Determination of kinetic parameters in a pilot scale BNR system treating municipal wastewater

Kinetics for the biological processes of nitrification, denitrification and carbon oxidation were
studied in the aerobic and anoxic phases of a pilot scale Biological Nutrient Removal (BNR)
plant treating municipal wastewater. The configuration of the treating system is based on the
combination of the UCT (University of Cape Town) design and the step feeding process in a
cascade denitrification.
In order to study the process kinetics and to obtain reliable values for the investigated kinetic
parameters batch experiments were performed. For this purpose, continuous feeding of the
treating system was interrupted for a given period of time and the pilot plant was turned into a
batch mode of operation. Thereafter, addition of NO3
--N and NH4
+-N into the anoxic and
aerobic compartments of the treating plant, respectively, followed, whereas adequate initial
concentration of a carbon source (municipal wastewater or synthetic substrate) was ensured
in the mixed liquor. Experimental data indicated that the examined biological processes
followed saturation kinetics.
The maximum specific denitrification rate, qDN,max , was found to obtain values, depending on
the type of the carbon source, between 0,045 and 0,390 gNO3
--N/(gXHET·d), whereas the
extremely low value of the half saturation constant for the denitrification process (Km,NO3-N <<
1mgN/l) indicated its description by zero order kinetics. The maximum specific nitrification
rate, qN,max, was determined to vary in a narrow frame, between 1,28 and 1,60 gNH4
+-
N/(gXAO·d). The half saturation constant for the nitrification process, Km,NH4-N, was estimated
graphically at 3,1 – 6,1 gNH4
+-N l-1, corresponding to 62 – 122 μgNH3-N l-1. These values are
considered to be in good agreement with the literature.
The determination of kinetic parameters can be considered as a useful tool for the process
design, operation and improvement of wastewater treatment plants. Furthermore, the study of
the biological process kinetics contributes to the better understanding and outline of the
complicated biological processes that contemporarily take place within the various phases of
BNR wastewater treatment plants.