Equation Used To Estimate Correlation Coefficient

TKN Removal ln CJC0 = -0.0129 (detention time)

TKN removal rate = 0.809 (TKN loading rate)

TKN removal rate = 0.0946 (BOD5 loading rate)

TKN fraction removed = 0.0062 (detention time)

Ammonia Nitrogen Removal ln CJC0 = -0.0205i

NH3-N removal rate = 0.869 (NH3-N loading rate)

NH3-N removal rate = 0.0606 (BOD5 loading rate)

NH3-N fraction removed = 0.0066

Correlation Coefficient

0.911 0.983

0.967

0.959

0.798 0.968

0.932

0.936

Hydraulic Detention Time

125 132

79 92

Comparison with Maximum Detention Time (% Difference)

14.4

40.2

30.3

System

Ponds 1, 2, and 3 (mean monthly data) Total system (mean monthly data)

Total system (mean monthly data)

Ponds 1, 2, and 3 (mean monthly data)

All data (mean monthly data) Total system (mean monthly data)

Total system (mean monthly data)

(detention time)

Source: Middlebrooks, E.J. and Pano, A., Water Res., 17(10), 1369-1378, 1983. With permission.

Using any of these expressions will result in a good estimate of the TKN removal that is likely to occur in diffused-air aerated lagoons. Unfortunately, data are not available to develop relationships for surface aerated lagoons. The relationships developed to predict ammonia nitrogen removal yielded highly significant (1% level) relationships for all of the equations presented in Table 4.22; however, the agreement between the calculated detention times for ammonia nitrogen removal differed significantly from that observed for the TKN data. This variation is not surprising in view of the many mechanisms involved in ammonia nitrogen production and removal in wastewater lagoons, but this variation in results does complicate the use of the equations to estimate ammonia nitrogen removal in aerated lagoons.

Statistically, a justification exists to use either of the expressions in Table 4.22 to calculate the detention time required to achieve a given percentage reduction in ammonia nitrogen. Perhaps the best equation to use during design to predict ammonia nitrogen removal is the relationship between the fraction removed and the detention time. The correlation coefficient for this relationship is higher than the correlation coefficient for the plug-flow model, and both equations are equally simple.

Rich (1996, 1999) has proposed continuous-feed, intermittent-discharge (CFID) basins for use in aerated lagoon systems for nitrification and denitrifica-tion. The systems are designed to use in-basin sedimentation to uncouple the solids retention time from the hydraulic retention time. Unlike sequencing batch reactor (SBR) systems, the influent flow is continuous. A single basin with a dividing baffle to prevent short-circuiting is frequently used. Some CFID systems have experienced major operational problems with short-circuiting and sludge bulking; however, by minimizing these problems with design changes the systems can be made to function properly. CFID design modifications can be made to overcome most difficulties, and details are presented by Rich (1999). The basic CFID system consists of a single reactor basin divided into two cells with a floating baffle. The two cells are referred to as the influent (cell 1) and effluent cell (cell 2). Mixed liquor is recycled from cell 2 to the headworks to provide a high ratio of soluble biodegradable organics to organisms, and the oxygen source is primarily nitrates. This approach is used to control bulking. Although some nitrification will occur in the influent cell, the system is designed for nitrification to occur in the effluent cell. To learn more about the operation of the CFID systems, consult Rich (1999).

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