## 2 Materials and Methods
### Electron Beam Radiolysis Process
#### 2.1.1 EB Technology  
A typical EB device is illustrated in Figure 1: a cathode releases electrons under high vacuum, and these are accelerated by high voltage (DC) or radiofrequency sources, while electrostatic or magnetic fields focus and deflect the direction of their beam on a window carved in thin metal foil. Electrons escape this window with energy proportional to applied voltage, in quantity that depends on cathodic current. Both voltage and current can be adjusted to control beam penetration depth in the exposed medium (proportional to energy) and dose rate (proportional to current), respectively [18]. Aside from the amount of energy involved, the entire apparatus is conceptually quite similar to a cathodic-tube television set. \begin{table}
\begin{tabular}{l l} \hline \hline
**Species** & **Potential, E\({}^{\circ}\) (V, 25 \({}^{\circ}\)C)** \\ \hline Hydroxyl radical (-HO) & 2.86 \\ Atomic oxygen (O) & 2.42 \\ Ozone molecule (O\({}_{3}\)) & 2.07 \\ Hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) & 1.78 \\ Chlorine (Cl\({}_{2}\)) & 1.36 \\ Oxygen molecule (O\({}_{2}\)) & 1.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Oxidation potential of some common oxidizing molecules and radicals [4]. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Radiation source** & **Energy (kW)** & **Calculated dose-Rate (MGy/h)** \\ \hline \multicolumn{4}{l}{\({}^{60}\)Co \(\gamma\)-source} \\ \hline \(0.5\times 10^{6}\) Ci \({}^{\star}\) & 0.18 & 0.65 \\ \(1.0\times 10^{6}\) Ci & 0.36 & 1.30 \\ \hline \multicolumn{4}{l}{Electron Beam (EB)} \\ \hline \(1\) mA, \(1\) MeV & \(7.2\times 10^{3}\) & \\ \(10\) mA, \(10\) MeV & 100 & \(3.6\times 10^{5}\) \\ \(50\) mA, \(10\) MeV & 500 & \(1.8\times 10^{6}\) \\ \hline \hline \end{tabular} \({}^{\star}\) Curie (1 Ci = 37 GBq).  
\end{table} 
Table 2: Achievable (measured) dose-rates of Gamma and EB radiation sources [4]. \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & & & **Components in Solution** & \\ \hline \multicolumn{4}{l}{**Metals**} & \multicolumn{3}{c}{**Organic Molecules**} & **Pathogens and Algae** \\ \hline \multicolumn{4}{l}{} \\ \multirow{7}{*}{-} & \multirow{7}{*}{Reduction (most species & - & Complete decomposition (mineralization to & \\  & & CO\({}_{2}\), H\({}_{2}\)O) & \\  & & - & Partial decomposition (to forms more & \\  & & susceptible to biodegradation or other) & \\ \cline{1-1}  & & - & Organic solids cell walls destruction (promotes & \\ \cline{1-1}  & & - & coagulation and improves sludge dewatering) & \\ \cline{1-1}  & & - & Removal/degradation of toxic groups & \\ \cline{1-1}  & & - & (improves biodegradation and lowers & \\ \cline{1-1}  & & - & intake risks) & \\ \cline{1-1}  & & - & Removal of odors \& color causing molecules & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Possible action mechanisms of EB-generated radicals in a water medium. Emitted energy is measured in electronvolt (eV) units (defined as the amount of energy gained by the charge of an electron across an electric potential difference of 1 V). As the electronvolt is a very small quantity (approximately \(1.602\times 10^{-19}\) J), the keV (\(10^{3}\) eV) is commonly used as reference unit. EBs used in water/wastewater applications are usually rated in the range 500 keV-1.2 MeV, but may also reach 10 MeV in older models or very large applications. Irradiation dose is measured in Grey (Gy, defined as absorption of 1 J of radiation energy by 1 kg of matter). Use of high DC voltage allows conversion of input AC to beam power with high efficiency (\(>\)95%), making this one of the higher energy-efficient processes available (by comparison, last generation UV systems applied in water disinfection show conversion efficiencies--electric to UV- of about 30%).