Defoamers are surface active agents that are added to a system or process to control or eliminate the foam. Within the defoamer industry, there is no single accepted defoaming mechanism, but rather a compilation of several adopted methods. It is best to first review a brief description on foam creation and stabilization in biological wastewater treatment systems:
1. Foam is the result of contamination of a pure liquid by surfactants, minerals and salts, starches, proteins, metabolized waste from microbes and metabolized organics. Foam begins when a gas is entrained into liquid media either by mechanical or chemical means.
2. In biological treatment systems, oxygen and other gases are either added to the process or may be produced as a by-product of the process. These gases are introduced into a liquid environment where there is a tremendous amount of exposed surface area in the form of Nocardia spp. or Microthix parvicella.
3. The combination of these gases in a liquid environment with various contaminants and vast amounts of exposed surface area creates the right conditions for very stable foam that is brownish/grayish in color and susceptible to drying upon contact with air at the surface.
4. Because of the drastic difference in density between foam and water, the newly forming foam rises to the surface (air – liquid interface). It is at this stage, that the lamella (foam bubble) is formed and the surfactants that comprise the lamella (contaminants) orient themselves to the lowest thermodynamically stable state.
5. The resulting foam is brownish/gray in color, relatively small in structure and very stable.
Most defoamer manufacturers agree that if their products are to be effective, the following steps must occur:
1. The defoamer must reduce the surface tension of the liquid media to which it is added, and must have a lower surface tension that the system it is attempting to defoam.
2. The defoamer must have the proper carrier (vehicle) to actively spread throughout the foaming media – rapid spreading coefficient.
3. The defoamer must have a degree of incompatibility with the foaming media. Most defoamer chemists work on a “half-in / half-out” premise. In other words, defoamers are hydrophobic by design, but are made sufficiently dispersible so that they can be placed into a hydrophilic environment where they must be effective. A defoamer that is completely soluble in a liquid media will not be effective.
4. The more hydrophobic the defoamer, typically, the more effective the product is at eliminating and/or controlling foam.
The chemistry of defoamers is varied because these products are system- and process-specific. Fortified and surfactant-based defoamers are two of the most widely used chemistries employed in today’s marketplace. Fortified defoamers contain hydrophobic materials such as fatty acids, silicon dioxide, fatty amides, waxes, fats and metal soaps.
Enterprise Specialty Products, Inc. (ESP) defoamers for biological-based foam are surfactant-based products. This type of defoamer does not contain added hydrophobic materials as mentioned previously. The surfactant-based defoamers work in contrast to traditionally accepted methods:
• Surfactant-based defoamers typically work throughout the foaming media; whereas, fortified defoamers typically are more active at the air / liquid interface (Top down method). Surfactant-based defoamers are more compatible with hydrophilic systems.
• Fortified defoamers demonstrate immediate defoaming action at the surface, in contrast to surfactant-based defoamers that may take 15 to 20 minutes to demonstrate the product effectiveness.
ESP’s surfactant-based defoamers work in the following manner:
• Our surfactant-based defoamers are effective throughout the liquid media. ESP designs the emulsification properties of our defoamers and we evaluate these properties and their impact on the spreading coefficient. This explains why we currently promote and sell four different products into this market.
• Our products work by destabilizing the formation of the lamella (foam bubble) throughout the media; therefore, the gases are released from the liquid media to the air/liquid interface and then into the atmosphere. This explains why our products appear to work from the “bottom up” and require time in order to destabilize the formation of surface foam.
• As our surfactant-based defoamers destabilize the foam blanket on the surface of the liquid, organics (BOD) are brought back into the process for degradation. Surfactant based defoamers “re-wet” the foam blanket at the air/liquid interface and this contributes greatly to promoting continuing defoaming action. The foam is being dissipated at the underside of the foam blanket, returning solids to the liquid phase without the common visible bubble- breaking action seen with fortified defoamers.
• As with the case with all defoamers, the effectiveness is diminished over time because the defoamer goes from a hydrophobic to hydrophilic state. The defoamer is “wetted” or made hydrophilic by the surfactants (contaminants) found in the liquid media.