## 3 Results and Discussion
### Effect of Peroxone-Pretreated Wastewater on BWTP  
When using AOP as pretreatment method for BWTP, the effect of AOP-pretreated wastewater on the microorganisms in BWTP should be carefully examined. The respirometer system adopted in this study is very useful for this purpose because it can rapidly determine the toxicity, biodegradability, and even pollutant biodegradation kinetics of the concerned wastewater [26; 27; 28; 29; 35; 36]. First, we investigated the toxicity of the raw and peroxone-pretreated reclaimer wastewater on the microbial sludge of the BWTP treating the cokes wastewater. The PH and PA toxicity of the raw reclaimer wastewater were determined to be 10.61% and 20.04%, respectively. These rather high toxicities imply that direct feeding of the raw reclaimer wastewater could adversely affect the performance of the BWTP. On the other hand, it was revealed that the PH and PA toxicities of the peroxone-pretreated wastewater were only 1.25% and \(-\)1.06%, respectively, which means that the peroxone method could be effectively combined with the BWTP without the concerns of inhibition effect. One can find the toxicity results for the Fenton and ozone pretreatments in Figure S2. Figure 5a shows the \(OUR_{exo}\) profiles for the cokes, raw reclaimer, and peroxone-pretreated wastewaters, from which the information about the biodegradability and the pollutant biodegradation kinetics of the wastewaters can be obtained. The \(OUR_{exo}\) profiles for other AOP methods are also given in Figure S3 for comparison. The short-term BOD (\(BOD_{st}\)) of the cokes wastewater was calculated to be 1200 mg/L, and its consequent \(BOD_{st}\)/COD ratio, which could represent its biodegradability, was determined to be 0.302. This \(BOD_{st}\)/COD value should be the reference when comparing the biodegradability of other wastewaters, since the microbial sludge used in the respirometer was obtained from the BWTP treating the cokes wastewater. The \(BOD_{st}\)/COD ratio of the raw reclaimer wastewater was 0.103, which implies that its biodegradability was much lower than the cokes wastewater. This might be due to the presence of high concentration of MDEA in the wastewater. In a separate respirometer test using pure MDEA solution, it was proved that the microbial sludge of the BWTP treating the cokes wastewater can hardly degrade MDEA (see Figure 5b). The estimated \(BOD_{st}\)/COD ratio of pure MDEA was only 0.004. The low biodegradability of the reclaimer wastewater could be remarkably improved by peroxone pretreatment up to the level corresponding to the \(BOD_{st}\)/COD ratio of 0.147. The partial oxidation of MDEA by peroxone pretreatment seems to be responsible for this improvement of biodegradability. Figure 4: Actual ozone consumption to MDEA degradation ratio in the ozone and peroxone pretreatment tests. The \(OUR_{exo}\) profiles shown in Figure 5a can also be used to investigate the microbial degradation kinetics of the pollutants present in the wastewaters. With an appropriate kinetic model like the Monod equation, the involved model parameters can be estimated by numerical regression of \(OUR_{exo}\) profile [35; 36]. In this study, however, we just focused on the qualitative analysis of the \(OUR_{exo}\) profile because there were so many pollutants in the wastewater, and thus, the consequent mathematical model system was extremely complicated. However, it should be noted that in the respirometer test it was basically assumed that the observed \(OUR_{exo}\) profile is the sum of the individual \(OUR_{exo}\) profile, which results from the biodegradation of the distinct pollutant in the wastewater [27; 35]. Therefore, we conducted additional respirometer tests for the major pollutants using pure chemicals, which would provide some clues to be able to interpret the observed \(OUR_{exo}\) profile (see Figure 5b). As can be seen in Figure 5a, the \(OUR_{exo}\) of the raw reclaimer wastewater rapidly increased immediately after the sample injection.