Technical Applications

Foam formation during treatment of sewage

The increase of living standards and comsumption of goods has resulted in a growth of waste products. In the field of water supply and sewage treatment this situation has led to a higher direct and indirect water consumption and therefore to an increase of waste water quantities. The amount of industrial sewage produced has considerably increased more than communal sewage. Simultaneously the percentage of purified industrial sewage has increased because of stronger environmental awareness, laws and restrictions. Communal sewage is often mixed with industrial waste water to achieve a better blend of substances contained.

Sewage entering purification plants is often a variety of very different components, particularly the foam active ingredients i.e. detergents, proteins etc. Due to this, the degree of foam generation is very different in sewage treatment plants. Pure communal sewage tends to foam less than industrial sewage. However, communal sewage can also cause foam formation when the detergent content is higher.

The method of sewage treatment has the major influence on foam development. Foam occurs if gas escapes from liquids that contain foam active substances. This especially applies to aerobic sewage treatment according to the activated sludge process. All other chemical, mechanical or biological sewage treatment processses are considerably less foam active due to their structure.

Foam prevention and foam destruction with Struktol antifoam agents

The foam active substances in sewage are very different, therefore antifoam agents have to be adapted to the medium to be defoamed. A careful choice is necessary in order to achieve effective defoaming without any negative influence on the sewage system. Lab pre-trials are recommendable in order to select the most appropriate materials. These trials should only be carried out with fresh sewage i. e. in the purification plant. However, due to international experience we provide recommendations in many cases.

Apart from good defoaming properties the antifoam used should not have a negative impact on the sewage treatment itself. In the case of aerobic sewage treatment, microorganisms have to be supplied with sufficient oxygen for an optimum of contaminants digestion.  Microorganisms can only take up oxygen dissolved in water. 

If the percentage of dissolved oxygen decreases, the digestion will deteriorate. Therefore it is essential, that the antifoam agent does not influence the oxygen transfer as far as possible.

Struktol antifoam agents have a remarkably low effect on the oxygen transfer. And they are low viscosity materials and therefore easy to use. All Struktol antifoam agents listed in the following - with the exception of Struktol SB 2077 - are free from mineral oils or other paraffinic hydrocarbons and conform to OECD recommendations. With the exception of Struktol SB 2077 all Struktol products stated in the following tables are almost completely degradable. Struktol SB 2077 is a silicone antifoam agent and silicones are not biodegradable.

The dosing quantities of antifoam agents depend on many conditions e.g. the concentration of foam active substances. In pure communal purification plants the dosing quantity is usually less than 1 ppm calculated on total sewage amount. Industrial sewage treatment plants often have a higher percentage of foam active substances so dosing quantities of 10 ppm or more can be required. Therefore it is essential to find out the necessary quantity in each case.

Furthermore the choice of the best possible dosing point is also important. The dosing point depends on the defoaming procedure i.e. whether already existing foam has to be destroyed or foam generation has to be avoided. Struktol antifoam agents can be used for foam prevention as well as for foam destruction. However, foam prevention is most advantageous. Experience has shown that in this case dosage should be introduced at the inlet to the biological stage.

Reduction of scum

In many purification plants the undesired effect of scum during final sedimentation occurs. It is caused by gas bubbles (air, nitogen or methane) entrapped in the sludge agglomerates, that floats them to the surface. Some Struktol types reduce the linkage force between gas bubbles and sludge agglomerates settle again.

To optimize the performance of these scum reducers the choice of the right dosing point is essential. Dosage has to be carried out in that way that sufficient distribution of the scum reducers ia achieved. In many cases the activated sludge stage is the best dosing point. An additional dosage of antifoam agent is normally not neccessary.

Struktol antifoam agents ensure process stability and contribute to energy savings leading to capacity improvements.

The formation of foam during the production of paints and varnishes is caused by the presence of foam active substances such as emulsifiers, tensides and high turbulences etc. Struktol antifoams are very effective during the production and application of paint, ink and coatings under acid or alkaline conditions. The presence of surface defects such as pinholes is minimal when processed correctly. They are in conformity with most relevant food laws, such as FDA 176.210 and BfR XIV and XXXVI. Further details of regulatory status are available on request.

The dosage rates for Struktol antifoam agents depend on several parameters such as used raw materials and type of application. The most effective antifoam product and necessary dosage depends on used raw materials and processing method and has to be identified individually for every recipe by carrying out pre-trials. Also the potential influence on the coating surface must be found out by pre-tests.

The formation of foam during the production of adhesives and glues is caused by the presence of foam active substances such as emulsifiers, tensides and high turbulences etc. Struktol antifoams are very effective during the production and application of paint, ink and coatings under acid or alkaline conditions. The presence of surface defects such as pinholes is minimal when processed correctly. They are in conformity with most relevant food laws, such as FDA 176.210 and BfR XIV and XXXVI. Further details of regulatory status are available on request.

The dosage rates for Struktol antifoam agents depend on several parameters such as used raw materials and type of application. The most effective antifoam product and necessary dosage depends on used raw materials and processing method and has to be identified individually for every recipe by carrying out pre-trials. Also the potential influence on the coating surface must be found out by pre-tests.

Thin stock preparation and white water systems

High-efficiency, waterfree concentrates
Due to the fact, that the consumption of water-based dispersion defoamers/deaerators in the paper- and paperboard production has been increased rapidly during the past few decades (water system closure, higher machine speed rates and therefore high white water temperatures, application of waste paper as a significant raw material source, etc.) the usage of high-efficiency, waterfree concentrates becomes more and more interesting. Consisting of 100 % active components only (no water, no emulsifiers which tend to decrease the defoaming activity) these concentrates can offer both more effective defoaming/deaeration and a significant reduction in costs and handling.

The most important properties are mentioned:

• Very effective dosage levels at 1/2 up to 1/3 compared to the well-known water-based dispersion antifoam agents.
• Very effective combination of both deaeration and surface-defoaming: due to the unique combination of active components, we can offer the most balanced combination of a.m. properties for each specific application.
• Applicable at all pH-levels and temperature ranges from 30°C to 80°C.
• Indifferent against hydrophobing agents and wet strength resins.
• Due to the non-ionic character no effect on cationic/anionic additives.
• Application at the usual dosage points: white water, prior to the dilution pump, thin stock cleaners etc., it is recommended to use the mentioned products undiluted.
• Low viscosity medium, without non-Newtonian viscosity effects, i. e. easily pumpable.
• Clear homogeneous products, no mixing in storage tank is necessary, no separation
• At least 12 months shelf life, no danger of freeze

Dosages rates depend on the kind of paper/paperboard produced, the nature of the raw materials used, machine speed rates etc. Our technical personal is prepared to support our customer with application optimizing.

Size-press and coating

Normal and highly filled coatings
Until recently, foam build-up and air entrainment during the preparation and the application of coating formulations could quite easily be prevented with defoamers using tri-N-butylphosphate or simple esters as active components. However, in the last few years, due to increased machine speeds and the development of coating formulations with higher solid contents (> 68 % dry substance), these defoamers are not sufficient anymore. During the preparation of these so-called highly filled coatings air is entrained quite often and, due to the high viscosity of the formulation, the entrained air causes surface failures during the coating application.

As our special high solid coating defoamers are added already during the first phase of the coating preparation, they prevent the coating substance from air entrapment during the complete preparation process, thus avoiding the formation of dispersed air particles in the coating.

As the products have proven to have outstanding long-lasting defoaming capabilities, the necessity of further defoamer addition during the coating application can most often be avoided.

In general, the properties of the mentioned products are:

• Addition during the preparation of the coating.
• Due to the compatibility with the other coating components spot-building does not occur.
• Outstanding long-term defoaming properties, avoiding additional dosages.
• 100% active components only, do not contain silicones

Low dosage rates are sufficient in most situations (0,01-0,2 parts on 100 parts pigment). Exact dosage levels should be determined during evaluations in practice.

Struktol specialty chemicals cover all specific applications in the production of phosphoric acid from the ore treatment to sludge filtration.

Application Areas: Recycling of PET-bottles, foils/films, PS-cups as well as mixed plastic materials, recycling of sized packaging board. The selected STRUKTOL products offer a well-balanced relation between foam destruction, foam prevention and deaeration. The prevention of foam in advance is advantageous for a smooth factory process; the antifoam product should be added continuously in concentrated form by a dosage pump. A sufficient distribution in the medium should be achieved.

The formation of foam depends on foam active substances in the process water (e.g. proteins, tensides, modified cellulose), temperature, intensity of water circulation and water treatment. The most favourable dosage quantity and the best adding point depend on factory conditions and have to be found out by trials.