1. Bepaling van het Chemisch Zuurstofverbruik (CZV), 2e druk, NEN 6633,1990
2. Standard Methods for Examination of Wastewater;APHA,1990
3. Activated sludge and its process modifications;Benefield,1980
4. DIN Catalogue of Technical Rules, based on German Standard Methods for Examination of Water and Wastewater and Sludge;Beuth,1989
5. Biological denitrification of sewage: a literature review;Christensen;Prog. Water Technol.,1977