Foreword
Manganese greensand is a common media used in the water treatmentindustry to remove iron, manganese and hydrogen sulphide fromdrinking water. But what if the manganese greensand gets saturatedwith these contaminants? How does it get cleared from the system andre-generated?
In this article we will discuss the various methods used for the removalof manganese greensand, their pros and cons, and the process ofregeneration.
What is Manganese Greensand?
Manganese greensand is a mixture of sand, greensand and manganesedioxide. Greensand is a kind of sedimentary rock that is found in someparts of the United States and contains a large amount of the mineralglauconite.
Manganese dioxide is used in water treatment as an oxidant to removecontaminants such as iron, manganese and hydrogen sulphide. As waterflows through the media, the manganese dioxide oxidises thecontaminants, which are then trapped in the greensand.
The manganese greensand becomes exhausted after a period of useand needs regeneration or replacement.
Removal Techniques
Manganese greensand can be removed from a water treatment systemin a number of ways. Each method has its pros and cons and the choiceof removal method depends on several factors like size of the treatmentsystem, type of contaminants present and desired outcome.
1. Reversal
Manganese greensand is a frequent media in water treatment systems,and it is removed by backwashing. Backwashing is the sending of thewater through the media in the reverse direction to wash away thetrapped contaminants.
During backwashing, the water flows in the opposite direction of thenormal treatment flow, expanding the media and dislodging trappedcontaminants from the greensand. The contaminated water is then sentto a waste stream or filtration system where the contaminants areremoved.
Advantages
- Backwashing is a low cost and easy way to remove the manganesegreensand from the system.
- It does not require chemicals and the process can be automated.
- Normal treatment process is not interrupted during backwashing.
Disadvantages
- Backwashing creates a large amount of wastewater that needs to bedisposed of correctly.
- The process does not regenerate the media, it only removes thetrapped contaminants.
2. Regeneration by chemicals
Chemical regeneration involves the use of chemicals to removecontaminants from the media or regenerate the media"s oxidizingagent. The kind of chemical used depends on the kind of contaminantspresent.
The media is soaked in the chemical solution so that the chemical reactswith the trapped contaminants, dislodging or oxidising them. The mediais then rinsed to remove the contaminants and excess of the chemicalsolution.
Advantages
- The oxidising agent in the media may be regenerated chemically toprolong the life of the media.
- It is an effective way of removingcontaminants that cannot be removed by backwashing.
- The process isvery fast with minimal downtime.
Disadvantages
- Chemical regeneration can be expensive and involves the carefulhandling of hazardous chemicals.
- The procedureChemical regenerationuses chemicals to either strip contaminants from the media or toregenerate the media's oxidising agent.
- The type of chemical will dependon the type of contaminants.
3. Mechanical control
Mechanical removal is the physical removal and replacement of thesaturated media with new media. The procedure involves manuallyremoving media and shutting down the system.
Mechanical removal is generally used when the media is severelysaturated or damaged beyond repair.
Advantages
- Mechanical removal guarantees the complete removal of the saturatedmedia and trapped contaminants.
- It is an efficient way to dispose ofdamaged media.
Disadvantages
- It is costly and labour intensive to remove mechanically.
- It requires asystem shutdown which results in a lot of downtime.
- It produces a lot ofwaste and needs to be properly disposed of.
Regeneration Process
No matter how manganese greensand is removed, the media must beregenerated before it can be reused. Regeneration is the process ofrestoring the oxidising agent in the media or removing the contaminantsthat are trapped in the media to extend the life of the media.
The process of regeneration is as follows:
1. Back-flushing
Backwash the media to remove any loose contaminants and debris priorto regeneration.
2. Chemical Regeneration
If the removal method is chemical regeneration, the media is soaked inthe appropriate chemical solution to restore the media"s oxidising agentor to remove the trapped contaminants.
3. Rinse The media is flushed with clean water to remove any residualchemicals and contaminants.
4. Rinse again
Then the media is rinsed and backwashed once more to remove theresidual contaminants.
5.Service
After the media has been regenerated it can be returned to service andused again.
Conclusion
Water treatment plants rely on manganese greensand as an essentialmedium to eliminate impurities such as iron, manganese, and hydrogensulphide. But the media eventually gets saturated and has to be purgedand rebuilt.
There are a number of ways to remove Manganese greensand, eachwith its advantages and disadvantages. The method used depends onmany factors including the size of the system, the type of contaminantspresent and the desired outcome.
Regeneration is an important step in ensuring that the media can bereused, whatever the method used. The regeneration process consistsin reconstituting the oxidising agent of the medium or in eliminating thetrapped pollutants so as to extend the lifespan of the medium.
