Resumen
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.