Safeguarding Water: Arsenic Removal with Filtration Media (DMI-65, Greensand & Greensand Plus)
- Everfilt® Admin
- 1 day ago
- 5 min read
Water professionals and newcomers alike know that arsenic in water is a silent threat. Let’s unpack why arsenic matters, and how filtration media like DMI‑65®, Greensand (and its advanced variant Greensand Plus™) can play a key role in tackling it.
Why Arsenic Removal is Critical
Arsenic is a naturally occurring element found in some soils, rocks, and groundwater. Under certain geochemical conditions (e.g., reducing environments), it can dissolve into water supplies. Long-term exposure is linked to serious health risks, including skin lesions, cancers, and cardiovascular disease.
Regulatory & Health Benchmarks
Many jurisdictions set maximum contaminant levels (MCLs) for arsenic (inorganic forms like As III and As V). For example, a water treatment media manufacturer reports treatment of feedwater from ~78 ppb down to <1 ppb arsenic using DMI-65® in a pilot test.
Because arsenic behaves differently depending on its oxidation state (As III vs As V), pH, competing ions, iron/manganese presence, etc., removal isn’t trivial. Pre-oxidation, co-precipitation (especially with iron), adsorption, and/or catalytic filtration steps are often necessary.
Filtration Media Options: DMI-65®, Greensand & Greensand Plus™
Let’s look at how these specific media work, their strengths/weaknesses, and when each might fit best.
DMI-65® – Catalytic Silica Sand Media
Mechanism & Benefits
DMI-65® is a silica sand-based media infused (not just coated) with catalytic sites.
It acts as a catalytic oxidation medium: when an appropriate oxidant (often chlorine) is present (target ~0.1-0.3 ppm free chlorine residual), it oxidizes dissolved iron/manganese and precipitates them for filtration.
Regarding arsenic: It doesn’t necessarily chemically “grab” arsenic directly; rather, it relies on arsenic co-precipitating with iron hydroxides/oxides (when iron is present or added). Thus, if water has arsenic but no iron present, you may need to add a coagulant such as ferric chloride.
Certified for drinking-water use (e.g., NSF/ANSI 61) in certain markets.
Advantages: Doesn’t require chemical regeneration with potassium permanganate (unlike some older media). Lower maintenance of that sort.
Considerations / Limitations
For arsenic removal specifically, DMI-65's arsenic removal capability is contingent on the presence of iron or coagulant dosing and proper design/pilot testing. You cannot assume “install DMI-65 and arsenic goes away” without checking context.
Operating parameters matter: pH, oxidant residual, filtration velocities, backwash, and media life (typically 5-10 years claimed) must be accounted for.
While focused strongly on iron/manganese, arsenic removal is a secondary benefit (not necessarily the primary design case).
Greensand & Greensand Plus™ – Manganese Oxide Coated Media
Mechanism & Benefits
Greensand media are typically core sand (glauconite or silica sand) coated with manganese dioxide (MnO₂). The MnO₂ acts as an oxidant/oxidation catalyst for iron, manganese, hydrogen sulfide, etc.
Greensand Plus™, specifically, has been documented to remove radium and arsenic (via adsorption onto manganese/iron precipitates) under the right conditions.
In practice, when iron is present or added, arsenic removal is improved: for arsenic removal with Greensand Plus™, iron must be present (or added) to form precipitates that capture arsenic.
Widely used, well-known technology in water treatment.
Considerations / Limitations
Requires regeneration with chemicals like potassium permanganate (KMnO₄) or strong oxidants and good operator oversight for maintaining the manganese dioxide coating.
Arsenic removal capability again depends heavily on system design: presence of iron, oxidant dosing, pH, etc. Not simply plug-and-play.
Compared to DMI-65®, some article sources say that Greensand Plus™ may offer more versatility for contaminants (including arsenic, radium) but with higher operational chemical/regeneration demands.
Which Media for Arsenic Removal & How to Choose
Here’s a practical checklist and comparison to help you, whether you’re new to the field or a seasoned pro.
Assessment of Raw Water & Goals
Measure arsenic concentration (both total and speciation if possible: As III vs As V)
Check iron, manganese, pH, alkalinity, competing ions, organic matter, presence of hydrogen sulfide, etc. These influence media performance.
Define target effluent arsenic level (e.g., meet regulatory MCL or lower)
Consider flow rate, head loss/backwash frequency, operating budget, operator availability, and chemical handling capability
Media Comparison at a Glance
Design Tips & Practical Best Practices
Pilot testing is strongly recommended. Even manufacturer literature for DMI-65® emphasizes that for arsenic removal, you should establish correct chemical dosing, filtration velocities, and pilot plant design.
Ensure pre-oxidation or dosing if needed: e.g., for arsenic removal via iron co-precipitation, you might dose ferric chloride or other iron salts if raw water lacks iron. (Especially for DMI-65®).
Monitor and maintain oxidant residuals (chlorine, etc) for catalytic media. If the oxidant falls too low, performance will degrade.
Backwashing frequency: design for hydraulic loading and media life. Avoid fouling or channeling in the media bed.
pH matters: Many media perform best in certain pH ranges (for example, DMI-65® claims stable performance at pH 5.8-8.6).
Keep head losses and pressure drop in check: fouled media will not perform well.
Consider secondary polishing or parallel filters for ultra-low arsenic targets (for example, multiple stages, media in series).
Operator training & maintenance regimen: Chemical handling (if required), backwash timing, media conditioning (especially initial start-up for greensand or similar) are essential.
Real-World Case Pointers
One case with DMI-65®: A regional water authority in Australia used DMI-65® to reduce arsenic levels to <0.001 mg/L (~1 ppb) for a community supply.
GreensandPlus™ technical documentation states that arsenic and radium removal occur via adsorption onto manganese/iron precipitates, but only if sufficient iron or manganese is present or added.
Take-Away for the Industry Pro & Newcomer
For newcomers: Don’t assume “media solves everything”. The key is water chemistry + correct design + maintenance.
For industry pros: The incremental costs of pilot testing, proper hydraulics design, monitoring, and ensuring media life often make the difference between a “just meets spec” system and a robust “low-operating cost, long life” system.
When arsenic is the contaminant of concern, iron-based co-precipitation plus filtration is often a good base strategy; filtration media such as DMI-65® or Greensand/Greensand Plus™ are tools in that strategy, not magic bullets.
Media choice isn’t purely technical: operational context matters (operator expertise, budget for chemicals/regeneration, maintenance frequency, regulatory targets).
Lifecycles matter: Media replacement, chemical consumption, downtime, backwash volumes, take the “whole-life cost” view, not just “initial media cost”.
Keep monitoring: Even a well-designed system may drift if raw water quality changes (iron load, pH, oxidant demand, etc) or media fouls.
Arsenic removal remains a pressing challenge in many water supplies. By selecting the right filtration media (and designing around it), whether DMI-65®, Greensand, or Greensand Plus™, operators can build effective systems that safeguard health, meet regulatory standards, and operate reliably.