Abstract
In the external nitrification (EN) biological nutrient removal (BNR) activated sludge (AS) system, the nitrification process is removed from the main BNRAS system to a fixed media system external to the AS system (Hu et al., 2003). The ENBNRAS system provides considerable advantages over the conventional BNRAS system, e.g. reduced bioreactor volumes, secondary settling tank surface area and oxygen demand. Further, the ENBNRAS system provides opportunity for substantial system intensification. The performance and characterization of the ENBNRAS system has been successfully demonstrated at lab-scale (Hu et al., 2000, Sötemann et al., 2002), but has not yet been tested in full-scale implementation. In collaboration between the City of Tshwane Metropolitan Municipality (CTMM) and the University of Cape Town, ENBNR activated sludge is being implemented at fullscale at the Daspoort Waste Water Treatment Works (DWWTW) in Central Pretoria, South Africa. This paper describes the preliminary design of this full-scale plant and initial implementation. Water SA Vol. 30 (5) 2005: pp.37-43
Highlights
In the external nitrification (EN) biological nutrient removal (BNR) activated sludge (AS) system, the nitrification process is removed from the main BNRAS system to a fixed media system external to the AS system (Hu et al, 2003)
The sludge age of the system can successfully be reduced from typically 20–25 days in conventional BNRAS systems to 8–10 days in the ENBNRAS system, resulting in a 30% reduction in the activated sludge system volume required (Hu et al, 2000)
The aerobic mass fraction can be reduced from 50–60%, to less than 30% in the ENBNRAS system, and, concomitantly, the anoxic mass fraction can be increased from 25–35% to 55%
Summary
In the external nitrification (EN) biological nutrient removal (BNR) activated sludge (AS) system, the nitrification process is removed from the main BNRAS system to a fixed media system external to the AS system (Hu et al, 2003). This paper describes the design and initial implementation of full-scale external nitrification biological nutrient removal (ENBNR) activated sludge at the Daspoort Waste Water Treatment Works (DWWTW) operated by the City of Tshwane Metropolitan Municipality (CTMM) in Central Pretoria, South Africa. It presents a general description of the DWWTW, an overview of the main elements in the initial evaluation of DWWTW as a candidate site for EN implementation, and a summary of current performance of the EN system at DWWTW. The initial design to evaluate DWWTW for full-scale implementation of ENBNR is contained in detail in Muller et al (2003), and is summarised here
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