Effect of carbon to nitrogen ratio on the physical and chemical properties of activated sludge

Durmaz B., Sanin F.

ENVIRONMENTAL TECHNOLOGY, vol.24, pp.1331-1340, 2003 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 24
  • Publication Date: 2003
  • Doi Number: 10.1080/09593330309385677
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1331-1340
  • Keywords: activated sludge, carbon to nitrogen ratio, extracellular polymers, physical properties, surface characteristics, EXTRACELLULAR POLYMERS, BIOFLOCCULATION, MECHANISMS, SETTLEMENT, SURFACES
  • Middle East Technical University Affiliated: Yes


The effect of carbon to nitrogen ratio (C/N) of the feed on the physical and surface chemical properties of activated sludge is investigated. Semi-continuous reactors with 2 liters volume were operated at a mean cell residence time of 8 days. These mixed culture reactors were operated at 3 different carbon to nitrogen ratio. The operation of conventional activated sludge plants treating municipal wastewater is represented with reactors having a C/N ratio of 21 (in terms of the ratio of COD to TKN). Carbon and nitrogen limited activated sludge systems are represented by reactors with a C/N ratio of 9 and 43, respectively. The results show that C/N ratio has a profound effect on the ultimate physical and surface chemical properties of activated sludge. Both the steady state microorganism concentration and the amount of microbial extracellular polymers produced increase with increasing C/N ratio. The sludge becomes much harder to dewater and settle and it becomes more viscous as the C/N ratio increases. A decrease in surface hydrophobicity and an increase in surface charge of the sludge accompany these physical changes.