MIL-HDBK-1138
sludge stream, or both streams of a treatment facility. The
selected mode of septage addition will depend on the capacity and
type of processes at the facility. The ability of a treatment
facility to treat septage is typically limited by the available
aeration and solids handling facility. Before the septage enters
the treatment facility, it should be pretreated, including, at a
minimum, screening, equalization, and adequate blending with the
raw sewage.
Septage can also be chemically stabilized by using lime
(CaOH2) in a batch operation and by then applying the septage to
a permitted land application site. Lime can effectively destroy
most pathogenic and odor-producing microorganisms and has been
shown to improve dewaterability. The Code of Federal Regulations
(Part 503) requires that, to land-apply the septage, it must be
mixed with the lime to raise the pH to 12 or higher for a minimum
of 30 minutes. Special sludge spreading equipment is necessary
to ensure an even application of the septage on the land.
Because this treatment method would typically be independent of
the domestic wastewater treatment processes, it will not be
discussed further in this section.
6.4.1
Estimating Treatment Capacity. The available
treatment capacity of a system for receiving and treating septage
can be estimated by calculating the difference between the design
capacity of the system and the current loading to the system.
This information should be available in your environmental
office. Given the estimated available capacity, the volume of
septage that can be discharged to the treatment system can be
estimated by using the suggested organic and nutrient
concentrations presented in Table 4.
For example, assume that the available treatment
capacity of the treatment system was calculated to be 500 pounds
(227 kilograms) per day of BOD. The volume of septage that can
be discharged to the system can be estimated by dividing the
500 pounds (227 kilograms) by the estimated BOD concentration in
septage of 6,500 mg/L (Table 4). This equates to an allowable
septage volume of approximately 9,000 gallons (36 cubic meters)
per day [500 pounds per day x 1,000,000/(8.34 x 6,500 mg/L)].
Co-Treatment of Septage in Liquid Stream. Septage
6.4.2
addition in the liquid stream is the most common method of
septage treatment at a WWTP. The screened and degritted septage
can be added upstream of the primary or the secondary treatment
units. Adding septage upstream of the primary treatment units
will decrease the organic and solids loadings to the secondary
treatment units (e.g. activated sludge system) and will reduce
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