## 4 Conclusions  
The results showed that, in the case of all investigated processes (IME, IME/H\({}_{2}\)O\({}_{2}\) and IME\({}^{*}\)), the separation of HS in the PC step improved the efficiency of COD removal. PC almost eliminates the negative phenomena of the settling flocks of HS on the microelectrodes and blocks their active surface. Studies on the IME process showed a high efficiency of COD removal--the maximum efficiency of the process ranged from 34.4 to 92.2%, depending on the doses of microelectrodes used (Fe/GAC from 20/2 to 40/120 g/g/L), and was obtained for the process carried out in a modified way (after PC) at pH 3 and for 120 min. It is also worth noting that, for lower doses of GAC, the oxidation processes (mainly ZVI) dominate over the sorption process. For optimal conditions of the process, after each step of the following treatments, the PC, m-IME and IME/H\({}_{2}\)O\({}_{2}\) processes, an increase in COD removal was observed, and it was up to 12.5%, 44.6% and 82.2%, respectively. COD removal correlated well with a decrease in TOC values from 381 in raw LL to 326 mg/L after PC and after m-IME and m-IME/H\({}_{2}\)O\({}_{2}\) was 130 mg/L and 88 mg/L, respectively. The results indicate a strong correlation between the effectiveness of the IME process and doses of Fe and GAC microelectrodes. However, higher doses of Fe and GAC resulted in a higher efficiency of COD removal; the increase was not the same across the range of doses. Changes in GAC microelectrodes affected the effectiveness of the process much more strongly. The COD removal efficiency rose also with the time of the process up to 120 min. The highest increase in the efficiency of the m-IME process for the microelectrode doses of Fe/GAC 40/4 and 40/10 g/g/L was observed for 120 min: 38.4 and 44.6%, respectively. The addition of hydrogen peroxide from the beginning of the m-IME/H\({}_{2}\)O\({}_{2}\) process improved the efficiency of COD removal compared to the m-IME process. After 120 min of the IME/H\({}_{2}\)O\({}_{2}\) process, the efficiency of COD removal for the ratio COD/H\({}_{2}\)O\({}_{2}\) = 1/2 was 76.0%, which was almost two times higher than in the case of the m-IME process. What is more, the addition of that dose of H\({}_{2}\)O\({}_{2}\) after 120 min of the m-IME process allowed us to achieve better results in a shorter time--after a total time of 150 min of the process (120 min m-IME + 30 min m-IME/H\({}_{2}\)O\({}_{2}\)), the COD removal was almost equal to that obtained after 240 min of the m-IME/H\({}_{2}\)O\({}_{2}\) process (77.7%) with the addition of H\({}_{2}\)O\({}_{2}\) from the beginning, regardless of the pH correction. Additionally, high efficiency in color removal was achieved--the solution became almost colorless. The values of UV\({}_{254}\) absorbance were reduced by 99.0%, and a significant improvement in biodegradability was observed by the rise of the BOD\({}_{5}\)/COD ratio up to 0.39. All of those factors allow us to conclude that the IME process conducted in the way proposed in presented studies improves the quality of LL and enables biological treatment in municipal plants. The presented results show that after 24 h of soaking in LL, the GAC still could adsorb some impurities from the new portion of LL--after transferring the preliminarily soaked in LL GAC to the new batch of LL and after 60 min of an additional sorption process, an additional value of COD removal was obtained--up to 38.1%. Therefore, the presented results clearly show that the assumption that is made by some authors that after soaking GAC in LL the sorption is eliminated from the IME process is not correct. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15042201/s1](https://www.mdpi.com/article/10.3390/app15042201/s1)]([https://www.mdpi.com/article/10.3390/app15042201/s1](https://www.mdpi.com/article/10.3390/app15042201/s1)). Conceptualization, methodology and validation: [PERSON] and M.K. ; formal analysis: J.L.