1. Moodley R, Wentzel MC, Ekama GA. External nitrification in BNR activated sludge systems with varying aerobic mass fractions. Proceedings of the Sixth Biennial WISA Conference and Exhibition, Suncity, May, CDROM ISBN 0-620-25661-3, Water Institute of Southern Africa, PO Box 6001, Halfway House, 1685, South Africa. 2000.
2. Hu Zhi-rong, Wentzel MC, Ekama GA. External nitrification in biological nutrient removal activated sludge systems. Water SA 2000;26(2):225–38.
3. Hu Zhi-rong, Wentzel MC, Ekama GA. External nitrification in biological nutrient removal activated sludge systems. Water Sci Technol 2001a;43(1):251–68.
4. Hu Z, Sötemann SW, Vermande SM, Moodley R, Little C, Lakay MT, Wentzel MC, Ekama GA. External nitrification in biological nutrient removal activated sludge systems. Final Report to the Water Research Commission on the Contract K5/970, Water Research Commission, P/Bag X03, Gezina 0031, South Africa, 2001b.
5. Hu Zhi-rong, Sötemann SW, Moodley R, Wentzel MC, Ekama GA. Experimental investigation on the external nitrification biological nutrient removal activated sludge system—The ENBNRAS system. Biotech Bioeng 2003, in press.