Model 1 Nitrogen Removal in Facultative Lagoons Plug Flow Model

where:

Ne = effluent total nitrogen (mg/L) N0 = influent total nitrogen (mg/L)

KT = temperature dependent rate constant = K2o(6)(t-20) = rate constant at 20°C = 0.0064, where 9 = 1.039

t = detention time in system (d)

pH = pH of near-surface bulk liquid

Note: See USEPA (1983) or Reed (1984) for typical pH values or estimate using pH = 7.3e00005ALK, where ALK = expected influent alkalinity (mg/L) (EPA, 1983; Reed, 1984).

Use the Mancini and Barnhart (1976) equation to determine lagoon water temperature:

where:

A = surface area of pond (m3) Ta = ambient air temperature (°C) T = influent temperature (°C) Q = influent flow rate (m3/d)

Source: Reed, S.C., J. WPCF, 57(1), 39-45, 1985. With permission.

of these models are written in terms of total nitrogen, and they should not be confused with the still-valid equations reported by Pano and Middlebrooks (1982) that are limited to the ammonia fraction. Calculations and predictions based on total nitrogen should be even more conservative.

A high rate of ammonia removal by air stripping in advanced wastewater treatment depends on a high (>10) chemically adjusted pH. Algae-carbonate interactions in wastewater lagoons can elevate the pH to similar levels for brief periods. At other times, at moderate pH levels, the rate of nitrogen removal may be low, but the long detention time in the lagoon compensates.

Figure 4.30 illustrates the validation of both models using data from lagoon systems not used previously. The diagonal line on the figure represents a perfect fit of predicted vs. actual values. The close fit and consistent trends verify that either model can be used to estimate nitrogen removal. In addition, the models have been used in the design of several lagoons systems and have been found to work well.

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