## 2 Materials and Methods
### Nonthermal Plasma Processes
#### 2.2.1 Non-thermal Plasma Technology  
NTP technology is to date confined to low-flow, mostly bench scale applications, due to its limited water penetration, which demands a thin-flow configuration, similarly to the situation of EB systems. It can be expected that technical solutions similar to those adopted with the latter could promote upscaled NTP applications. One of the better known pilot-scale NTP units reported in literature is an \"electrode-to-plate\" prototype described by [PERSON] [21], consisting of two reactors in series. In the 1 st reactor, water flows in a thin film (about 5 mm) along an electrode (anode), while exposed to high-voltage pulses from carbon fiber (cathode). The space between carbon electrode and water surface may be adjusted for process optimization according to each specific water matrix. Electric pulses were characterized by frequencies in the range 500-1000 Hz, maximum voltage of 8.0 kV, 100 A current, 1 J energy, and rise time of 18 ns. The pilot unit scheme is illustrated in Figure 2.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Compound** & **Bimolecular Rate Constants (M\({}^{-1}\)s\({}^{-1}\) 10\({}^{9}\))** & **Relative Importance of Species (\%)** \\ \hline
**Target Organic Compounds \({}^{*}\)** & -OH & e-aq & -H & -OH & e-aq & -H \\ \hline MTBE & 2 & 0.0175 & 0.0001 & 99 & 1 & 0 \\ Trichoethylene & 2.9 & 1.9 & NF & 61 & 39 & 0 \\ Tetrachloroethylene & 2 & 1.3 & 5 & 46 & 29 & 25 \\ Benzene & 7.6 & 0.009 & 0.91 & 97 & 01 & 3 \\ Toluene & 5.1 & 0.011 & 2.6 & 90 & 0.1 & 10 \\ Ethylbenzene & 7.5 & NF & NF & 100 & 0 & 0 \\ o-Xylene & 6.7 & NF & 2 & 94 & 0 & 6 \\ Chloroform & 0.054 & 11 & 0.073 & 0.4 & 99 & 0.1 \\ CHBrCl\({}_{2}\) & NF & 21 & NF & 0 & 10 & 0 \\ CHBr\({}_{2}\)Cl & NF & 20 & NF & 0 & 10 & 0 \\ Bromoform & 0.11 & 26 & 1.9 & 0.5 & 97.5 & 2 \\ Ethylene dibromide & 0.26 & 14 & NF & 2 & 98 & 0 \\ DBCP & 0.73 & NF & NF & 100 & 0 & 0 \\ NDMA & 0.33 & NF & NF & 100 & 0 & 0 \\ Atrazine & 2.6 & NF & NF & 100 & 0 & 0 \\ Sinazine & 208 & NF & NF & 100 & 0 & 0 \\ \hline \hline \end{tabular} \({}^{*}\) Rates determined in synthetic, mono-component solutions—NF not found.  
\end{table}
Table 4: Organic compounds removal efficiencies by radicals formed due to water radiolysis (modified from [15]).  
After flowing through the 1 st reactor, water is stored in a side tank. Before entering an ozone contactor (2 nd reactor) for additional contact time, an injector system mixes ozone-rich air (about 2 g/m\({}^{3}\)) from the 1 st reactor headspace with a fraction of the treated water before discharge. Excess air from the contactor is extracted and sent to an ozone quenching unit before discharge into the atmosphere. Hydraulic residence times (HRT) in reactor and storage tank vary depending on flow rate, whereas in the ozone contactor HRT remains relatively constant. For flows between 10 and 15 L/min, tested HRTs were approximately 0.5 min (reactor), 4-7.5 min (storage tank) and 1.5 min (ozone contactor), respectively.  
The level of treatment can be adjusted by adjusting the frequency within the operating range and/or voltage (up to 40 kV) of electrical pulses. Depending on voltage and frequency, a reactor requires approximately 0.4-1.0 kW [25].  
Other process configurations, such as wetted-wall or falling liquid film reactors have been used in PPCPs degradation experiments, in the attempt to improve process efficiency. [PERSON] tested an aluminum oxide-coated, rotating drum electrode, with the solution flowing on its outer surface as a thin film (Figure 3A), while [PERSON] used a dielectric barrier discharges (DBD) unit with falling film (Figure 3B) [26,27]. Some recent developments in plasma technology include combination of atmospheric pressure plasma and photocatalysts (e.g., TiO\({}_{2}\)) for microorganisms control in aqueous solutions [28].  
Figure 3: (**A**) Rotating drum film, corona discharge NTP unit (**B**) DBD unit with falling film. dielectric barrier discharges (DBD).  
Figure 2: Schematics of a NTP unit. non-thermal plasma (NTP).