## 3 Results and Discussion
### EE2 Biodegradation in Minimal Salt Medium Enriched with Hydrocarbons and Nutrients (MSM + 2%LB)  
This experimental section was conducted to determine whether the presence of other available carbon sources and nutrients have an inhibitory effect on the EE2 biodegradation rate. A medium that is enriched with various nutrients might simulate a domestic effluent that contains some residual biochemical oxygen demand (BOD), nitrogen and phosphorus. Figure 2B presents the EE2 biodegradation rate of encapsulated _R. zopfi_ and _P. putida_ F1 in MSM medium enriched with 2% LB. After 1 h of incubation, the EE2 concentration decreased significantly only in the _P. putida_ test system. EE2 concentration reductions after 1 h were 11.6% for the _R. zopfi_ system and 24.5% for the _P. putida_ system. The significant EE2 reduction in the two test systems occurred during the first 24 h of incubation. Our results indicate that SBP-encapsulated _R. zopfi_ and _P. putida_ F1 can successfully biodegrade EE2 molecules within 24 h, from an initial concentration of 0.352 mg/L and 0.396 mg/L to 0.088 mg/L (75%) and 0.174 mg/L (56.1%), respectively. At the final incubation time point, after 72 h, the EE2 concentration decreased to a final biodegradation efficacy of 94.9% and 73.1% in the _R. zopfi_ and the _P. putida_ systems, respectively. The EE2 concentration in the control system after 72 h was not significantly different from the starting point. These results indicate that most of the EE2 molecules were consumed during the first 24 h of incubation, even in the presence of other hydrocarbons and nutrients. Again, it is shown that the _R. zopfi_ capsules biodegrade EE2 faster than the _P. putida_ capsules. This shows that the encapsulated culture may be a good candidate for biological treatment of EE2 in future studies, in pilot studies or in laboratory studies for treating effluents, since effluents contain a significant amount of available organic matter. Table 2 presents a literature summary of EE2 biodegradation by a suspended _R. zopfi_ culture in the presence of other carbon sources. [PERSON] et al. [14] presented a biodegradation rate similar to the rate found in the present study, indicating that the SBP encapsulation method did not have an inhibitory effect on the EE2 reduction rate. Moreover, the SBP-encapsulated _R. zopfi_ presented superior biodegradation results regarding its kinetic and efficiency parameters compared to the findings reported by [PERSON] and [PERSON] [8]. Figure 2: (**A**) EE2 biodegradation in minimal salt medium (MSM) medium supplemented with EE2 as the sole carbon source. All experiments were conducted in triplicates. Points represent means of triplicates and bars represent standard deviations. (**B**) EE2 biodegradation in MSM medium enriched with 2% lysogeny broth (LB) solution providing an additional source for hydrocarbons and nutrients. All experiments were conducted in triplicates. Points represent means of triplicates and bars represent standard deviations. (**C**) EE2 biodegradation by _R. zopfi_ SBP capsules in sanitary secondary effluents that contain some residual organic matter and other substances (\(\sim\)88 mg/L COD, \(\sim\)20 mg/L BOD). All experiments were conducted in triplicates. Points represent means of triplicates and bars represent standard deviations. [PERSON] et al. [9] reported that EE2 is partially biodegradated by three _Rhodococcus_ strains in the presence of co-substrates. In their work, _Rhodococcus equi_ removed up to 39% of the initial EE2 concentration (1.4 mg/L) after 65 h, whereas no significant EE2 removal was observed using _R. rhodocrotus_ and _R. zopfii_. On the contrary, our results present an almost complete biodegradation efficacy of 94.9% after 72 h of incubation with MSM + 2% LB and 91.7% after 96 h in secondary effluents (-88 mg/L COD). Table 3 presents a literature summary of EE2 biodegradation by _P. putida_ in the presence of other carbon sources.