Activated sludge vs. biofilm – effect of temperature on ammonia and nitrite oxidation rate in the hybrid reactor

Olga Zając, Monika Żubrowska-Sudoł, Martyna Godzieba, Sławomir Ciesielski

Nitrification is considered one of the most temperature-sensitive biological steps in wastewater treatment. Nitrifying bacteria are highly sensitive to temperature drops, resulting in a rapid decrease
in their activity. This study compares the effect of a rapid temperature decrease on the ammonia oxidation rate (AOR) and nitrite oxidation rate (NitOR), with consideration of the form in which
biomass develops in the IFAS-MBSBBR. Ammonia Utilisation Rate Tests and Nitrite Utilisation Rate Tests were conducted for two temperatures, namely 20°C and 12°C, for the following forms
of biomass: activated sludge (AS), biofilm (B), and combination of both – hybrid (H). The tests showed that nitrite oxidising bacteria inhabiting biofilm were more sensitive to a rapid temperature
change than those in activated sludge. A sudden drop of temperature caused a 15% higher than predicted decrease in AOR for AS. At 12°C, AOR changed more considerably than NitOR in tests
carried out for H. A temperature correction coefficient of 1.107–1.087 was proposed, applicable in hybrid wastewater treatment systems. Microbiological analysis shows that nitrifiers occurred more
abundantly in biofilm than in activated sludge.

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