This study used high and low concentrations of glucose and acetic acid as carbon sources in two aerobic-anoxic-oxic (A₂O) processes. Trials were shock loaded with different concentrations of Cd²⁺. It was observed that the substrate utilization rate decreased when glucose concentration increased and thus the activated sludge of A₂O preferred acetic acid as a carbon source over glucose. Under anaerobic conditions, activated sludge readily transformed the substrate into poly-b-hydroxybutyrate (PHB) by the Entner–Douderoff (ED) pathway with ease, but not into poly-b-hydroxyvalerate (PHV) by the Embden–Meyerhof–Parnas (EMP) pathway. However, ED pathway was suppressed more severely by cadmium shock loading than that of the EMP pathway. The shock loading of Cd²⁺ greatly inhibited the anaerobic phosphate release rate with a half inhibition concentration of 10 mg L⁻¹ when acetic acid was used as a substrate. The phosphate removal efficiency of A₂O with acetic acid was affected by Cd²⁺ shock loading more than that of glucose. Therefore, A₂O with glucose as a substrate could tolerate the Cd²⁺ shock loading better than that of A₂O with acetic acid. This study also showed that polyphosphate accumulating organisms (PAOs) were more sensitive to Cd²⁺ toxicity than that of glycogen accumulating organisms (GAOs). With the addition of Cd²⁺, PHB/PHV synthesis/degradation was inhibited more apparently in acetic acid trials than that of glucose trials.

The purpose of this study was to study how temperature variation affects the tolerance of phosphorus accumulating organisms (PAOs) in a toxic environment. To exclude the interference of glycogen accumulating organisms (GAOs), shock loading experiments were conducted to study the effect of Cu(II) toxicity on the metabolisms of PAOs in 10, 20, and 30 °C conditions. The experimental data showed that the temperature effects on aerobic phosphorus uptake, PHA degradation, and glycogen synthesis were remarkable in the presence of Cu(II). Nevertheless, insignificant effects on anaerobic phosphorus release and PHA synthesis were found. The largest inhibition of PAO metabolism occurred in the low temperature case (10 °C). This study also experimentally demonstrated the loss of PAO metabolic ability in the subsequent aerobic stage, after the anaerobic stage. The presence of Cu(II) toxicity mainly resulted from the inhibition of biochemical reactions in the aerobic stage, and it was irrelevant to the inhibition of previous anaerobic metabolisms.