## 3 Results and Discussion
### Monitoring of Decolorization of TB and BR in RTWW: COD and FTIR Analyses
Comparing to conventional biological treatment processes, BES could improve the efficiency of the degradation of several pollutants such as volatile organic compounds and azo dyes [6; 35]. In fact, these systems have the particularity of coupling microbial metabolisms and electrochemical oxidation-reduction reactions into a single integrated unit [36]. Figure 5: (**A**) Evolution of the anodic current recorded on the 6 cm\({}^{2}\) carbon felt working electrode polarized at \(-\)0.1 V/SCE in reactor contained RTWW and SCD (a) or SSM as inoculum (b). (**B**) Decolorization rate achieved by bioremediation or bioelectroremediation. (**C**) Related cyclic voltammetry \(\text{CV}_{\text{i, SCD}}\) (\(-\)), \(\text{CV}_{\text{f, SCD}}\) (\(-\)); (**D**) related cyclic voltammetry \(\text{CV}_{\text{i, SSM}}\) (\(-\))and \(\text{CV}_{\text{f, SSM}}\) (\(-\)). The comparison of COD removal rates between the bioelectrochemical reactor and the biological control showed a significant treatment improvement of 18% for the SCD and 37% for the SSM (Figure 5B). According to the literature, biological treatment of textile effluents loaded with azo dyes shows in most studies poor to moderate COD removals ranging from 37 to 63% [37; 38; 39]. In fact, the slow microbial process, the incomplete degradation of azo dyes, and the toxicity towards the purifying microorganisms are the three main limitations of conventional biological treatment that significantly limit the COD treatment efficiency [40]. With bioelectrochemical treatment processes, much higher COD abatement rates have been reported. Here, we have demonstrated that the abatement rate can rise significantly to 85%, and other recent work in the literature reports abatements as high as 90% [21; 41; 42]. Recent studies have confirmed that the capacity of electroactive bacteria (EAB) for extracellular electron transfer (EET) perfectly meets the requirements of the extracellular reduction pathway of azo dyes. Thus, EABs with high EET capacity should also be efficient azo dye reductants due to the role of extracellular cytochrome C (OmcB, OmcC, and OmcE), which are identified as key outer membrane proteins for extracellular dye reduction [43; 44]. Compared to the intracellular decolorization common to the conventional biological reactor, extracellular decolorization can be completely catalyzed by these outer membrane proteins directly, thus protecting bacteria from toxin effects by keeping azo dyes and their decolorized products out of the cells, resulting in superior decolorization rates with EAB. The combination of these two approaches necessarily involves a combination of different reduction pathways: extracellular (by EAB) and intracellular (by bacteria in the anolyte). Indeed, having a polarized electrode for bioelectrocatalyst biofilm formation seems to be an efficient way to boost the degradation of organic matter within an effluent, but also to escape the bacterial toxicity caused by the classical intracellular reduction pathway. To gain insights into azo dyes degradation by the BES, FTIR was used to reveal possible transformations in their structures. The FTIR spectrum (Figure 6) of the two control azo dyes (control group-TB (a) and control group-BR (b)) revealed that peaks around 3400 cm\({}^{-1}\) corresponds to -NH2 of aniline; however, the presence of weak bands at 2900 and 2850 cm\({}^{-1}\) indicated -CH stretching. The peak at 1610 cm\({}^{-1}\) represents the stretching vibration of the C=C group on the benzene ring, and the peak at the region from 1400 to 1600 cm\({}^{-1}\) represents the absorption band of the azo doublebond of TB and BR. The band observed at 1350 cm\({}^{-1}\) is the characteristic -CN absorption peak of N atoms linked to the benzene ring. The peak at 1100 cm\({}^{-1}\) for the BR and 1150 for the TB represents the asymmetric stretching vibrations of sulfonates. The peak at 450-1000 cm\({}^{-1}\) represents the out-of-plane bending vibration absorption peak of the benzene ring.