## 3 Results and Discussion
### Hybrid Process m-IME/H\({}_{2}\)O\({}_{2}\)  
The results of the studies comparing the efficiency of the total COD removal in the m-IME process and m-IME/H\({}_{2}\)O\({}_{2}\) process, with the addition of H\({}_{2}\)O\({}_{2}\) at the beginning of the m-IME process (t\({}_{\text{IME}}\)0) and the sorption process for the GAC dose used in the m-IME process (10g/L), are presented in Figure 6 for sample 1.3. The hydrogen peroxide was added in the m-IME/H\({}_{2}\)O\({}_{2}\) process in three different doses of H\({}_{2}\)O\({}_{2}\) in relation to COD: 1/1, 2/1 and 3/1. Generally, the addition of hydrogen peroxide from the beginning of the m-IME/H\({}_{2}\)O\({}_{2}\) process resulted in an improvement of the efficiency of COD removal compared to the m-IME process. For the dose of hydrogen peroxide in the mass ratio COD/H\({}_{2}\)O\({}_{2}=1/1\), the improvement of COD removal ranged from 8.0% after 15 min to 10.7% after 240 min. For higher doses (mass ratio COD/H\({}_{2}\)O\({}_{2}=1/2\) and 1/3), the improvement was higher and rose with the time of the process: from 11.6% after 15 min to 23.2% after 240 min for COD/H\({}_{2}\)O\({}_{2}=1/2\) and from 20.5% after 15 min to 31.3% after 240 min for COD/H\({}_{2}\)O\({}_{2}=1/3\). It is also worth noticing that the differences in efficiency between higher doses (COD/H\({}_{2}\)O\({}_{2}\) 1/2 and 1/3) decreased with time, and, after 60 min, it almost  
Figure 5: pH changes in time of m-IME process (sample 1.3). disappeared. After 120 min of the process conducted with H\({}_{2}\)O\({}_{2}\) the efficiency of COD removal (for ratio COD/H\({}_{2}\)O\({}_{2}\) = 1/2) was 76,0%, which was almost two times higher than in case of the m-IME process without H\({}_{2}\)O\({}_{2}\). In the available literature, there are some papers in which the authors investigated the efficiency of the IME process with H\({}_{2}\)O\({}_{2}\) added from the beginning of the process. [PERSON] achieved a COD removal of 74.59% at a H\({}_{2}\)O\({}_{2}\) dose of 12.32 mL/L [5], whereas [PERSON] achieved a COD removal of 79.2% at a H\({}_{2}\)O\({}_{2}\) dose of 0.75 mM [28]. Other authors obtained higher efficiency in COD removal, but they used higher doses of H\({}_{2}\)O\({}_{2}\). [PERSON] et al. achieved a COD removal of 86.9% at a dose of H\({}_{2}\)O\({}_{2}\) of 1687.6 mg H\({}_{2}\)O\({}_{2}\)/L [29] and [PERSON] et al. obtained a COD removal of 90.2% at a dose of H\({}_{2}\)O\({}_{2}\) of 3.57 g H\({}_{2}\)O\({}_{2}\)/L [26] or carried out a process with aeration of [PERSON] et al. (D COD 87.0%, dose of H\({}_{2}\)O\({}_{2}\) 100 mg H\({}_{2}\)O\({}_{2}\)/L and D COD 93.0%, dose of H\({}_{2}\)O\({}_{2}\) 200 mg H\({}_{2}\)O\({}_{2}\)/L) [2; 3; 4]. In methods based on hydroxyl radicals, the excess of hydrogen peroxide could inhibit the process by acting as hydroxyl radical scavengers. To overcome this problem, some authors recommend dosing H\({}_{2}\)O\({}_{2}\) in stages [37; 38]. Therefore, in the presented work, the effect of the addition of H\({}_{2}\)O\({}_{2}\) in the m-IME process was investigated not only at the beginning of the process but also after 120 min. As was mentioned before, the pH value of the solution increased during the m-IME process, and, after 30 min of the process, it reached values over 6. Therefore, in the presented study also, the effect of the pH correction to a value of 3, before the addition of H\({}_{2}\)O\({}_{2}\), was investigated. The results of the research on the efficiency of the m-IME/H\({}_{2}\)O\({}_{2}\) process carried out with H\({}_{2}\)O\({}_{2}\) added after 120 min of the z-IME process with and without pH correction are presented in Figure 7 for sample 1.3. The addition of hydrogen peroxide after 120 min of the m-IME/H\({}_{2}\)O\({}_{2}\) process (t\({}_{\rm{IME}}\) 120 min) caused a further decrease in COD values compared to the m-IME process. The highest increase in COD removal was observed up to 15 min after the addition of H\({}_{2}\)O\({}_{2}\).