Summary of Application of Ultrafiltration Membrane Technology by Hongjie Water

Application of ultrafiltration technology

The Technical Application of Ultrafiltration UF

The working principle of ultrafiltration (UF):

Ultrafiltration technology is an advanced membrane separation technology developed in recent years based on materials science, which has been widely applied in various fields of industry and municipal construction.

Ultrafiltration (UF) is a pressure driven membrane separation process that utilizes the interception ability of porous materials to separate particulate matter from fluids and dissolved components. The typical pore size of ultrafiltration membranes ranges from 0.01 to 0.1 microns, and they have extremely high removal rates for bacteria and most viruses, colloids, sludge, etc. The smaller the nominal pore size of the membrane, the higher the removal rate. The materials commonly used in ultrafiltration membranes are high molecular weight polymers, whose basic properties are mainly hydrophobicity. Capable of hydrophilic modification such as blending. This process operates at room temperature without any phase changes and does not generate secondary pollution.

The ultrafiltration adopts polyvinylidene fluoride (PVDF) material, which is a double layered hollow fiber structure. In industrial PVDF ultrafiltration membranes, ultrafiltration has the smallest nominal pore size and can remove almost all particles, bacteria (4-log removal rate), most viruses, and colloids. Although the pore size is small, its extremely high porosity allows ultrafiltration to achieve flux comparable to microfiltration, making it a better choice than microfiltration in most cases.

Ultrafiltration adopts an external pressure structure that is not easily clogged, with higher interception capacity, larger filtration area, and easier and more thorough cleaning. The flow design is mainly based on full flow filtration, but the components can also be easily converted to cross flow filtration mode. Compared with cross flow, full flow filtration has lower energy consumption and operating pressure, resulting in lower operating costs. On the other hand, cross flow filtration can handle fluids with higher suspended solids. Therefore, the specific operation form needs to be determined based on the suspended solids content in the influent.

Ultrafiltration usually operates in a constant flow mode, and the transmembrane pressure difference (TMP) will gradually increase with running time. At this time, the fouling layer can be removed by regular backwashing or air scrubbing, while using fungicides or other cleaning agents can more thoroughly control microbial growth and remove pollutants.

In the field of water treatment, ultrafiltration can be used to remove particles, colloids, bacteria, viruses, heat sources, proteins, and high molecular weight organic compounds from water, purifying it.

Advantages and disadvantages of ultrafiltration

The advantages and characteristics of ultrafiltration

Long service life: Ultrafiltration uses special performance PVDF material and undergoes hydrophilic modification, which has excellent antioxidant and fatigue resistance, pollution resistance, and clarity resistance, greatly extending the service life of membrane fibers.

High water production quality: The average filtration accuracy of ultrafiltration reaches 0.03m, the bubble point pressure is higher, and the bacterial removal rate reaches 6-log, resulting in better water production quality.

Wide application range: The external pressure structure and patented water distribution method of ultrafiltration allow for a wider suspended solids content in the influent, making it more suitable for applications with poor water quality while ensuring a high water recovery rate.

Low operating cost: The ultrafiltration external pressure type can adopt a low-cost gas water mixing cleaning method, efficiently maintaining long-term stability of flux and saving chemical cleaning agent consumption.

The main applications of ultrafiltration

The application of ultrafiltration mainly involves three aspects: industrial applications, food biochemistry, and drinking water. The following will introduce them separately.

The industrial application of ultrafiltration can be divided into three types: (1) concentration, (2) separation of small molecule solutes, and (3) classification of large molecule solutes.

The vast majority of industrial applications belong to the field of concentration. Small fraction solutes can be separated by combining or recombining with macromolecules. The separation of free calcium and protein bound calcium is an example. Small molecule solute separation, such as desalination and salt exchange, can be achieved through ultrafiltration or by combining ultrafiltration with dialysis. Membranes with different molecular weight cutting values can be used for the classification of macromolecular solutes, or a combination system can be used, consisting of several ultrafiltration tanks. The liquid from one ultrafiltration tank can enter the next ultrafiltration tank, and the molecular weight value cut by the membranes in each tank gradually decreases.

Industrial applications

·Recovery of electrophoretic paint using ultrafiltration

·Recovery of oily wastewater using ultrafiltration

·Using ultrafiltration to treat wastewater containing heavy metals

·Other industrial applications

1. One of the industrial applications of ultrafiltration - using ultrafiltration for electrophoretic paint recovery

In the process of metal electrophoretic painting, charged metal objects are immersed in a paint pool containing opposite charges. Due to electrostatic attraction, the coating can form a uniform layer on the metal surface, and the metal object is taken out of the pool and washed with water to remove the accompanying coating. To achieve the goal of environmental protection and energy-saving closed loop, ultrafiltration process can be used to retain polymer resin and pigment particles, while allowing inorganic salts, water, and solvents to pass through the ultrafiltration membrane. The retained components are then returned to the electrophoretic paint storage tank. As shown in the following figure.

As early as 1968, the patent of PPG Company in the United States proposed the combination technology of ultrafiltration and reverse osmosis to treat electrophoretic paint wastewater. At present, this technology has been widely used in automated assembly lines, and hundreds of membrane modules with a membrane area greater than 100m2 have been put into operation, mainly tubular. Due to the charged solution in the pool, a membrane with the same surface charge has been developed, which is less prone to contamination due to the repulsion of the same species. The membrane permeation flow rate remains above 1m/d for several months without cleaning, and the membrane lifespan is generally over 2 years.

2. Ultrafiltration Industry Application II - Recovery of Oily Wastewater through Ultrafiltration

Oil water emulsion is widely used as a tool and workpiece for repeated cold drawing operations, metal rolling forming, lubrication and cooling during cutting operations in metal machining processes. However, due to its tendency to mix metal debris, bacteria, and rinse water for cleaning metal machining surfaces during use, its service life is very short. In terms of molecular weight, individual molecules are small enough to pass through ultrafiltration membranes, while ultrafiltration can successfully separate the oil phase from these oily wastewater. This is because the interfacial tension between oil and water is sufficient to prevent oil droplets from passing through the membrane that has been soaked in water. After ultrafiltration, the oil concentration in the permeate is usually less than 10g/m3, which meets the emission standard and can be discharged into the sewer. The final oil content in the concentrated solution, which reaches 30% to 60%, can be used for combustion or other purposes. The operation process is shown in the following figure. In addition, alkaline cleaning solution baths are often used to clean oily or dirty metal parts. Ultrafiltration can also be used to treat this cleaning solution to remove lubricating grease, oil, and dirt particles, and to recover the vast majority of cleaning agents in the form of filtrate. As shown in the following figure.

3. Application Three of Ultrafiltration Industry - Utilizing Ultrafiltration to Treat Wastewater Containing Heavy Metals

Application Three of Ultrafiltration Industry - Utilizing Ultrafiltration to Treat Wastewater Containing Heavy Metals

Micelle enhanced ultrafiltration (MEIJF) is a recently developed ultrafiltration method that combines surfactant technology. The principle is shown in the following figure. Injecting surfactants with concentrations higher than the critical micelle concentration into industrial wastewater results in the hydrophobic end entwining inward, while the negatively charged hydrophilic end is arranged on the surface, resulting in a negative charge on the surface of the adhesive. Metal cations in wastewater are adsorbed on them due to electrostatic interactions. By using ultrafiltration membranes with a molecular weight smaller than that of micelles, metal ions can be intercepted.

The surfactant sodium dodecyl sulfate (SDS) was added to simulated wastewater to separate four types of ions: Cd2+, Zn2+, Cd+, and Ca2+. The retention rates were all above 96%, and the membrane permeation flow rate was the same as pure water, indicating that the industrial application of MEUF is possible. Some researchers also used natural deoxycholic acid and phospholipids as surfactants, and the results showed that their separation efficiency for Ca2+, Pb2+, Cu2+, Ni2+, and Zn2+was better than SDS, with a retention rate of over 99.9%. Due to the fact that the concentration of surfactants in MEUF must be higher than the critical micelle concentration to form micelles, MEUF cannot be used for the separation of low concentration metal ions.

By using polyelectrolytes such as carboxymethyl cellulose (CMC) and sodium polystyrene sulfonate (PSS), which do not depolymerize even in small amounts, instead of surfactants, to add to the wastewater, the polyelectrolyte dissociates and counterions (Na+) enter the water. The polymer is negatively charged, and heavy metal ions such as Cu2+in the wastewater combine with the polymer. A ultrafiltration membrane with a molecular weight smaller than the polymer can intercept Cu2+in the wastewater. × 10-6 to 1 × 10-6.

There is a ultrafiltration process called IEIJF (Ion Expulsion Ultrafiltration) that utilizes the repulsive effect of ions for separation. As is well known, micelles combine less than a stoichiometric number of counter ions in water and therefore carry a charge, which is close to a constant over a considerable range of ion concentrations. IEUF utilizes this characteristic of micelles to separate ions with the same charge as them. The following figure is a schematic diagram of the IEUF process. According to Donnan's equilibrium principle, when the dissociated anions and cations in the solution are in equilibrium in the permeate and concentrate on both sides of the membrane, their ion activity products are equal, and thus the concentration of each ion can be calculated. The calculation results indicate that when reaching equilibrium, Cr042- can be concentrated 21.5 times in the permeate.

Other industrial applications of ultrafiltration

Other industrial applications of ultrafiltration:

(1) Application of ultrafiltration in the preparation of high-purity water

Many industrial water requirements are very strict, especially in the electronics industry, where high purity water is used in many places, which plays an important role in ensuring product quality. For example, in the process of slicing, grinding, epitaxy, diffusion, and evaporation of integrated circuit semiconductor devices, it is necessary to repeatedly clean with high-purity water. In a small area of integrated circuits, there are many adjacent components with a distance of only about 0.002mm between them, so the cleaning water requirements are very strict. General requirements include no ions, no soluble organic matter, no bacterial cells, and no greater than 0.5 μ The particles of m. Each integrated circuit factory has a central system for manufacturing high-purity water, which is then transported to the point of use through a distribution system. The purification process is as follows:

Tap water → Pre filtration → Ultrafiltration (or microfiltration) → Reverse osmosis → Mixed bed of anion and cation exchange resins → Ultrafiltration → Distribution system microfiltration → Point of use microfiltration → Use

Ultrafiltration is mainly used in the preparation of high-purity water to remove colloids, particles, and bacteria. The ultrafiltration components used for the preparation of high-purity water are mostly hollow fiber type, with a membrane permeation flow rate of up to 2-4m/d.

(2) Wastewater treatment containing starch and enzymes.

In certain food processing industries, such as potato processing, the wastewater contains low concentrations of starch, and the emissions from the brewing industry contain enzymes. Ultrafiltration can be used to recover starch and enzymes, and produce wastewater that can be allowed to be discharged.

(3) The treatment of desizing water in the textile industry.

Sizing materials such as starch and water-soluble polymers (polyvinyl alcohol) are often used in textile processes to facilitate the process. Wash the woven fabric to remove the slurry, resulting in a dilute solution containing the sizing material. Ultrafiltration can be used to recover this sizing material for reuse and produce high-quality water filtrate, which can be discharged or reused.

(4) Lotion concentration.

In the manufacture and application of synthetic rubber, the washing water of containers, reactors, etc. contains dilute lotion solution, which is successfully concentrated by ultrafiltration process.

(5) Treatment of the discharge solution for washing wool.

This discharge liquid contains lanolin type oils emulsified by detergents, which can be dehydrated by ultrafiltration (often combined with centrifugation).

(6) Treatment of effluent from pulp factories.

This discharge liquid contains high molecular weight lignosulfonate, which can be separated and concentrated using ultrafiltration method.

(7) Application in the process of traditional Chinese medicine preparation.

Food Biochemical Application of Ultrafiltration

Food Biochemical Application of Ultrafiltration - Using Ultrafiltration to Treat Dairy Products

The production process of milk vinegar in the dairy industry will produce a large amount of whey. According to statistics, 25 million cubic meters of whey are produced annually in the United States alone, making this field the largest application of ultrafiltration. As shown in the figure below, a concentrated solution containing 10% protein can be obtained by ultrafiltration. If it is dried by spray, a whey powder containing 65% protein can be obtained, which can replace skimmed milk powder in bread products. If it is further desalinated, a product with a protein content higher than 80% can be obtained, which can be used for baby food. The permeate containing lactose can be used as animal feed after being concentrated and dried.

Ultrafiltration process for processing whey

Various forms of components are used in whey ultrafiltration, with the largest having a membrane area of 1800m2 and a daily whey processing capacity of 1000m3. Usually operated at 50 ℃. The membrane permeation flow rate is initially greater than 1m/d, but when the whey is concentrated 10 times, its viscosity exceeds 0.002Pas (0.02P) and the membrane permeation flow rate decreases to 0.5m/d. Therefore, its concentration limit is largely determined by membrane fouling and an increase in the viscosity of the whey concentrate. The most important issue for ultrafiltration in the food industry is daily cleaning and sterilization. Generally, alkaline washing is used first, followed by acid washing, and finally sterilized with sodium hypochlorite solution. The lifespan of the membrane can reach over 1 year.

A new cheese production process involves first concentrating skim milk 3-4 times through ultrafiltration, and then using the concentrated liquid for fermentation to produce milk vinegar, as shown in the figure below. With its great advantages, it is gradually being promoted. Because using processed concentrate to produce milk enzymes can increase the yield by more than 20%, it is conservatively estimated that 6% of milk can be saved; In addition, the removal of lactose from milk enhances the taste of milk vinegar and ultimately reduces the amount of whey processed.

A new process for producing milk enzyme with ultrafiltration

Food Biochemical Application of Ultrafiltration - Clarification of Fruit Juice by Ultrafiltration

Fresh fruit juice extracted from apples appears cloudy due to the presence of compounds such as pectin. The traditional method uses enzymes, bentonite, and gelatin to precipitate it, and then filters the supernatant to obtain clear fruit juice [see Figure (a) Traditional process]. Clarifying fruit juice through ultrafiltration or microfiltration only requires partial removal of pectin, which can reduce the amount of enzyme used, save soap and gelatin, save raw materials, and save labor and time [see the new ultrafiltration process in the figure (b) below]. At the same time, the juice recovery rate has also increased, reaching 98% to 99%. In addition, the quality of the juice treated by ultrafiltration has also been improved, with a turbidity of only 0.4~0.6 NTU (traditional process is 1.5~3.0 NTU). Moreover, ultrafiltration can remove bacteria from fruit juice by heating, thus extending the shelf life of fruit juice.

Food Biochemical Application of Ultrafiltration - Extraction of Serum Albumin by Ultrafiltration

The separation of serum albumin from plasma involves a series of complex processes. As shown in the figure below, the processed components containing 3% albumin, 20% ethanol, and other small molecule substances were separated from ethanol using a three-step method using an ultrafiltration membrane with a molecular weight of 30000. In the first and second steps, the membrane permeation flow rate is 0.5-0.7m/d, and in the last step, it drops below 0.1m/d. According to the latest report, using a zirconia metal membrane with a molecular weight of 10000 can result in a longer membrane lifespan and greater energy. In addition, using recoil and pulse feeding can reduce membrane fouling. The permeability of the first and second steps can be increased by nearly twice, and the albumin concentration in the permeate is lower, usually below 0.4g/L.

Food Biochemical Application of Ultrafiltration - Extraction of Serum Albumin by Ultrafiltration

The separation of serum albumin from plasma involves a series of complex processes. As shown in the figure below, the processed components containing 3% albumin, 20% ethanol, and other small molecule substances were separated from ethanol using a three-step method using an ultrafiltration membrane with a molecular weight of 30000. In the first and second steps, the membrane permeation flow rate is 0.5-0.7m/d, and in the last step, it drops below 0.1m/d. According to the latest report, using a zirconia metal membrane with a molecular weight of 10000 can result in a longer membrane lifespan and greater energy. In addition, using recoil and pulse feeding can reduce membrane fouling. The permeability of the first and second steps can be increased by nearly twice, and the albumin concentration in the permeate is lower, usually below 0.4g/L.

The above is a summary of the application of ultrafiltration membrane technology introduced by Hongjie Water, hoping to be helpful to you.