Under the environmentally green slopes of the presently utilized landfills are sophisticated barrier systems that keep waste firmly imprisoned. Most importantly, the landfill liner, in fact, accomplishes the task of separating waste from the outer world. These are not simple plastic covers; these are high-tech geosynthetics developed to disallow the contamination of soil and water for a prolonged period. The existence and usage of these landfill liner materials as well as their effectiveness pave a way for the protection of natural resources while the disposal of municipal solid waste (MSW) still remains a solution to the ever-growing global waste problem.
Before the introduction of the sanitary landfill system that became a standard, waste was mostly disposed of in open dumps. Rains that soak through these dumps generate leachate—a very harmful liquid—directly from the riddled soil where heavy metals, pathogens, and organic compounds eventually end up, thus polluting the groundwater. Environmental crises in the middle of the previous century were the turning point which led to the establishment of stricter rules such as the U.S. Resource Conservation and Recovery Act (RCRA). These laws made it compulsory to have modern landfill liners, which changed the face of landfills from mere pits of waste into elaborate engineering facilities for containment. The main function of the liner system is to reduce the level of leachate and control landfill gases, therefore, keeping safe the public health as well as nature.
Present-day landfill liners are mostly composite systems with each layer performing a separate function:
Great care is taken to compact and level the soil base in order to provide a solid and even support for the liner system.
The clay used is of very low permeability (≤ 1x10⁻⁷ cm/s) or it can be a sodium-bentonite based GCL that thus become the main water barriers. Once bentonite is hydrated it expands and seals small holes thereby giving a self-healing feature under the geomembrane.
While ending the clay or GCL, polymer sheets made of high-density polyethylene (HDPE) or other materials act as the ultimate impermeable barrier. Their main function is to assure safety for decades against the penetration of leachates.
Nonwoven geotextiles help the briquettes from snap injury due to erecting and material dropping operations.
Packing materials such as granules or specially fabric-like geonets are used for the effective collection of leachate, a process which thus helps in the relief of the primary liner and the direcion of the liquid to collection pipes.
There are overlaps between the functions of the clay and the geomembrane layers, thus providing the double functionalities. The hermetic layer is the plastic one, while the earth layer is the auxiliary, backing up it by decelerating the leaks and resealing small perforations.
Besides others, the present boundary layer between the garbage and the environment tends to be pefomanced by geomembranes, thus selected are them due to their chemical resistance, longevity, and ease of installation. Usually, these are:
3.1.1 High-Density Polyethylene (HDPE): This is a very strong candidate for chemical resistance, it is almost impermeable, and it has good tensile strength. In specific circumstances, stress cracking may be induced, and the material is less flexible at low temperatures and thus seam welding should be done with care.
3.1.2 Linear Low-Density Polyethylene (LLDPE): This material has higher flexibility and elongation than HDPE, thus it can easily adjust to uneven surfaces of the subgrade, although the chemical resistance is a little bit lower than that of HDPE.
3.1.3 Polyvinyl Chloride (PVC): It is a flexible material which can be easily welded. However, due to the migration of plasticizer and low chemical resistance, the lifetime is limited to a few years.
3.1.4 Flexible Polypropylene (fPP) and Reinforced Polyethylene: The two main features, i.e., the flexibility and the chemical resistance, are kept intact, while the reinforced version is equipped with a scrim for higher tensile strength.
GCLs are essentially on-site liners constructed with bentonite, which is the major component of the nature, and they offer a wide range of advantages such as:
- Fast Installation: The installation of large rolls can be done very quickly in comparison with clay layers which are compacted on site.
- Uniform Quality: Every detail in the production of the material is strictly controlled, thus the product has both a uniform thickness and a fixed value of hydraulic performance.
- Extraordinary Hydraulic Barrier: The permeabilities of the hydrated bentonite layer can be as low as 1x10⁻⁹ to 1x10⁻¹⁰ cm/s.
- Repair the Little Holes by Themselves: If the bentonite comes into contact with water it expands so as to close small holes in the geomembrane lying over it.
The disadvantages are that it can be sensitive to chemicals and may experience a decrease in its ability to swell if the leachate has a high ionic strength.
Such mineral-origin barriers are very effective and possess significant adsorption capacities, specifically if they are constructed with the appropriate levels of compaction, moisture, and lift thickness that also contribute to the prevention of cracks or voids.
Landfill liners are made to last for several decades while waste may stay toxic for thousands of years. The main problems are:
4.1 Degradation Over Time: The process of oxidative degradation, stress cracking, and the loss of additives may be the reasons for the degradation of polymers. The use of carbon black and antioxidants better the longevity of polymers.
4.2 Resistance to Chemicals: The materials used for liners should be able to resist variations in the chemical composition of leachate, acids and solvents occurring in the long run.
4.3 Physical Hardships: The sinking down of the surface, an earthquake, and the penetration of roots (for the caps) are among the mechanical stresses that could be imposed on liners.
- Advanced Polymers & Nanocomposites: Improving chemical resistance, mechanical strength, and barrier properties.
- Apart from the current systems for monitoring, there could be intelligent monitoring systems that use sensors to identify changes such as temperature, strain, or leakage and thus allow prompt maintenance to be carried out.
- Biochemical Barriers: Modules that allow microbial decomposition of pollutants prior to their movement through the soil.
Without landfill liners, the waste management system would not be able to function effectively. These materials are very good examples of the “concentrate and contain” method that is used and, thereby, they guarantee environmental protection and safety disposal. It takes a great amount of knowledge in the fields of geotechnical engineering, hydrogeology, and polymer science to be able to select, design, and put them in place. As global waste continues to increase, the innovation of these materials together with their prudent use is still pivotal to the development of sustainable waste infrastructure.
GEOSINCERE Geosynthetics (Shandong Geosino New Material Co., Ltd.) is devoted to the production of top-quality geosynthetics. The company produces the best HDPE geomembranes and other geosynthetic products with the use of state-of-the-art and fully automated production lines where $10 million has been invested. GEOSINCERE provides dependable engineering solutions, professional support, and reasonable prices for civil, mining, and environmental projects anywhere in the world. Their products, which are durable, high-performing and cost-efficient, have earned them the status of a reliable partner for landfill and containment projects.
