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Some advantages of pacs when used in water treatment

  • 14/05/2021
  • Publish at: 16:14:08
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In the process of water treatment as well as wastewater, it is almost indispensable to do the water-making process - reducing turbidity, separating suspended sediment. This process in the scientific language is called flocculation. It is the process that causes extremely small suspended particles (called colloidal particles), which are dispersed in water to settle, and create turbidity or water color thanks to the help of chemicals. PAC, aluminum sulfate alum, iron alum ... they will stick together - gather together into larger, heavier particles that can be deposited into mud and separated from water. Along with this sludge, there are many impurities and impurities such as organic substances, some heavy metals ... so these chemicals not only reduce turbidity in the water but also reduce the content of some impurities. Toxicity differs to varying degrees depending on the type of flocculation used.

Traditionally, people still use aluminum sulfate alum or double alum (acid alum) to treat drinking water. However, with the research achievements of scientists on the nature of the flocculation process - the formation of colloidal cotton and the effect of aluminum residue in water, there are two following problems:

  • Residual aluminum in the water will increase the aluminum residue in the human body leading to many diseases, such as impaired nervous system - Eczeimer disease ...
  • The process of flocculation with salts - the aluminum compound associated with polymer hydrolysis - the prefix to the formation of cotton, which is influenced by the length of the polymer formed - is determined by anionic composition of aluminum salts. Specifically, if it is chlorine anion, the formed aluminum polymer has a chain of 13 aluminum cores, sulfate form - 7 aluminum cores, nitrate form - 3 cores ... The glue will be larger, it will hold more dirt and it will settle more easily.

To ensure people's health, advanced countries around the world have been interested in investigating the effects of using aluminum-based flocculants. As mentioned above, the chlorine base for the cotton is larger, so the sedimentation process is more thorough, the dirt entails more, the amount of chemicals used is less, so the residue of aluminum is less than that of aluminum sulfate.

Assoc.Prof. Dr. Le Mai Huong is currently the Chairman of the Scientific Council of the Institute of Natural Products Chemistry under the Vietnam Academy of Science and Technology.

From a technical and operational perspective, PAC has many advantages

The PAC form is a chloride based salt but is alkaline, so when used, it has many advantages, such as not changing the pH of water, not having to add lime or alkali like when using aluminum sulfate. The salt form of chlorine itself is easy to dissolve, not hydrated and hard to dissolve like alum aluminum sulfate. The saturated concentration of aluminum alum is low, making it difficult to dissolve, consuming energy and the device is cumbersome. When adding lime, aluminum alum easily creates CaSO4 residue clinging to the pipes ... We can summarize the advantages of PAC as follows:

  • Chemical consumption decreased 4-5 times (20-25%) compared to the amount of aluminum sulfate;
  • Practically does not change the pH of the purified water, allowing the use of alkaline neutralizing agents to be avoided;
  • Broader active pH range;
  • The product has a higher polymerization capacity, increasing the rate of agglutination and precipitation of colloidal cotton;
  • Better filtration efficiency of suspended solids, organic impurities and metals;
  • Good in winter with low water temperature;
  • Reducing the corrosive activity of water (no excess sulfate);
  • When in use, low residual aluminum residue in the water;
  • Do not freeze cakes when storing, have a long use time;
  • Reducing equipment corrosion due to the alkaline, high pH PAC solution;
  • Better industrial hygiene, easier automation and lower operating costs;
  • Reducing storage space, reducing transportation costs because the aluminum content in PAC is twice as high as aluminum alum.

With such advantages, PAC increasingly replaces aluminum alum in the treatment process for water supply and wastewater

Associate Professor, TS. Le Thi Mai Huong

Deputy Director, Institute of Rare Radiation Technology,

Vietnam Atomic Energy Institute

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