Aplicação de ultrafiltração in drinking water treatment

Water is the source of life. my country has very little water resources per capita, and this limited water resource is constantly threatened by the deterioration of water quality and the destruction of the water ecosystem. Various production wastewater and domestic sewage are directly discharged to the In the water body, it causes great harm to the surface water source, and the water quality of the water source drops sharply. There are many types of pollutants in water sources, including inorganic toxic substances and organic harmful substances. Organic pollutants can be divided into two categories: natural organic matter (NOM) and synthetic pollutants (SOC). NOM includes humus, microbial secretions, and dissolved animal tissue. And animal waste, etc., while SOC is mostly toxic organic pollutants, including three organic pollutants, which are difficult to remove. On the other hand, conventional treatment processes have certain difficulties in reducing treatment costs, reducing the turbidity of produced water, and reducing disinfection by-products in water. In order to meet the current and future more stringent water quality requirements, it is a general trend that microfiltration and ultrafiltration technologies are used in drinking water treatment.
In my country, with the rapid development of economic construction, water pollution is on the rise. Water pollution in industrially developed areas is particularly serious, water shortages are becoming increasingly prominent, and urban water shortages are becoming more and more serious. Drinking water problems in rural areas are even worse. The water sources of drinking water in rural areas are characterized by dispersion, diversity and instability. The water sources cannot be effectively protected. The drinking water treatment often only undergoes simple precipitation or clarification treatment, which cannot effectively kill bacteria, viruses and other microorganisms, let alone remove organic substances. Pesticide residues seriously affect the life and health of people living in rural areas. Traditional drinking water treatment technology and enhanced conventional treatment technology have been unable to meet people’s requirements for drinking water quality. At present, the advanced water treatment technologies at home and abroad mainly include biological oxidation, ozone oxidation, activated carbon adsorption technology, potassium permanganate oxidation, and membrane treatment. Among them, membrane drinking water treatment technology, as a revolutionary technology, has been widely used in developed countries, and has also been widely concerned in my country. In this paper, an example of a small ultrafiltration membrane water plant with a capacity of 150 tons per day is used to analyze the actual treatment effect of ultrafiltration technology on surface drinking water sources whose iron, manganese and microbial indicators seriously exceed the standard.

1. Application status of microfiltration and ultrafiltration technology in drinking water treatment

  1.  Modelo
    Membranes used in drinking water treatment can be divided into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) according to the membrane pore size. In industrial applications, the membrane needs to be installed into a membrane module. The membrane modules that have been used in industry are mainly divided into: hollow fiber type, roll type, plate and frame type and tubular type. The hollow fiber type and roll type modules have high filling density, low cost and good hydrodynamic conditions in the module, but these two modules have high requirements on manufacturing technology, difficult sealing, poor anti-pollution ability in use, and high requirements for pretreatment of material and liquid . Plate-and-frame and tube-type modules have low membrane packing density and high cost, but the modules are easy to clean and resistant to pollution.
  2. Material
    At present, dozens of materials have been used to prepare separation membranes. Organic materials include cellulose, polyamide, aromatic heterocycles, polysulfones, polyolefins, silicone rubbers and fluoropolymers. Inorganic materials include Ceramic, glass, metal and carbon. Among them, the membrane made of ceramic material has better chemical stability, acid and alkali resistance, and high mechanical strength. Its tubular component can handle water containing larger suspended particles, and it is not easy to block the channel of the membrane, so it is suitable for in water treatment.
  3. Advantages
    Membrane technology can remove a wide range of pollutants, from inorganic substances to organic substances, from viruses, bacteria to particles, without adding chemicals, reliable operation, compact equipment and easy automatic control. Technically speaking, microfiltration and ultrafiltration have a good effect on removing pathogenic microorganisms such as suspended matter, turbidity and bacteria in water, which are unmatched by conventional treatment and some other advanced treatments. In the past, it was not suitable for use in urban water plants due to price. In recent years, due to the advancement of membrane technology, the price has also dropped significantly. It has a wide range of application prospects in drinking water treatment. It is an inevitable trend to replace conventional treatment. Among them, the submerged system can be used for To build a new water plant or to renovate an existing water plant, the membrane can be directly put into the clarifier or sand filter.
  4. Membrane technology defects, solutions, and future research directions
    Although membrane technology has good prospects for development, there are still certain problems. At present, the short service life of membranes and the increase in operating costs caused by membrane flux attenuation make it difficult to apply membrane technology in large-scale water plants. From the perspective of the membrane itself, membrane materials and membrane modules need to be improved. The preparation of anti-fouling, high-flux membranes and prolonging the service life of membranes is a future development direction, and the preparation of membrane modules with low energy consumption is conducive to the further development and application of membrane technology. From the perspective of membrane operation, membrane fouling is a very serious problem. Frequent chemical cleaning is required to ensure a certain flux, and the increase in membrane replacement frequency will result in an increase in the operating cost and cost of the entire treatment process, which will become a problem in the future. A difficult problem to solve for quite a long time.

2. The process principle of ultrafiltration to filter raw water

1. Ultrafiltration for the removal of suspended solids and microorganisms

The main feature of ultrafiltration membrane separation technology is that it has high filtration accuracy. The project uses an ultrafiltration membrane with a nominal filtration accuracy of 0.03 microns, which can achieve:
(1) It has a high removal capacity for suspended solids that cause water turbidity; the turbidity of produced water usually reaches below 0.2NTU;
(2) It has more than 99.99% removal ability for microorganisms such as Escherichia coli. Since microorganisms are usually above 0.5 microns, ultrafiltration membranes of 0.03 microns are very effective for removing microorganisms;
(3) For iron, manganese, aluminum and other colloids, it has a removal capacity of more than 90-95%. However, it has no ability to remove iron ions in a dissolved state.

2. Ultrafiltration for the removal of iron and manganese

Ultrafiltration can remove iron and manganese in the form of colloids or suspended solids, but it cannot remove ferrous ions and divalent manganese ions dissolved in water. It must be combined with oxidation treatment to rapidly oxidize ferrous iron to ferric iron. At neutral pH Insoluble iron colloids are formed nearby, and the divalent manganese is oxidized to tetravalent manganese, which is removed by ultrafiltration. In conventional water treatment processes, iron and manganese removal filters are used to remove iron and manganese dissolved in water. In this project, considering the factors such as land occupation and investment, the method of adding sodium hypochlorite to the ultrafiltration influent water is adopted to achieve this purpose, and the added amount is 6ppm.

3. Ultrafiltration for the removal of fluorine

The fluoride in the water source water exceeds the standard, but the ultrafiltration itself cannot remove the dissolved fluoride ions. At present, the defluorination processes mainly include activated alumina adsorption and filtration, bone charcoal adsorption and filtration, aluminum salt coagulation and precipitation, electroflocculation, electrodialysis, etc. In this project, domestic polyaluminum chloride (PAC) is used as a flocculant, and the alum formed by aluminum salt The flower particle Al(OH)3(S) has a certain adsorption capacity for fluoride ions in water, and then the purpose of fluoride removal is achieved by the interception of the colloid formed by the hydrolysis of aluminum salt by ultrafiltration. During the operation of the project, the addition of PAC is 10ppm, and the removal rate of fluoride 6 is 49%, which can already meet the drinking water requirements. If the removal rate is to be increased, more PAC needs to be added.

3. Features of advanced ultrafiltration membrane method drinking water treatment process Compared with traditional drinking water treatment technology and conventional advanced drinking water treatment technology, ultrafiltration membrane method has the following advantages:

  • The filtration precision is extremely high, and it has a high removal rate for suspended solids, microorganisms and colloids;
  • The quality of the produced water is stable, and is less affected by the fluctuation of the influent;
  • Modular device design not only meets the needs of large water plants, but also is more suitable for small decentralized water supply systems;
  • The process is short, and there is no need to add or add a small amount of chemicals, which is convenient for automatic control.

4. Conclusão

Microfiltration and ultrafiltration membrane processes have the effect of removing pollutants in water that cannot be achieved by traditional processes. With the advancement of membrane technology and the decline in prices, membrane technology may completely replace conventional water treatment processes. It not only occupies a small area, but also can It can realize automatic control, easy maintenance, low energy consumption, and can remove turbidity, NOM, taste and smell, and DBPs, etc., to ensure stable effluent water quality, so the market prospect is very broad. The use of membrane technology for drinking water production has been extensively studied abroad, and many countries have established large-scale practical projects, which provide reference for my country’s drinking water production.

Xi'an CHIWATEC A Water Treatment Technology é uma empresa de alta tecnologia especializada em vários dispositivos de processamento de água. Além desses produtos individuais, que abrangem vários tipos e séries, também podemos ajudar com projetos de engenharia abrangentes relacionados. Graças ao nosso trabalho árduo e dedicação desde a nossa fundação, somos agora um dos fabricantes de equipamentos de tratamento de água com desenvolvimento mais rápido na China Ocidental.

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