## 3 Technologies for Treating Landfill Leachate
### Physical-Chemical Method
#### 3.1.2 Coagulation-Flocculation Method  
Coagulation-flocculation (CF) represents a relatively straightforward yet efficient process, particularly effective in the treatment of mature landfill leachate. For young leachate, it serves as an advantageous pretreatment step, enhancing the efficacy of subsequent physicochemical or biological treatment processes in municipal domestic landfills [107]. CF employs chemical coagulants to neutralize and aggregate suspended particles in leachate through charge neutralization and aggregation mechanisms, facilitating the formation of denser flocs that are subsequently efficiently separated via sedimentation. Table 3 lists the efficiency of some physicochemical methods for landfill leachate. [PERSON] [108] conducted a comparative study on leachate treatment efficiency using ultrasonic-assisted CF with sodium ferrite versus standalone ultrasonication. Experimental results demonstrated that the integrated process achieved significantly higher removal rates of 87.5% for COD and 88.6% for color under optimized parameters (15 min ultrasonication duration, pH 5.5). This performance markedly surpassed that of ultrasonic treatment alone, which exhibited limited efficacy, with both COD and color removal rates below 50%.  
[PERSON] [109] investigated the efficacy of ferric chloride-based coagulation pretreatment and its synergistic combination with powdered activated carbon (PAC) adsorption for leachate treatment. Experimental data revealed that the optimized ferric chloride dosage (12 g/L as Fe\({}^{3+}\)) achieved maximum removal efficiencies of 50% COD, 89.9% turbidity, and 80% color in single-stage coagulation. Notably, the integration with PAC adsorption under optimized operational parameters significantly enhanced treatment performance, attaining 59% COD removal along with 99% reductions in both turbidity and color. Thiscomparative analysis demonstrates that the coagulation-adsorption integrated system provides substantially superior contaminant removal capabilities compared to standalone coagulation processes, confirming its technical viability for advanced leachate treatment.  
[PERSON] [110] systematically investigated the application of a cationic polymer flocculant (Himoloc DR3000) in CF treatment for landfill leachate. Through central composite design optimization, the study established optimal operational parameters: pH 7.66, coagulant dosage 9.48 g/L, flocculant dosage 9.05 mL/L, and mixing duration 10.22 min. Under these optimized conditions, the process achieved significant contaminant removal efficiencies of 68.81% for color, 77.46% for polyphenols, and 80.99% for nitrate. This parametric optimization demonstrates the technical feasibility of cationic polymer-enhanced CF processes in advanced leachate treatment.  
Landfill leachate treatment through physical methods demonstrates distinct advantages, including straightforward operability, reduced infrastructure demands, enhanced process efficiency, and favorable energy economics. However, the efficacy of these methods diminishes when confronting leachate containing recalcitrant macromolecular organic compounds or endocrine-disrupting chemical mixtures (EGCMs), presenting significant technical limitations in contaminant speciation management.