How do you regenerate manganese greensand filter media just purchased prior to placing it into service-
How to Properly Regenerate Manganese Greensand Filter Media
Introduction to Manganese Greensand
Manganese greensand is a versatile and effective filter media used since the 1950s to remove iron, manganese, and hydrogen sulfide from water. Derived from organic deposits once part of the ocean floor, this bluish-green substance, known as "glauconite," is stabilized and coated with manganese oxide to enhance its oxidation-reduction properties. This coating is crucial for the removal of contaminants from water supplies.
The Importance of Regeneration
Before placing new manganese greensand into service, it must be fully regenerated to ensure optimal performance. The regeneration process involves several steps, and the choice of regeneration method depends on whether the primary goal is to remove iron or manganese.
Continuous and Intermittent Regeneration
There are two primary methods of regeneration: Continuous Regeneration (CR) and Intermittent Regeneration (IR). CR is typically used when iron removal is the primary objective, involving the continuous feeding of oxidizers such as chlorine or potassium permanganate into the raw water before it reaches the filter. This method can effectively remove up to 15 milligrams per liter of soluble iron.
On the other hand, IR is more suitable for manganese removal. In this process, manganese oxidation occurs directly using the properties of freshly regenerated manganese greensand. However, a drawback of IR is the additional time required for backwashing, which can take up to 75 minutes, compared to CR, which can be as fast as 15 minutes. When both iron and manganese levels are high, a combination of both methods can be employed.
Regeneration Procedure
To regenerate new greensand, follow the printed instructions on each bag, which typically involve soaking the media for several hours in a 2 to 3 percent solution of potassium permanganate (KMnO4). This can be done in a bucket or directly in the filter unit. A simple procedure is to mix one pound of KMnO4 per five gallons of water, cover the filter media with the solution, and let it rest overnight.
The minimum depth of the greensand bed varies depending on the regeneration method: 24-30 inches for IR and 18-20 inches for CR. If dealing with large amounts of pre-oxidized iron, reducing the depth of the greensand can allow for a deeper cap of anthracite.
Maintenance and Performance
The effectiveness of the filter can vary based on the levels of contaminants. If manganese and hydrogen sulfide are the primary contaminants, the filter may remain effective for several weeks before regeneration is needed. However, with iron levels ranging from 0.5 to 10 mg/L, regeneration may be required as frequently as every two days or as infrequently as every four hours, depending on the flow rate.
Using chlorine and/or potassium permanganate for pre-filter oxidation can extend the run time for higher iron levels, especially with an additional anthracite layer on top of the greensand media. It is crucial to avoid trapping excessive ferric hydroxide within the greensand, as this can lead to higher pressure requirements for backwashing and regeneration.
Automated Systems and Safety
Many manufactured units come with timers and are set up for automated backwashing and regeneration, similar to water softeners. For example, if a filter recommends a 36-hour backwash and regeneration cycle for a specific iron level, this is based on continuous flow time. The actual duration can vary depending on water usage patterns.
The following morning, the marinated media is backwashed until no permanganate (pink color) remains in the wash water. If using chlorine as a pre-oxidant followed by potassium permanganate for continuous regeneration, maintaining a chlorine residual of more than 0.5 mg/L at the filter effluent ensures the greensand retains its manganese oxide coating.
Before making any changes to the filter bed configuration, it is essential to consult with the supplier or manufacturer. Safety should always be a top priority during these procedures.
Conclusion
Proper regeneration of manganese greensand is essential for maintaining the effectiveness of water filtration systems. By following the appropriate regeneration methods and maintaining the system regularly, you can ensure clean and safe water for consumption. Always adhere to safety guidelines and consult professionals when necessary to ensure the best performance of your water filtration system.
Related Links: