## 3 Technologies for Treating Landfill Leachate
### Membrane Technology  
Currently, the most widely used membrane technologies for landfill leachate are membrane bioreactors (MBRs) and membrane distillation (MD). Table 6 presents the efficiencies of membrane treatment for landfill leachate. In the last decade, nanofiltration (NF) and reverse osmosis (RO) were extensively used for treatment of landfill leachate due to stringent legal regulations. [PERSON] [148] investigated the treatment of landfill leachate using RO membranes (XLE) and NF membranes (NF90 and NF270), achieving significant treatment efficiency. Both the XLE and NP90 membranes demonstrated COD and TOC removal rates exceeding 80%. However, the application of RO and NF membranes posed challenges of membrane fouling. Ultrafiltration (UF) is a low-pressure (40-1000 kPa) membrane process that yields higher permeate flux and saves significant operating costs compared to NF/RO [149]. [PERSON] [149] investigated the removal of selected heavy metals from landfill leachate by electrospun polyacrylic acid (PAA)/polyallylamine hydrochloride (PAH)-laminated UF membranes (PAA/PAH-UF). The effect of the leachate matrix on metal removal by the PAA/PAH-UF membrane was also examined. In synthetic metal solutions, the PAA/PAH-UF membrane exhibited 38-85% higher removal efficiency when compared to the unmodified membrane. However, due to the relatively large pore size of UF, it is not commonly employed. MBR technology has emerged as a state-of-the-art biological treatment solution for mature landfill leachate management, particularly through its unique combination of microbial degradation and precise membrane separation [150]. [PERSON] et al. [151] combined a MBR and NF technology to treat leachate, and this system provided good removal of COD (87%). A two-stage MBR system was applied to the treatment of partially stabilized leachate from solid waste landfill in Thailand, and during a steady operation of 200 days, BOD, COD, and NH\({}_{3}\)-N removals were found to be 99.6, 68, and 89%, respectively [152]. [PERSON] et al. [153] treated landfill leachate using MBR with different configurations. An aerobic MBR (AMBR) system was operated in three phases. In the first phase, an AMBR alone, in the second phase, an anaerobic reactor followed by an anoxic reactor and an AMBR, and in the third phase an anoxic reactor followed by an AMBR were operated. The three MBR configurations removed more than 93%, 64.8%, and 59% of BOD, COD, and total nitrogen, respectively. [PERSON] et al. [154] engineered an innovative hybrid membrane bioreactor-nanofiltration (MBR-NF) system through strategic membrane replacement, substituting conventional microfiltration (MF, 0.1-0.2 um pore size) with polyamide thin-film composite \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Method** & **pH** & **Parameter** & \
\begin{tabular}{c} **Concentration** \\ **(mg/L)** \\ \end{tabular} &
\begin{tabular}{c} **Removal** \\ **Rate (\%)** \\ \end{tabular} & **Ref.** \\ \hline GSBR & 7.5 & \(\mathrm{COD_{f}}\) & 810.0 & 67.0 & [139] \\  & \(\mathrm{COD_{i}}\) & 267.0 & & 67.0 & [139] \\ AGR & 7.5 & \(\mathrm{COD_{f}}\) & 1149.0 & & \\  & \(\mathrm{COD_{i}}\) & 287.0 & 75.0 & [140] \\ A/O & 8.2 & \(\mathrm{COD_{i}}\) & 3387.7 & & \\  & \(\mathrm{COD_{f}}\) & 1605.6 & & 52.9 & [141] \\ USAB & 7.5 & \(\mathrm{COD_{i}}\) & 6000.0 & & \\  & \(\mathrm{COD_{f}}\) & 900.0 & 85.0 & [146] \\ USAB & 7.1 & \(\mathrm{COD_{i}}\) & 73,000.0 & & \\  & \(\mathrm{COD_{f}}\) & 12,848.0 & & 82.4 & [147] \\ TBFR & 7.6 & \(\mathrm{COD_{i}}\) & 2360.8 & & \\  & \(\mathrm{COD_{f}}\) & 272.7 & & 88.5 & [142] \\ \hline \hline \end{tabular} Note: : refers to initial; \(\mathrm{f}\) refers to final; ASP refers to activated sludge process; SBR refers to sequencing batch reactor; GSBR refers to granular sludge SBR; AGR refers to aerobic granular reactor; A/O refers to continuous plug-flow multistage anoxic/oxic; USAB refers to up-flow anaerobic sludge blanket; TBFR refers to tower biofilter.  
\end{table} 
Table 5: _Cont._nanofliltration membranes.