Respirometric anatomy of the OSA process: microbial basis of enhanced sludge reduction mechanism

Nevin Yağcı, İlke Pala-Özkök, Feraye Sarıalioğlu, Buşra Allı, Nazik Artan, Derin Orhon, Seval Sözen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


BACKGROUND: Extensive research effort has been devoted to the performance of the OSA system. Despite all studies focused on the assessment of observed sludge yield values, their explanations of the mechanisms causing sludge reduction remained highly speculative. RESULTS: A laboratory-scale OSA system fed with peptone mixture was operated together with a system consisting only of a sequencing batch reactor. The experimental program focused on the assessment of the nature and characteristics of all streams by calibrating an appropriate model by oxygen uptake rate profiles obtained under different conditions. Results indicated that the interchange stream contained a significant fraction of heterotrophic biomass. Therefore, interpretations of the microbial functions in the OSA/oxic reactor should account for active heterotrophic input through the interchange stream. As also justified by corresponding mass balance expressions, the OSA/oxic reactor sustained a substantially higher active biomass concentration as compared with the control reactor. In this way, the relative magnitude of the endogenous decay was significantly increased with respect to microbial growth and the observed experimental results totally accounting for the excess sludge reduction in the tested lab-scale OSA system. CONCLUSION: The experimental results in this study provided conclusive proof that enhanced endogenous decay due to higher active biomass level sustained in the OSA/oxic reactor should be regarded as the major cause of excess sludge reduction in the OSA system.

Original languageEnglish
Pages (from-to)3462-3471
Number of pages10
JournalJournal of Chemical Technology and Biotechnology
Issue number12
Publication statusPublished - Dec 2018

Bibliographical note

Publisher Copyright:
© 2018 Society of Chemical Industry


The work was supported financially by Research Fund of Istanbul Technical University (Project #38071). The authors would like to recognize with gratitude, the time and effort devoted by Prof. Mark van Loosdrecht to reviewing the manuscript and expressing his comments for improving it.

FundersFunder number
Istanbul Teknik Üniversitesi38071


    • enhanced endogenous decay
    • excess sludge reduction
    • modeling
    • OSA process
    • respirometry


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