## 3 Results and Discussion
### Algal Growth in Different Initial pH Treatments  
ODs rapidly increased to about 2.1 for maximum algal yield until day 2 in all initial pH treatments, almost the same as those in the Tap medium (Figure 7a), due to amounts of residual glucose from the pretreated ADPEs. After that point, ODs in pH 9.0 treatment showed almost identical plateau value to those in Tap medium, increasing until the end of the experiment, but ODs in pH 7.0 and 8.0 treatments declined to about 1.3 (Figure 7a). In the pretreated ADPE, pH values gradually decreased to 7.0 in pH 9.0 treatments but sharply declined to about 3.4 in pH 7.0 and 8.0 treatments (Figure 7b). The sharp drops of pH in both pH 7.0 and 8.0 treatments were attributed to consumption of residue glucose and NH\({}_{4}\)\({}^{+}\) as described above, and resulted in decrease in algal yields due to cell damage induced by pH level below 5.0. However, these constant algal yields obtained in the pH 9.0 treatment might be because the level of pH above 7.0 (Figure 7b) failed to inhibit algal growth. As the hydroxide ion concentration at initial pH 9.0 was ten and hundred times quite higher than initial pH 8.0 and 7.0, respectively, the higher hydroxide ion concentration at initial pH 9.0, as well as that generated from algal photosynthesis, might partially neutralize hydrogen ion produced by consumption of residue glucose and NH\({}_{4}\)\({}^{+}\) in the pretreated ADPE, resulting in the pH levels above 7.0 during algal cultivation. These results suggested that the initial pH of 9.0 in the pretreated ADPE was the optimal treatment for constant maximum algal yield during the experiment. NH\({}_{4}\)\({}^{+}\)-N and TP concentrations were lessened during the first 2 or 3 days and then kept constant onward until the end of the experiments in all pH treatments (Figure 8a,c). NH\({}_{4}\)\({}^{+}\)-N concentrations decreased from 300 mg L\({}^{-1}\) to 60 mg L\({}^{-1}\) in pH 9.0 treatment, while those were lowered to 116 mg L\({}^{-1}\) in both pH 7.0 and 8.0 treatments at the end of the experiment (Figure 8a), in response to final algal yields. In pH 9.0 treatment, partial removal of NH\({}_{4}\)\({}^{+}\)-N might include volatilization losses during the first two days due to pHlevels of more than 8.0 (Figure 7b). This was because high pH above 8.0 favored ammonia volatilization [46]. Likewise, TP concentrations decreased from 21 mg L\({}^{-1}\) to 8 mg L\({}^{-1}\) in pH 9.0 treatment and reduced to 14 mg L\({}^{-1}\) in both pH 7.0 and 8.0 treatments through the study period (Figure 8c). pH levels of more than 7.0 helped to enhance phosphorus removal from wastewater through phosphate precipitation with metals, such as calcium phosphate and/or struvite [47; 48]. Due to pH levels of over 7.0 in the pH 9.0 treatment (Figure 7b), the TP removal was associated with algal assimilation and phosphate precipitation. NH4+ volatilization and phosphate precipitation, as well as assimilation by algal growth, resulted in relatively high NH4+-N and TP removals in pH 9.0 treatment. TN concentrations decreased from 380 mg L\({}^{-1}\) to 182 mg L\({}^{-1}\) until day 2 in pH 9.0 treatment and then remained almost constant (Figure 8b). In both pH 7.0 and 8.0 treatments, TN concentrations declined to about 250 mg L\({}^{-1}\) by day 3 but increased to 310-330 mg L\({}^{-1}\) on the final day, 1.7-1.8 times higher than those in pH 9.0 treatment (Figure 8b). The concentrations of COD showed similar trajectories to those of TN, slumping from 3000 mg L\({}^{-1}\) to about 617 mg L\({}^{-1}\) until day 2 in pH 9.0 treatment and then being constant (Figure 8d). However, in pH 7.0 and 8.0 treatments, the concentrations declined to 700 and 600 mg L\({}^{-1}\) by day 4 but increased to 900 and 785 mg L\({}^{-1}\) at the end of the experiment, respectively.