Cometabolic degradation and inhibition kinetics of 1,2‐dichloroethane (1,2‐DCA) in suspended‐growth nitrifying systems

Abstract

Cometabolic degradation of 1,2‐dichloroethane (1,2‐DCA) and its inhibitory impact on nitrification were investigated by the use of a mixed suspended‐growth culture enriched for nitrifiers. 1,2‐DCA was found to be cometabolically degradable by the nitrifier culture. This degradation rate was found to be dependent on the initial 1,2‐DCA level. The first‐order 1,2‐DCA degradation rate constants ranged between 0.42 and 0.87 L (g VSS)⁻¹ h⁻¹. Increase in NH₄‐N utilization favoured cometabolic degradation of 1,2‐DCA. The amount of 1,2‐DCA degraded per unit mass of NH₄‐N strongly correlated with initial NH₄‐N and 1,2‐DCA concentrations, ranging between 50 mg L⁻¹ and 200 mg L⁻¹ and 1600 µg L⁻ and 100,000 µg L⁻¹, respectively. The presence of 1,2‐DCA caused inhibition of oxygen uptake and NH₄‐N utilization. In spite of the adverse effect of 1,2‐DCA on the nitrifying biomass, the system had a high capacity for cometabolic removal of this compound even at inhibitory concentrations. 1,2‐DCA had mainly mixed inhibitor characteristics, but at low concentrations (<25,000 µg/L) it acted rather as a competitive inhibitor. The inhibition constants belonging to 1,2‐DCA, K _ic (the dissociation constant of the enzyme–inhibitory compound complex) and K _iu (the dissociation constant of the enzyme–substrate–inhibitory compound complex) were determined to be 6000–8000 µg L⁻¹ and 188,000–200,000 µg L⁻¹, respectively.

Keywords:

• activated sludge
• biodegradation
• cometabolism
• nitrification
• inhibition
• 1,2‐dichloroethane

Acknowledgements

The financial support of this study by the Research Fund of Bogazici University (Project No: B.A.P. 02Y101D) is gratefully acknowledged. We are grateful to Ercument Aktuz for his assistance in GC analyses.