# Rationale for the Combined Use of Biological Processes and AOPs in Wastewater Treatment Tasks
## 1 Introduction  
The introduction of various types of toxicants--in particular, antibiotics and surfactants--into aquatic ecosystems is becoming an increasing problem. For example, a global problem in the conservation of aquatic ecosystems is the active pollution of water resources worldwide with pharmaceutical products, including antibiotics, whose concentration in some rivers of the world exceeds the safety limit [1, 2]. As noted in studies, up to 90% of antibiotics used will end up in components of the natural environment, such as soil and water bodies. Medicinal drug residues enter riversfrom human and animal waste, as well as from suboptimal treatment facilities, including those of pharmaceutical companies [3; 4]. Additionally, antibiotics can significantly change the biocenosis of water bodies [3]. The predominant contribution to the pollution of natural objects with non-ionic and cationic surfactants is made by industrial enterprises and their auxiliary structures. The latter use surfactants as high-molecular-weight flocculants in the pretreatment of wastewater and clarification of sludge. In addition, surfactants are widely used as active ingredients in detergents and cleaning agents, as well as in a wide range of applications such as paints, pesticide formulations, pharmaceuticals, moisturizers, and personal care products [1; 5]. They can be divided into four main groups according to their charge: anionic, nonionic, cationic, and amphoteric. Despite their relatively high solubility, these compounds have moderate-to-high sorption capacity, and several intermediates are formed during their degradation [5]. Given the high probability of some of the high-molecular-weight reagents entering the biological treatment unit, there is a need to investigate their effects on the activated sludge's biocenosis in order to study the possible effects on the biological treatment process of the wastewater. Surfactants destroy activated sludge flocs and disrupt the oxygen regime; as such, we should expect significant destruction of zoogloea and the appearance of free-floating cells, which leads to steady turbidity of the nadir fluid, as well as an intensive damaging effect on hydrobionts, as confirmed by previous studies [4; 5; 6]. At the same time, in recent decades, wastewater and drinking water treatment technologies have undergone rapid development. Wastewater treatment methods are divided into four basic groups [7; 8]:  
* Mechanical methods are generally the cheapest, and are used for the separation of suspended solids in the preliminary stage of water treatment;
* Chemical methods are classically used to remove inorganic impurities from wastewater. When treated with reagents, dissolved compounds are neutralized, and decolorization and disinfection take place;
* Physicochemical methods are mainly used for the removal of coarse and fine dispersed particles, as well as the neutralization of colloidal impurities and dissolved compounds;
* Biological methods of wastewater treatment are used to remove organic compounds from wastewater. They use the ability of microorganisms to decompose organic compounds. It should be noted that in order to obtain high efficiency of water treatment at real facilities, combined installations are used, including several known methods of impact on water solutions [9]. At the same time, there is a need to implement comprehensive solutions for intensification of purification at volley releases of toxic substances, such as antibiotics and surfactants, since these toxicants are widely used in human activities and their entry has a negative impact on the operation of sewage treatment plants in both individual enterprises and municipalities. This reduces the efficiency of wastewater treatment systems, and also suppresses the metabolic activity of various ecology-trophic groups involved in the biological phase of treatment.