By Gary Battenberg
In the first three parts of this series, we looked at applications in which activated carbon (AC) has proven to be effective for removal or reduction of organic chemicals, chemical compounds, and other contaminants such as detergents and heavy metals. In this final installment, we will look at those contaminants for which carbon may have only a limited application and those for which remediation by activated carbon is not recommended.
Fair Affinity
AC may yield limited results with the contaminants listed below because of their complexities, so caution is recommended when specifying treatment for removal or reduction from a challenge water source. After interpreting the water analysis, it may be necessary to augment the AC with additional treatment, such as a filter cap or chemical injection to increase the removal efficiency during the filtering process.
- Emulsion: A combination of two liquids that typically do not mix, such as water and oil, which creates a type of colloid in which one liquid disperses the other.
- Fluorides: A combination of fluorine and a mineral salt, especially of an anionic group.
- Formaldehyde: Used in the production of fertilizer, paper, plywood, and products such as antiseptics, medications, and cosmetics.
- Hydrogen bromide: In aqueous solution, a reagent commonly used in the production of inorganic and organic bromide compounds.
- Hydrogen iodide: Used for both therapeutic and diagnostic purposes, especially in the case of thyroid illness.
- Oil-suspended: See emulsions.
- Precipitated iron: Ferrous iron converted to ferric iron through oxidation with air, chlorine, hydrogen peroxide, or ozone, filtered out using AC. Chlorine is removed and ozone is converted back to oxygen during the filtering process.
- Precipitated sulfur: Oxidized hydrogen sulfide gas creates elemental sulfur, filtered out along with chlorine, hydrogen peroxide, or ozone during the filtering process.
- Sediment: Can be filtered from water using AC in an automatic backwash filter.
- Soluble iron: May be reduced using AC but should be oxidized to precipitated iron to effectively remove it from the water source. Commonly referred to as clear-water iron.
- Suspended matter: Fine solids that float or are suspended in solution. May require chemical dosing to coagulate the solids into filterable clumps for efficient filtration using AC.
Where these contaminants are present, a backwash carbon filter is recommended to flush away the accumulated solids. A minimum 36-inch bed depth is recommended. And remember, an accurate water analysis is essential to ensure effective removal of the contaminants.
Poor Affinity
This is a list of contaminants for which activated carbon is a poor choice and not a recommended application. Where these contaminants are present, additional treatment methods will be required.
- Alkalinity: Typically removed using a Type II strong-base anion resin regenerated using salt (softener) in the chloride form.
- Arsenic: Can be slightly reduced after oxidation and converted to arsenate. Contaminants such as iron will help to bind the arsenic for more efficient removal using AC. Oxidizing filters or arsenic-specific media are a preferred method for effective arsenic removal. Others include reverse osmosis, distillation, and bone char.
- Boron: Requires specific treatment, including selective anion resin, reverse osmosis (60 percent), distillation, or disposable mixed-bed resin cartridges.
- Inorganic chemicals: Barium, cadmium, and chromium, for example. Require anion exchange, reverse osmosis, and distillation for effective removal.
- Seawater: Best pretreated for sediment and suspended solids, and then the salt is separated using high-pressure reverse osmosis.
AC may be used as part of the treatment process, but use caution and consult your media supplier for recommendations to avoid costly mistakes in system design.
Final Thoughts
When working with activated carbon, always factor in pH, water temperature, and mesh size, along with the available hydraulic characteristics of the source water, including flow rate and pressure. Remember to check flow rates at 30 pounds per square inch (psi) and 40 psi to assess the well pump for well-water applications. The consistent water quality and performance of the filter system are crucial to customer satisfaction and the growth of your business.
About the author
Gary Battenberg is a senior business development manager for Argonide Corporation. His four decades of experience in the water industry covers mechanical and adsorptive filtration, ion exchange, UV sterilization, reverse osmosis, and ozone technologies. He has worked in the domestic, commercial, industrial, high-purity, and sterile water treatment arenas. A contributing author to WC&P and a member of its Technical Review Committee since 2008, Battenberg was voted one of the magazine’s Top 50 most influential people in the water treatment industry in 2009. He can be reached by email at [email protected] or by phone at (407) 488-7203.
About the company
Founded in 1994, Argonide Corporation is a family-owned business focused on water filter manufacturing. Today, Argonide sells filtration cartridges and systems all over the world, commercially and residentially, across many applications and markets. Products include NanoCeram, DEAL carbon blocks (diatomaceous earth media coated with aluminum oxide-hydroxide), and the COOLBLUE Microbiological Water Purifier System.