GPS-X Technical Reference

Modelling Fundamentals 24
Nitrogenous Compounds
Based on our experience, the most important parameter to calibrate in the IAWQ model
is the autotrophic growth rate. It is possible to calibrate this parameter using field
ammonia and nitrate data, if:
1. The plant is not overloaded, i.e. the plant is at least partially nitrifying; or
2. The plant is not seriously under loaded. In such a case, almost any value of the
growth rate constant (typically between 0.2-0.5 d -1 ) will provide complete
nitrification.
The autotrophic growth rate is easier to identify in a partially nitrifying plant. Process
start-up data (i.e., corresponding to a slowly developing nitrifier population) can
sometimes be used. Laboratory testing (oxidation of an ammonia spike) is also a
possibility.
Settling Characteristics (Primary and Secondary)
The settling velocity function in Hydromantis' layered settler model contains five
parameters, which have to be determined separately for the primary and the secondary
clarifiers. A preliminary version of the model is described in detail elsewhere
(Takács et al., 1991). The model is based on the use of a unified settling velocity
equation described in the chapter on sedimentation and flotation models. The parameters
of the settling velocity equation can be estimated from a combination of experimental and
numerical procedures.
A short summary of the proposed experimental procedures is given below for each
parameter:
Minimum solids attainable – In general, this parameter for final settlers is
usually less than 10mg/L. For most plants, xmin will be close to zero. A sludge
sample is allowed to settle for about two hours. The suspended solids
concentration of the supernatant is measured and equated to xmin. Alternatively,
xmin can be said to be equal to the suspended solids concentration take from the
final settler under dry-weather flow conditions, when the hydraulic load to the
plant is minimal.
Maximum floc settling velocity parameter - Dilute the activated sludge to
1 2 g/L, measure the settling velocity of large individual floc particles in a batch
test. In general, no floc particle will settle faster than the settling velocity of
individual floc particles under quiescent conditions.
GPS-X Technical Reference