## 1 Introduction  
Sewage composition analysis stands at the forefront of environmental research, offering critical insights into water quality and pollution levels [1, 2, 3]. Understanding the intricate makeup of sewage is essential for effective treatment strategies and safeguarding environmental health [4, 5]. As a reflection of societal activities, sewage reveals chemical and industrial pollutants that pose significant risks to ecosystems and human health [6]. Investigating its composition highlights pollutant sources, impacts and potential mitigation strategies [7]. Industrial pollutants are harmful, because they can significantly impact both the environment and human health [8]. The ether extract represents the content of organic substances in sewage. The ether extract includes petroleum products, fats and oils, which are extracted from water and sewage with petroleum ether; this substance is resistant to comprehensive sewage treatment [9]. Ether extract is one of the significant parameters which must be considered in food industry sewage. In particular, sewage from meat, fat, poultry, dairy and fish processing plants is heavily loaded with this substance [10]. The content of the ether extract is also significant in sewage coming from production processes of confectionery plants [11; 12]. Ether extract is also one of the main pollution indicators in rainwater discharged from roads [13]. Fatty and oily substances make a thin and transparent layer on the surface of the water, blocking access to oxygen [14]. This inhibits the process of water self-treatment and disrupts the functioning of aquatic ecosystems [15]. Removal of fats and oils from sewage in the mechanical stages of wastewater treatment plants (WWTPs) is not sufficient; a significant amount of fatty and oily substances flows into the WWTP in the form of emulsion and persists into the biological stages of the WWTP [15]. Phenols, chlorides and sulfates represent a class of industrial pollutants that warrant particular attention due to their significant environmental impact and potential risks to human health. Examining their presence in sewage sheds light on their sources, effects and mitigation strategies [16]. Phenols are among the basic substances found in significant amounts in sewage from the process of coal coking and obtaining coal derivatives [17]. Phenolic compounds are prevalent pollutants in sewage, originating from industries such as petrochemicals, pharmaceuticals, and pulp and paper production. These compounds pose a threat to aquatic ecosystems due to their toxicity and persistence [18]. Phenols can disrupt the balance of aquatic flora and fauna, inhibit photosynthesis in plants and impair the reproductive success of aquatic organisms. Additionally, exposure to phenolic compounds has been linked to adverse health effects in humans, including respiratory irritation and skin disorders. Effective treatment methods, such as advanced oxidation processes and activated carbon adsorption (including a cost-effective and environmentally friendly sewage-based activated carbon adsorption method, which supports the sustainable management of huge amounts of sewage [19]), are essential for removing phenols from sewage and minimizing their environmental impact [20]. Hybrid cavitation techniques for phenol removal show potential. While cavitation alone may not be efficient or cost-effective, its combination with oxidation processes, catalysts, or additives could prove beneficial [21]. Chloride ions are ubiquitous in industrial sewage, particularly in sectors such as metal processing, chemical manufacturing and food processing. Chlorides can enter water bodies through direct discharge or runoff from road salts and de-icing agents. While chloride ions themselves are not typically toxic, elevated chloride concentrations can have detrimental effects on freshwater ecosystems [22]. High chloride levels can disrupt the balance of aquatic organisms, corrode infrastructure and impair the quality of drinking water sources [23].