27 October 2026

Oxygen Quality Is Ozone Quality: Why Medical Oxygen Concentrators Don't Belong in Industrial Ozone Systems

Introduction

When buying an ozone system, attention usually goes to the generator's g/h rating. Yet what happens inside the generator is determined almost entirely by what is fed to it. The same generator delivers its rated performance when fed dry, clean oxygen at the right flow and purity; fed humid, contaminated, insufficient, or fluctuating gas, it produces less ozone, uses more energy, ages faster, and may even fail.

A scenario we often see in the field: to cut cost, a home-use medical oxygen concentrator is connected to an industrial ozone generator. For the first few days the system seems to work; after a few weeks or months, ozone output falls, the generator raises temperature or low-flow alarms, and stainless steel parts begin to discolour and show white powdering. This post is a reference article explaining, at an engineering level, why: feed gas quality, dew point, the two faces of nitrogen, NOx and nitric acid formation, how to calculate oxygen capacity correctly, and the cost of getting it wrong.

In Brief

An ozone generator's feed gas has four criteria: purity, dew point, pressure/flow stability, and cleanliness (oil, particles, chemical vapours).
Moisture lowers ozone production and, together with nitrogen, forms nitric acid; industrial generators are therefore typically designed for gas with a dew point of -60 °C or drier.
Nitrogen has two faces: a very small amount can support production, while excess produces NOx and nitric acid.
Home-use medical oxygen concentrators are designed for a patient to breathe: low flow, low pressure, cyclic output, uncontrolled dew point, and no purity interlock. They do not meet the needs of an industrial ozone system.
If oxygen flow is too low, the generator overheats and efficiency falls; if too high, concentration drops and ozone transfer to water weakens. Flow must be calculated from the generator's nominal output and the chosen concentration.
When selecting a PSA oxygen generator, purity, dew point, outlet pressure, buffer tank, and flow margin should be specified together.

Why Does Feed Gas Matter So Much in an Ozone Generator?

Industrial ozone generators work on the corona discharge (silent electrical discharge) principle. Gas passes through a narrow gap between two electrodes separated by a dielectric barrier; when high voltage is applied, the micro-discharges split oxygen molecules (O₂) into atoms, and free oxygen atoms combine with another oxygen molecule to form ozone (O₃). In the same discharge zone there are also reactions that destroy ozone; net ozone production is the result of the balance between formation and decomposition.

That balance is shifted by the oxygen fraction in the gas, the moisture in the gas, gas temperature, foreign components in the gas (nitrogen oxides, hydrocarbons, water vapour), and the gas flow through the discharge gap. In other words, generator performance is determined not only by electricity and geometry but also by gas chemistry. In general, oxygen-fed generators can reach roughly 6-12 percent ozone by weight, while in air-fed systems the figure typically stays around 1-3 percent. We covered the general comparison of air and PSA oxygen feed in PSA Oxygen Generator vs Air-Fed Ozone System; this post goes one step deeper: once oxygen feed is chosen, the quality of that oxygen.

The Four Quality Criteria of Feed Gas

Criterion	Typical expectation for an industrial ozone generator	What happens if not met?
Purity	Generally 90-95 percent oxygen (PSA); the remainder mostly argon and a small amount of nitrogen	If nitrogen rises: NOx and nitric acid; ozone yield and concentration drop
Dew point	For most manufacturers about -60 °C or drier (check the manufacturer's specification)	Yield loss, nitric acid, electrode and dielectric damage
Pressure and flow stability	Within the generator's nominal flow and operating pressure range, without pulsation (usually via a buffer tank)	Concentration fluctuation, overheating, protection trips
Cleanliness	Oil-free, particle-free, chemical-vapour-free gas	Dielectric fouling, fire risk (oil + oxygen), faulty measurements

These values vary between manufacturers; exact limits should always be taken from the specification of the generator concerned. Below we explain why each criterion matters.

Moisture and Dew Point: Small Numbers, Big Difference

Dew point is a direct expression of the amount of water vapour in the gas. Approximate figures: a -40 °C dew point corresponds to roughly 125 ppmv of water vapour, -60 °C to about 11 ppmv, and -70 °C to about 2.5 ppmv. The difference between -40 and -60 °C is therefore roughly tenfold in moisture; a dew point gap that looks small on paper creates a very large chemical difference inside the generator.

Why is it harmful? In the discharge zone, water vapour is split into radicals such as OH and HO₂; these radicals destroy ozone catalytically and reduce production. At the same time, if nitrogen is present in the gas, moisture converts nitrogen oxides into nitric acid (below). The effect of moisture does not appear all at once but accumulates: first ozone output quietly drops, then deposits and corrosion begin on surfaces.

The Two Faces of Nitrogen: Helper or Harm?

A very small amount can support production

There is a common misunderstanding here: in an oxygen-fed generator, nitrogen does not have to be exactly zero, and in fact that is not ideal. In the literature and in many manufacturers' design approaches, it is known that in corona generators running on ultra-pure oxygen, ozone yield can decline over time, and that adding a very small amount (on the order of roughly one percent) of nitrogen or a similar dopant gas improves discharge behaviour and supports production. In the 90-95 percent output of a PSA oxygen generator, most of the remainder is argon and a smaller part nitrogen; this composition is generally suitable, even advantageous, for ozone generators. The question is therefore not "is there nitrogen?" but "how much, at what moisture and temperature?" The exact contribution depends on generator design, so the feed gas composition stated by the manufacturer should be the reference.

Excess produces NOx and nitric acid

When nitrogen fraction rises, for example with air feed or an oxygen source whose purity has dropped, nitrogen also splits in the discharge zone and the following chain begins (simplified):

N₂ + electron → 2 N (nitrogen atoms in the discharge)
N + O₂ → NO + O
NO + O₃ → NO₂ + O₂ (ozone loss)
NO₂ + O₃ → NO₃ + O₂ (ozone loss again)
NO₂ + NO₃ ⇌ N₂O₅
N₂O₅ + H₂O → 2 HNO₃ (nitric acid; if water vapour is present)

The consequences of this chain appear at three levels:

Inside the generator: nitrogen oxides consume ozone (catalytic decomposition), and nitric acid and nitrate salts build up on dielectric and electrode surfaces. Deposits disturb the discharge, yield drops, local hot spots and partial discharges form; later, dielectric damage or electrode corrosion may appear.
In piping and equipment: nitric acid vapour and NO₂ carried with the ozone gas corrode pipes, valves, venturis, and fittings; when they dissolve in water they lower pH and add a nitrate load.
In the process: especially in closed-loop water systems (for example RAS), nitrate accumulation and pH swings are unwanted side effects; moreover, NO₂ is a toxic and irritating gas from an occupational health standpoint.

In air-fed systems this chemistry is unavoidable; it is managed through design and drying but cannot be eliminated entirely. This is why dew point control, discharge gap design, and periodic cleaning are especially important in air-fed generators. With PSA oxygen feed the NOx risk is greatly reduced, but it is not gone: it can reappear when purity drops, when dew point degrades, or in a hot, poorly cooled generator.

How can you tell in the field?

Ozone concentration falling over time at the same power and flow
Low pH in condensate collected from the ozone line (a quick check with pH paper is possible)
White-yellowish powdering or staining on dielectric or electrode surfaces during generator maintenance
Discolouration and corrosion on metal fittings in the ozone line
NO₂ odour, particularly in enclosed spaces, or gas detector alarms (measurement is needed for a definitive diagnosis)

Why Is a Home-Use Medical Oxygen Concentrator Unsuitable?

Home-use oxygen concentrators also work on the PSA principle, so at first glance they give the impression of "the same technology, much cheaper". But the same principle does not mean the same design goal. A medical concentrator is optimised for a patient breathing through a nasal cannula; an industrial ozone generator demands a different gas quality and a different operating regime.

1. Insufficient flow

Common home concentrators deliver a few litres per minute of oxygen (typically 5 L/min, some 10 L/min). As you will see in the section below, roughly 11-12 L/min of oxygen is needed for 100 g/h of ozone at 10 percent by weight. A 5 L/min unit can on its own feed roughly 40 g/h of ozone; any demand beyond that means either a flow deficit or a low ozone concentration.

2. Low outlet pressure

The outlet pressure of medical devices is generally well below one bar and designed to be sufficient for breathing. Ozone generators have internal resistance, flow meters, dryers, and line losses; manufacturers generally require a specific feed pressure range. Running on low-pressure gas either throttles flow or triggers the generator's protections.

3. Cyclic (pulsating) flow and lack of buffer

PSA devices work by alternating pressure between two or more beds. Industrial units smooth this fluctuation with a buffer tank; small home units have limited internal volume. Pulsating flow means fluctuating ozone concentration and unstable measurement.

4. Outlet dew point is not guaranteed

The moisture limit for patient breathing is not the same as the requirement of an ozone generator. There is no dew point measurement or alarm at the outlet of a medical device, and no -60 °C commitment is given for the outlet gas. In most cases an additional dryer and dew point measurement are needed; if the ozone side is run without this integrity, the moisture and nitric acid problems above appear.

5. No purity monitoring or process interlock

Many medical devices monitor purity and alarm below a threshold of about 82 percent; this makes sense for breathing safety but offers no protection for the ozone process. In an industrial system, the generator is expected to shut itself down automatically (interlock) when purity or dew point goes out of limits. The molecular sieve is affected over time by moisture and contamination; purity drops silently, the nitrogen fraction rises, and NOx chemistry starts.

6. Duty regime and environment

Home units are designed to run in a closed home, within a limited ambient temperature, and in relatively clean air. In an industrial plant there can be 24/7 operation, high ambient temperature, dust, oil vapour, and chemical vapours such as solvents or chlorine. The zeolite bed is sensitive to these contaminants; inlet filters are small and maintenance intervals are not set for this regime.

7. Warranty and liability

Medical devices are certified for a specific intended use. Adapting them for industrial use as the feed source of an ozone generator creates an unclear area for manufacturer warranty and device liability. For the operator too, the ozone generator's warranty depends on the feed gas conditions being met.

A fair note: in micro-scale laboratory work, using a concentrator for a low-capacity generator with an added dryer and measurement may be possible. But this is a controlled, short-term arrangement at that scale; it is not a suitable solution for continuous industrial processes.

How Is Oxygen Capacity Calculated?

The ozone mass flow at the generator outlet is the product of gas flow and concentration:

Ozone production (g/h) = Oxygen flow (Nm³/h) x Ozone concentration (g/Nm³)

Ten percent ozone by weight in oxygen is roughly 143 g/Nm³; six percent is roughly 86 g/Nm³. Required oxygen flow follows from this. The table below gives approximate values in litres per minute (normal conditions):

Ozone capacity (g/h)	Required O₂ @ 10% (L/min)	Required O₂ @ 6% (L/min)
10	1.2	1.9
25	2.9	4.8
50	5.8	9.7
100	11.6	19.4
250	29	48
500	58	97
1000	116 (about 7 Nm³/h)	194

Short rule: at 10 percent concentration, every 100 g/h of ozone needs roughly 11-12 L/min, about 0.7 Nm³/h, of oxygen. As concentration rises, the same amount of ozone can be carried by less gas, so the required flow falls (which is why the 6% column is larger than the 10% column). This does not mean that raising concentration indefinitely is advantageous: at high concentration the discharge zone heats up more, ozone decomposition increases, and kWh/kg gets worse. Every generator therefore has its own optimum operating point. This table is approximate; exact flow should be set from the generator's nominal operating point (flow-concentration curve).

What to watch on the PSA side

Flow-purity trade-off: In PSA units purity drops as nominal flow is exceeded. So "the unit delivers this flow" does not mean "it delivers this flow at the required purity". The specification should state both flow and purity together.
Ambient conditions: Ambient temperature, altitude, and inlet air quality affect capacity and purity; a design margin should be left.
Buffer tank: Smooths flow fluctuation and pressure waves; gives the generator stable gas.
Outlet pressure: The pressure required by the generator and line should be chosen taking into account back pressure on the venturi or diffuser side.
Redundancy and capacity margin: A margin above the generator's maximum flow is generally left; a PSA run right at its limit loses purity and molecular sieve life.

The Cost of Wrong Oxygen Capacity

If oxygen flow is insufficient

The generator cannot reach the target g/h or, trying to, runs at a very high concentration; as concentration rises, the energy spent per unit of ozone rises too.
Gas heats up with less flow; as temperature rises, ozone decomposes faster in the discharge gap and yield falls. If cooling is insufficient, the low-flow protection trips or the dielectric is subjected to thermal stress. (For cooling methods see our water-cooled vs air-cooled generator comparison.)
If the PSA is pushed beyond its nominal flow, purity drops, the nitrogen fraction rises, and NOx/nitric acid risk appears. The molecular sieve also tires faster.
Result: actual ozone output falls below the nameplate value, process targets (for example dissolved ozone ppm) are not met, and the operator often reads this as "the generator is weak" and unnecessarily asks for a bigger one.

If oxygen flow is more than needed

Concentration drops; the gas-phase partial pressure, which is the driving force of transfer to water, falls, ozone transfer to water weakens, and the off-gas share rises.
An oversized PSA means unnecessary investment and energy; surplus gas is vented or creates imbalance on the venturi/diffuser side.
If the generator's allowed maximum flow is exceeded, internal pressure rises and protection trips occur.

In short, the right oxygen capacity is not a copy of the generator capacity; it is a design decision made by considering together the generator's flow-concentration curve, the target concentration, the ozone transfer system to water, and the PSA's purity-flow curve. For details on the transfer side see our post Oxygen and Ozone Transfer to Water, and for why performance should be measured as dissolved ozone rather than g/h see Why ppm, Not g/h?.

The Energy Dimension: What Does the Oxygen Source Cost?

At 10 percent concentration, roughly 7 Nm³ of oxygen is needed per kilogram of ozone. The specific energy of PSA oxygen production varies with plant size and purity but is roughly in the 0.3-0.5 kWh/Nm³ range; that means about 2-3.5 kWh on the oxygen side per kilogram of ozone. The ozone generator's own consumption is generally a much larger item, depending on concentration and cooling. These figures vary by design and are approximate, but the conclusion is clear: oxygen source quality is a relatively small but critical part of the energy bill, because the wrong source spoils the generator's kWh/kg.

Also remember: about 90 percent of the oxygen leaves the generator without being converted to ozone. Since this is high-purity oxygen, in some applications it can serve a second purpose; for example, designs in aquaculture that manage ozone and oxygenation from the same source rely on this approach.

From Symptom to Cause: Quick Diagnosis Table

Symptom	Possible oxygen-related cause	First check
Ozone concentration falls over time	Moisture, purity drop, dielectric fouling	Dew point and purity measurement, dielectric surface
Generator gives temperature or low-flow alarms	Insufficient oxygen flow/pressure, insufficient cooling	Inlet flow and pressure, buffer tank, cooling water/air
Corrosion on lines and fittings, low pH in condensate	Nitric acid formation (nitrogen + moisture)	Feed gas purity and dew point, condensate pH
Concentration fluctuates	Pulsating flow, no/insufficient buffer	Pressure fluctuation, PSA cycle, buffer tank volume
g/h is on paper but no ppm in the water	Low concentration (excess flow) or generator below target	Gas-side concentration measurement, transfer system
Generator fails within a short time	Moisture, oil/particles, continual overheating	Filter and dryer condition, gas source quality

Technical Specification Checklist When Choosing an Oxygen Source

Is it clearly stated which ozone generator it will connect to, its nominal ozone capacity (g/h), and target concentration (weight percent)?
Has the O2 flow been calculated from the generator's flow-concentration curve, with a capacity margin on top?
At what flow and pressure is purity guaranteed? (Ask for the purity curve that falls as flow rises.)
Is the dew point value specified, measured, and linked to the ozone generator by alarm/interlock?
Are outlet pressure and buffer tank chosen for the needs of the generator and line?
Is the gas oil-free; are filters and ozone-compatible materials (such as 316L stainless steel, PTFE, PVDF) used?
Are 24/7 operation, ambient temperature range, and maintenance intervals (molecular sieve, filters, valves) defined?
Process monitoring: are ozone concentration, generator temperature, dew point, and purity trends recorded? Is kilograms of ozone per kilowatt-hour (kWh/kg) tracked over time?

Frequently Asked Questions

What if I add a dryer to a medical concentrator?

It can partly solve the dew point problem, but flow, pressure, pulsating output, purity monitoring, duty regime, and warranty issues remain. We do not recommend it outside small, controlled laboratory scale.

Can't I use an air-fed system?

You can; it makes sense in low-to-medium capacity, non-continuous, or budget-limited applications. But the moisture and NOx management described above, along with drying and periodic maintenance, is even more critical in these systems. For a comparison see this post.

Is 99 percent pure oxygen (cylinder or liquid oxygen) better?

It is good in that it is dry and clean; however, with very high-purity oxygen containing no dopant gas, yield is known to decline over time in some generators. Which composition is suitable should be in the generator manufacturer's specification. The choice between liquid oxygen and PSA is a question of scale and continuity; we covered it separately in an aquaculture context.

How do I know whether there is NOx in the feed gas?

There is no reliable method by eye. Condensate pH, the surface condition inside the generator, and gas detectors give clues; a definitive result needs gas analysis or the manufacturer's service measurement.

The OCS Ozone Approach

Because OCS Ozone manufactures the oxygen generator, ozone reactor, and transformer in-house, we design the feed gas and the generator as a single system: PSA capacity, purity, dew point, buffer tank, and cooling are sized together around the generator's operating point. OCS AQUA PRIME, which we developed for aquaculture, is likewise a solution that manages oxygen and ozone generators together in one system.

If efficiency is falling in an existing ozone system, or you want to size oxygen capacity correctly for a new investment, get in touch for a free technical assessment.