EEC, the electricity cost and the cost of chemicals were calculated and their results are presented in Table 2. As can be seen, the order of ECC and electrical cost values of the processes followed the COD removal efficiency order based on Equation (8), the fraction numerator is constant for all the processes, while the fraction denominator depends on COD removal efficiency. Hence, with the increase in COD removal efficiency, ECC is decreased. On the other hand, the main costs of chemicals were directly based on the price of oxidants. PC had the lowest price in comparison with other oxidants, thus the chemical costs of the UV/PC and UV/PC/Fe2+ processes were less than those of the other ones. In comparison to PS, H2O2 was an oxidant with a lower cost. H2O2-based processes consume less mass of oxidant in comparison with others due to the low molar mass of hydrogen peroxide. As can be seen, chemical costs have a greater contribution to the total costs of the processes, while electrical costs play a non-significant role in comparison with the chemical costs. Therefore the total cost is highly dependent on chemical cost. Among the oxidants, PC was an inexpensive oxidant compared to the two other oxidants. Accordingly, the order of total costs was: UV/PS/Fe2+ > UV/PS > UV/H2O2/Fe2+ > UV/H2O2 > UV/PC/Fe2+ > UV/PC.

Table 2

ECC, electrical cost, chemical cost and total cost of the studied processes at 60 min reaction time

Parameters
ProcessesECC (kWh/kg COD removed)Electrical cost (US$/ kg COD removed)Chemical cost (US$/ kg COD removed)Total cost (US$/ kg COD removed) UV/PC 186.04 2.73 9.11 11.84 UV/PC/Fe2+ 145.69 2.14 10.87 13.01 UV/H2O2 131.14 1.92 11.25 13.17 UV/H2O2/Fe2+ 113.33 1.66 13.01 14.76 UV/PS 127.01 1.86 21.1 22.96 UV/PS/Fe2+ 113.03 1.66 22.86 24.52 Parameters ProcessesECC (kWh/kg COD removed)Electrical cost (US$/ kg COD removed)Chemical cost (US$/ kg COD removed)Total cost (US$/ kg COD removed)
UV/PC 186.04 2.73 9.11 11.84
UV/PC/Fe2+ 145.69 2.14 10.87 13.01
UV/H2O2 131.14 1.92 11.25 13.17
UV/H2O2/Fe2+ 113.33 1.66 13.01 14.76
UV/PS 127.01 1.86 21.1 22.96
UV/PS/Fe2+ 113.03 1.66 22.86 24.52

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