## 5 Comparison between Mature Methods and More Recent Non-Thermal Plasma Technology
### Materials and Methods
#### 5.1.2 Planning-Energy and Costs  
A selection of compounds was made using the research described under tertiary water and wastewater pollutants. Each considered compound fell into one of four groups: organics, inorganics, pathogens or CECs. The most problematic or most ubiquitous compounds were selected from each of the aforementioned groups. The selection process for this is described below.  
To represent the organics group, phenol was selected. Phenol is a well-established model compound in the water purification industry [8; 69] and is a good representation of the organic compounds one is likely to encounter when purifying water. For the CECs, one persistent contaminant was chosen from each of the three subgroups of EDCs: pharmaceuticals, oestrogens and PFCs. The EDC selected for pharmaceuticals was carbamazepine, because it was the most persistent in its subgroup. Oestrone was selected for the oestrogens group because it was the main source of oestrogens in water. Lastly, PFOS was selected to represent the PFCs group, because it is widely studied, thereby making literature data more readily available.  
For each of the compounds, the efficiency and percentage removal for both chlorination and ozonation were determined. The efficiency was measured in terms of the CT value, which is the product of concentration (C) of the oxidant used with the contact time (T) [70]. However, for plasma processes, it is difficult to quantify a plasma concentration. Thus, it was more suitable to represent its performance in terms of power consumption and the percentage of contaminant removal. In some studies, only the voltage requirements of a plasma reactor are reported. To obtain the corresponding power consumption, a graph was used that displays the current in a DBD reactor at varying voltages [71].  
The literature data used were obtained between 25 \({}^{\circ}\)C and 30 \({}^{\circ}\)C, the ideal temperature for water treatment [72]. Furthermore, in this temperature range, additional heat exchanger equipment is not required, which keeps the operating costs lower.  
Next, the results reported were obtained at a pH between 4 and 10. The range is wide because data are scarce in this field, and narrowing the pH range severely limits the number of studies that can be utilised.  
For chlorination analysis, since chloramine is used to prevent contamination at later points in the pipeline, it is a secondary disinfectant. Hence, data surrounding chlorine as a disinfectant was used, as opposed to chlorine and chloramine as the disinfectants.  
For the plasma reactors, PCD and DBD reactors are the most and second most energy-efficient plasma generators, respectively [38]. Gliding arc reactors lie below PCD and DBD reactors in terms of energy efficiency. Hence, emphasis was placed on finding results from PCD reactors first, and then DBD reactors, with gliding arc reactors only being considered as a last resort.  
Finally, the literature indicates that UV radiation is unfeasible for tertiary wastewater purification. It was therefore not considered when gathering the results.