## 3 Results and Discussion
### The Impact of Different Parameters on the Efficency of IME Process  
#### 3.2.1 The Impact of pH and PC on the Efficiency of IME Process  
The results of studies on the impact of pH values (2, 3 and 4) on the efficiency of the m-IME process (after 120 min) for Fe/GAC doses ranging from 20/2 to 40/120 g/L are presented in Figure 1. The results show a clear relationship between the efficiency of the PC process and pH--the decrease in the pH value increased the COD removal of the LL caused by the PC increase. At pH 2, the PC process allowed for a reduction in the COD value by 15.6%, at pH 3 by 9,4% and at pH 4 by with 3.1% (Figure 1). The PC process was first described by [PERSON] et al. [35], who used it to treat LL from a stabilized municipal waste landfill before the Fenton process. The PC process at pH 2, 3 and 4 allowed the reduction of COD values by 42.2, 33.3 and 22.2%, respectively [35]. The high efficiency of PC was probably due to the presence of a large amount of humic substances in the LL, as evidenced by the low degree of the biodegradability of organic compounds present in the leachate (BOD\({}_{5}\)/COD 0.073) [35]. The PC process is based on the phenomenon of decreasing the solubility of humic substances as the pH value of the LL decreases. The decrease in the solubility of these substances results from the regression of their dissociation and the disappearance of the negative charge stabilizing the macromolecule. [PERSON] et al. obtained a 22.4% reduction in COD value in the PC process at pH 3 (before the IME/O\({}_{3}\)/H\({}_{2}\)O\({}_{2}\) process). Similarly, [PERSON] et al., in the PC process at pH 3 applied before the ZVI process, achieved a reduction in COD values by 22.9% [36]. Lower values of COD removal by PC obtained in this research were probably related to the lower amount of humic substances in LL. The highest COD removal was obtained in the m-IME process conducted at pH 2 in the full range of Fe/GAC doses--20/2-40/120 g/L (Figure 1a-c). The COD removal obtained in the same process conducted at pH 3 was slightly lower, maximally by 11,0% (Figure 1a-c). The lowest purification effect was obtained in the m-IME process conducted at pH 4 (Figure 1a-c). The COD removal was lower by 14.1-8.6% for all Fe/GAC ranges of doses than COD removal obtained in pH 3. \begin{table}
\begin{tabular}{c c c c c} \hline
**Sample nr** & **1.1** & **1.2** & **1.3** & **1.4** \\ \hline COD & 1073 & 1045 & 1092 & 1715 \\
[mg O\({}_{2}\)/L] & & & & \\ \hline pH & 7.81 & 7.31 & 8.20 & 7.80 \\ \hline Conductivity [mS/cm] & 11.8 & 11.6 & 8.19 & 9.8 \\ \hline N\({}_{\text{total}}\) [g/L] & 298 & 236 & 343 & 432 \\ \hline Cl\({}^{-}\) [mg/L] & 420 & 390 & 370 & 412 \\ \hline TOC [mg/L] & 376 & 362 & 381 & 543 \\ \hline BOD\({}_{5}\) & 92 & 104 & 131 & 190 \\ [mg O\({}_{2}\)/L] & & & & \\ \hline BOD\({}_{5}\)/COD & 0.08 & 0.10 & 0.12 & 0.11 \\ \hline N-NH4 & 268 & 197 & 294 & 387 \\
[g/L] & & & & \\ \hline Absorbance & 11.80 & 11.75 & 11.82 & 11.92 \\
254 nm & & & & \\ \hline SUVA [m\({}^{2}\)/gC] & 0.0314 & 0.0324 & 0.0309 & 0.0219 \\ \hline \end{tabular}
\end{table} 
Table 3: Characteristics of raw LL samples. The effect of pH on the efficiency of the m-IME process varied depending on the Fe/GAC dose. The strongest effect of pH on the process efficiency was observed for the lower doses of microelectrodes, up to Fe/GAC doses of 20/60, 30/60 and 40/80 g/g/L. Above these doses, the differences in COD removals between pH 2 and pH 3 were less significant (Figure 1) and did not exceed 3,1%. In the m-IME process at pH 4, this effect was not observed. The COD removal obtained for all Fe/GAC doses was about 10% lower than  
Figure 1: Total COD removal after 120 min of the m-IME process conducted after PC at pH: 2, 3 and 4 for Fe/GAC doses in range: (**a**) 20/2–20/60 g/L, (**b**) 30/3–30/90 g/L and (**c**) 40/4–40/120 g/L— sample 1.1.  
the COD removal obtained at pH 3. This phenomenon can be explained by the complex mechanism of the IME process.