Glossary of Terms

Below is a list of common terms in wastewater treatment and pretreatment.


Absorb Bag
A bag that will prevent carryover of mechanically emulsified oil or oily coated solids.
Chemical Emulsified Oil
An oil droplet size of 5 microns or less. It usually is caused by the addition of surfactants. A chemical emulsion is stable and will not break down. Can be removed with chemical pre-treatment followed by an oil water separator or a DAF system with chemical pre-treatment.
Clean Water Act
A regulation of pollutant discharge in any US waters and the quality standards of surface waters. See regulations.
Floc formation as the result of adding chemicals. Coagulants destabilize suspended particles by reducing repulsive forces, allowing them to agglomerate.
To unite together to form a larger mass. Our oleophilic coalescing media unites oil droplets to form a larger oil mass. According to Stokes’ Law, the larger the oil droplet size, the faster it will rise to the surface, therefore separating the oil from water.
Very small, insoluble, non-diffusible solid or liquid particles that remain in suspension in a surrounding liquid. Particles are usually 2 micron or less.
Discharge Compliance
Meeting the established limits of the NPDES permit. The regulations could differ from state to state and for different applications.
Dispersed Oil
Has a droplet size of 20 microns to 149 microns. Can be removed by a coalescing oil water separator.
Dissolved Solids
Any solid material that will dissolve in the liquid that is being filtered, such as sugar in water.
Any colloidal suspension of a liquid in another liquid that is normally immiscible.
The growing together of colloidal particles to form larger ones, which are called flocs and are easier to filter.
Clear space between the top of the liquid and the rim of the vessel.
Free Oil
Has a droplet size of 150 microns or greater. Can be removed by an API oil water separator.
Having a high affinity to water. Capable of uniting with water or dissolving in water.
Not capable of uniting or mixing with water.
Hydrostatic Test
A leak check that is performed by filling the vessel with water for a minimum of 4 hours or pressurizing the vessel with 5psi air to ensure the integrity of the vessel’s structure.
Incapable of being mixed.
Laminar Flow
Term synonymous with streamline flow and viscous flow. It is a flow in which the parallel layers are not disrupted. Laminar flow occurs at a low Reynolds number of less than 500.
Mechanical Emulsified Oil
An oil droplet size of 20 microns or less. It is usually caused by turbulence in the flow or by mixing in centrifugal pumps. Over time, a mechanical emulsion will break down. Can be removed by an oil water separator with a post treatment DAF system or clay filter.
Different material that separates oil and solids from water or that absorbs oil from water. There are a wide variety of media types, such as coalescing plates, inclined plates, clay, carbon and mesh packs.
One millionth of a meter.
NPDES Permits
National Pollutant Discharge Elimination System (NPDES). A permit program that controls water pollution by regulating point sources that discharge pollutants into waters of the United States. See regulations.
A material that attracts oil and not water. Our coalescing media has oleophilic characteristics that cause the oil droplets to grow in size, which speeds up to separation process.
A unit of concentration in parts per million
A unit of concentration in parts per billion
pH Range
An arbitrary scale of numbers from 0 to 14 indicating acidity or alkalinity of a solution. A neutral solution will have a pH close to 7, acidity is below 7 and alkalinity is above 7.
Reynolds Number
A dimensionless number. Re=(D*V*L)/M where D=density of the fluid; V=Velocity of the fluid; L= length between plates; M=Viscosity of the fluid. Need a Reynolds number of less than 500 for an oil water separator to perform properly.
Settlable Solids
Solid particles that have a greater specific gravity than water that will naturally settle out.
A device that removes the already separated oil from a separator.
Soluble Oil
A droplet size of 0.05 micron or less and transparent to the eye. This is also considered as a micro-emulsion.
Spill Prevention, Control and Countermeasure (SPCC). A plan for oil spill prevention, preparedness and response to prevent oil from getting into navigable waters and the shorelines. See regulations.
Stokes’ Law
A physical law that approximates the velocity of a particle falling under the action of gravity through a fluid. The particle will accelerate until the frictional drag of the fluid just balances the gravitational acceleration, after which it will continue to fall at a constant velocity known as the terminal or free-settling velocity.
Surface active agents, which are found in cleaning agents.
Suspended Solids
Naturally buoyant solid particles. They have a specific gravity close to water. Requires pre-treatment to prevent clogging of coalescing media.
Any liquid containing undissolved solids.
Total Dissolved Solids
Terminal Velocity
Steady velocity achieved by a moving particle when gravitational forces are balanced by viscous forces.
Total Suspended Solids
Turbulent Flow
A flow regime in which the flow characteristics are governed mainly by the inertia of the liquid. Occurs at a high Reynolds number greater than 500.
The degree of fluidity. The property of the fluid’s molecular structure by which the resist flow.