Impact of biological clogging on the barrier performance of landfill liners

Visualization of physicochemical parameters' behavior in leachate, baseliner, and surface water during dry and rainy seasons at a sanitary landfill

Landfill leachate, a major environmental contaminant, is influenced by multiple factors and can migrate through landfill systems, spreading over considerable distances and polluting surrounding ecosystems. This study utilized Ball Mapper, a topological data analysis tool, to qualitatively explore hidden relationships between physicochemical parameters in leachate, surface water, and the baseliner, which can aid in pollution monitoring. The resulting Ball Mapper topological graphs uncovered behavioral similarities and relationships among parameters across different seasonal conditions. The analysis effectively revealed underlying patterns and interconnections by clustering parameters with similar behavior into the same nodes and linking those with hidden similarities. Additionally, Spearman correlation was used to validate the Ball Mapper output, the analysis showed that baseliner and surface water had a weak linear relationship with leachate, except for PO₄3 (r = 0.99), SO₄2⁻(r = 0.71), TSS (r = 0.82), and pH (r = 0.95) in surface water across seasons, which could be as a result of runoff, sediment transport, and environmental factors rather than direct leachate infiltration. The study also demonstrated that while seasonal variations in precipitation influenced leachate volume and pollutant concentrations, the landfill's engineered barriers effectively mitigated the potential environmental impact of leachate migration. Ball Mapper successfully showed the hidden behavior that traditional clustering methods may miss, highlighting its potential as a valuable tool for environmental monitoring.

Theoretical one-dimensional porous media model for microbial growth on pore plugging and permeability evolution and its verification

The growth, reproduction, and metabolic activities of microorganisms can lead to blockages within porous media, a phenomenon commonly observed in landfill engineering. Termed as microbial plugging, this phenomenon is significantly influenced by the inherent permeability characteristics of the system. In this study, we propose a simulation model based on the Monod equation to elucidate the clogging process caused by microorganisms in one-dimensional pore channels. Our primary focus is on the application of this model in landfill bioreactor systems. We demonstrate that microbial clogging in these systems is predominantly affected by factors such as the maximum environmental carrying capacity and pore size. These factors are directly influenced by the presence of solid waste within the landfill. By offering a theoretical foundation for mitigating microbial clogging in pore channels of landfill bioreactor systems, this research has the potential to contribute to the development of more efficient and effective waste management practices.Implications: Microbial plugging is a hot research topic in the field of environmental geotechnical engineering. Previous papers often only considered the reduction of pore volumes, while neglecting the role of clogging and the uneven distribution of permeability. In this paper, we established a permeability model for porous media that considers microbial growth and plugging. This model can reflect the temporal variation of permeability with microbial growth and predict the spatial distribution of permeability. This paper can promote on the utilization of microbial plugging technology in landfills or solid waste.

Isolation and characterization of quorum quenching bacteria from municipal solid waste and bottom ash co-disposal landfills

Co-landfilling of bottom ash (BA) accelerates the clogging of leachate collection systems (LCSs) and increases the risk of landfill failure. The clogging was mainly associated with bio-clogging, which may be reduced by quorum quenching (QQ) strategies. This communication reports on a study of how isolated facultative QQ bacterial strains from municipal solid waste (MSW) landfills and BA co-disposal landfills. In MSW landfills, two novel QQ strains (Brevibacillus agri and Lysinibacillus sp. YS11) can degrade the signal molecule hexanoyl-l-homoserine lactone (C6-HSL) and octanoyl-l-homoserine lactone (C8-HSL), respectively. Pseudomonas aeruginosa could degrade C6-HSL and C8-HSL in BA co-disposal landfills. Moreover, P. aeruginosa (0.98) was observed with a higher growth rate (OD600) compared to that of B. agri (0.27) and Lysinibacillus sp. YS11 (0.53). These results indicated that the QQ bacterial strains were associated with leachate characteristics and signal molecules and could be used for controlling bio-clogging in landfills.

Spatial-temporal clogging development in leachate collection systems of landfills: Insight into chemical and biological clogging characteristics

The clogging of leachate collection systems (LCSs) is a typical challenge for landfills operation. Although clogging occurs in different LCS components, its spatial-temporal distributions remain unclear. This study aimed to systematically investigate the dynamic clogging development in simulated LCSs by monitoring changes in clogging characteristics over time. Results revealed that clogging accumulated in all components of the simulated LCS during a 215-day period, including chemical clogging and bio-clogging. Distinct spatial variations in clogging components were observed along the leachate flow of the simulated LCS, with the geotextile being severely clogged due to bio-clogging (70.1 ± 3.0%-80.0 ± 0.5%). Additionally, chemical clogging mainly occurred at the top (85.4 ± 0.8%-95.0 ± 0.9%) and middle (91.2 ± 0.8%-94.9 ± 1.1%) gravel layers. Nevertheless, the percentage of chemical clogging decreased from 72.0 ± 2.1% (day 42) to 42.5 ± 2.7% (day 215) at the bottom gravel layer. Chemical clogging was the main type in the pipe, accounting for 69.6 ± 0.5% (day 215). In addition, the ratios of bio-clogging to chemical clogging changed over time in all LCS components. The spatial-temporal characteristics of clogging across LCS components can enhance the understanding of clogging mechanisms, facilitate the design optimization of LCSs, and promote the formulation of effective control strategies.

Tricks and tracks in waste management with a special focus on municipal landfill leachate: Leads and obstacles

Landfilling is the most widely used disposal method for municipal solid waste around the world. The main disadvantage of this strategy is formation of leachate, among other aspects. Landfill leachate contains highly toxic and bio-refractory substances that are detrimental to the environment and human health. Hence, the risk(s) of discharging potentially harmful landfill leachate into the environment need to be assessed and measured in order to make effective choices about landfill leachate management and treatment. In view of this, the present review aims to investigate (a) how landfill leachate is perceived as an emerging concern, and (b) the stakeholders' mid- to long-term policy priorities for implementing technological and integrative solutions to reduce the harmful effects of landfill leachate. Because traditional methods alone have been reported ineffective, and in response to emerging contaminants and stringent regulations, new effective and integrated leachate treatments have been developed. This study gives a forward-thinking of the accomplishments and challenges in landfill leachate treatment during the last decade. It also provides a comprehensive compilation of the formation and characterization of landfill leachate, the geo-environmental challenges that it raises, as well as the resource recovery and industrial linkage associated with it in order to provide an insight into its sustainable management.

Coupled effect of microbiologically induced calcium carbonate and biofilms in leachate

Fouling and clogging are persistent challenges to the collection and treatment of leachate. The main components of fouling and clogging are calcium carbonate (CaCO₃) and biofilms. However, the relationships between CaCO₃ and biofilms remain to be clarified. In this study, the interaction between microbially induced CaCO₃ precipitation (MICP) and biofilms was investigated using Luria-Bertani (LB) or urea media. Results showed that the bacteria promoted the precipitation of CaCO₃ and the formation of a complex mixture of biofilms. The amount of formed CaCO₃ in the urea medium was 12.9 times of that in the LB medium. The high MICP potential in the urea medium was associated with increased pH and alkalinity. In addition, the clogging materials exhibited a layered structure and uneven distribution over the clogging width and depth profile. These results indicated the presence of nucleation sites of CaCO₃ on the surface of and inside the bacteria. This research provides insights into the regulation of MICP and biofilms through dynamic control of clogging and fouling.

Role of surface physicochemical properties of pipe materials on bio-clogging in leachate collection systems from a thermodynamic perspective

Bio-clogging in pipes poses a significant threat to the operation of leachate collection systems. Bio-clogging formation is influenced by the pipe materials. However, the relationship between bio-clogging and the physicochemical properties of different pipe materials has not been clarified yet, especially from a thermodynamic aspect. In this study, the dynamic bio-clogging processes in pipes of different materials (high-density polyethylene (HDPE), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE)) were compared, and their correlation with the physicochemical properties was investigated. Results showed that the bio-clogging in HDPE and PVC pipes was more severe than that in PP and PE pipes. In bio-clogging development, the predominant factor changed from the surface roughness to the electron donator parameter (γ^-). In the initial phase, the most severe bio-clogging was observed in the HDPE pipe, which exhibited the highest roughness (432 ± 76 nm). In the later phase, the highest γ^- (2.2 mJ/m²) and protein content (2623.1 ± 33.2 μg/cm²) were observed in the PVC simultaneously. Moreover, the interaction energy indicated that the bacteria could irreversibly and reversibly adhere to the HDPE, whereas irreversible adhesion was observed in the PVC, PP, and PE cases. The findings clarify the thermodynamic mechanism underlying bio-clogging behaviors and provide novel insights into the bio-clogging behaviors in pipes of different materials, which can facilitate the development of effective bio-clogging control strategies.

Factors Affecting Soybean Crude Urease Extraction and Biocementation via Enzyme-Induced Carbonate Precipitation (EICP) for Soil Improvement

Enzyme-induced carbonate precipitation (EICP) is a new biogeotechnical ground improvement technique that uses calcium carbonate (CaCO3) formed by biochemical processes to increase soil strength and stiffness. In this paper, crude urease extracted from soybeans was employed to catalyze the precipitation of CaCO3 in sand. To optimize the urease extraction efficiency, factors affecting the soybean crude urease extraction, including the powdered soybean particle size, concentration, soaking time, and soaking temperature, were addressed. This paper also provided further insight regarding the impact of the urease activity of soybean crude extract on the chemical conversion efficiency and the biocementation performance in EICP. The findings revealed that the powdered soybean concentration and the particle size were the two most important factors affecting the urease activity of the soybean crude extract. The enzyme activity utilized in the EICP process might further lead to different reactant efficiencies of urea-CaCl2 solution, and consequently, the improvement in the physical and mechanical properties of biocemented sand. Considering the chemical conversion efficiency and the biocementation performance, 60 g/L of powdered soybean was concluded as the preferred quantity for extracting the crude urease, with an enzyme activity of 6.62 mM urea min−1. Under this condition, a chemical conversion efficiency of approximately 95% for 0.5 M urea-0.5 M CaCl2 could be obtained in merely 12 h, and the unconfined compressive strength (UCS) of the EICP-treated sand exceeded 4 MPa with a CaCO3 content of ~8%. As a high-efficient cost-effective alternative to the purified enzyme for carbonate precipitation, the soybean crude urease showed great potential for ground improvement.

Insight into the effect of calcium on bio-clogging behavior via quartz crystal microbalance with dissipation monitoring

Bio-clogging of leachate collection systems has attracted much attention because of its threat to landfill slope stability and landfill landslide events. Calcium in leachate plays a vital role in the formation of bio-clogging. However, the influence of calcium on bio-clogging remains unclear. This study examined the effects of calcium concentration on bio-clogging, including 0, 1.25, 5, 25, and 75 mM CaCl₂ groups. A technique involving quartz crystal microbalance with dissipation monitoring (QCM-D) was applied to evaluate the bacteria adhesion behaviors in real time. The results showed that the presence of Ca²⁺ accelerated the bacterial attachment and increased the viscoelasticity of deposited layers. The deposition mass for 75 mM CaCl₂ was 1442 ± 260 ng/cm², which is 1.5 times that for 1.25 mM CaCl₂. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory could explain the bacterial adhesion behaviors in low calcium concentrations (<25 mM). In comparison, the effect of calcium bridge was shown in high calcium concentrations (>25 mM). The development of biofilms was a dynamic process, and the Ca²⁺ concentration was positively related to the amount of biofilm generated. In low CaCl₂ concentration (less than 5 mM) groups, the degree of bio-clogging increased from the exponential growth phase to the decline phase; in contrast, in high CaCl₂ concentration (above 25 mM) groups, the degree of bio-clogging increased and later declined. Therefore, the calcium concentration should be controlled at a low level in leachate to mitigate bio-clogging in LCSs.

Effect of solid waste landfill leachate contaminants on hydraulic conductivity of landfill liners

Landfilling is one of the most widely used methods to reduce the impact on the environment and human health by ensuring the management of solid wastes. For the process in question to be called landfill, the landfill leachate must be controlled and liner impermeability conditions must be provided. For this reason, compacted clay liners (CCL) and geosynthetic clay liners (GCL) with very low hydraulic conductivity are often used as hydraulic barriers in landfills to prevent the risk of leachate mixing with groundwater. However, as a result of various interactions between leachate-clay liners, changes occur in the hydraulic conductivity of the liners. In this review, the change (increase/decrease) in the hydraulic conductivity of the landfill liners caused by the contaminants in the leachate composition and the mechanisms responsible for this change were examined. In addition, deficiencies in the literature on this subject were identified and directions for future studies were presented.

Impact of bottom ash co-disposed with municipal solid waste on geotextile clogging in landfills

Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is commonly used for BA management. However, BA co-disposal may cause clogging of geotextiles in MSW landfills. This study investigated the effect of different BA co-disposal ratios on geotextile clogging, including MSW, low ash co-disposed (BA_L), high ash co-disposed (BA_H) landfills, and BA mono-fill. Results showed that the BA_L group increased the geotextile clogging by 0.1-0.6 times, compared to that in the MSW landfill. In contrast, the geotextile clogging of the BA_H and BA groups was reduced than that in the MSW landfill. The clogging was in a dynamic process during the experimental period in all the conditions, including chemical clogging and bio-clogging. Moreover, bio-clogging was the main contributor to the geotextile clogging, accounting for 64-83% of the total clogging mass. The BA co-disposal affected the leachate characteristics, such as pH, calcium concentration, and alkalinity, resulting in chemical clogging. When pH was above 7.0, calcium concentration and alkalinity were limiting factors for the calcium carbonate formation. In terms of the bio-clogging, the microbial analysis indicated that different BA co-disposal ratios influenced the diversity and structure of microbial community. These findings could help clarify the effect of BA co-disposal on geotextile clogging, thus useful to landfill operation in practice.

Comparison of bio-clogging characteristics of geotextiles in MSW and bottom ash co-disposal landfills

Bio-clogging of geotextile is a big challenge for the leachate collection system in landfills. It is important to understand the characteristics of geotextile bio-clogging to develop control technologies. This study investigated the characteristics of geotextile bio-clogging in municipal solid waste landfill (MSW_G) and bottom ash (BA) co-disposal landfill (BA_G). Results showed that the bio-clogging mass of per area in MSW_G and BA_G was 49 ± 5 g/m² and 57 ± 3 g/m², respectively. Bio-clogging was dominated by live cells in both MSW_G and BA_G. The confocal laser scanning microscopy images revealed that live cells percentage was 46% in MSW_G, while it increased to 77% in BA_G. In contrast, the percentage of the dead cells was 47% and 9% in MSW_G and BA_G, respectively. The biofilm formed in BA _G was thinner and denser than that in MSW_G. Based on the microbial analysis, the biofilms of BA_G had a higher genetic amount and diversity than these of MSW_G. The total amount of extracellular polymeric substances in BA_G was 45.29 ± 4.52 mg/g volatile suspended solids, which was 1.5 times of that in MSW_G. The co-disposal of BA increased the microbial diversity and accelerated bio-clogging due to the high calcium concentration. These findings provide a better understanding of the bio-clogging characteristics, which is helpful to control bio-clogging in co-disposal landfills.

Framework, method and case study for the calculation of end of life for HWL and parameter sensitivity analysis

Mass construction and operation of hazardous waste landfill infrastructure has greatly improved China’s waste management and environmental safety. However, the deterioration of engineering materials and the failure of landfill may lead to the release of untreated leachate rich in persistent toxic pollutants to the soil and shallow groundwater. Accordingly, we develop the framework and process model to predict landfill life by coupling the landfill hydrological performance model and material degradation model. We found that the decrease rate of the concentration of persistent pollutants in leachate was significantly slower than the deterioration rate of the landfill engineering materials. As a result, when the materials failed, the leachate with high concentrations of persistent pollutants continued to leak, resulting in the pollutants concentration in surrounding groundwater exceeding the acceptable concentration at around 385 a, which is the average life of a landfill. Further simulation indicated that hydrogeological conditions and the initial concentration of leachate will affect landfill lifespan. The correlation coefficients of concentration, the thickness of vadose zone and the thickness of aquifer are − 0.79, 0.99 and 0.72 respectively, so the thickness of vadose zone having the greatest impact on the life of a landfill. The results presented herein indicate hazardous waste landfill infrastructure reinvestment should be directed toward long-term monitoring and maintenance, waste second-disposal, and site restoration.

Environmental application of basic oxygen furnace slag for the removal of heavy metals from leachates

Industrial waste is a major environmental concern nowadays, stimulating the thorough study of the minimization and recycling of solid wastes and of the containment and treatment of liquid contaminants. Basic oxygen furnace (BOF) slag, a solid waste from the steel industry, has been found to be effective in the removal of heavy metals. However, this has not been applied so far in low permeability barriers, such as those used as bottom liners in landfills. This work studies the performance of BOF slag in both containment and treatment technologies for toxic leachates. Flow models are developed to assess the transport of metal ions through a permeable reactive barrier and a composite clay barrier. Reactive transport through the slag barrier and adsorption in the clay barrier are coupled for different conditions to find the residence time, the barrier life span and the optimum operative conditions. The results show that the use of BOF slag increases the breakthrough time of the contaminants, enabling improve design of low and high conductivity reactive barriers, and expands the life cycle of the material.

Isolation distance between municipal solid waste landfills and drinking water wells for bacteria attenuation and safe drinking

Groundwater pollution and human health risks caused by leachate leakage have become a worldwide environmental problem, and the harm and influence of bacteria in leachate have received increased attention. Setting the isolation distance between landfill sites and groundwater isolation targets is particularly important. Firstly, the intensity model of pollutant leakage source and solute transport model were established for the isolation of pathogenic Escherichia coli. Then, the migration, removal and reduction of bacteria in the aerated zone and ground were simulated. Finally, the isolation distance was calculated based on the acceptable water quality limits, and the influence of hydrogeological arameters was analyzed based on the parameter uncertainty. The results of this study suggest that the isolation distances vary widely ranging from 106 m–5.46 km in sand aquifers, 292 m–13.5 km in gravel aquifers and 2.4–58.7 km in coarse gravel aquifers. The gradient change of groundwater from 0.001 to 0.05 resulted in the isolation distance at the highest gradient position being 2–30 times greater than that at the lowest gradient position. There was a difference in the influence of the thickness of the vadose zone. For example, under the same conditions, with the increase of the thickness of the aeration zone, the isolation distance will be reduced by 1.5–5 times, or under the same thickness of the aeration zone, the isolation distance will be significantly shortened. Accordingly, this needs to be determined based on specific safety isolation requirements. In conclusion, this research has important guiding significance for the environmental safety assessment technology of municipal solid waste landfill.

Geotextile clogging at different stages of municipal solid waste landfills co-disposed with bottom ash

Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is a common way for BA management. However, BA co-disposal in MSW landfills may accelerate geotextile clogging and reduce the performance of leachate collection system. This study compared geotextile clogging in a simulated MSW landfill leachate (MSWL) and a BA co-disposed landfill leachate (BAL) at different landfill stages. Geotextile clogging test was conducted using the MSWL and BAL taken from the simulated landfills on the 10th, 80th, 140th and 200th day, respectively. The results demonstrated that geotextile clogging varied with landfill age, due to the change of leachate characteristics. The mass of clogging material in geotextiles with BAL increased from 0.45 g to 2.74 g, which was 43.87%-63.73% greater than those with MSWL. The formation of biofilm was the main contributor for the geotextile clogging. At the same stage, the amount of biofilm formed on geotextile in different leachate was comparable. However, the amounts of CaCO₃ precipitation on geotextile in BAL were 3.85-10.44 times of those in MSW leachate. The pH of leachate played a critical role in CaCO₃ precipitation. The microbial analysis revealed that the co-disposal of the BA greatly influenced the microbial community diversity and structure.

A bilayer coarse-fine infiltration system minimizes bioclogging: The relevance of depth-dynamics

Bioclogging is a main concern in infiltration systems as it may significantly shorten the service life of these low-technology water treatment methods. In porous media, biofilms grow to clog partially or totally the pore network. Dynamics of biofilm accumulation (e.g., by attachment, detachment, advective transport in depth) and their impact on both surface and deep bioclogging are still not yet fully understood. To address this concern, a 104 day-long outdoor infiltration experiment in sand tanks was performed, using secondary treated wastewater and two grain size distributions (GSDs): a monolayer system filled with fine sand, and a bilayer one composed by a layer of coarse sand placed on top of a layer of fine sand. Biofilm dynamics as a function of GSD and depth were studied through cross-correlations and multivariate statistical analyses using different parameters from biofilm biomass and activity indices, plus hydraulic parameters measured at different depths. Bioclogging (both surface and deep) was found more significant in the monolayer fine system than in the bilayer coarse-fine one, possibly due to an early low-cohesive biofilm formation in the former, driven by lower porosity and lower fluxes; under such conditions biomass is favorably detached from the top layer, transported and accumulated in depth, so that new biomass might colonize the surface. On the other hand, in the bilayer system, fluxes are highest, and the biofilm is still in a growing phase, with low biofilm detachment capability from the top sand layer and high microbial activity in depth, resulting in low bioclogging. Overall, the bilayer coarse-fine system allows infiltrating higher volume of water per unit of surface area than the monolayer fine one, minimizing surface and deep bioclogging, and thus increasing the longevity and efficiency of infiltration systems.