MIL-HDBK-1005/9A
to NAVFACINST 4862.5). It is important to avoid the loss of a
key unit operation during either scheduled or unscheduled
maintenance downtime for any piece of equipment.
Guidelines for LET design require multiple units and
redundant capacity for normal operation of the gravity
separation process (refer to paragraph 3.10.2). It is also
recommended that 100 percent redundancy be provided for
downstream polishing treatment units, transfer pumping
equipment, and effluent monitoring instrumentation.
3.9.3
Sulfide Control
a) Sulfide Formation. The presence of sulfides in
oily wastewater is primarily due to biological reaction
involving anaerobic bacteria that use hydrocarbons as their
energy source and convert sulfates to sulfides. The pH of
wastewater affects the distribution of sulfide species. If low
pH oily wastewater is exposed to the atmosphere, hydrogen
sulfide (H2S) gas is released causing severe odors and corrosion
problems. At alkaline pH, the sulfide species do not escape to
the atmosphere. Exposure to small concentrations of H2S in the
air is also a health hazard as it can affect the respiratory
system.
The time gap between the generation and treatment/
disposal of oily wastewater is a major factor for sulfide
formation. During this time, oxygen is rapidly depleted causing
a decrease in the ORP which favors the activity of sulfate
reducing bacteria. This time should be kept at a minimum to
limit sulfide production.
b) Control Techniques. The principal physical and
chemical methods for sulfite control at oily waste treatment
plants include chemical oxidation, chemical precipitation, and
wastewater aeration. Other techniques such as biological
processes or adsorption have limited application at Navy oily
waste treatment plants due to cost and operational requirements
of these processes.
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