## 2 The Formation, Characteristics, and Composition of Landfill Leachate
### Emerging Contaminants  
In recent years, advancements in analytical technologies have led to the detection of a growing number of emerging contaminants (ECs) in landfill leachate [32]. These pollutants encompass both inorganic (e.g., heavy metals) and organic (e.g., detergents and pesticides) compounds, including personal care products (PCPs), pharmaceuticals, insecticides, flame retardants, surfactants, and related chemical substances [83]. These compounds are typically either recently detected in environmental matrices or have only recently had their impacts recognized. Such contaminants lack comprehensive regulatory frameworks due to insufficient data regarding their environmental and health implications.  
Notably, many persist in environmental matrices and bioaccumulate through food chains, posing latent risks to ecosystems and human health over extended temporal scales [33]. These substances exhibit bioaccumulative potential, environmental persistence, and intermittent endocrine-disrupting activity, demonstrating significant ecotoxicological impacts on biota and public health even at environmentally relevant concentrations [84]. For example, certain pharmaceuticals possess endocrine-disrupting capabilities, including interfering with the reproduction and development of animals, and these substances may enter the environment and ultimately come into contact with humans through various pathways, thereby increasing the likelihood of cancers and birth defects in humans [85; 44; 86]. However, traditional water treatment methods are often ineffective in removing them, and as a result, these substances are frequently unintentionally released into the environment [84; 87]. Therefore, technological retrofitting and upgrades of existing systems are imperative. For ex  
\begin{table}
\begin{tabular}{c c c} \hline
**Species** & **Examples** & **Ref.** \\ \hline \multirow{3}{*}{Dissolved organic matter} & Organic acid & \\  & Humic acid-like compounds & [56; 60; 61] \\  & Fulvic acid-like compounds & \\ \hline \multirow{3}{*}{Metal ions} & Fe\({}^{2+}\), Fe\({}^{3+}\), Mn\({}^{2+}\), Zn\({}^{2+}\), Pb\({}^{2+}\), & \\  & Cr\({}^{3+}\), Cr\({}^{6+}\), Ni\({}^{2+}\) & [62; 63; 64] \\ \hline \multirow{3}{*}{Metalloid ions} & Cl\({}^{-}\), PO\({}_{4}\)\({}^{3-}\), SO\({}_{4}\)\({}^{2-}\), As\({}^{3+}\), As\({}^{5+}\) & [65; 66] \\ \hline \multirow{3}{*}{Antibiotics} & Macrolides & \\  & Quinolones & \\  & Sulfonamides & \\  & Tetracyclines & \\ \hline \multirow{3}{*}{Endocrine disrupters} & Polycyclic aromatic & \\  & hydrocarbons & \\  & Polychlorinated biphenyls & [69; 70; 71] \\  & Bisphenol A & \\ \hline \multirow{3}{*}{Pesticides} & Dichlorophenyltrichlorootehane & [72; 73] \\  & Hexachlorocyclohexane & \\ \hline \multirow{3}{*}{Pharmaceutical and personal care products} & Bezafibrate & \\  & Carbamazepine & \\  & Sulfamethoxazole & [74; 75; 76] \\  & Metoprolol & \\ \hline \multirow{3}{*}{Commercial organic matter} & Perfluoroalkyl acids & \\  & Perfluorocotane sulphonate & [77; 78; 79] \\ \hline \multirow{3}{*}{Microplastics} & Polystyrene & \\  & Polypropylene & \\  & Polyethylene & [80; 81; 82] \\ \cline{1-1}  & Polyvinyl chloride & \\ \hline \end{tabular}
\end{table}
Table 2: Composition of landfill leachate [34].  
ample, [PERSON] et al. [88] innovatively engineered a zirconium-based metal-organic framework (Zr-MOF) to enhance both selective adsorption and photocatalytic degradation efficiency of EC, and the synthesized catalyst VNU-1 exhibited 100% photodegradation efficiency for ampicillin, limomycin, and sulfamethoxazole. [PERSON] et al. [89] fabricated a heterojunction catalyst by supporting Co\({}_{3}\)O\({}_{4}\) nanoparticles on \(\beta\)-MnO\({}_{2}\) nanorods, and about 99.4% of tetracycline underwent rapid oxidative degradation within 60 min in this system.