Foam concentrate activation

Surfactants retain their foaming properties in natural waters in concentrations as low as 1 mg/L, and although such concentrations are nontoxic to humans [24], the presence of surfactants in drinking water is esthetically undesirable. More important, however, is the generation of large volumes of foam in activated sludge plants and below weirs and dams on rivers. 

When considering the application of foam to hazardous material spills, key requirements include an adequate water supply, the foam concentrate, appropriate proportioning equipment, piping, foam makers, and discharge devices and protective equipment for the personnel involved. Activation may be automatic, but in most cases it is manual. There are four types of application systems. They include fixed, semifixed, mobile, and portable (NFPA 11, 1988). 

Figure 5-58. Lightweight, durable covers for pickup track beds are made of structural foam moldings of Prevex resin with a foam concentrate called Spectratech FM1776L, firom Quantum Chemical Corp. This chemically activated blowing agent does not attack the injection-molding barrel and screw or the mold s surfaces. Furthermore, since there is very little postblow with the blowing agent, the parts can be painted within four hours of being molded.

Flotation processes are an important part of water treatment technologies in modern water treatment plants. Flotation is based on the principle of adhesion of insoluble particles to air bubbles and adsorption of dissolved surfactants at the surface of air bubbles. Flotation allows for different kinds of admixtures to be removed from water bulk in a physical and chemical manner. In this way, suspended and colloidal particles, emulsions of oils and fats, the separate surfactant molecules and their micelles, complexes of surfactants with colloid rust, and multivalent ions of heavy metals can be removed. At present, the flotation processes and equipment for their realization are widely described in the literature [12]. Flotation involves the injection of small bubbles of air or other gas into the water bulk. Surface-active impurities are adsorbed at the bubble surface and transferred through the water bulk to its surface. As a result, the foam concentrate is formed on the surface of bubbling water. It contains surfactants, suspended solid particles (water impurities), emulsified substances, bacterial cells, etc. This foam is evacuated from the surface by means of special scrapers and other devices. 

Wang and co-workers (2009) successfully used foam fractionation to separate lysozyme from chicken eggs and reported that separation efficiency was significantly influenced by pH and sodium chloride concentration. Activity recovery and protein recoveries were highest (40% and 60%, respectively) at pH 7 and 0.3 M NaCl concentration. Addition of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide, Triton-X and Tween 80, resulted in protein recoveries of 93%, 88%, 68% and 72% and activity recoveries of 30%, 20%, 55% and 58%, respectively. 

The xylenes are mildly toxic. They ate mild skin irritants, and skin protection and the cannister-type masks are recommended. The oral LD q value for rats is 4300 ppm. The STEL for humans is 150 ppm. Xylenes show only mild toxicity to fish, and the threshold limit for crop damage is 800—2400 ppm. Biodegradation with activated seed is slow, and sewage digestion is impaired by 0.1% concentrations. In the event of a spih, oil-skimming equipment, adsorbent foam, and charcoal maybe used for cleanup. 

Abbreviations of prominent use properties of the various classes of commercial surfactants are shown in Table 1. Antimicrobial activity includes germicidal, bactericidal, and bacteriostatic effects emolliency describes lubrication or a soft feel imparted to skin by surfactants a hair conditioner is a substantive surfactant appHed from aqueous solution to impart a lubricating or antistatic effect and opacifters are used to thicken hand-dishwashing products and cosmetic preparations to convey an appearance of high concentration and to retard solvent drainage from foam. 

Anionic Surfactants. PVP also interacts with anionic detergents, another class of large anions (108). This interaction has generated considerable interest because addition of PVP results in the formation of micelles at lower concentration than the critical micelle concentration (CMC) of the free surfactant the mechanism is described as a "necklace" of hemimicelles along the polymer chain, the hemimicelles being surrounded to some extent with PVP (109). The effective lowering of the CMC increases the surfactant s apparent activity at interfaces. PVP will increase foaming of anionic surfactants for this reason. 

The second type is a stable dispersion, or foam. Separation can be extremely difficult in some cases. A pure two-component system of gas and liquid cannot produce dispersions of the second type. Stable foams can oe produced only when an additional substance is adsorbed at the liquid-surface interface. The substance adsorbed may be in true solution but with a chemical tendency to concentrate in the interface such as that of a surface-active agent, or it may be a finely divided sohd which concentrates in the interface because it is only poorly wetted by the liquid. Surfactants and proteins are examples of soluble materials, while dust particles and extraneous dirt including traces of nonmisci-ble liquids can be examples of poorly wetted materials. 

Activities associated with bioreactors include gas/hquid contacting, on-hne sensing of concentrations, mixing, heat transfer, foam control, and feed of nutrients or reagents such as those for pH control. The workhorse of the fermentation industry is the conventional batch fermenter shown in Fig. 24-3. Not shown are ladder rungs inside the vessel, antifoam probe, antifoam system, and sensors (pH, dissolved oxygen, temperature, and the like). Note that coils may lie between baffles and the tank wall or connect to the top to minimize openings... 

In 1991 the use of amidether carboxylate in combination with anionics like alkanesulfonate, alkylbenzolsulfonate, and alkyl ether sulfate to improve mildness and foam properties in the presence of soil was described [72]. Later a comparison study of the use of alkyl ether carboxylate, amidether carboxylate, and cocamidopropylbetaine in concentrated dishwashing formulations showed, in addition to the above-mentioned properties, the advantage of ether carboxylates in the construction of highly active formulations [144]. 

The stability of a foam can be explained by the Gibbs elasticity (E). The Gibbs elasticity results from reducing the surface concentration of the active molecules in equilibrium when the film is extended. This causes an increase in the equilibrium surface tension o, which acts as a restoring force. 

To demonstrate the fungistatic activity in another type of plastic polyurethane foams, equipped with different concentrations of OIT, have been investigated. Results of the NSA test on those samples are listed in table 2. 

This is very similar to the flotation procedure described under basic physical treatments. In the case of foam fractionation, not only are the pollutants raised to the surface where they can be skimmed off, but a froth, like beer foam, is produced in which the pollutants become concentrated. The key to the process is the adsorption of the pollutants onto the surface-active agents that cause the froth to form. Sometimes a surfactant is added so that non-surface-active components can be removed. 

There are two different classes of surface-active materials in seawater, those that are naturally present and those that have been added to the oceans by man s activities. Most of the analytical methods proposed for use in seawater actually measure the anthropogenic input, and attempt as much as possible to eliminate interferences from naturally occurring compounds. Yet sea foam was known to exist long before detergents. It is to be expected that both kinds of surfactants would be concentrated at the air-sea interface. 

---