MIL-HDBK-1005/16
separator, and proper flow attenuation/flow equalization of the
influent. The designer should work to identify the user's needs
and the capability of any vendor-supplied equipment. These
aspects of system design are discussed in the following
paragraphs.
5.6.1
Wastewater Characterization. If possible, the
wastewater to be treated should be analyzed for total oil and
grease using conventional methods given by EPA, Standard Methods,
or American Society for Testing and Materials (ASTM). In
addition, the free, emulsified, and dissolved oil fractions
should be determined by the method described in API Publication
421 referred to in par. 5.2.3. In the absence of data, a design
globule diameter of 150 microns can be assumed for the design of
conventional separators and 60 microns for parallel-plate
separators.
As indicated previously, although OWSs are designed to
remove free oil they also remove solids. Therefore, the solids
content of the wastewater is important in overall system design.
Analyses should include TSS, volatile suspended solids (VSS), and
settleable solids. These analyses will help determine the amount
and frequency of settled materials that will need to be removed
from the bottom of the OWS and the advisability of providing grit
removal upstream of the OWS.
Other wastewater characteristics important in the
design of OWSs are the specific gravities of the oil and water
phases and the absolute viscosity of the wastewater, both at the
minimum design temperature. Wastewater temperature has a major
impact on the efficiency of the separator, with poorer separation
occurring at lower temperatures. Separators are not designed to
remove pollutants such as phenols, solvents, and heavy metals.
These pollutants should be addressed by the use of pollution
prevention techniques.
5.6.2
Site Considerations. The OWS should be designed to be
readily accessible for maintenance and inspection. Visual
inspection and the ability to probe for solids levels are
critical to good operation. Aboveground units are the easiest to
access for maintenance and inspection. If belowground units are
used, they should have adequate access points for inspection and
cleaning. Belowground units should also be installed with a
liner and leak-detection system.
5.6.3
Establishing the Design Flow. The efficiency of
separation also decreases when flow exceeds the design capacity
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