Thesis - faculty.ait.ac.th - Asian Institute of Technology

C.1 OUR Determination
In this study a selected volume of wastewater of known total COD is mixed with a
selected volume of mixed liquor of known MLVSS concentration in a batch reactor. After
mixing, the OUR is measured approximately every 5 to 10 minutes until OUR attains to a
constant value that is approximate or equal to OUR in the endogenous phase (Ekama, et al.,
1986). The respirogram is obtained by plotting the curve of OUR versus time as shown in
Figure C-1.
Where
OUR (mg/L.h)
D
A
g
g
B
C
Time (min)
Figure C-1 OUR Response in Respirometer (Ekama, et al., 1986)
Area A: This area gives the concentration of readily biodegradable COD
oxidized by the biomass.
Area B: This area represents the amount of less readily biodegradable
material being oxidized.
Area C: This area shows the amount of oxygen being used to convert
ammonia into oxidized nitrate (nitrification).
Area D: The area under the whole curve shows the total oxygen demand of
the liquor. This is the total amount of oxygen which must be
supplied to the sludge to achieve full treatment.
OUR at line e: The respiration rate at the end of the curve is the endogenous
respiration rate. This rate is proportional to the activity of the
biomass.
OUR at line f: This rate is the average respiration rate for the period where
nitrification and the breakdown of less readily biodegradable
substrates are occurring.
150
f
T
e
e