Table of Contents
2.2.8: Disc filter
2.2.9: Ultrafiltration
2.2.10: Summary of pretreatment process
2.2.8: Disc filterDisc filters, also known as laminated filters, have a modular design in which water flows through laminated sheets when the filter is working properly, using sheet walls and grooves to collect and intercept debris. The composite inner section of the sheet groove provides a three-dimensional filtration similar to that produced in a sand filter. As a result, it has a high filtration efficiency. Several advantages of disc filters.
Accurate filtration: filter discs of different precision can be selected according to water requirements, including 5 m, 20 m, 55 m, 100 m, 130 m, 200 m, 400 m and other specifications, and the filtration ratio is greater than 85%.
Thorough and efficient backwashing: Due to the complete opening of the filter pores during backwashing, coupled with centrifugal spraying, the cleaning effect that other filters cannot achieve is achieved. The backwash process takes only 10 to 20 seconds for each filter unit to complete.
Fully automatic operation, continuous water discharge: time and differential pressure control backwash start. In the filter system, the individual filter units and stations are backwashed sequentially. Automatic switching between working and backwash states ensures continuous water discharge, low system pressure loss, and no deterioration of filtration and backwash effects due to time of use.
Modular design: the user can choose the number of filter units in parallel according to their needs, which is flexible and changeable, and has strong interchangeability. The corner space of the site can be flexibly used, and the installation occupies less land according to local conditions.
In the process of pure water preparation, the large flow rate of the disc filter is often combined with ultrafiltration as a pretreatment process to replace the role of traditional sand filtration.
2.2.9: Ultrafiltration
Ultrafiltration is a pressure-driven membrane separation process that can be screened with a diameter of 0001-0.Particle and impurity retention between 02 m (1-20 nm) for effective removal of colloids, silicon, proteins, microorganisms, and macromolecular organics from water. When the liquid mixture flows through the membrane surface under a certain pressure, the solvent and small molecule substances pass through the membrane, while the large molecule substances are intercepted, so as to achieve the separation and purification of the size and molecules, and the operating pressure is generally 01–0.5 mpa。
Fundamentals of ultrafiltration
Under a certain pressure, the small molecule solute and solvent pass through the special film with a certain pore size, and the macromolecular solute is impermeable and remains on one side of the membrane, so that the macromolecular substance is partially purified. The principle of ultrafiltration is also a membrane separation process principle, ultrafiltration uses a pressure-active membrane to intercept colloids, particles and relatively high molecular weight substances in water under the action of external driving force (pressure), and water and small solute particles pass through the membrane separation process. Substances with molecular weights of 3x10000-1x10000 can be retained through micropores on the membrane surface. When the treated water passes through the membrane surface at a certain flow rate with the help of external pressure, water molecules and solutes with molecular weights less than 300-500 pass through the membrane, and particles and macromolecules larger than the membrane pores are intercepted due to sieving, so that the water can be purified. In other words, when the water passes through the ultrafiltration membrane, most of the colloidal silicon contained in the water can be removed, and a large amount of organic matter can be removed at the same time.
In the process of pure water preparation, ultrafiltration is often used as a pretreatment process in the front end of high-flow equipment, which plays the role of a security filter. In the preparation process of ultrapure water in the semiconductor industry, ultrafiltration is also often used as a terminal effluent filtration, replacing general microporous membrane filtration.
2.2.10: Summary of pretreatment process
The commonly used pretreatment processes in the process of pure water preparation include coagulation, sand filtration, carbon filtration, softening, fine filtration, ultrafiltration, disinfection, etc. We often select the necessary and appropriate process according to the quality of different raw water quality to treat it in turn, and in most cases, it is a series relationship between the front and back, and basically followsLow precision in the front, high precision in the back, low cost in the front, high cost in the backprinciples.
A brief review of the role of common pretreatment processes:
Heat exchanger: Regulates the water temperature.
pH adjustment: a kind of dosing device that adjusts pH
Quartz sand filter: retains, adsorbs sediment, colloids, metal ions and organic matter, and reduces water turbidity.
Activated carbon filter: adsorption of electrolyte ions and ion exchange adsorption, which can remove discoloration in water, broad-spectrum adsorbents.
Multi-media filter: Fill more than two filter media, which can effectively remove suspended impurities and make the water clear.
Bag filter: a kind of precision filter, often selected 5 m precision filtration, playing the role of security filter.
PP meltblown filter element filter: a kind of precision filter, often selected 5 m precision filtration, playing the role of security filter.
Disc filter: high-efficiency filter, often selected 50 100 m precision filtration, suitable for large flow equipment.
Ultrafiltration: hollow fiber membrane filtration technology, often selected 001 m precision filtration, playing the role of security filter, the cost is high.
Reducing agent: a kind of dosing device, residual chlorine reducing agent eliminates residual chlorine.
Flocculant: a kind of dosing device to strengthen the flocculation and precipitation of suspended solids and colloids.
Fungicide: A type of dosing device that reduces the impact of microorganisms on the system.
Iron and manganese filter: aeration, iron and manganese ion oxide, adsorption, filtration to remove iron and manganese ions.
Dispersant: A kind of dosing device, silicon dispersant can weaken SiO2 scaling.
Scale inhibitor: A type of dosing device that reduces the risk of fouling in the system.
Water softener: ion exchange technology, the effect of calcium and magnesium ion removal is obvious.
Degasser (decarbonizer): Combined with the water softener, it has obvious effect on CO2 removal.
Air flotation: Strengthen the separation of solid-liquid and liquid-liquid in the water body, reduce turbidity and suspended solids index.
Common pretreatment process combination sequences for different raw waters