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

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.


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Durmaz, B; Sanin, Faika Dilek (2001-01-01)
Effect of carbon to nitrogen ratio (C/N) on the sludge extracellular polymer composition is studied in synthetically fed semi-continuous reactors with 8 days of sludge age. Results show that C/N ratio influences the relative distribution of polymer carbohydrate and protein. At low C/N ratio of 5, polymer extracts have high protein and low carbohydrate content. As the C/N ratio is increased to 17.5 and then to 40, carbohydrate concentration increases sharply and protein concentration decreases.
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Citation Formats
B. Durmaz and F. D. Sanin, “Effect of carbon to nitrogen ratio on the physical and chemical properties of activated sludge,” ENVIRONMENTAL TECHNOLOGY, pp. 1331–1340, 2003, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/49022.