## 3 Technologies for Treating Landfill Leachate
### Membrane Technology
By comparing the treatment effect of the two different reactors on landfill leachate, as a result, the performance of the MBR-NF was 20-30% higher than that of the MBR-MF in removing refractory organics. MD, an emerging thermally-driven desalination technology, operates through vapor pressure differentials across hydrophobic microporous membranes (pore size 0.1-0.5 \(\upmu\)m). This process demonstrates exceptional hypersaline concentration capabilities, achieving brine salinity levels of 25-30% \(w/w\)--3-5 times higher than conventional pressure-driven membrane technologies like NF (5-8% salinity limit) and RO (7-10% salinity limit) [155; 156]. The technical merits of MD in landfill leachate treatment are threefold: (1) effective operation at moderate temperatures (60-80 \({}^{\circ}\)C) with low-grade thermal energy (specific energy consumption 120-180 kWh/m\({}^{3}\)), (2) simultaneous removal of multi-contaminants through combined vapor-liquid equilibrium mechanisms, and (3) compatibility with high osmotic pressure solutions (>5 MPa) [157; 158; 159]. However, due to the high operational energy consumption required to maintain the necessary temperature driving force in MD processes, their cost-effectiveness may be lower compared to other membrane technologies [160]. [PERSON] [161] pioneered the application of surface-modified direct contact membrane distillation (DCMD) for leachate treatment. Under optimized conditions (feed temperature 65 \({}^{\circ}\)C, permeate temperature 20 \({}^{\circ}\)C, cross-flow velocity 0.3 m/s), the system achieved remarkable contaminant removal efficiencies: 94.2% COD, 91.5% sulfate, and 93.8% hardness (as CaCO\({}_{3}\) equivalent), with concurrent 98.4% ammonia rejection and >90% heavy metal removal (Cr\({}^{6+}\), Zn\({}^{2+}\), and Pb\({}^{2+}\)). [PERSON] [162] engineered an integrated two-stage membrane distillation (ITMD) system with optimized thermal gradients (feed stage: 75 \(\pm\) 2 \({}^{\circ}\)C, permeate stage: 15 \(\pm\) 1 \({}^{\circ}\)C), achieving exceptional contaminant removal efficiencies of 99.2-99.8% COD, >99.5% inorganic salts (TDS < 50 mg/L), and 99.1-99.7% metal ions (Cr\({}^{6+}\), Pb\({}^{2+}\), and Cd\({}^{2+}\)) through synergistic vapor-liquid separation mechanisms. However, practical MD applications face two critical challenges: (1) irreversible membrane fouling caused by organic foulants (humic acids) and scaling (CaSO\({}_{4}\)/CaCO\({}_{3}\) deposition), and (2) concentrated brine management (salinity >25% \(w/w\)) requiring specialized disposal protocols. To address these limitations, [PERSON] [163] developed a novel pretreatment strategy using lignin-derived biochar coupled with MD. Compared to the MD system without adsorption assistance, this MD showed better performance, such as 40% total membrane flux recovery, a 42% increase in filtration flux, and a 53% reduction in concentrate yield. Membrane treatment for landfill leachate offers several advantages, including stable effluent quality, effective removal of impurities, small footprint, and ease of operation and maintenance. However, its disadvantages are relatively high treatment costs, susceptibility to damage and fouling, which results in frequent replacement, and specific requirements for raw wastewater quality.