CORRECTION OF METABOLIC PARAMETERS AND UNIT PROCESS PERFORMANCE DATA

In the design of aquatic culture and holding systems, the metabolic characteristics of the culture animal must be known as a function of feeding and other important operational parameters. This includes consumption of dissolved oxygen, production of carbon dioxide, total ammonia nitrogen, and fecal solids. For laboratory work, the preferred method for determining metabolic rates is the intermittent-flow respirometer. For large commercial systems, the use of intermittent-flow techniques is physically impossible because the flow cannot be stopped.

The source of error in measurement of metabolic parameters in a flow-through system is due to a lag in system response. The system response depends strongly of  or  for a negative step change at t = 0:

The equations used to compute metabolic rates, performance of unit processes, and process efficiencies can be biased and under some conditions may be quite misleading. While a number of diverse procedures have been developed to correct these parameters for the lag times between input water and effluent water, their accuracy has not been documented . Six correction approaches (Steady-state, Fry, Northby, Niimi, Spline, and Poly) and three analytical

approaches  (Point, Mean, and Detailed) were evaluated.  For an assumed sine response  of  and  the Mean analytical approach, the variation of (a) with time, and (b) deviation of Steady, Fry, Northby, Spline, and Niimi are shown below:

In terms of the smallest  deviation, the ranking of the correction approaches are: Spline and Northby (best), Fry and Niimi, and Steady (worst).The Detailed analytical approach had the smallest error, followed by M ean and Point.