## 3 Results and Discussion
### The Impact of Different Parameters on the Efficency of IME Process
#### 3.2.3 Effects of Fe/GAC Doses  
The results of research on the efficiency of the m-IME process (pH 3, 120 min) with the use of Fe/GAC microelectrodes in the following ratios and doses are depicted:  
* On Figure 2: Fe/GAC dose range 20/2-40/120 g/L--sample 1.1,
* On Figure 3a: Fe/GAC ratio 10/1 in dose range 20/2-70/7 g/L--sample 1.2,
* On Figure 3b: Fe/GAC ratio 5/1 in dose range 20/4-70/14 g/L--sample 1.2,
* On Figure 3c: Fe/GAC ratio 2/1-12/1 in dose range 20/2-48/4 g/L--sample 1.2.  
However, the COD removal in the m-IME and c-IME processes increased with the increase in carbon and iron doses in the Fe/GAC; the dose of the microcathode in the system strongly affected that rise. Moreover, this increase was not the same across the dose range. In the m-IME process (sample 1.1--Figure 2a) for the Fe dose of 20 g/L, an intensive increase in the total COD removal was observed up to the Fe/GAC dose of 20/40 g/L (COD\({}_{\text{total}}\) removal 84.4%); in the case of 30 g/L up to the Fe/GAC dose of 30/60 g/L (COD\({}_{\text{total}}\) removal 90.6%); and in the case of 40 g/L up to the Fe/GAC dose of 40/40 g/L (COD\({}_{\text{total}}\) removal 92.2%). With a further increase in the GAC dose, the COD removal increased maximally by 6.2, 0.8%, for cast-iron doses of 20 and 30 g/L, respectively. For the Fe dose of 40 g/L, an increase in the GAC dose from 40 to 60 g/L did not cause any change in the COD removal.  
Figure 2: Total COD removal after 120 min of the m-IME and c-IME process at pH 3 for Fe/GAC microelectrode doses ranging (**a**) 20/2 to 20/60 g/L, (**b**) 30/3 to 30/90 g/L and (**c**) 40/4 to 40/120 g/L (sample 1.1).  
On the other hand, the m-IME process conducted with low GAC doses was characterized by a low efficiency of COD removal. In Fe/GAC doses ranging from 20/2 to 70/7 g/L, the total COD removal was from 36.1 to 44.3% (Figure 2a). In the case of Fe/GAC doses from 20/4 to 70/14 g/L, the total COD removal was in the range of 40.2-54.9% (Figure 2b).  
An increase in the cast-iron dose in the system for the fixed, low-carbon dose (2, 3 and 4 g/L) did not cause significant differences in the process efficiency in all ranges of Fe/GAC doses.  
Figure 3: Total COD removal after the m-IME process (120 min, pH 3) for Fe/GAC doses in the following ranges: (a) 20/2–70/7 g/L, (b) 20/4–70/14 g/L and (c) for Fe/GAC ratio 2/1–12/1 in range doses: 4/2–48/4, sample 1.2.  
ratios 2/1-12/1. In the range of Fe/GAC doses from 4/2 to 48/4 g/L, minor changes in the total COD removal were observed (Figure 2c). With the increase in the microanode dose from 4 to 24 g/L in the system, and the fixed microachode dose of 2 g/L, the total COD removal changed slightly--only by 4%. An increase in the cast-iron dose from 6 to 36 g/L for 3 g/L GAC caused an increase in the total COD removal also by 4%, while an increase in the cast-iron dose from 8 to 48 g/L at a GAC dose of 4 g/L only increased by 2.5%.  
It is difficult to compare those results with the results achieved by other authors. As was mentioned, most papers concern the use of single-dose Fe/GAC 12/4 g/L [31] or Fe/GAC ratios: 1/1 [2; 29], 3/0 [28] and 3/1 [5]. Although [PERSON] et al. presented the results of studies for a wider range of Fe/GAC ratios (1/3; 2/3; 3/3; 4/3; 5/3; and 6/3), they also do not specify the specific amounts of microelectrodes used [2]. [PERSON] et al. noted that an increase in COD removal was observed up to a Fe/GAC ratio of 3/3. A much lower IME process efficiency of 48.9% and 45.0% was obtained by [PERSON] in. and [PERSON] et al. [2; 31]. The authors conducted the IME process at a higher pH (pH 5) and used different doses of Fe/GAC microelectrodes, which could have resulted in lower process efficiency.  
Also, [PERSON] et al. conducted studies with the use of different doses of GAC (10, 20, 40, 60, 80, 100 and 120 g/L) with the same dose of cast iron at 20 g/L [34]. In this case, a noticeable increase in COD removal was observed up to the Fe/GAC dose of 20/80 g/L (76.7% reduction in COD after 60 min of the process at pH 3).