494
W.W. Eckenfelder, Jr., CD. Magee and C.E. Adams, Jr.
CONCLUSIONS
This investigation has led to the conclusion that the rate of BOD removal is
proportional to the equilibrium, or effluent, concentration of soluble BOD in a
completely-mixed system. A new approach has been proposed for designing aerated
lagoons which eliminates the direct influence of biological, solids in the basin. It is
recommended that the active mass, instead of simply volatile suspended solids, be
employed in the design.
The authors have concluded that the benefits of multi-stage systems relevant to a
single basin are marginal in warmer climates with relatively low strength wastes.
However, in colder environments, the total detention time can be reduced considerably
by employing two or more basins in series due to the thermal effects in the first basin.
When designing aerated lagoon systems, certain variables such as power level and
temperature can modify the design approach due to potential biological solids deposition
and BOD feedback during warmer months. These factors must be considered or an
underdesigned system may result.
DESIGN PROCEDURE
The aerated lagoons may be designed as single or multiple basins depending on which
configuration yields the greatest economy in land area and aeration horsepower. The
information required for design is as follows: wastewater flow; wastewater characteristics,
including BOD, suspended solids, nitrogen, phosphorus and temperature; mean ambient
temperature; treatment parameters including k, a, a', and b. Procedures for developing
these coefficients from laboratory or pilot plant studies have been described elsewhere (17).
Depending on the waste such factors as oil, COD, etc., may be required.
A suggested design procedure for the completely-mixed basins is as follows:
1. Assume various temperatures (T w ) for the basin (or the first basin if two basins in
series are to be considered) and calculate the retention time required in the basin to
achieve this temperature using Equation (14). The selected basin depth will usually be
selected between 8 and 16 feet, the deeper depths being preferred in cold climates for
maximum heat retention.
2. Calculate k t from Equation (15) for the various temperatures computed in (1).
3 Calculate the soluble effluent BOD for each detention period from Equation (5) and
plot as shown in Fig.5.
4. Compute the equilibrium suspended solids within the basin from Equation (4). This
will be the concentration discharged if one basin is used or the suspended solids entering a
second basin if two basins are used in series.
5. If only one basin is being considered, estimate the BOD contribution due to the
effluent suspended solids from Equation (8) and add this to the soluble BOD to obtain
the total effluent BOD. This completes the detention time calculations for a one-basin
design. Proceed to step (12).
6. Select a detention time for Basin One (tj) and enter Basin Two with the
corresponding effluent concentration of BOD (Se^ from Fig.5. Thus, the effluent from
Basin One (Sex) will be the influent to Basin Two (So 2 ).
7. Assume the temperature in Basin Two (Tw 2 ), correct k to this temperature and
W.W. Eckenfelder, Jr., CD. Magee and C.E. Adams, Jr.
CONCLUSIONS
This investigation has led to the conclusion that the rate of BOD removal is
proportional to the equilibrium, or effluent, concentration of soluble BOD in a
completely-mixed system. A new approach has been proposed for designing aerated
lagoons which eliminates the direct influence of biological, solids in the basin. It is
recommended that the active mass, instead of simply volatile suspended solids, be
employed in the design.
The authors have concluded that the benefits of multi-stage systems relevant to a
single basin are marginal in warmer climates with relatively low strength wastes.
However, in colder environments, the total detention time can be reduced considerably
by employing two or more basins in series due to the thermal effects in the first basin.
When designing aerated lagoon systems, certain variables such as power level and
temperature can modify the design approach due to potential biological solids deposition
and BOD feedback during warmer months. These factors must be considered or an
underdesigned system may result.
DESIGN PROCEDURE
The aerated lagoons may be designed as single or multiple basins depending on which
configuration yields the greatest economy in land area and aeration horsepower. The
information required for design is as follows: wastewater flow; wastewater characteristics,
including BOD, suspended solids, nitrogen, phosphorus and temperature; mean ambient
temperature; treatment parameters including k, a, a', and b. Procedures for developing
these coefficients from laboratory or pilot plant studies have been described elsewhere (17).
Depending on the waste such factors as oil, COD, etc., may be required.
A suggested design procedure for the completely-mixed basins is as follows:
1. Assume various temperatures (T w ) for the basin (or the first basin if two basins in
series are to be considered) and calculate the retention time required in the basin to
achieve this temperature using Equation (14). The selected basin depth will usually be
selected between 8 and 16 feet, the deeper depths being preferred in cold climates for
maximum heat retention.
2. Calculate k t from Equation (15) for the various temperatures computed in (1).
3 Calculate the soluble effluent BOD for each detention period from Equation (5) and
plot as shown in Fig.5.
4. Compute the equilibrium suspended solids within the basin from Equation (4). This
will be the concentration discharged if one basin is used or the suspended solids entering a
second basin if two basins are used in series.
5. If only one basin is being considered, estimate the BOD contribution due to the
effluent suspended solids from Equation (8) and add this to the soluble BOD to obtain
the total effluent BOD. This completes the detention time calculations for a one-basin
design. Proceed to step (12).
6. Select a detention time for Basin One (tj) and enter Basin Two with the
corresponding effluent concentration of BOD (Se^ from Fig.5. Thus, the effluent from
Basin One (Sex) will be the influent to Basin Two (So 2 ).
7. Assume the temperature in Basin Two (Tw 2 ), correct k to this temperature and