Vehicle wash facilities create a great deal of wastewater that can be either discharged, recycled or a combination of the two. Discharges of wastewater from wash facilities usually contain pollutants and are either discharged through a sewer system (e.g., combined, storm or sanitary),
discharged to surface waters, or percolated into the soil. Motor vehicle service industry increasingly faces more stringent regulations covering the treatment and discharge of oily wastewater. Pollutant discharges from service stations can potentially result in revoking of licenses and even
further legal action. Oil water Separators (OWSs) are devices commonly used to remove oils and greases (and sometimes solids) from industrial waste streams and storm water discharges. OWSs operate by employing various physical or chemical separation methods, including gravity separation,
filters, coagulation/flocculation, and flotation. The use of separation process depends on the properties of the oil in the oil/water mixture and discharge requirements. The factors such as detention time, flow patters, density, size and concentration of contaminants to separate,
temperature, presence of degreasers, detergents, and type of flow (intermittent or continuous) will influence the performance of the separator. With proper detention time, an engineered separator that ensures a smooth flow path performs better than a conventional, rectangular separator that
causes scouring and re-suspension due to turbulence. Experiences as well as supporting data from various site conditions are needed to select a unit with confidence. For successful operation and installation of OWS, installation personnel should obtain as much information as possible about
the characteristics of the waste stream to be treated and use these details and measures for the selection OWSs. Installations should not rely on manufacturer's literature or claims to determine separator performance. Then, once a separator is installed, it must be properly monitored and maintained. Gravity
OWSs are the type of separator most common at motor vehicle service stations. These are designed to remove only free oil, not oil that is emulsified or dissolved. Installations should not rely on gravity separators to remove emulsified oils. One common problem with service station OWSs is
the introduction of detergents and cleaning agents into the process stream prior to discharge to the separator. These products will emulsify oil and prevent its removal by gravity separation and may result in not meeting effluent requirements for oil and grease limits. Installations should
try to eliminate emulsifiers altogether and divert stormwater flow to the greatest possible degree. New developments in primary and secondary water treatment technologies for oil-water separation with coalesces and advanced filtration systems (AFSs) allow removal of oil and petroleum hydrocarbons
from water to very low levels.
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