## 1 Introduction  
With the intensifying global water crisis and climate breakdown, water is a wealth we must conserve. The global water crisis is a serious threat and not only to those who suffer water-borne diseases or die due to dirty water drinking and use. While the global population increases, the amount of water available presents an opposing trend, being limited to 1250 cubic meters in 1995. Moreover, it is predicted that by 2025, the amount of water available will decrease further to 650 cubic meters worldwide [1]. As a consequence, limited access to clean water has a severe impact on society development and economic growth. From an economical perspective, effective wastewater treatment has important effects on saving water and preventing unnecessary water losses [2]. Water reuse in closed loops in different industrial processes is a very promising approach and one of the pillars of a sustainable circular economy. Moreover, more and more studies have recently underlined the increased common presence of antibiotic resistant bacteria in wastewater generated by household, municipal and industrial activities [3, 4]. One must bear in mind that contaminated water is also a major threat to the environment. Wastewater is a complex aqueous solution, containing not only chemical inorganic and organic substances and physical contaminants, but also wide scope of the harmful microorganisms. Additionally, wastewater effluent contains pollutants of various types depending on its origin, thus sludge of different characteristics requires different specific treatment processes. Therefore, many physical, chemical, biological and hybrid processes have already been applied to wastewater treatment over the last few decades. Most treatment facilities employ several steps or combine steps in wastewater treatment [5]. Every stage of the wastewater treatment process is important to achieve the desired treatment results. However, primary and tertiary treatment are critical to the overall process. In the primary treatment process, solid particles are reduced to fragments and grit is removed. However, this has little effect on the pathogens present in the wastewater [6]. Nevertheless, without this step, subsequent treatment stages would be less effective. Tertiary treatment employs advanced treatment technology aimed at the removal of special pollutants such as harmful microbes to make the water ready for safe reuse [7]. Nevertheless, each treatment method has its own limitations regarding feasibility, cost, efficiency, environmental impact, or pre-treatment requirements [8]. Hence, advanced, simple, low-cost, and easy-to-use methods need to be developed to tackle the problem of wastewater remediation effectively. Electron beam technology is a proven technology which has been applied commercially for sterilization, food hygenization or polymer cross-linking for decades [9; 10; 11]. The high purification degree of sewage provided by EB treatment, and unachievable in some cases by conventional purification technologies, is the one of the most important advantages of radiation treatment of wastewater [12; 13]. Moreover, detailed knowledge on the radiation mechanism of organic compounds conversion and decomposition, including available qualitative and quantitative data on primary events of energy absorption is another strong point of radiation-based wastewater treatment [14]. Additionally, while using electricity to generate electrons, the EB accelerators used in the industry are tools with a conventional turn on and off system, therefore, they do not face the security, transportation, storage, and disposal issues that gamma-ray emitting sources, such as cobalt-60 cells confront. Application of EB wastewater treatment decreases the time of treatment and saves the costs of chemical solutions [15]. It is important to underline that in the radiation-based wastewater remediation process, no secondary waste and no radioactive residues are generated.