Oil/Water Separation (OWS)

What has the Army done? What does the Army have planned? Why is this important? Read more about it.

What is it?

The Army has a variety of maintenance and industrial operations essential to its combat readiness. These activities include vehicle wash racks; maintenance facilities; petroleum, oil and lubricants (POL) storage; grease racks; and runoff containment. The waste stream produced by these activities may be contaminated with oil or grease. OWS are used to remove the contamination from the waste stream. After leaving an OWS the wastewater is often sent to a wastewater treatment plant for final polishing.

What has the Army done?

The DoD Clean Water Act Service Steering Committee (CWASSC) tasked the U.S. Army Environmental Command (USAEC) to develop guidance, tools and technologies for addressing OWS problems through the creation of the OWS subgroup. The OWS subgroup published a DoD OWS Guidance Document in 1999 that included a considerable volume of technical and regulatory literature related to the planning, design, construction, procurement, operation, maintenance and record keeping associated with OWS.

A team of representatives from USAEC, U.S. Army Construction Engineering Research Laboratory (USACERL) and the U.S. Army Aberdeen Test Center (USAATC) visited Army National Guard units in California and South Carolina and Wright-Patterson Air Force Base to conduct OWS evaluation studies. The OWS were evaluated during a maintenance wash event and water samples were taken before and after the water entered the separator. Records of operation and maintenance were also evaluated to determine if the OWS was being maintained properly.

The USAEC sponsored an effort with USAATC to examine technologies used to retrofit existing Army OWS. The primary technology examined was the vertical tube coalescer (VTC) packs. The oleophilic tube packs increase the effectiveness of oil separation.

Several concentrations of oil and soil were run through a pilot scale OWS. These three influent concentrations had a known amount of total petroleum hydrocarbons (TPH) and total suspended solids (TSS). The concentrations used in the study were based on typical Army Reserve facilities wastewater characteristics determined by USACERL. The concentrations of TPH were monitored before and after running through the OWS. The differences in the concentration determined the oil removal efficiency.

The tests were run not only at different concentrations of TPH but also at different flow rates. This was to determine if the use of VTC could allow for the increased flow through the OWS while still meeting discharge criteria.

In order to determine the true effectiveness of the VTC, all tests were repeated with and without the tubes installed. This gave the study a baseline to compare the removal efficiencies.

Results of this bench scale study are available in the document Final Report of the Coalescing Tubes Test for OWS.

Several Army installations were identified that either installed OWS with VTC tube packs or had retrofitted existing OWS with VTC tube packs. A site visit and reconnaissance was conducted to evaluate the feasibility and applicability of their OWS for further testing. A case study was developed to investigate the installation's experience with the retrofitted units. The OWS performance was investigated by evaluating the effectiveness of the unit with and without the VTC tube pack assembly in place. Observations and recommendations were made on design selection, construction, materials, operation & maintenance, and effectiveness of the tube systems. Results of the study can be found in the final report "Replacing or Retrofitting OWS."

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What does the Army have planned?

OWS are an important part of pretreatment of wastewater discharges from washrack operations. The OWS is the first line of defense in the proper handling of washrack wastewater. USAEC, USACERL and USAATC collaborated to evaluate OWS as an intricate part of a washrack system. A decision tree was produced with the data gathered from the investigation. The decision tree was designed to assist facility and environmental mangers in dealing with their OWS environmental compliance problems. The decision tree complements other guidance documents dealing with pretreatment of washrack wastewater.

The decision tree format is a series of questions in flowchart form aimed to help the OWS assessors define any necessary corrective actions. The evaluator must have knowledge of separator design and maintenance in order to utilize the decision tree. The decision tree is sequenced such that responses to questions are often dependent on corrective actions being completed from the previous level.

Results of the study and the decision tree can be found in the final report A Decision Tree for Improving Washrack OWS Operations.

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Why is this important?

The military's mission requirements make it one of the largest purchasers of OWS in the United States. Unfortunately, some of the separators the military installed are not performing as anticipated. Inadequacies result from poor design, improper selection of off-the-shelf units, failure to understand the characteristics of the wastewater and lack of maintenance. The same problems can be found with field-constructed separators.

Most OWS are designed to remove oil and grease from waste streams. In reality OWS encounter significant quantities of dirt, cleaning aids, fuels, floatable debris, improperly disposed litter and other material.

Primarily, military OWS fail because of improper or inadequate maintenance. At times this is due to lack of convenient access for maintenance of the OWS. Some designs have only manhole access ports or are installed completely below paved surfaces. When OWS fail they become ineffective. As a result, oil does not separate out of the OWS. Improper discharge of the wastewater can lead to regulatory action, treatment plant overload, or contamination of a storm water discharge system.

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Oil/Water Separation (OWS)