GPS-X Technical Reference

Appendix C – Respirometry C-1
A P P E N D I X B
Respirometry
INTRODUCTION
Advanced mathematical models summarize knowledge of the activated sludge
wastewater treatment process. The models are useful for design and operational
assistance of the activated sludge process. For their application, information on the
wastewater and activated sludge characteristics must be available. Batch
measurements are generally considered valuable for determination of these
characteristics, which, in terms of the activated sludge models, are expressed as
concentrations of components, kinetic parameters and stoichiometric coefficients.
Respirometry provides a good means for the assessment of these characteristics.
Respirometry is the measurement of the respiration rate of activated sludge under
well-defined experimental conditions and the application of the measurements for
modelling, design and operation of the activated sludge process. This appendix
summarizes the biological background of respiration, and the measurement and
application of respiration rate.
THEORETICAL BACKGROUND
Microorganisms obtain energy for growth and maintenance from the biodegradation
of substrate. In the process, referred to as respiration, electrons removed from the
substrate enter the electron transport chain and are ultimately accepted by a terminal
electron acceptor. In the aerobic biodegradation the terminal electron acceptor is
molecular oxygen. This means that oxygen consumption is directly associated with
both biomass growth and substrate removal. The consumption of other electron
acceptors like nitrate, in an anoxic environment, is also associated with these
processes. This document, however, deals with the measurement and application of
oxygen consumption. The mass of oxygen that is taken up per unit of volume and
unit of time is called oxygen uptake rate or respiration rate.
Modelling is important in the design and control of the activated sludge process, as
well as for understanding the basics of respiration and the application of respiration
rate measurements in practice. In the Activated Sludge Model No.1 oxygen
consumption is associated with aerobic growth of heterotrophic and autotrophic
biomass. The model implies that, even when all the substrate originating from the
wastewater is oxidized, there remains an oxygen consumption associated with the
growth on substrate released from decay and hydrolysis, respectively. The amount
of new biomass from released substrate is always less than the amount of biomass
lost. Hence, if the biomass is left on its own the oxygen consumption will gradually
decrease until all the biomass has decayed (see also further). The respiration rate
during this process is called endogenous respiration rate. The endogenous
GPS-X Technical Reference