## Design Equations Developed for Facultative Ponds

Note: t, hydraulic residence time (days); C0, influent BOD5 concentration (mg/L); Ce, effluent BOD5 concentration (mg/L); k, reaction rate constant (units vary); maximum reaction rate for Monod-type kinetics (units vary); KS, substrate concentration at 0.5 |m; a = V1 + 4ktD ; D, dimensionless dispersion number; e, base of natural logarithms (2.7183); kd, decay rate (d-1); Y yield coefficient (mass of TSS or VSS formed per mass of BOD5 removed); AR, areal BOD5 removal (kg/ha-d); AL, areal BOD5 loading (kg/ha-d); C0u, ultimate influent BOD or COD (mg/L); 8, temperature coefficient (dimensionless); T, pond water temperature (°C); f, algal toxicity factor (dimensionless); f', sulfide oxygen demand (dimensionless); L, light intensity (langleys); pH, pH value; a, b, c, d, e, reaction orders; Z, constant; k2, k1, T2, T1, reaction rate constants and temperatures.

Source: Middlebrooks, E.J., Water Sci. Technol., 19, 12, 1987. With permission.

4.2.2 Gloyna Method

Gloyna (1976) proposed the following empirical equation for the design of facultative wastewater stabilization ponds:

where

La = Ultimate influent BOD or chemical oxygen demand (COD) (mg/L).

8 = Temperature correction coefficient = 1.085.

f = Algal toxicity factor.

f = Sulfide oxygen demand.

The BOD5 removal efficiency is projected to be 80 to 90% based on unfiltered influent samples and filtered effluent samples. A pond depth of 5 ft (1.5 m) is suggested for systems with significant seasonal variations in temperature and major fluctuations in daily flow. The surface area design using Equation 4.1 should always be based on a depth of 3 ft (1 m). The algal toxicity factor f) is assumed to be equal to 1.0 for domestic wastes and many industrial wastes. The sulfide oxygen demand f') is also equal to 1.0 for sulfate equivalent ion concentration of less than 500 mg/L. The design temperature is usually selected as the average pond temperature in the coldest month. Sunlight is not considered to be critical in pond design but can be incorporated into Equation 4.1 by multiplying the pond volume by the ratio of sunlight at the design location to the average found in the southwestern United States.

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