Comparison of the Influences of Cadmium Toxicity to Phosphate Removal in Activated Sludge Separately Fed by Glucose and Acetic Acid as Carbon Sources

Abstract

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.