## 4 Immobilized Systems in Microbiological Degradation of EDCs  
Physico-chemical methods based on materials with a large specific surface and high porosity are used to remove EDC from water and wastewater. The most commonly used materials are zeolite, carbon nanotubes, graphene, mesoporous silica, activated carbon, fullerene or metal-organic frameworks as well as waste materials such as lignocellulosic-based hydrocarbons. The effectiveness of hormone adsorption on these materials depends on many factors, including the nature of the environment, pore filling, and the potential for generated interactions, including electrostatic, hydrophobic, hydrogen and \(\pi\)-\(\pi\) interactions [60; 61]. Despite promising results and economic viability, conventional adsorption technology does not solve the problem of EDCS degradation, but only allows for their removal from a given environment. However, the adsorbents require regeneration during which EDCs are removed practically unchanged. Hence, it is justified to search for safe methods allowing for complete degradation of EDCs. The promising results were obtained with usage microorganisms. However the main problem is the sensitivity of functional strains to environmental factors. The limitation for bacteria with increased degradation potential is the competition between these strains and indigenous microflora, and the low tolerance to changing environmental conditions. Protection of microorganisms against negative environmental factors, such as radiation, antibacterial substances, hazardous materials and high osmotic pressure, as well as against competition with an indigenous microbiome and attenuation of phagocytosis is possible due to their immobilization in the matrix of the carrier [4; 6]. Figure 9: Proposed biotransformation mechanism of 17\(\alpha\)-ethynylestradiol by _Lentinualéodes_[44]. Currently, the dynamic development of immobilization techniques is observed and new types of carriers, both natural and synthetic, are being designed and introduced [62]. Classical carriers include calcium alginate that has been used for a long time in immobilization [4; 41; 63; 64; 65; 66], e.g., promising results were obtained by [PERSON] et al. [4], who entrapped the cells of the _Novoshingobium_ sp. ARI-1 strain in this matrix. They showed that the immobilized strain had a greater degradation potential than free cells. After immobilization they observed that estrone, 17\(\beta\)-estradiol and estriol were degraded in 80.43%, 94.76% and 100%, respectively. Also, the _Rhodococcus_ sp. strain JX-2 had a higher yield of degradation of 17\(\beta\)-estradiol in a harsh environment and removed this compound from wastewater and cow dung after immobilization in calcium alginate [6]. Despite the numerous advantages of this carrier, such as low cost, low toxicity, rapid exchange of nutrients and metabolites, these authors have noticed that the reuse of immobilized microorganisms caused clogging in the pores in the carrier and as the number of cycles increased, the diffusion of oxygen and nutrients was more limited. This feature and the relatively low mechanical strength of this carrier may adversely affect biodegradation processes using strains immobilized in calcium alginate [4]. However, biopolymers could still be successfully used in immobilization, i.e., glutaraldehyde cross-linked chitosan was used to immobilize fungal lacase during bisphenol-A degradation [67]. Chitosan is a natural biopolymer characterized by good biocompatibility, biodegradability, low cost and easy modification, however, the mechanical properties of pure chitosan must be improved for efficient reuse. Nonetheless, the authors used cross-linkages with glutaraldehyde. The additional reaction with the amino polysaccharide of chitosan improved the mechanical resistance of the chitosan beads. Because of its cationic nature, glutaraldehyde dehyde stabilizes chitosan solubilization in an aqueous acidic environment as well.