Oil /Water Separators Best Environmental Practices for Auto Repair and Fleet Management


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OIL/WATER SEPARATORS

Best Environmental Practices for Auto Repair and Fleet Maintenance • November 1999

Simplified diagram of OWS operation
WASTEWATER-oil, water and solids

SLUDGE— dirt, sand, sweepings

Heavier or Lighter Than Water? OWSs treat vehicle
and floor wash water by allowing substances lighter
than water to float and substances heavier than water
to sink. Many OWSs also have baffles, coalescers,
and oil skimmers to speed-up or enhance separation
of these substances.

Why be concerned
about oil/water separators?

Oil/water separators (OWS) can be costly to maintain, and if not prop-
erly managed, can pollute surface and ground water, and lead to costly
violations. Have you taken steps to minimize the effects of your OWS
on your budget and the environment? This fact sheet discusses the
basic operation of OWSs in handling vehicle and floor wash water, and
techniques to improve OWS performance and reduce costs and liabili-
ties. To make sure your OWS works properly, remember:

Eliminate contaminants: Don't rely on the OWS to handle wash
water from fuel, coolant, solvent, oil, or paint spills. Instead, clean
up spills when and where they occur with dry methods (see the
Floor Cleanup fact sheet).

Wash without detergents: Emulsifying cleaning compounds dis-
perse oil in wash water and make OWSs ineffective-oil passes
right through to the sewer. High pressure water or non-emulsifying
cleaners are sufficient for most cleaning applications.

Minimize Loading: Minimize the amount of solids and oils that
enter your OWS. The less solids and oils that reach the OWS, the
less frequently sludge and floating oil must be removed from the
OWS and the better it will work. Also, minimize the amount of wash
water reaching the OWS. Excessive water flow can flood an OWS,
forcing wastewater through it too fast to allow separation; the
result: oil and other contaminants pass right through to the sewer.
OWSs should not be used to treat storm water runoff.

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TROUBLE SITUATIONS

POTENTIAL IMPACT

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REMEDY

Chemicals and spills
reach OWS

•	Sewer discharge violation

•	Sludge requires disposal
as hazardous waste

•	Eliminate floor drains from shop

•	Clean up spills when and where they occur

•	Use dry cleanup techniques in shop

Sludge builds up in OWS

• OWS is less effective because
solids have less time to settle

•	Eliminate storm water flow into the OWS using berms or curbs

•	Install additional grates and screens on drains

•	Use sloping pavement and sediment traps around drains

Excessive floating oil
accumulates in OWS

• Oil discharged to sewer
during high flow periods

•	Pump out accumulated oil on a regular schedule

•	Use oil-only absorbent pads to remove and recycle oil

•	Use high-pressure, low-volume sprays for vehicle washing

Detergents reach OWS

• Oil is emulsified and
flows out of OWS to sewer

•	Do not use oil-emulsifying cleaning solutions (detergents)

•	Wash vehicles and engines less often

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Oil/Water Separators

Best Environmental Practices for Auto Repair and Fleet Maintenance

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How do I keep oil and solids out?

Filter filter filter. The best way to reduce OWS sludge is to keep
solids out of vehicle and floor wash water. Install progressively finer
grates and screens over the drains to the OWS inlet in order to
maximize solids separation:

• Begin with steel bars spaced 3/4 to 1-inch apart at the
OWS drain inlet

• Add sequentially finer grates and screens

(3/4 and l/4-inch screens or l/4-inch expanded steel mesh)

• Finish with reusable absorbent material to remove
very small particles.

• Use oil-only absorbents to separate and recycle oil from your OWS.

In some older OWSs, it is not easy to collect and remove separat-
ed oil. If your OWS does not have an oil trough or other oil collec-
tion device, you can use reusable absorbent pads that absorb
only oil and grease. Put these pads on the water surface to collect
floating oil. Once saturated, squeeze the oil from the pads; this oil
can be managed with your used oil, if the squeezed oil is not cont-
aminated with hazardous waste (get data on your wash water
quality or analyze a sample at least once to verify). The squeezed
absorbent pads can be reused.

• Use microbes to digest oil in your OWS. Bioremediation is a
proven technique to minimize the oil content in OWS effluent and
sludge and to reduce OWS cleanout frequency. Microbes added
to an OWS break down petroleum products suspended or dis-
solved in the wastewater, floating oil, or sludge. Facilities using
bioremediation have eliminated wastewater violations and have
reported reducing their sludge petroleum content by more than
80 percent. Such reductions can lower the regulatory status of
OWS sludge, which will affect the required disposal method
and disposal costs. Bioremediation is typically performed under a
vendor service contract. Microbes are added to an OWS or inter-

ceptor lines on a regular basis to replenish microbe populations.
Microbes are nontoxic and completely safe; the main by-products
of bioremediation are water and carbon dioxide. Vendor service
contracts usually cover all materials and labor; monthly costs
range from $75 to $130 depending on the size and contaminant
loading of the OWS.

Bioremediation Benefits:

• Lower hydrocarbon levels in OWS effluent

¦ Less contaminated sludge and lower volume of sludge

• Reduction or elimination of odor

Limitations of Bioremediation:

¦ Microbe populations can be killed by harsh chemicals
or pH levels greater than 8.5; do not use detergents
that are caustic or contain emulsifiers

Case studies:

Car Repair and Car Wash

Salem Boys Auto of Tempe, Arizona used sloping pavement, grates, and
screens to minimize OWS loading. These controls, together with biore-
mediation, decreased the sludge cleanout frequency and cost by 75%.

U.S. Postal Service Fleet
Maintenance Facility

The Huntington Beach, California facility used bioremediation to
reduce OWS effluent hydrocarbon concentration by more than 80%.

Your state or Local government environmental agency has more information about compliance and pollution prevention for auto repair shops and
fleet maintenance operations in your state or area. Additional fact sheets and information can be found at www.epa.gov/region09/p2/autofleet.
This fact sheet is part of a package of fact sheets entitled either "The Pollution Prevention Tool Kit, Best Environmental Practices for Auto Repair"
(publication number EPA-909-E-99-001) or "The Pollution Prevention Tool Kit, Best Environmental Practices for Fleet Maintenance"
(publication number EPA-909-E-99-002). To obtain copies of either package, call (800) 490-9198. Accompanying videos, "Profit Through Prevention",
are available at the same phone number for either auto repair (number EPA-909-V-99-001) or fleet maintenance (number EPA-909-V-99-002).

This fact sheet was produced by the Environmental Protection Agency (EPA) Region 9 pollution prevention program. Mention of trade names, products, or services
does not convey, and should not be interpreted as conveying, official EPA approval, endorsement, or recommendation.

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