## 4 Immobilized Systems in Microbiological Degradation of EDCs
The chitosan matrix has achieved great storage stability, 90% of the initial activity, whereas the free enzyme showed only 47.3%, after 28 days at 4 \({}^{\circ}\)C. Also, activity after 10 oxidation cycles decrease no more than 30%. Hence, many research centres are looking for new solutions with more stable carriers [67]. [PERSON] et al. [7] obtained promising results by developing an innovative macro-encapsulation technology, the \"small bioreactor platform\" (SBP) capsule (patent application No. PCT/IL2010/256). The SBP method is based on the macro-encapsulation of a bacterial culture in a closed environment using a cellulose acetate microfiltration membrane as a protective barrier. The capsule separates the suspended microbial culture inside the capsule from the autochthonous microorganisms in the effluent, while allowing the diffusion of nutrients through the capsule membrane. As a result, the biomass in SBP capsules quickly acclimizes. In addition, the physical barrier prevents leaching of selective microorganisms from the bioreactor. The _Rhodococcus zopfii_ and _Pseudomonas putida_ strains encapsulated using this technology degraded 17\(\alpha\)-ethynylestradiol with an efficiency of 73.8% and 86.5%, respectively. The authors showed that macro-encapsulation enables the practical application of bacterial cultures in the removal of steroid hormones in wastewater treatment processes. The SBP encapsulation method can be implemented in the sewage treatment plant processes because it overcomes the main obstacles that usually make biological bioaugmentation ineffective: it enables achieving long-term selective biomass implementation in wastewater treatment plants, controls culture location and gives relatively efficient biodegradation that can be synchronized with the hydraulic retention time of the wastewater treatment plant [7]. [PERSON] at al. [41] attempted to used immobilized cells of _Chlorella vulgaris_ in nonylphenol removal. The authors achieved over 98% degradation with immobilized beads in the presence of 1 mg/L nonylphenol, but alginate carriers still have many limitations as mentioned above. One of those used in microbial immobilization biopolymers could be cellulose triacetate (CTA). [PERSON] et al. [68] used the entrapment technique with CTA to degrade estrone and 17\(\beta\)-estradiol with two bacteria strains--_Sphingomonas_ sp. AHC-F and _Sphingobium_ sp. AX-B. Cellulose triacetate is characterized by high hydrate permeation and mechanical strength. CTA presents a great balance of the hydrophilic/hydrophobic character important for effective enzyme adsorption and its biological activity. Additionally, hydrophilic/hydrophobic properties could be modified by acetylation/deacetylation [69]. Both strains were able to degrade 2 mg/L of estrone and 17\(\beta\)-estradiol for free strains in 24 h and for immobilized in 72 h, which is probably caused by the compounds transfer limitation in a porous carrier Additionally, the authors reported that a continuous-flow degradation on an IBRC reactor of 850 ng/L 17\(\beta\)-estradiol is possible [69]. On the other hand, not only immobilized microorganisms could be used in EDCs degradation. Immobilized enzymes are widely used systems in xenobiotic degradation experiments. Many of the enzymes used are fungal lacases and peroxididases, with a wide range of substrate specificity, high pH and temperature tolerance. Another popular carrier is luffa sponge fibres. The desirability of natural fibres includes complete biodegradability, low cost, renewable nature and relatively high surface area. [PERSON] et. al. [70] compared the activity of free and immobilized _Luffa cylindrica_ fibres lacases being able to degrade 17\(\alpha\)-ethinylestradiol. They showed the possibility of reusing immobilizes lacases systems, despite nonoptimal reaction conditions. It could be a compromise between the degradation level and the possibility of using carriers in many cycles. Lacase, as a wide spectrum oxidative enzyme, was used in many other degradation experiments.