Ozone Iron and Manganese Removal for Well Water: A Guide

Ozone removes iron and manganese from well water by oxidizing the dissolved metals into solid particles that a filter can then catch. It works quickly and needs relatively little ozone: U.S. EPA guidance gives 0.43 mg of ozone per mg of iron and 0.88 mg per mg of manganese. The catch is that ozone is only half of the system. Without a contact stage and a good filter, the oxidized metals simply flow on to stain your sinks.

Ozone iron and manganese removal is a water treatment process in which ozone gas is dissolved into raw water to convert soluble ferrous iron (Fe²⁺) and manganese (Mn²⁺) into insoluble forms, which are then removed by sedimentation or filtration. It is used for wells, groundwater supplies, buildings and industrial process water.

Why iron and manganese are a problem

Iron and manganese are common in groundwater. At the levels usually found, they are mainly an aesthetic and operational nuisance rather than a health hazard, according to the EPA Alternative Disinfectants and Oxidants Guidance Manual, but they cause staining and taste problems.

Penn State Extension describes the typical signs:

• a metallic taste;
• orange-brown stains in sinks and laundry from iron;
• dense black stains or particles from manganese;
• water that comes out clear, then turns cloudy or develops particles after standing in air.

The EPA secondary (non-enforceable) standards in 40 CFR 143.3 are 0.3 mg/L for iron and 0.05 mg/L for manganese. Penn State Extension also notes an EPA health advisory level of 0.3 mg/L for manganese. Over time, the metals can also accumulate as deposits in pipes and fixtures.

How ozone removes iron and manganese

Dissolved iron and manganese pass straight through ordinary filters. Ozone changes their chemistry. According to the EPA manual, ozone converts ferrous (2+) iron to the ferric (3+) state and manganese (2+) to the 4+ state, and the oxidized forms precipitate as ferric hydroxide and manganese dioxide or hydroxide. The reactions are fast, “on the order of seconds.”

The process has three stages:

1. Ozone injection: ozone gas is dissolved into the raw water, commonly with a venturi injector or diffuser.
2. Contact and reaction: a contact tank gives the metals time to oxidize and the particles time to form, and lets undissolved gas separate.
3. Filtration: a sand, multimedia or similar filter captures the particles and is backwashed periodically.

How much ozone do you need?

The EPA manual, citing Langlais and colleagues, gives the stoichiometric ozone demand:

• Iron (Fe²⁺): 0.43 mg O₃ per mg Fe
• Manganese (Mn²⁺): 0.88 mg O₃ per mg Mn

For comparison, the same EPA table lists 0.62 mg of chlorine per mg of iron and 0.77 mg per mg of manganese.

Worked example

Suppose a well delivers 5 m³/h containing 2.0 mg/L iron and 0.3 mg/L manganese. The theoretical ozone demand is:

• Iron: 2.0 × 0.43 = 0.86 mg/L
• Manganese: 0.3 × 0.88 = 0.26 mg/L
• Total: about 1.12 mg/L, which at 5 m³/h equals about 5.6 g of ozone per hour actually dissolved in the water.

Treat that figure as the floor, not the design value. Anything else that consumes ozone adds to the dose. The EPA manual lists natural organic matter among the main sources of ozone demand, and notes that ozone also oxidizes sulfides. On top of that, not all the ozone you generate will dissolve, so the generator must be larger than the dissolved requirement. This is why testing your actual water is essential.

pH and the manganese trap

Iron and manganese behave differently, and manganese is the harder of the two:

• EPA states that iron oxidizes at pH 6 to 9, while manganese oxidation is more effective at around pH 8, with an optimum of pH 8 to 8.5 cited in the EPA dose table.
• Overdosing does not harm iron removal, but EPA warns that over-ozonation “will resolubilize manganese,” turning it into a dissolved form that passes the filter. It must then be reduced back to manganese dioxide downstream.

In practice, manganese-rich water calls for careful dose control rather than simply turning the generator up. Measuring dissolved ozone after the contact tank helps. HSVN lists a DOZ dissolved ozone meter from HSVN for this kind of check.

Ozone compared with other iron removal methods

Penn State Extension matches treatment to the water:

• Water softener: generally for dissolved iron below 5 mg/L, pH above 6.7 and suitable hardness.
• Oxidizing filters such as manganese greensand: when combined iron and manganese is 3 to 10 mg/L.
• Oxidation followed by filtration: for combined iron and manganese above 10 mg/L. Chlorine is the most common oxidant, with potassium permanganate and hydrogen peroxide as alternatives.
• Ozonation: “generally more expensive,” but useful where several problems, such as bacteria and metals, must be treated together.

That last point is ozone’s real advantage. One ozone stage can oxidize iron and manganese, oxidize sulfides and reduce odor, and disinfect at the same time, without adding chlorine taste to the water. The EPA manual lists all of these among ozone’s uses in drinking water treatment.

Design tips for a reliable system

• Test first. Analyze iron, manganese, pH, hardness, organic matter, hydrogen sulfide and bacteria. Penn State Extension stresses that both the concentration and the form (dissolved or already oxidized) of the metals shape the treatment plan.
• Use an injector rather than fine diffusers where possible. EPA notes that diffuser pores can clog when iron and manganese oxidation is required.
• Give enough contact time before filtration, and vent undissolved gas from the contact tank safely. Off-gas must not be released into occupied rooms; the workplace limit for ozone is 0.1 ppm according to the NIOSH Pocket Guide.
• Size the filter for the solids load and plan backwash water and frequency.
• Use ozone-resistant materials such as 316 stainless steel, glass or ceramics for wet parts, and Teflon or Hypalon gaskets, as recommended by EPA.
• Pilot test if manganese is high or water quality varies seasonally.

Choosing the ozone generator

Use the worked example above as a template: calculate the theoretical demand, add margin for organic matter and other demand, then allow for transfer losses. In that example the dissolved requirement is about 5.6 g/h before margins, which shows the scale involved for a small well. The Dr.Ozone D-20S industrial ozone generator, for example, is listed at 20 g/h with a 5 L/min oxygen supply and fan and water cooling. For larger flows, see the full range of industrial ozone generators from HSVN.

HSVN also explains the chemistry in Vietnamese in its article on using ozone to remove iron and manganese from water. For related Dr.Ozone projects, read how a residential complex treats its living water supply with a Dr.Ozone D70 and how ozone is used at an urban water supply station.

Frequently asked questions

Does ozone remove iron from well water?

Yes. Ozone oxidizes dissolved ferrous iron into ferric iron, which forms solid particles. EPA guidance gives a dose of 0.43 mg of ozone per mg of iron, and the reaction takes seconds. The particles must then be removed with a filter, so an ozone iron removal system always includes contact and filtration stages, not just a generator.

Can ozone remove manganese?

Yes, but it needs more care than iron. EPA gives 0.88 mg of ozone per mg of manganese, with oxidation most effective around pH 8. Too much ozone can convert manganese back into a dissolved form that passes through the filter, so the dose should be controlled and checked with dissolved ozone measurements.

Is ozone better than chlorine for iron removal?

Both oxidize iron and manganese effectively. Chlorine is cheaper and simpler, while ozone also disinfects strongly, reduces odor and sulfides, and leaves no chlorine taste. Penn State Extension describes ozone as generally more expensive but useful when several problems, such as bacteria and metals, must be treated at once.

What size ozone generator do I need for iron removal?

Multiply flow in m³/h by the total ozone demand in mg/L, using 0.43 times the iron level plus 0.88 times the manganese level as a starting point. Then add margin for organic matter and other ozone demand, and divide by the transfer efficiency of your injector. A water test and pilot run give the most reliable answer.

Struggling with rusty or black-stained water? Send your water test results and flow rate to our engineers through the Dr.Ozone contact page for a sizing recommendation, or explore the industrial ozone systems built by HSVN, the manufacturer behind Dr.Ozone.