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(70-88) Inhibition of Nitrification in Activated Sludge by Copper: Effect of Heterotrophic Population. Allen, Herbert*,1, Cha, Daniel1, Song, June Sup1, 1 University of Delaware, Newark, DE, USA ABSTRACT- Autotrophic microbial oxidation of ammonia to nitrate is the key process in the removal of ammonia from wastewater. Because of the low growth rate of nitrifying bacteria and their sensitivity toward a wide variety of inorganic and organic compounds, nitrification process is often most susceptible to toxic compounds in wastewater. Copper is one of the heavy metals that is known to inhibit the activity of nitrifiers. However, most of reported studies on the effect of copper on nitrification were based on results from either pure culture or short-term batch mixed culture studies while the impact of heterotrophic communities present in mixed culture was rarely considered. The objective of this study was to investigate the role of heterotrophic population in nitrifying activated sludge in ameliorating the copper toxicity. A distinctive feature of the activated sludge morphology in systems which are characterized by temporal substrate gradients (i.e., sequencing batch reactor systems) is the presence of large amorphous zoogleal colonies that produce substantial amounts of negatively charged ECPs. We hypothesize that the presence of large quantities of these ECPs, which can bind soluble metals, will play a significant role in ameliorating copper toxicity. We conducted a series of copper inhibition experiments with laboratory-scale SBR systems to determine the impacts of this shift in heterotrophic population on the response of nitrifiers to copper. Three different feed cycles were used to introduce the substrate gradient in SBR systems. At longer operating cycle, ECP-producing heterotrophs were selected. As operating cycle increases (6 hr to 24 hr), toxicity curve shifts to the right, indicating that as heterotrophs produced more ECPs nitrifiers become less susceptible to Cu. Results thus far indicate that nitrifiers seem no more sensitive than heterotrophs to Cu based on IC50 results. Bench-scale continuous flow activated system has been constructed to further investigate the steady-state effect of copper discharge on nitrification. Effect of different MCRT and relationship between Cu speciation in the aeration tanks and nitrification inhibition were assessed. The shifting of microbial community structure inactivated sludge system receiving copper was monitored with fatty acid methyl ester (FAME) technology. Key words: Copper, Nitrification Inhibition, Heterotrophs |
