## 2 Materials and Methods
### Respirometer Experiments  
The respirometer system was setup as shown in Figure 2a, which consists of bioreactor containing microbial sludge, air supplier, and an online dissolved oxygen (DO) meter (HQ40d, HACH, Loveland, CO, USA). This respirometer system can assess the toxicity, the biodegradability based on short-term biochemical oxygen demand (BOD), and the microbial pollutant degradation kinetics of wastewater using the DO profile or its relevant exogenous oxygen uptake rate (\(OUR_{exo}\)) profile, which is obtained by injecting a wastewater sample into the bioreactor. The sludge used in the respirometer tests was obtained from the biological cokes wastewater treatment process of POSCO (Pohang Iron and Steel Company, Pohang, Republic of Korea).  
To estimate the toxic effect of the sample wastewater on the microorganisms, two additional reference wastewater injections are required before and after the sample wastewater injection (see, Figure 2b). Then, the toxicity of the sample wastewater can be calculated by  
Figure 1: Schematic diagram of the ozone and peroxone oxidation experiments: (a) oxidation equipment; (b) ozone concentration of effluent gases during the reaction; H\({}_{2}\)O\({}_{2}\) injection was made only in the peroxone experiment.  
Figure 2: Schematic diagram of respirometer experiments: (a) respirometer equipment; (b) DO profiles for toxicity, short-term BOD, and kinetics tests; (c) determination of short-term BOD or kinetics analysis using \(OUR_{exo}\) profiles.  
comparing the peak height (PH) or peak area (PA) of the References 1 and 2 injections as follows [26; 27; 28]:  
\[\%\;\textit{Toxicity}=\frac{PH(\textit{or PA})_{\textit{reference 1}}-PH(\textit{or PA})_{\textit{reference 2}}}{PH(\textit{or PA})_{\textit{reference 1}}}\times 100\;. \tag{1}\]  
In this study, the raw and AOP-treated reclaimer wastewaters were used as the sample wastewater, and the cokes wastewater was used as the reference wastewater. As such, 3 mL of sample or reference wastewater was injected for each toxicity test.  
The short-term \(BOD\) of the sample wastewater (\(BOD_{st}\)) can be calculated from the \(OUR_{exo}\) profile as follows [27; 29]:  
\[BOD_{st}=\int_{t\_pulse}^{t-final}OUR_{exo}(t)dt\times\frac{V_{Sludge}+V_{ sample}}{V_{sample}}\;, \tag{2}\]  
where \(OUR_{exo}(t)\) is the oxygen uptake rate at time \(t\) by the exogenous respiration of the microorganisms, \(t\_pulse\) is the time of the sample wastewater injection, \(t\_final\) is the time when \(OUR_{exo}\) returns to zero (endogenous respiration phase), \(V_{Sludge}\) is the sludge volume before the sample wastewater injection, and \(V_{sample}\) is the volume of the injected sample wastewater. The \(OUR_{exo}\) profile can be obtained from the DO profile using the following equation:  
\[OUR_{exo}=k_{L}a(O_{2,sat}-O_{2})-OUR_{endo}-\frac{dO_{2}}{dt}\;, \tag{3}\]  
where \(k_{L}a\) is the volumetric mass transfer coefficient for DO, \(O_{2,sat}\) is the saturation concentration of DO, \(O_{2}\) is the DO concentration, and \(OUR_{endo}\) is the oxygen uptake rate by the endogenous respiration.  
For all respirometer tests, the same following operating conditions were applied: initial bioreactor sludge volume of 700 mL, initial MLSS concentration of 5000 mg/L, air flowrate of 2 L/min, agitation of 300 rpm, and room temperature. For each respirometer test, at least two air off/on procedures were also conducted to determine \(OUR_{endo}\), \(k_{L}a\), and \(O_{2,sat}\), which are required for the \(OUR_{exo}\) calculation [27; 28].