## 1 Introduction
Available literature on the economic feasibility of EB's application in wastewater treatment plants indicates that operational and maintenance cost are nearly competitive, with conventional technologies widely applied nowadays [16]. Annual savings calculated on the basis of a preliminary investigation carried out for the pilot wastewater plant equipped with an integrated EB unit were estimated in the range of USD 0.2-2.7 million depending upon specific application [16]. The redundancy and reliability of the EB accelerator operation are the most important factors influencing economic feasibility. However, substantial improvements in reliability and operational stability of electron accelerators have been made recently, therefore the requirements concerning the continuous failure-free operation of wastewater plant employing EB units are more easily fulfilled. Nevertheless, the procurement, transportation and installation costs of electron accelerators vary from USD 0.6 to 2 million, depending on accelerator parameters [17], therefore there is still a need to reduce the capital cost of electron accelerators irradiation facility. It is also worth noting that electric power consumption by other eco-friendly disinfection methods such as UV or ozone is three orders of magnitude higher than in the case of EB treatment [18]. Electron beam processing in wastewater treatment is an additive-free process that uses the short-lived reactive species formed during the radiolysis of water for the efficient decomposition of organic and microbiological pollutants therein [19]. Absorbed energy ratio is proportional to mass fraction of given species and water is the main component of wastewater and ballast water as well. Hydrated electron \(\mathrm{e_{aq}}^{-}\), H atom, \({}^{\bullet}\) OH and \(\mathrm{HO_{2}}^{\bullet}\) radicals and hydrogen peroxide \(\mathrm{H_{2}O_{2}}\) and \(\mathrm{H_{2}}\) are the most important products of the primary interactions (radiolysis products):  
\[\mathrm{H_{2}O}\xrightarrow{}\mathrm{e_{aq}}^{-},\mathrm{H,}\ ^{\bullet}\mathrm{OH,}\ \mathrm{HO_{2}}^{\bullet},\mathrm{H_{2}O_{2},}\ \mathrm{H_{2}} \tag{1}\]  
with yields (G value, \(\mathrm{\upmu mol/J}\)) of 0.28(\(\mathrm{e_{aq}}^{-}\)), 0.062(H), 0.28(\({}^{\bullet}\)OH), 0.072(\(\mathrm{H_{2}O_{2}}\)). Hydrogen peroxide H\({}_{2}\)O\({}_{2}\) and \({}^{\bullet}\)OH and HO\({}_{2}\)\({}^{\bullet}\) radicals are oxidizing species, while H atom and e\({}_{\text{aq}}\)\({}^{-}\) are reducing species. The addition of ozone before or during irradiation converts the reducing species formed during water radiolysis into \({}^{\bullet}\)OH radicals [20] and consequently enhances the \({}^{\bullet}\)OH radical yield from water radiolysis by a factor of 2. Bacteria cells contain water (e.g., _E. coli_ cell contains roughly 72% water by mass and 80% by volume) and the species listed in Eq.1 are capable of degrading and altering biopolymers such as DNA and protein. Breakage of DNA chains in radiation, direct and chemical pathways, and degradation of enzymes lead to the death of the irradiated cells. The bacteria cell wall, a rigid and non-living envelope around the cell, is an important structure. It is present just above the cell membrane and gives a specific shape to the cell. In addition, the reactive compounds formed in matrix matter attack bacteria walls. Damage to the cell wall disturbs the state of cell electrolytes, which can activate death pathways (apoptosis or programmed cell death). It has been demonstrated that inactivation of fecal _Coliforms_ in municipal wastewater can be achieved with doses lower than 1 kGy. It is observed that nearly 100% of _E.Coli_ and total _Coliforms_ were inactivated with a dose of 0.8 kGy. Even with the lower dose of 0.2 kGy, the _E.Coli_ and total _Coliforms_ were successfully inactivated to the level of the guideline for effluent discharge. Besides the disinfection of total _Coliforms_, an approximately 50% removal in biochemical oxygen demand (BOD) was pronounced at a dose of 0.2 kGy.