induced organic fouling through biopolymers and humic acid (HA), while ALFL introduced inorganic salt ions (e.g., Ca2+ and Mg2+) and organics, resulting in scaling and hybrid organic-inorganic fouling. Acid cleaning proved more efficacious than alkali cleaning for ALFL treatment, as it dissolved ions and disrupting the crystal-organic cross-linked fouling layer. This study sheds new light on membrane fouling control during DCMD-based treatment of LFL at varying ages.

Experimental investigation and multi-performance optimization of the leachate recirculation based sustainable landfills using Taguchi approach and an integrated MCDM method

Landfill leachates contain harmful substances viz. chemicals, heavy metals, and pathogens, that pose a threat to human health and the environment. Unattended leachate can also cause ground water contamination, soil pollution and air pollution. This study focuses on management of leachate, by recirculating the rich, nutrient-filled fluid back into the landfills, turning it to a bioreactor, thereby maximising the performance parameters of landfills favourable for electricity production by the waste to energy plants. This study demonstrates a sustainable alternative method for utilising the fluid, rather than treating it using an extremely expensive treatment process. Further, it also experimentally investigates the effect of varying levels of five input parameters of the landfill including waste particle size, waste addition, inorganic content in waste, leachate recirculation rate, and landfill age, each at five levels, on the multiple performance of the landfill using Taguchi’s L25 standard orthogonal array. Experimental results are analysed using an integrated MCDM approach i.e. MEREC-PIV method and statistical techniques such as analysis of mean (ANOM) and analysis of variance (ANOVA). The results indicate that the optimal setting of the input parameters is waste particle size at 9 ppm, waste addition at 80 Ktoe, inorganic content in waste at 2%, leachate recirculation rate at 250 l/day and landfill age at 3 years. Further, inorganic content waste is found to be the most significant parameter for the multiple performance of the landfill. This study presents a novel approach to produce input parameters for power plants which may enhance their profitability and sustainability.

Effects of landfill age, climate, and size on leachate from urban waste landfills in Portugal: A statistics and machine learning analysis

The leachate generated by in urban waste landfills can cause environmental pollution if not controlled and treated. With different proportions of biodegradable waste, urban waste degrades over several phases in anaerobic conditions within a landfill. Using multivariate leachate data from 32 engineered landfills in Portugal, each with a similar waste composition, and all classified as non-hazardous waste landfills receiving urban waste, statistical inference was applied to categorise and deduce significant statistical differences in leachate volume and quality between landfill age, size, and climate, as well as the interactions and effects within these categories. The findings show that the effects of size and age on the leachate volume are prevalent over local, Mediterranean climate conditions; in larger landfills, waste may not be degrading as efficiently as in medium-sized landfills; hotter zones showed higher levels of COD and lower levels of BOD5 than warmer zones, indicating increased biological activity under higher temperature conditions; TN and NH4-N increase significantly with age and size; Cl- also significantly increases with age, showing higher levels, along with SO42-, in hotter zones as well as a concentration effect in the dry season, along with K+; heavy metals maintain levels as landfills age from intermediate to old, with only Cd2+ and Pb2+ showing significant reductions. High correlations between macro inorganics and between heavy metals were found. Cluster analysis showed two main branches, one representing the initial to intermediate stages of anaerobic degradation, and the other the interactions between leaching parameters in the later methanogenic phase of landfill stabilisation.

Influence of leachate microenvironment on the occurrence of phthalate esters in landfills

Phthalate esters (PAEs) are added to various products as plasticizers. Plastic waste containing PAEs enters landfills as they age with use. However, the influence of microenvironmental changes on the occurrence of PAEs during landfill stabilization is still unknown. In this study, we evaluated the relationship between the physical and chemical properties of leachate, the structure of bacterial communities and the chemical structure of dissolved organic matter (DOM), and the occurrence of PAEs and the mechanism underlying their responses to changes. Landfill leachate in different stabilization states had high Cl− and NH4+ contents and its metal element (Cr, Pb, and Zn) contents generally decreased with the increase in landfill ages. Proteobacteria, Bacteroidetes, and Firmicutes were important phyla and had an average relative abundance of 68.63%. The lignin/carboxylate-rich alicyclic molecule structure was the main component of DOM (56%–64%). Of the 6-priority controlled PAEs in leachate, di-n-butyl phthalate was the most abundant (1046 μg L−1), while butyl phthalate was not detected. The results showed that pH, the relative abundance of Chloroflexi, and the value of SUVA254 can directly influence the occurrence of PAEs in leachate. The positive and negative effects vary depending on the PAE content and molecular weight. DBP and DEHP have higher environmental risks in the aquatic system. These results are intended to provide a scientific basis for the evolutionary characterization of the microenvironment in complex environmental systems and the control of novel contaminants, such as PAEs.

Microbial contamination risk of landfilled waste with different ages

Landfills are reservoirs of antibiotic resistance genes (ARGs) and pathogens, and humans are exposed to these pollutants during extensive excavation of old landfills. However, the microbial contamination risk of landfilled waste with different ages has not been assessed. In this study, human bacterial pathogens (HBPs), ARGs, and virulence factors (VFs) were systematically determined using metagenomic analysis. Results showed that the abundance of HBPs, ARGs, and VFs increased with landfill age, the percentage of HBPs in refuse with deposit age of 10–12 years (Y10) was 23.75 ± 0.49%, which was higher than that in fresh refuse (Y0, 17.99 ± 0.14%) and refuse with deposit age of 5–6 years (Y5, 19.14 ± 0.15%), indicating that old refuse had higher microbial contamination risk than fresh refuse. Multidrug, macrolide, lincosamide, streptogramine, and tetracycline resistance genes were the primary ARGs, whereas lipooligosaccharides, type IV pili, and polar flagella were the dominant VFs in refuse. The HBPs showed a significant positive correlation with ARGs and VFs. Listeria monocytogenes, Salmonella enterica, Streptococcus pneumoniae, Acinetobacter baumannii, and Escherichia coli possibly possess both multiple ARGs and VFs and could be listed as high-risk HBPs in refuse. Mobile genetic elements, especially transposons, showed positive correlations with most ARGs and VFs, and they were identified as the primary factors accounting for the variations in ARGs and VFs. These findings will help understand the spread of ARGs and VFs in landfills and evaluate the potential risk of microbiological contamination in refuse of different landfill ages, thus providing guidance for preventing disease infection during landfill excavations.

Application of Landfill Gas-Water Joint Regulation Technology in Tianjin Landfill

Landfills have long been widely used to dispose of Municipal Solid Waste (MSW). However, many landfills have faced early closure issues in recent years due to overload operations. Although in-situ aeration technology can quickly stabilize MSW, low oxygen utilization rates present a general problem that results in high energy-consuming and operating costs. This research aims to improve oxygen utilization efficiency by observing the dynamic respiratory index and the removal of contaminants. Three continuous reactors were constructed and designed with targeted aeration and re-circulation schemes for different landfill ages. The results show that a well-designed aerobic, semi-aerobic, and anaerobic reactor can fully degrade the organic components of MSW with different landfill ages, and the quantity of waste has been reduced by more than 60%. Additionally, it was disclosed that gas-water joint technology has a promotional effect on activating microorganisms.

Technologies for Treatment of Landfill Leachate: A Brief Review

Abstract: Landfill leachate contains organic compounds like amines, ketones, carboxylic acid, alcohols, aldehydes, phenols, phosphates and inorganic pollutants such as ammonia, phosphorous, sulphate, emerging contaminants like per-and polyfluoroalkyl substances (PFAS) and also the toxic heavy metals like Mn, Cd, Pb, Fe, Ni, Zn and As. In young landfill leachate, the concentration of volatile acid and simply degraded organic matter is high while pH is low. However, in mature landfills, there is more leachate production with high pH. The age of landfill and determination of parameters like BOD, COD, COD/BOD ratio are important to know the appropriate treatment methods. Physicochemical, biological and combined methods are the most reported landfill leachate treatment methods. Advanced oxidation process, adsorption, coagulation-flocculation, bioremediation, phytoremediation, bioreactor, membrane process and air striping are some of the common categories of effective treatment of landfill leachate. For better apprehension, it has been reviewed that treatment efficiencies of different kinds of leachate depend on their composition and method adopted. Studies related to the removal of organic matter and heavy metals are predominant which reported excellent removal efficiency ranging from 80-100%. In addition, physical parameters like color and turbidity can also be removed effectively using appropriate treatment methods. The present article deals with a concise review of existing literature on sustainable landfill leachate treatment technologies which include physical, chemical, biological and combined techniques.

Mass concentration and distribution characteristics of microplastics in landfill mineralized refuse using efficient quantitative detection based on Py-GC/MS

Landfilling is the most traditional disposal method of domestic waste. Plastic waste in landfill sites could degrade to microplastics (MPs) and diffuse to the surrounding environment with leachate. However, MPs pollution in landfill mineralized refuse has not been well recognized. In the present research, a detection method for mixed MPs of polyethylene (PE), polypropylene (PP), and polystyrene (PS) based on Py-GC/MS was established and verified. The method is suitable for the rapid quantitative detection of large-batch of complex solid matrix samples, with an average deviation of less than 10%. Based on the method, samples from a landfill site in South China were studied, where PE was found to be the main component. The total concentration of MPs in mineralized refuse was 7.62 kg/t in the old area and 5.49 kg/t in the young area. Further analysis showed that the content of MPs was correlated with that of plastic waste and the landfill age, indicating that a considerable proportion was secondary MPs. The reserves of MPs in landfill sites may have reached an alarming number. In the absence of adequate safeguards, quantities of MPs may spread from the landfill sites, resulting in serious pollution of the surrounding soil and groundwater.

Efficient removal of nitrogen and organic matter strategy from landfill leachate under high seasonal substrate variations

Landfill leachate is commonly used as a co-substrate in aerobic granular sludge (AGS) systems due to its high nitrogen concentration and variable organic matter content, which have a substantial impact on the removal efficiency. Typically, the nutrient content and biodegradability of leachate are categorized based on landfill age, often overlooking important factors such as seasonal variations. To address this limitation, a two-step process consisting of an anaerobic digestion (AD) reactor followed by an AGS reactor was evaluated over 431 days. Landfill leachate from the winter and spring seasons was chosen for its favorable biodegradability characteristics.Raw landfill leachate assays revealed a biodegradability range of 25%–92% within a single year, with higher values observed during winter compared to summer. To effectively handle the nutritional variations of landfill leachate, the hydraulic retention time (HRT) emerged as a crucial parameter influencing the performance of the reactors. When the AD reactor was operated in a hydrolytic configuration with an OLR of 68.4 g COD L−1 d−1, the proposed system showed 76.9% and 78.3% of organic matter and nitrogen removals, respectively. Best performance was obtained with COD/N 6.30 in the influent, ensuring required conditions for anoxic reactions (denitrification) at the center of the AGS.The proposed system offers valuable design tools for effectively removing nitrogen and organic matter from landfill leachates, despite significant seasonal nutrient variations. This approach can also be applied to wastewater with organic and nitrogen variations to face organic matter fluctuations in the AD and nitrogen fluctuations in the AGS.

Effects of moisture content and landfill age on the shear strength properties of municipal solid waste in Xi'an, China.

With the continued expansion of waste landfills, accidents may occur if the landfills are not properly stabilized. In this study, samples of municipal solid waste (MSW) from a waste landfill in Xi'an, China were collected through on-site drilling. Considering the effects of nine landfill ages (1, 2, 3, 11, 12, 13, 21, 22, and 23 y) and six moisture contents (natural, 20, 40, 60, 80, and 100%), 324 groups of MSW were tested in the laboratory using a direct shear test apparatus. The results indicate the following: (1) with an increase in horizontal shear displacement, the shear stress of MSW gradually increases without a peak stress phenomenon, which is a displacement hardening curve; (2) with an increase in landfill age, the shear strength of MSW increases; (3) with an increase in moisture content, the shear strength of MSW increases; (4) with an increase in landfill age, the cohesion (c) decreases and the internal friction angle (φ) increases; and (5) with an increase in moisture content, the c and φ of MSW increases. The c range found in this study was 6.04-18.69kPa, while the φ was 10.78-18.26°. The results of this study can provide a reference for stability calculations for MSW landfills.

Estimating the Mass of Pharmaceuticals Harbored in Municipal Solid Waste Landfills by Analyzing Refuse Samples at Various Ages and Depths.

Pharmaceuticals have been detected at high concentrations in municipal solid waste (MSW) landfill leachates, which are recognized as an underestimated source of pharmaceutical residues in the environment. However, limited efforts have been made to characterize pharmaceuticals in MSW landfill refuse, which is also of significant concern given the potential long-term environmental impact. Herein, we excavated landfill refuse from six cells with landfill ages of 7-27 years in the largest MSW landfill in Shanghai (in each cell, landfill refuse was collected from different depths of 2-8 m) and analyzed samples for the presence of 55 pharmaceuticals, including antibiotics and non-antibiotics. The results reveal the presence of 42 pharmaceuticals in landfill refuse, with median concentrations ranging from 0.30 to 116 μg/kg. Antibiotic and non-antibiotic pharmaceuticals exhibited diverse concentration trends with age, related to changes in policy intervention and consumption over time. Different concentration variations of individual pharmaceuticals were observed in refuse samples excavated at different depths and positively correlated to their sorption ability. The mass of pharmaceuticals in the investigated landfill was estimated from the obtained concentrations to be 80-220 tons with 95% probability, based on Monte Carlo analysis. To the best of our knowledge, this study provides the first estimate of pharmaceutical mass in an MSW landfill. The results will be helpful for understanding the potential long-term environmental impact of pharmaceuticals in landfills.