## 1 Introduction  
Landfill leachate is a highly contaminated liquid that forms when precipitation (e.g., rainwater) filters through waste materials in landfills. As a result of solid waste breaking down, this liquid comprises a variety of organic and inorganic compounds, as well as additional contaminants [1]. The landfill leachate's composition usually varies depending on the landfill age, the type of waste deposited, meteorological conditions, and the landfill operation methods [2]. Typical contaminants found in landfill leachate include ammonia, nitrates, phosphates, metals, and organic compounds [3]. Furthermore, compounds such as pesticides, pharmaceuticals, personal care products, endocrine-disrupting chemicals (EDCs), and industrial chemicals have been identified in raw landfill leachates, raising interest and attention due to their potential bioaccumulation and environmental risk [4, 5, 6]. The management and treatment of this complex mixture is a critical environmental challenge worldwide, as untreated landfill leachate can cause severe pollution to soil and water bodies, posing a serious threat to the environment and, by extension, to human health [7]. In Greece, studies on medium-sized landfills indicate that existing secondary treatment methods fail to meet regulatory discharge limits, highlighting the need for improvedtreatment technologies [8]. Globally, landfill leachate contains high concentrations of both biodegradable and persistent toxic compounds, making effective treatment essential for environmental protection [9]. Traditional methods of treating leachate include various technologies such as physicochemical and biological ones, membrane technology, and advanced oxidation [10; 11]. The physicochemical processes include coagulation/floculation, adsorption, chemical precipitation, and chemical oxidation. These processes are usually used in combination with other processes as a pre- or post-treatment to improve the quality of landfill leachate that is discharged to water bodies [12]. Coagulation and flocculation are processes applied to solutions where suspended solids are present, aiming to reduce the forces that hold suspended solids in the aqueous solution. In the coagulation process, chemical compounds such as ferric chloride or aluminum sulfate are added to neutralize or reduce the electrical charge of the suspended particles. In the flocculation process, to increase the formation of flocs, chemical compounds such as polymers are added. From the above, it is clear that the amount of chemicals used in these processes affects the cost of treating landfill leachate. In addition, the coagulation-floculation process produces large amounts of sludge [2; 12; 13]. Biological treatment technologies refer to the use of microorganisms to degrade organic pollutants and are categorized into aerobic and anaerobic processes. They can be used alone or in combination with other traditional methods to increase the effectiveness of the treatment [2]. These methods include aerated lagoons, activated sludge processes, trickling filters, sequence batch reactors (SBRs), etc., [14; 15]. The effectiveness of biological treatment technologies depends on their operating conditions being suitable for the growth of microorganisms. While these systems perform well in pollutant removal, they have several disadvantages, including the production of large quantities of sewage sludge (activated sludge), high electricity requirements (activated sludge), the need for an extensive land area (aerated lagoons), significant clogging and odor issues (trickling filters), and the requirement for specialized personnel (SBRs) [16; 17; 18]. Membrane technology is a fairly effective method used to treat landfill leachate by removing contaminants such as heavy metals, organic compounds, suspended solids, and microorganisms. Membrane technology includes reverse osmosis, nanofiltration, ultrafiltration, and membrane bioreactors [12; 19].