Walking in the saline-alkali land of the Bohai Sea, there is endless desolation. Nothing can be done without clean water. Today, thin membranes solve the problem of water scarcity.

In the "Twelfth Five-Year Plan" period of the major water pollution control and treatment project, the “Industrialization of Drinking Water Treatment PVDF Membrane Modules and Equipment” supported by the Ministry of Housing and Urban-Rural Development has established 30 sites in the Yangtze River, Yellow River, Huai River, and Haihe River Basin Several "membrane" water plants filter out nearly one million tons of purified water every day.

Membrane filtration, safe and efficient

In mid-August, the reporter came to visit the Tianjin Nangang Industrial Zone Water Distribution and Distribution Center Project. Nangang Industrial Zone is built on saline land. The ground is white salt, and no deep water is in the deep well. Covering an area of ​​nearly 100,000 square meters, the water distribution center that produces 50,000 tons of tap water per day is the only water source in Nangang Industrial Zone. Tianjin Metian Membrane Co., Ltd. provides the core technology of ultrafiltration membrane purification equipment for water plants.

I reporter here saw the production process of tap water. The raw water of the water plant comes from the Luanhe River. The reservoir water is pressurized by the pumping station and comes through a polyester water main. After flocculant was added to the raw water, a large number of floc appeared on a circuitous circuit flanked by dozens of grids, and then flowed into the inclined plate sedimentation tank to remove the floc. Then enter the "ultrafiltration system" and get in close contact with the membrane.

The so-called membrane is formed by “membrane wires” connected in parallel. Membrane wire is a tube with a thickness of 1.8 meters, such as the thickness of Lanzhou ramen, with an inner diameter of 0.7 mm and an outer diameter of 1.2 mm. The seemingly smooth surface of the membrane wire is densely covered with nano-sized fine holes. Water flows from the outer surface of the membrane wire, penetrates into the membrane through the holes, and large and small particles and microorganisms are intercepted.

A hundred or more membrane filaments were bundled into a tube ultrafiltration membrane module. There are 1,200 such components in the Nangang Waterworks. After the raw water is fed into the membrane module under pressure, the crystal clear filtered water continuously flows out, which is clean drinking water. Bacteria, algae, colloids, and fine particles are blocked from the membrane.

Dirt particles will adhere to the film and affect its operation, so the film also needs to be cleaned daily. The most commonly used method is reverse cleaning. The clean water is pressed from the inside of the membrane filament to the outside of the membrane filament to flush away the dirty particles. It can also be sent into compressed air to enhance the backwash effect. The cleaned sewage is discharged from the sewage outlet of the membrane module. At a certain time, chemical cleaning is required to restore the filtration capacity of the membrane. If properly maintained, membrane life can exceed six years.

Tianjin Motian Membrane Company's water delivery project will be officially operated in May 2013. After the completion of the second phase, its water supply capacity will double. The ultrafiltration membrane system is stable and efficient. Its operating cost is less than a penny of a ton of water. The unit capacity cost is less than 300 yuan per ton. Tianjin Metian Membrane Co., Ltd. previously focused on sewage treatment. With the support of the water project, it successfully entered the drinking water market and became a highlight of the water project. More than a dozen projects including Shandong Tai'an Sanhe 80,000-ton water plant have applied their technology.

Diaphragm manufacturing, domestic products

A special drinking water industrialization project funded in 2011 began. In response to the problems of unstable performance and low competitiveness of domestic ultrafiltration membranes at that time, research was conducted on key technologies for large-scale production of membrane separation equipment, and low-cost, high-performance The serialization and complete set of ultrafiltration membrane equipment provide protection for large-scale application of ultrafiltration membrane technology in urban water plants and rural drinking water, and enhance the competitiveness of domestic membrane enterprises. This project is hosted by Tianjin Motian Film Co., Ltd. Shandong Zhaojin Motian Co., Ltd. and Suzhou Mohua Co., Ltd. are the sub-project undertakers.

In Shandong Zhaojin Metian Company, the reporter saw the production process of the film. The polymer raw material was drawn from the spinning machine into a long thin tube and the film was shaped into a liquid. Hundreds of membrane filaments were manually bundled into bundles on a "chopping board", and then soaked in a special liquid, slowly changing from beige to ivory.

The diaphragm is made of high-molecular material PVDF (polyvinylidene fluoride). When viewed from a scanning microscope, its cross section is densely perforated with an average pore diameter of less than 0.03 microns, which is equivalent to one-thousandth of a hair. After the “science popularization” of Yang Min, an expert of the Chinese Academy of Sciences, the reporter understands that the process is to mix the “pore-forming agent” into PVDF to form tubular filaments, and then dissolve the hole-forming agent, leaving a frozen tofu-like mesh. structure. The pore former formulation and processing technology of each company are different.