## 1 Introduction
It was found that an enriched nitrifying microbial flora in sludge containing ammonium as its sole energy source could degrade EE2 with a calculated EE2 half-life of around 24 h. Other studies showed that the EE2 half-life in WWTPs is less than 24 h, and its concentration is halved within hours, suggesting that the rate of the EE2 biodegradation mechanism is affected by the bacterial concentration and diversity [17]. Only one previous study, performed by [PERSON] et al. [10], investigated the co-metabolic biodegradation of E2 and EE2 by six strains isolated from compost. They reported that EE2 was notdegraded even after 100 h when used as a sole carbon source. However, the EE2 degradation rate improved in the presence of E2. Another metabolic path for indirect EE2 degradation is mediated by manganese-oxidizing bacteria (MnO). In natural environments, manganese-oxidizing microorganisms are able to oxidize Mn\({}^{2+}\) to Mn\({}^{4+}\), resulting in the formation of biogenic Mn oxides. [PERSON] et al. [18] reported that the manganese-oxidizing bacteria _Leptothrix discophora_ and _Pseudomonas putida_ can oxidize Mn\({}^{2+}\) to form Mn oxides, which are then used to facilitate the oxidative cleavage of EE2. Considering the aforementioned information regarding metabolic and co-metabolic consumption of EE2, there might be two major reasons for only partial removal of EE2 from DWWTP effluents: (1) The hydraulic retention time (HRT) within the bioreactor is too short for co-metabolism activity; (2) The bacterial flora that can metabolize EE2 are present in insufficient concentrations. The proven ability of microorganisms to biodegradable EE2 and other OMPs suggests the potential of using known biochemical paths for OMP treatment, especially in large water bodies. Use of the bioaugmentation treatment approach might present a solution for OMPs treatment, especially by providing a sufficient amount of selective biomass that enables rapid EE2 biodegradation within hours. However, bioaugmentation presents many problems when the suspended culture is introduced into common DWWTPs, since the short HRT (8-24 h) causes dilution of the augmented culture and biomass washout from the bioreactor due to continuous influents. Some protection and immobilization of the bioaugmented culture must therefore be provided in order to prevent loss of the added biomass [19]. A novel encapsulation technology, the'small bioreactor platform' capsules (SBP) (Figure 1), was recently developed. The SBP method is based on macro-encapsulation of a bacterial culture in a confined environment using a microfiltration membrane as a protective barrier. The 3D capsule (2.5 cm long and 0.8 cm diameter) physically separates the suspended microbial culture inside the capsule from the natural microorganisms in the wastewater, while enabling the diffusion of nutrients through the capsule membrane. The capsules are introduced into the WWTP bioreactor or other water bodies such as the secondary clarifier using a perforated cage that enables controlling of the location of the capsules (for example, above the air diffuser), and enables a very simple operation. The SBP capsule creates an appropriate growth environment by providing nutrients and physical protection and preventing competition with the natural microorganisms. This results in rapid biomass acclimation within the SBP capsules. Furthermore, the physical barrier prevents washout of the selective microorganisms from the bioreactor by a continuous outflow [20]. In our recent work on phenol biodegradation using a SBP-encapsulated _Pseudomonas putida_ F1 strain, it was found that the encapsulated culture had a biodegradation rate similar to that of a bacterial suspension (not encapsulated) [21]. As far as we know, this capsule may present an efficient encapsulation matrix in terms of biodegradation rate, which is a significant advantage for OMP degradation in most WWTPs that operate using a short HRT (less than 24 h).