## 2 Materials and Methods
### Advanced Oxidation Pretreatment Tests  
Fenton oxidation was conducted after adjusting the initial pH of the reclaimer wastewater to 3.0 using 1 N H\({}_{2}\)SO\({}_{4}\) referring to the optimal initial pH range of 2.5-4.5 [2]. After completely dissolving 7.69 g of FeSO\({}_{4}\).7H\({}_{2}\)O in 700 mL of pH-adjusted reclaimer wastewater, 34.5 wt% H\({}_{2}\)O\({}_{2}\) was continuously added at a flow rate of 2.34 mL/min using a peristaltic pump. The continuous H\({}_{2}\)O\({}_{2}\) feeding scheme was adopted to avoid the side reaction of hydroxyl radical with H\({}_{2}\)O\({}_{2}\), which could scavenge the hydroxyl radical available for MDEA degradation [25]. The Fenton reaction started with the addition of H\({}_{2}\)O\({}_{2}\) and proceeded for 60 min under room temperature and 300 rpm mixing condition. To check the reaction extent, 10 mL samples were collected every 5 or 10 min and all samples were kept refrigerated after the following procedures: 4 mL of 1 N NaOH solution was added per 1 mL of the sample immediately after sampling to terminate the Fenton reaction [2]; the samples were heated at 70 \({}^{\circ}\)C for more than 30 min because residual H\({}_{2}\)O\({}_{2}\) present in the sample could affect COD analysis [3]; the samples were centrifuged at 3000 rpm for 3 min and filtered using 0.45 \(\upmu\)m syringe filter (6746-2504, Whatman, Maidstone, UK) to remove the precipitate generated by the reaction of Fe\({}^{2+}\) and NaOH.  
In the ozone oxidation test, a specially designed experimental apparatus consisting of reactor (a closed system, 700 mL working volume), demister, ozone generator (PC57-10, Ozonetch, Daejeon, Republic of Korea), ozone analyzer (OM-1500B, Ozonetch, Daejeon, Republic of Korea), and gas flow meter was used as shown in Figure 1. No initial pH adjustment of the reclaimer wastewater was made since the optimum pH range for ozone oxidation was reported as over 8 [15,16]. The ozone generator supplied a O\({}_{3}\)/O\({}_{2}\) mixed gas containing 56.0 mg-O\({}_{3}\)/L of ozone into the reactor at a flow rate of 1 L/min. The ozone oxidation reaction began with the addition of the reclaimer wastewater into the reactor and lasted for 480 min under room temperature and 300 rpm. The ozone concentration in the effluent gas of the reactor was monitored in real time using the ozone analyzer. Ozone consumption in the reaction was calculated from the difference between the ozone concentrations before and after the wastewater addition. To investigate the efficiency of ozone oxidation pretreatment, 15 mL samples were collected every 60 min, and all the samples were preserved in a refrigerator after filtering using 0.45 \(\upmu\)m syringe filter until pending analysis.  
In the peroxone oxidation test, the ozone-supplying condition was slightly changed and H\({}_{2}\)O\({}_{2}\) was added together with ozone. An O\({}_{3}\)/O\({}_{2}\) mixed gas containing 32.5 mg/L of ozone was supplied at a flow rate of 1 L/min, and 5 wt% H\({}_{2}\)O\({}_{2}\) solution was continuously fed at a flow rate of 0.1 mL/min using a peristaltic pump. Other reaction conditions and sampling methods for peroxone test are the same as the ozone oxidation test.  
\begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Reclaimer Wastewater** & **Cokes Wastewater** \\ \hline COD (mg/L) & 44,721 & 3967 \\ TN (mg-N/L) & 3064 & 263 \\ NH\({}_{3}\) (mg-N/L) & 227 & 47 \\ MDEA (mg/L) & 20,548 & n.d. 1  \\ Formate (mg/L) & 20,420 & n.d. 1  \\ Phenol (mg/L) & 841 & 1024 \\ SCN\({}^{-}\) (mg/L) & 2479 & 455 \\ pH & 10.0 & 9.0 \\ \hline \end{tabular}
\end{table}
Table 1: Characteristics of wastewaters.