Remove chromium. The most common methods of wastewater treatment are reagent treatment, ion exchange treatment and electrochemical treatment. Chemical reagent treatment is most common method of chrome and heavy metals removal.
This method of treatment is based on the reactions of chemical reagents with pollutants. In case of chromium-containing wastewater, the reagents reduce hexavalent chrome to trivalent chrome followed by its precipitation. Some of the reducing agents are:
- copperas;
- sulfur compounds (sodium bisulfite, sulfite, etc.);
- scrap steel;
- scrap iron.
In practice, there are two approaches to purification of chrome containing wastewater. In the first approach hexavalent chrome is reduced to trivalent chrome in acidic environment followed by neutralization and precipitation. The other method is combined treatment of chrome and acid-alkaline wastewater in alkaline environment, with the parallel reduction of chrome by copperas. The process is completed by precipitation of heavy metals.
Obviously, wastewater treatment is not complete with the removal of chrome. It is also important to remove other heavy metals by neutralization with alkaline reagents. The best results are achieved by combined wastewater treatment removing several metals rather than removing each one separately.
In many facilities, the chemical treatment of wastewater by alkali is enough to reduce the content of heavy metal ions to values allowing wastewater discharge into the municipal sewage system. Deeper purification is achieved by post-treatment of wastewater through the ion-exchange filters.
Overall the chemical reagent wastewater treatment has both advantages and disadvantages. The disadvantages include insufficient degree of heavy metal removal, a high content of salts in the purified water, unrecoverable loss of metals, high reagent consumption, complexity and bulkiness of equipment.
As it is not possible to develop fundamentally new methods of wastewater treatment that do not use chemicals at the moment, improving the existing approaches is the solution.
One of the most promising ways to improve the treatment process is to use the electromagnetic nano-mill (AVS). The chemical reactions in the chamber of this device occur much faster: in seconds and fractions of a second. This is due to a number of effects, such as electromagnetic field effect, intensive dispersion and mixing and electrolysis.
The AVS reduces the consumption of reagents, reduces the footprint of equipment and significantly reduces the duration of wastewater treatment.