MIL-HDBK-1005/9A
3.9.2.2
Discharge to Navigable Water. To meet stringent
effluent quality requirements for direct discharge, additional
treatment is required after gravity separation in a LET.
Depending on specific load requirements, 80 to 90 percent of the
free and emulsified oil remaining after LET treatment must be
removed by secondary and tertiary treatment steps. An NPDES
permit would be required.
a) Batch treatment in a LET is the recommended
primary unit operation. Secondary treatment such as a dissolved
air flotation (DAF) or induced air flotation (IAF) unit will
remove significant amounts of residual and some emulsified oil
and grease. Normally, the effluent from a DAF/IAF unit will
contain 10 to 50 mg/L of oil and grease. Based on treatability
studies, it may be necessary to add coagulating and emulsion
breaking chemicals to the DAF/IAF influent to optimize removal
of contaminants. Sulfide control and metals removal may also be
necessary to meet stringent discharge criteria.
b) To provide consistent direct discharge quality
effluent, tertiary treatment is required. The recommended
process is multimedia filtration with relatively fine graded
media followed by carbon adsorption. In certain situations,
primarily where flows are higher and space limitations prevent
installation of a sufficient number or size of multimedia
filters, coalescing filtration units should be considered.
Coalescing filters are mechanically complex, but they perform
reliably if operated and maintained properly. Figure 12 shows a
schematic flow diagram for a treatment system to discharge to
navigable waters.
c) Design guidelines and criteria for these unit
processes are presented in paragraph 3.10.
3.9.2.3
Redundancy. The design of an oily waste treatment
system for either discharge criteria should provide 100 percent
redundancy for critical process equipment. (Determination of
criticality is based on the impact on effluent quality of loss
of a component, and on a specific hazard analysis. Also refer
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