July 2, 2024 Longchang Chemical

What is the full explanation of the biochemical tank foam problem and how to control it?

Foam type

Start-up Commissioning Foam

Start-up commissioning foam formation mechanism:

1. As the activated sludge in the aeration tank is not adapted to the quality of the incoming sewage water, it is easy to form foam due to the lack of adaptation to the growth environment. But with the adaptation of activated sludge to the water quality, the foam will be reduced.

2. The amount of activated sludge in the aeration tank is relatively small, and the load of activated sludge is relatively high, which is easy to produce foam, and with the increase in the amount of activated sludge, the foam will gradually disappear.

3. At the initial stage of activated sludge process operation, the sewage contains some surface active substances, which can easily cause surface foam. But with the gradual maturity of activated sludge, these surface active substances by biological degradation, foam phenomenon will gradually disappear.

Denitrification foam

Mechanism of denitrification foam formation: when activated sludge treatment system is running at low load, denitrification will occur in the sedimentation tank or the place with insufficient aeration and nitrogen will be generated, the release of nitrogen will reduce the sludge density to a certain extent and drive part of the sludge upward, so that foam phenomenon occurs, and the resulting suspended foam is usually not very stable.


Biological foam formation mechanism:

1. Most of the microorganisms related to foam contain lipids, therefore, these microorganisms are lighter than water and easy to float to the surface.

2. Most of the microorganisms related to foam are filamentous or branched, and are easy to form a net, which can trap particles and bubbles, etc., and float to the surface of the water. Bubbles surrounded by the screen, increasing its surface tension, so that the bubble is not easy to break, the bubble is more stable.

3. Aeration bubbles produced by the air flotation is often the main driving force for the formation of foam. Particles using air bubbles flotation, must be small, light and hydrophobic substances. Therefore, when the presence of oil in the water, lipid substances and lipid-containing microorganisms, it is easy to produce surface foam phenomenon.

Foam Generating Factors

Sludge retention time

Foam-producing microorganisms generally have lower growth rates and longer growth cycles, so a longer sludge residence time (SRT) is favorable to the growth of these microorganisms. Therefore, the activated sludge method with delayed aeration is more likely to produce foam phenomenon. In addition, once the foam is formed, the biological residence time of the foam layer is independent of the sludge residence time in the aeration tank, and it is easy to form stable and long-lasting foam.

pH value

Different filamentous microorganisms have different pH requirements, the growth of Nocardia is extremely sensitive to pH, the optimal pH value is 7.8, when the pH value drops from 7.0 to 5.0 to 5.6, it can effectively reduce the formation of foam. This is mainly because the low pH exceeds the pH limit of the microbial community that produces foam. Therefore when the pH is 5.0, it is effective in controlling their growth. However, changes in pH can also cause maladaptation of the activated sludge, which can lead to foaming.

Dissolved Oxygen

The Nocardia group in biofoam are strictly aerobic microorganisms that cannot utilize the substrate for growth under either anoxic or anaerobic conditions, but do not die, unlike filamentous bacteria, which can utilize nitrate as the ultimate electron acceptor. Therefore, even in the anoxic section or anaerobic section of the existing denitrification and phosphorus removal system, it can still be produced successfully. When the dissolved oxygen is insufficient and the system is operated at low load, denitrification foam is easily produced.


Bacteria related to the formation of biofoam have their own appropriate growth temperature and optimal temperature, when the environment or water temperature is favorable to the growth of bacteria, may produce foam phenomenon. Not only that, the temperature will also have an effect on the microbial community in the activated sludge system, resulting in the production of biofoam, which can be seen from the fact that many biofoam production has a seasonal nature.

Hazards of foam

1. It affects the normal display of the instrument, especially in wastewater treatment plants with DCS automatic control, which can cause system misoperation. For ultrasonic level meter, it will cause false level; sewage treatment station total discharge using nullah flow meter, may cause the total discharge of sewage flow error.

2. Affecting the environment, a large amount of biofoam is generated and spreads to the walkway boards, affecting normal maintenance. Biofoam may freeze in winter, making cleanup more difficult; in summer, it will flutter in the wind, forming bad odors and seriously polluting the environment.

3. Bio-foam is generally viscous, it will be a large amount of activated sludge and other solids into the floating foam layer of the aeration tank, the foam layer in the aeration tank surface tossing, hindering oxygen into the aeration tank mixture, reducing the oxygenation efficiency, especially on the mechanical surface aeration mode of the greatest impact.

4. When mixed with foam aeration tank mixture into the second sink, foam wrapped with activated sludge and other solids will increase the suspended solids content of the effluent caused by the deterioration of effluent water quality, and at the same time, in the second sink the formation of a large number of scum on the surface, resulting in an increase in SS, COD and other pollutants in the external drainage water.

Foam control methods

Spraying water

This is one of the most commonly used physical methods to reduce foaming by spraying streams of water or water droplets to break up air bubbles floating on the water surface. The broken up sludge particles partially regain their settling properties, but filamentous bacteria are still present in the mixture, so the foaming phenomenon cannot be eliminated at all;

Add anti-foaming agent

Biocides with strong oxidizing properties such as chlorine, ozone and peroxide can be used. There are also commercially available agents produced using polyethylene glycol, silicone, and a mixture of ferric chloride and copper pickling solution. The effect of the agents is only to reduce the growth of foam, but not to eliminate its formation. The widely used biocides generally have negative effects, because excessive amounts or improper placement of dosing can substantially reduce the number of flocculation-forming bacteria and the total amount of organisms in the reaction tank. Commonly dosed agents;

Shorten sludge residence time

Reducing the sludge residence time in the aeration tank, that is, lowering the average cell residence time, can effectively control biofoam in the activated sludge process. Reducing the sludge residence time is essentially a biological screening strategy, i.e., utilizing the characteristic of long average generation time of foaming microorganisms to inhibit the excessive proliferation of foaming microorganisms in the aeration tank or to exclude them, so as to achieve the purpose of controlling the biofoam;

Addition of carriers to the aeration reactor

In some activated sludge systems, mobile or fixed fillers are injected to make some microorganisms that are prone to sludge expansion and foaming grow solidly, which can not only increase the biomass in the aeration tank and improve the treatment effect, but also reduce or control the generation of foaming.

What does reverse osmosis mean?

Reverse osmosis, also known as reverse osmosis, is a membrane separation operation in which a pressure difference is used as the driving force to separate a solvent from a solution. It is called reverse osmosis because it goes in the opposite direction to natural osmosis. According to the different osmotic pressures of various materials, it is possible to use a reverse osmosis pressure greater than the osmotic pressure, i.e. reverse osmosis, to achieve the purpose of separation, extraction, purification and concentration.

What is the process principle of reverse osmosis?

1. semi-permeable membrane: can only allow solvent molecules to pass through, and does not allow the molecules of the solute through the membrane is called ideal semi-permeable.

2. osmosis: in the same external pressure, when the solution and pure solvent for the semi-permeable membrane separation, the pure solvent will pass through the semi-permeable membrane is the phenomenon of solution dilution is called osmosis. 3. osmotic equilibrium: the process of osmosis is called osmosis.

3. osmotic equilibrium: osmosis process, the number of solvent molecules per unit time from two opposite directions across the semipermeable membrane is equal to each other, that is, to achieve osmotic equilibrium.

4. osmotic pressure: when the semipermeable membrane separates the solution from the pure solvent, added to the original solution so that it is just enough to prevent the pure solvent from entering the solution of the additional pressure is called osmotic pressure. Usually the more concentrated the solution, the greater the osmotic pressure of the solution. 5.

5. reverse osmosis: if the pressure added to the solution exceeds the osmotic pressure, the solvent in the solution to the pure solvent direction, this process is called reverse osmosis.

Reverse osmosis is the use of reverse osmosis membrane selectively only through the solvent (usually water) and the retention of ionic substances, the static pressure difference between the two sides of the membrane as a driving force to overcome the osmotic pressure of the solvent, so that the solvent through the reverse osmosis membrane to achieve the separation of liquid mixtures of membrane processes.

Its operating pressure difference is generally 1.5 ~ 10.5MPa, the size of the retained component is 1 ~ 10197; the small molecule solute. In addition to this, all other suspended, dissolved and colloidal matter can be removed from the liquid mixture.

What are the technical characteristics of the reverse osmosis process?

1. under the condition of no phase change at room temperature, solute and water can be separated, suitable for the separation of heat-sensitive substances, concentration, and compared with the separation method of phase change, lower energy consumption.

2. Wide range of impurity removal, not only dissolved inorganic salts can be removed, but also all kinds of organic aryl impurities can be removed.

3. high salt removal rate and water reuse rate, and can retain solutes with a particle size of a few nanometers or more.

4, because only the use of pressure as the driving force of membrane separation, so the separation device is simple, easy to operate, self-control and maintenance.

5. Reverse osmosis device requires the feed water to reach a certain target in order to operate normally, medical this raw water into the reverse osmosis device before the use of certain pre-treatment measures. In order to prolong the service life of the membrane, the membrane should be cleaned regularly to remove the dirt.

What are the regular applications?

Reverse osmosis technology is usually used for seawater, brackish water, fresh water; water softening treatment; wastewater treatment, as well as food, pharmaceutical industry, chemical industry, purification, concentration, separation and so on.

In addition, reverse osmosis technology applied to the pre-desalination treatment also achieved better results, can make the load of ion exchange resin to reduce the loose more than 90%, resin regeneration agent dosage can also be reduced by 90%.

Therefore, not only saving costs, but also conducive to environmental protection. Reverse osmosis technology can also be used in addition to the particles in the water, organic substances, colloidal substances, to reduce the pollution of the ion exchange resin, prolonging the service life has a good effect.

What is the difference between RO reverse osmosis membrane, ultrafiltration membrane and nanofiltration membrane?

Comparison of reverse osmosis membrane, ultrafiltration membrane and nanofiltration membrane

1. Reverse osmosis membrane: It is the most delicate membrane separation product, which can effectively retain all dissolved salts and organic matter with molecular weight greater than 100, while allowing water molecules to pass through. Reverse osmosis membrane is widely used in the desalination of seawater and brackish water, boiler make-up water, industrial pure water and electronic high-purity water preparation, drinking pure water production, wastewater treatment and special separation processes.

2. Ultrafiltration membrane: It can retain large molecules and proteins between 0.002-0.1 micron. Ultrafiltration membrane allows small molecules and dissolved solids (inorganic salts), etc. to pass through, at the same time will leave colloids, proteins, microorganisms and macromolecules of organic matter, used to indicate the pore size of the ultrafiltration membrane molecular weight range of the cut is generally in the range of 1,000-500,000. The operating pressure of ultrafiltration membrane is generally 1-7 bar.

3. Nanofiltration membrane: It can retain nanoscale (0.001 micron) substances. Nanofiltration membrane operating range between ultrafiltration and reverse osmosis, the molecular weight of the retained organic matter is about 200-800MW, the ability to retain dissolved salts between 20%-98%, the removal rate of soluble monovalent ions is lower than the removal rate of high-valent ions, nanofiltration is generally used for the removal of organic matter and pigments in surface water, hardness and radium in the groundwater and partially remove the dissolved salts in the production of food and medicine. The extraction and concentration of useful substances. Nanofiltration membranes generally operate at pressures of 3.5-30 bar.

Advantages and disadvantages of reverse osmosis membranes versus ultrafiltration membranes

The pore size of reverse osmosis membrane is only 1/100 of the size of ultrafiltration membrane, so the reverse osmosis water treatment equipment can effectively remove heavy metals, pesticides, trichloromethane and other chemical pollutants in the water, and the ultrafiltration water purifier is powerless. Ultrafiltration water purifier can remove the particles of pollutants and bacteria, reverse osmosis all remove.

Reverse osmosis and ultrafiltration, the core components are membrane elements. There are two main differences:

1. Water quality and health department testing standards are different, to give you an example to illustrate, the water bacterial indicators, ultrafiltration in accordance with the “general water processor”, the total number of colonies of 100 / ml; and reverse osmosis water treatment equipment for the 20 / ml, the requirements of a more stringent, of course, the reverse osmosis water treatment equipment, the water quality is much better than the ultrafiltration. Also much better than ultrafiltration.

2. Reverse osmosis water treatment equipment is a quality water supply, pure water supply for drinking, concentrated water used for washing; and ultrafiltration is generally used for washing water; when the tap water quality is relatively high quality can also be used as drinking water ultrapure water equipment.

Advantages of ultrafiltration: generally do not use the pump, no power consumption, no electrical safety issues; fewer joints, low water pressure, failure rate and the probability of leakage is relatively low; simple structure, inexpensive;

The disadvantages are: poor removal of chemical pollutants in the water; poor effect on the water supply of special events; slightly poorer taste of water; can not reduce the hardness of water, such as tap water hardness, cooking water containers may be scaled. Ultrafiltration membrane can remove macromolecules, colloids, proteins, particles, etc. in solution, with the use of low pressure, large water yield, easy to operate. By testing the treatment effect of hollow fiber ultrafiltration membrane device for deep purification of raw water for making wine, it is proved that the ultrafiltration membrane water purification device can effectively eliminate the secondary contamination of water in the pipeline network and further improve the water quality.

Advantages of reverse osmosis water treatment equipment: water safety, can effectively remove all kinds of harmful impurities in the water quality; for the water supply of special events with better results; better water taste; can effectively reduce the hardness of the water, cooking water containers are not easy to scale; the disadvantages are: pumps, power consumption, electrical safety issues; more joints, high water pressure, failure rate and the probability of leakage is relatively high; the structure of the more complex, relatively expensive.

Ultrafiltration membrane and the difference between nanofiltration and reverse osmosis

Ultrafiltration membrane

Ultrafiltration membrane is a pressurized membrane separation technology, that is, under a certain pressure, so that small molecules of solutes and solvents through a certain aperture of the special film, while the macromolecule solutes can not pass through the membrane to stay on the side of the membrane, so that large molecules of substances have been partially purified.

The advantages of ultrafiltration technology are easy operation, low cost, without adding any chemical reagents, especially the mild experimental conditions of ultrafiltration technology, compared with evaporation, freeze-drying, no phase change, and does not cause changes in temperature, pH, and thus can prevent the denaturation, inactivation, and autolysis of biomolecules. In the preparation technology of biomolecules, ultrafiltration is mainly used for desalination, dehydration and concentration of biomolecules.

Ultrafiltration also has some limitations, it can not directly get the dry powder preparation. For protein solutions, generally only 10-50% concentration can be obtained. Domestic Industrial Both can be used. The key to ultrafiltration technology is the membrane. There are different types and specifications of membranes, which can be selected according to the needs of the work.


Nanofiltration, between ultrafiltration and reverse osmosis. Nowadays, it is mainly used as water plant or industrial desalination. Desalination rate of more than 90%. Reverse osmosis desalination rate of 99% or more However, if the water quality requirements are not particularly high, the use of nanofiltration can save a lot of cost.

Reverse osmosis

Reverse osmosis, is the use of pressure table difference for the power of membrane separation and filtration technology, originated in the United States in the 1960s aerospace science and technology research, and then gradually transformed into civilian use, has been widely used in scientific research, medicine, food, beverage, desalination and other fields.

It is used for the preparation of space water, pure water, distilled water, etc.; water for alcohol manufacturing and degradation; pre-preparation of water for medicine, electronics and other industries; concentration, separation, purification and preparation of water for chemical process; desalination of boiler make-up water; desalination of seawater, brackish water; water and wastewater treatment for papermaking, electroplating, dyeing and printing industries.

Application of different membranes in water treatment: forward osmosis, reverse osmosis, ultrafiltration, nanofiltration

Principle of Forward Osmosis (FO)

The solvent and solution are separated by a semi-permeable membrane that can only transmit solvent but not solute molecules, and the solvent molecules will spontaneously pass through the membrane from the solvent side to the solution side under the action of osmotic pressure, which is the osmosis phenomenon, also known as “forward osmosis”.

Application of forward osmosis membrane in water treatment

1. Seawater desalination FO for seawater desalination is one of the most widely studied areas. Early application studies are mainly found in some patents, but most of these studies are immature and not highly feasible.

2. Industrial wastewater treatment Early studies reported the use of FO membranes for the treatment of low concentration of heavy metal wastewater, but due to the serious contamination of the RO (reverse osmosis) membranes used, the flux decline rapidly, and thus has not been carried out in depth.

3.Waste leachate treatment The CoffinButte landfill in Corvallis, Oregon, USA, can produce (2-4) × 104 m3 of waste leachate annually, and in order to meet the water quality standards for land use, the TDS of the effluent must be reduced to below 100 mg/L.

Reverse osmosis membrane technology

1. Principle of reverse osmosis (RO)

Reverse osmosis is a kind of pressure as the driving force of the membrane separation process in use for the production of reverse osmosis pressure needs to be pumped to the saline solution or wastewater pressure to overcome the natural osmotic pressure and membrane resistance to make the water through the reverse osmosis membrane, dissolved salt in the water or contaminated impurities in the reverse osmosis membrane on the other side of the block.

2. Reverse osmosis membrane in the application of water treatment

2.1 reverse osmosis membrane in water treatment in the conventional application of water is people rely on the survival and production activities essential material conditions. Due to the increasing lack of freshwater resources, the world’s reverse osmosis water treatment device capacity has reached millions of tons per day.

2.2 Application of reverse osmosis membrane in municipal wastewater At present, the application of reverse osmosis membrane in the deep treatment of municipal wastewater, especially the secondary effluent reuse of wastewater treatment plant and water reuse, etc., has been highly valued.

2.3 Application of reverse osmosis membrane in heavy metal wastewater treatment The conventional treatment method of wastewater containing heavy metal ions is only a pollution transfer, that is, the wastewater dissolved heavy metals into precipitation or a more easily treated form, and its final disposal is often to landfill, and heavy metals on groundwater and surface water environment caused by secondary pollution of the hazards of the environment is still there for a long time.

2.4 reverse osmosis membrane in the application of oily wastewater oily wastewater is a large amount of industrial wastewater, if directly discharged into the water body, will produce oil film on the surface layer of the water body to prevent oxygen from dissolving into the water, thus resulting in a lack of oxygen in the water, biological deaths, emit a bad smell, seriously polluting the ecological environment. The oil 3.5mg/L, total organic carbon (TOC) (16 ~ 23) mg / L of oilfield water treatment to boiler water quality is treated water is used back to the power station boiler feed water.

Nanofiltration Membrane Technology

Principle of Nanofiltration (NF)

Nanofiltration (NF) is a new type of molecular membrane separation technology, which is one of the hotspots in the field of membrane separation in the world at present.The pore size of NF membrane is more than 1nm, generally 1-2nm; the retention performance of the solute is between RO and UF membranes; RO membrane has a high removal rate of almost all the solutes, but the NF membrane has a high rate of removal of the specific solutes only.NF membrane is capable of removing the divalent, trivalent ions, Mn ≥ 200 organic ions, and the organic water of the water treatment plant. , organic matter with Mn ≥ 200, as well as microorganisms, colloids, heat sources, viruses, etc. A big feature of nanofiltration membrane is that the membrane body has electric charge, which is the important reason that it still has high desalination performance under very low pressure (only 0.5MPa) and inorganic salts can be removed even if the molecular weight of the membrane is a few hundred, and it is also the main reason for the low operation cost of NF. NF is suitable for all kinds of salty water sources, and the utilization rate of the water is 75%~85%, and 30%~50% for seawater desalination, and there is no acid and alkaline waste water discharge. Wastewater discharge.

Application of nanofiltration membrane in water treatment

Application of nanofiltration membrane in drinking water Nanofiltration operates under low pressure and is the preferred process for the preparation and deep purification of drinking water. Nanofiltration technology can remove most of the Ca, Mg and other ions, so desalination (desalination) is the most popular application of nanofiltration technology.

Membrane water treatment technology in terms of investment, operation and maintenance and price and conventional lime softening and ion exchange process is similar, but with no sludge, no regeneration, complete removal of suspended solids and organic matter, easy to operate and occupies an area of the province, etc., more application examples. Nanofiltration can be used directly for groundwater, surface water and wastewater softening, but also as reverse osmosis (Reverse osmosis, RO), solar photovoltaic desalination device (Photovoltaic powered desalination system) and other pretreatment.

Application of nanofiltration membrane in seawater desalination Seawater desalination refers to the desalination of seawater with a salt content of 35,000 mg/L to drinking water below 500 mg/L.

Application of nanofiltration membrane in wastewater treatment A, domestic sewage B, textile, printing and dyeing wastewater C, tannery wastewater D, electroplating wastewater E, paper wastewater.

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