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Currently, one of the major challenges in activated sludge process is maintaining
appropriated process conditions. However, this system is exposed to the various negative
factors such as toxic agents, temperature and pH changes, shock hydraulic and pollutants loads as
well as aeration disturbance. Bioaugmentation is known as a technique which has been
applied to improve the removal of undesired compounds and to enhance the tolerance of
microorganisms against stressful conditions. For monitoring as well as the optimization purposes
the respirometry is a commonly applied tool in wastewater treatment plant operation. This
technique is based on oxygen uptake rate (OUR) measurement, which could be easily determined
during aerobic processes. The respiration rate reports the amount of oxygen per unit volume
utilized per time unit by the available microorganisms. Generally, this test has been applied to the
activated sludge process, especially to assess substrates’ toxicity and inhibition of biochemical
processes. Furthermore, the oxygen uptake rate has also been used to determine microbial
activity and viability.
In this study, the respiration activity in bioaugmented and non-bioaugmented activated
sludge under adverse conditions: low dissolved oxygen (DO) concentration and depletion of
external substrate was evaluated. The experiment was carried out in four laboratory scale
sequencing batch reactors (SBR), each with the volume of 8 dm3. The non-bioaugmented reactors
(SBR A and SBR B) were inoculated with activated sludge from biological reactor of municipal
wastewater treatment plant (MWWTP) Hajdów, in Lublin, Poland. The bioaugmented reactors
(SBR C and SBR D) were seeded with the same activated sludge but for the bioaugmentation the
commercial product Arkea® was used in dose 400 ml. The study was divided into two phases. In
the first one, in SBRs oxygen uptake rate was measured during average biological treatment in
SBRs. However, in the second part of investigation in SBR A and SBR C activated sludge was only
aerated, in the absence of substrate. Additionally, in SBR B and SBR D the low dissolved oxygen
level was maintained. It was observed that bioaugmented reactors were more resistant to negative factor
(low DO level and depletion of external substrate). The oxygen uptake rate was higher in
bioaugmented reactors than in non-bioaugmented reactors. Based on described experiment one
could notice that addiction of the Arkea® product improved tolerance of activated sludge for the
adverse conditions such a low DO level and the feeding inhibition, what is expressed by higher
respiration activity.
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