How do you regenerate manganese greensand filter media just purchased prior to placing it into service-
How to pretreat new manganese greensand filter media prior to its first use?
Manganese greensand has long been a reliable solution for water purification, removing iron, manganese, and hydrogen sulfide since the 1950s in the U.S. It hails from organic ocean floor deposits and is recognized for its bluish-green color, also referred to as "glauconite." Glauconite is treated with manganese oxide to enhance its redox capabilities, which are vital for removing iron, manganese, and minute amounts of hydrogen sulfide. This process usually involves Continuous Regeneration (CR) or Intermittent Regeneration (IR) methods, with CR preferred for iron removal and IR for manganese due to the freshly regenerated greensand’s oxidation abilities. Regeneration becomes necessary once the media’s oxidation capacity is exhausted, although IR regeneration requires a longer downtime of approximately 75 minutes compared to CR’s 15 minutes. A combination of both methods is advisable when both contaminants are present in high concentrations.
It is crucial to fully regenerate the greensand before integrating it into a filter system. Each bag includes regeneration instructions, which involve soaking the media in a 2-3% potassium permanganate solution for several hours. This can be done in a bucket or within the filter unit. A recommended method is dissolving one pound of KMnO4 in five gallons of water, submerging the media, and leaving it overnight. The ideal depth for the greensand bed varies between 24-30 inches for IR and 18-20 inches for CR, with a reduced bed depth beneficial for removing pre-oxidized iron.
The filter’s efficacy against manganese and hydrogen sulfide can endure for several weeks before requiring regeneration, whereas iron levels between 0.5 and 10+ mg/L may necessitate regeneration every two days to every four hours, depending on the flow rate. Pre-oxidation with chlorine or KMnO4 and the addition of an anthracite layer can extend the runtime for high iron concentrations. It is vital to prevent ferric hydroxide buildup to avoid clogging and ensure successful backwashing and regeneration. The filter unit’s operational duration in a private water system depends on the water flow rate. For example, with a pump output exceeding 10 gallons per minute and a 20-gallon storage tank, a 36-hour backwash and regeneration cycle for a given iron level and filter surface area is calculated based on continuous flow, potentially lasting a month depending on water usage.
The following day, backwash the media until the permanganate is no longer visible in the effluent. When using chlorine followed by KMnO4 for CR, maintaining a chlorine residual above 0.5 mg/L at the filter outlet preserves the greensand’s manganese oxide coating. Before modifying any filter bed configuration, consult with your supplier or manufacturer and prioritize safety. If chlorine residuals are excessive, reduce them to safe levels using carbon filtration.
Related Links: Water Problems — Manganese, Removing Iron and Manganese from Water, Can manganese issues arise in drinking water reservoirs due to temperature stratification?