Les eaux résiduelles sont une combinaison des liquides et résidus provenant de l'usage des eaux en différents milieux. La provenance des eaux usées est directement liée aux rejets urbains, industriels et agricoles. Principalement les polluants contenus dans les eaux usées sont de la matière organique, l'azote et le phosphore.

This report describes a full-scale evaluation of the split return mode for nitrification-denitrification of a combined domestic/ industrial wastewater. The investigation, which took place from July 1974 to December 1975 at the Ontario Ministry of the Environment's Ontario Experimental Facility at Brampton, followed pilot-studies at Kleinburg, Ontario. The evaluation investigated the effect of ferric chloride addition on phosphorous removal; the effect of solids retention times and sludge ages on nitrogen reactions at various temperatures; hydrogen peroxide addition and the use of a screen centrifuge on mixed liquor conditioning; as weIl as the suitability of the system for solids control and for maintenance of consistent nitrogen removal under different temperature conditions. It was concluded that the single-sludge, split-return system gave excellent nitrogen removal with minimal methanol application.