Characterization Of Slowly-Biodegradable Chemical Oxygen Demand (sbCOD) In Domestic Wastewater For Biological Denitrification-converted

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Authors: S. W. Howa, J. H. Sina, S. Y. Y. Wonga, P. B. Limb, A. M. Arisb, G. C. Ngoha, T. P. Curtiscand A. S. M. Chua

Department of Chemical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia
Indah Water Konsortium Sdn Bhd, No. 44, Jalan Dungun, Damansara Heights, 50490, Kuala Lumpur, Malaysia

Corresponding author: Adeline Chua Seak May

E-mail:;  | Tel: +603-79675291


Biological nitrogen removal is a common process to remove ammonia (NH3) and nitrate (NO3-) from domestic wastewater. The denitrification step in biological nitrogen removal process requires sufficient amount of biodegradable organics. Previous wastewater characterization study in the Klang Valley region suggested that our wastewater has low soluble biodegradable organics. Particulate settleable solids (PSS) in the wastewater made up the major portion of chemical oxygen demand (COD) in the wastewater. We hypothesized that the warm wastewater temperature (30 ± 2ºC) may accelerate PSS hydrolysis in wastewater. The hydrolysis of PSS may provide slowly-biodegradable chemical oxygen demand (sbCOD) for denitrification. This study aimed to investigate the potential of utilizing sbCOD for denitrification in treating wastewater in the Klang Valley. We sampled wastewater and sludge from six WWTPs across Klang Valley region. We characterized the fractions of COD in the wastewater by fractionation experiments. The PSS hydrolysis kinetic coefficients weredetermined at tropical temperature (30 ± 2ºC) by oxygen uptake rate (OUR) experiment. The wastewater samples was low in readily-biodegradable COD (rbCOD), which made up 3 –40% of total COD (TCOD). Most of the biodegradable organics was in the form of sbCOD (15–60% of TCOD). The amount of biodegradable COD (rbCOD + sbCOD) in the wastewater was sufficient for denitrification. The PSS hydrolysis rate was 3 times higher than that at 20ºC. The high PSS hydrolysis rate may provide sufficient sbCOD to achieve effective biological nitrogen removal performance for the wastewater in the Klang Valley region.

Keywords: Biological nitrogen removal; particulate settleable solids; hydrolysis; COD fractionation

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