## 5 Comparison between Mature Methods and More Recent Non-Thermal Plasma Technology
### Materials and Methods
#### 5.1.3 Calculations  
For the operating cost, capital cost and energy yield calculations, phenol was selected as the model pollutant, for the reasons outlined previously. Operating Cost Calculations  
By calculating the operating costs first, assumptions were made and a basis was selected, which greatly simplified the subsequent capital cost calculations. For each technology type, a hypothetical wastewater treatment plant was designed. This design specified an arbitrary basis flow rate: 100 m\({}^{3}\)/day of wastewater influent. A maximum influent phenol concentration of 53 ppm was reported in literature [73]; this was adopted as the influent's phenol concentration. Beginning with the hypothetical plasma plant, it was assumed that its operating costs are similar to those of the chlorination plant (apart from the electricity required for the plasma generator). This was justified because any water treatment plant will have similar equipment and maintenance demands. These costs are outlined in [21] and include maintenance, personnel and capital redemption costs (based on a 7% prime rate) [74]. Each of these costs was determined as a function of the capital investment cost. To determine the capital cost, the 0.6 rule [75] was used to scale down the capital cost approximation provided by [76]. The scaled capital cost was then adjusted for inflation [77] and used to calculate the maintenance, personnel and capital redemption costs. From the reported experiment, the number of watts required to remove one gram of phenol every hour was determined. This value was then adjusted to the hypothetical plant (which removes 221 g of phenol every hour). Assuming the plant operates 24 h a day, for 365 days a year, the kWh demand was then calculated. Using Eskom's business rate of R 1.46/kWh, the annual electricity cost was determined [78]. This electricity cost was added to the previous expenses to determine the annual operating cost. Then, the hypothetical chlorination and ozonation plants were investigated. Once the hourly chlorine and ozone dose is known, it can be used to determine the capital cost, which then specifies the operating cost [21]. Using the phenol experiments reported in Table 2, the mass of chlorine and the mass of ozone required to remove 1 g of phenol per hour was determined. This value was scaled up to the demands of the hypothetical plants to determine their capital costs. After adjusting the capital costs for inflation, the annual operating expense of each plant was determined. While performing the operating cost calculations outlined above, the capital expense for each plant was indirectly determined. Energy Yield Calculations  
Each technology type was compared based on its respective energy yield. This is de- fined as the mass of the pollutant removed per kWh supplied. A higher energy yield implies a more energy-efficient technology. As stated previously, phenol was selected as the model pollutant to be degraded. The plasma's energy yield was first calculated using the phenol experiment reported in Table 3. The same table was utilised to calculate the electricity costs  
For chlorination, a more complex approach was used. Using data from the phenol experiment reported in Table 2, the chlorine dose and effluent flowrate were calculated. This information was then used to determine the annual electricity cost of a plant operating under these conditions [21]. Next, using Eskom's business tariffs from 2009, the annual kWh consumption of the plant was found [79]. The energy yield was calculated thereafter. Finally, the ozonation experiment reported under the phenol results in Table 2 was used. The hourly ozone dosage required to remove 1 g of phenol was recorded, and it was noted that an ozone generator using air as feed gas consumes 13 kWh per kg ozone produced [80]. Using this information, the ozonation's energy yield was calculated.