## 2 Materials and Methods  
As microanodes, grey cast-iron-waste material after CNC machining processes (turning, milling, etc.) was used. As microcatods, granulated activated carbon (GAC) 4H Gryfskand from Hajnowka in Poland (Table 2) was used. Cast-iron and GAC filings were prepared before use according to the procedure described in the Supplementary Materials. The LL leachate samples were collected from Lubna--municipal waste landfill in Baniocha, Poland. Lubna was the largest municipal landfill in Poland; however, it was closed in 2011. LL were collected in polypropylene canisters and refrigerated until analysis (such LL were treated as raw leaches). Some samples of LL were acidified to pH 2, 3 or 4 and left for sedimentation within 4 h. Then, the leachate was separated from the sediment of precipitated humic substances (HSs) and refrigerated until analysis (LL after preliminary coagulation--PC). Studies on PC were performed to determine the effect of the removal of humic substances (HSs) on the efficiency of the IME process. The experiments preceded by PC were marked as a modified process (m-IME). The experiments conducted on raw leachates (without PC) were named as the classic process (c-IME) and were carried out only at pH 3. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Name of the Process** & **Characteristics of L** & **Characteristics of Microelectrodes** & **Process Parameters** & **Parameters** & **IME Efficiency** & **Bibliography** \\ \hline \multirow{4}{*}{ \begin{tabular}{c} Iron–carbon micro–electrolysis (ICME) coupled \\ with H\({}_{2}\)O\({}_{2}\) \\ 97.0-102.9 mgO\({}_{2}\)/L, \\ BODs/SOD 0.049 \\ \end{tabular}  } & \begin{tabular}{c} Cast-iron scraps soaked in 2\% \\ H\({}_{2}\)SO\({}_{4}\) and rinsed \\ in water. GAC \\ size 0.2–1.5x \\ 4 mm with a \\ specific surface area of \\ 97.0-102.9 mgO\({}_{2}\)/L, \\ 1500.200; \\ water. \\ \end{tabular}  & \begin{tabular}{c} Cylindrical reactor: \\ pH 0.64; 2; 4; 6; 7.36, \\ C/Fe with an area \\ 500000; \\ 4 mm with a \\ specific surface area of \\ 925.2 m\({}^{2}\)/g \\ 1500.200; \\ water. \\ \end{tabular}  & \begin{tabular}{c} C/Fe with an area \\ 500000; \\ 687500; 875000; \\ 1002836; \\ H\({}_{2}\)O\({}_{2}\) 693.1; 1000; \\ 1500.200; \\ water. \\ \end{tabular}  & \begin{tabular}{c} C/Fe with an area \\ 500000; \\ 687500; 87500; \\ H\({}_{2}\)O\({}_{2}\) 369.1; 1000; \\ 1500.200; \\ water. \\ \end{tabular}  & \ \begin{tabular}{c} Removal: \\ COD 86.9\% \\ pH 3.8 \\ 1500.200; \\ water. \\ \end{tabular}  & \begin{tabular}{c} Removal: \\ COD 40.27\% at \\ 100.25\%–total in \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ 100.25 \\ \end{tabular}  &  
An internal microelectrolysis (IME) process was conducted in glass reactors filled with 0.2 L of the LL samples. The following doses of microelectrodes were used in different mass ratios: cast iron (Fe): 4; 6; 8; 9; 12; 16; 18; 20; 24 30; 36; 40; and 48 g/L and GAC: 2; 3; 4; 5; 6; 7; 7; 5; 8; 10; 12; 14; 15; 20; 30; 40; 60; 80; 90; and 120 g/L. In the \(\mathrm{IME/H_{2}O_{2}}\) process, additional \(\mathrm{H_{2}O_{2}}\) in a proper \(\mathrm{COD/H_{2}O_{2}}\) mass ratio (1/1, 1/2 or 1/3) was added (at the beginning of the process or after 120 min of m-IME). To assure proper contact between the microelectrodes and LL, mechanical stirring was applied (120 rpm). After an appropriate process time, the sample was alkalized to pH 9 (with 3M NaOH) to inhibit the oxidation process and remove \(\mathrm{Fe^{2+}/Fe^{3+}}\) ions in the coagulation process. Additionally, to samples after the m-\(\mathrm{IME/H_{2}O_{2}}\) process, the proper amount of catalase solution was added to remove residual \(\mathrm{H_{2}O_{2}}\). Additionally, experiments with the use of GAC 4H subjected to preliminary saturation, before the IME process in the LL, were conducted. GAC was soaked for 24h in raw LL and LL after PC in pH 3.