The effect of short-term dissolved oxygen transients on activated sludge

Abstract

The effect of short-term dissolved oxygen (DO) disturbances on municipal activated sludge was studied, in a batch system, with respect to changes in infernatant turbidity, suspended solid (SS) concentrations, proteins, polysaccharides, and cations in the extracellular polymeric substances (EPS). Results showed that turbidity increased by 20 times when the DO concentration decreased below 0.5 mg/L, and infernatant SS concentrations increased by 1 to 2 times with DO reduction, implying the presence of more unsettled particles in the infernatant. Concomitantly, soluble proteins increased from less than 1 mg/L to up to 30 mg/L, and bound proteins decreased by more than 15% under DO limitation. Further enzymatic tests confirmed that, compared with polysaccharides, proteins were more involved in preventing sludge deflocculation. The DO stress also caused significant changes in the bulk concentrations of K+ and Ca2+; K+ increased by 40% and Ca2+ decreased by 30%. When the DO concentration was restored after 6 hours, reversible changes were observed in infernatant turbidity and SS, and concentrations of EPS proteins and cations, indicating a possible physiological response of microorganisms to a short-term low DO disturbance. © 2008, CAWQ.