In activated sludge (AS) biotreatment, septic compounds such as volatile organic acids and reduced sulphur compounds have been frequently cited as a major cause of Thiothrix and Type 021N filamentous bulking. These filaments are common in Canadian pulp and paper biotreatment systems, where they cause settling problems in secondary clarifiers. We conducted a 14-week study of a TMP/newsprint mill effluent to characterize the septic compounds entering the biotreatment, and to determine correlations with AS biomass characteristics and biotreatment operating parameters. A significant correlation was found between the sludge volume index, the abundance of Type 021N, and the propionic acid (PA) concentration in the primary clarified effluent. PA also induced a significant change in the flocculating bacteria size distribution determined by digital imaging. Consequently, the correlation observed between PA and Type 021N bulking is an indirect effect of inhibition of floc-forming microorganisms, giving a competitive advantage to filaments.
Impact of septic compounds and operational conditions on the microbiology of an activated sludge system
Carl Pelletier, Mary Ann Fitzsimmons, Sophie Deschênes, Michael Paice; Impact of septic compounds and operational conditions on the microbiology of an activated sludge system. Water Sci Technol 1 March 2007; 55 (6): 135–142. doi: https://doi.org/10.2166/wst.2007.221
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