Oxygen Generators for Wastewater Treatment
Aeration is the largest electrical load on most treatment plants, and it runs around the clock. OXYBERG® produces oxygen from compressed air on your own site, at the purity you set, so that peaks in the load are covered by gas rather than by a blower you do not have. This page works through what a plant actually needs, so that an oxygen generator for wastewater treatment gets sized from your load figures rather than from a brochure.
What oxygen does in wastewater treatment
The biological stage runs on bacteria that break down organic load and consume oxygen doing it. Normally that oxygen arrives as ambient air, pushed through diffusers by blowers that never switch off. It works, and on most plants it is the right answer for the base load.
What air is not good at is the last part of the range. Air carries roughly 21 % oxygen; the other four fifths get compressed, blown through the basin and released again without contributing anything. Pure oxygen changes the driving force rather than the volume. A higher partial pressure in the bubble increases the gradient into the water, so the same dissolved quantity goes in with a much smaller gas flow. That matters when the basin, the blower or the electrical supply has no headroom left.
Three places on a plant use that. Aeration, where oxygen supplements or replaces blower air in the biological stage. Peak loads, where an industrial discharger, a rain event or a seasonal swing pushes the demand above what the installed aeration can deliver. And the collection system, where oxygen injected into rising mains and pumping stations keeps conditions aerobic and stops hydrogen sulphide forming before the flow ever reaches the works. Ozone is a fourth use and different enough to have its own section further down.
A PSA generator makes the gas by passing compressed air through a molecular sieve that holds back nitrogen while oxygen passes, with one vessel regenerating while the other produces. The PSA oxygen generator page covers the process itself.
Dissolved oxygen in the basin, not purity at the generator
Nobody operating a treatment plant watches gas purity. What gets watched is dissolved oxygen in the aeration basin, and the working range there is normally 1 to 3 mg/L. Below it nitrification slows and the effluent values move in the wrong direction; above it the plant is paying for oxygen the bacteria are not using. Between the generator and that number sit four things, and only the first of them is a gas specification.
Purity at the generator
This sets what is available to transfer, and nothing beyond that. It is the easiest of the four to change and usually the least important.
The transfer system
Diffuser type, submergence, bubble size and basin geometry decide how much of the offered oxygen actually goes into solution. On most plants this is the largest term in the equation and it was fixed when the basin was built.
Load and temperature
A load peak consumes the dissolved oxygen faster than it can be replaced, and warm water holds less of it at the same input. Summer and the busiest discharge hour tend to arrive together.
Control
The dissolved oxygen controller holds the setpoint, but it can only hold what the plant is able to deliver. Once the aeration is at its limit the controller has nothing left to give.
So the useful order runs backwards from the usual one. Start with the load and the setpoint you have to hold, work out what your transfer system can put in, and only then decide what has to come out of the generator.
Which oxygen purity a treatment plant needs
For aeration, the lower end of the range is enough. Between 90 % and 93 % the gas is far past the point where partial pressure is the limiting factor, and going higher does not make the bacteria work faster. Ozone generation is the exception and has its own requirements, covered below.
| Purity | What it is used for | Output of an OXYBERG® 1500 |
|---|---|---|
| 90 % | Aeration, peak-load cover, collection system | 44.6 Nm³/h |
| 92 % | Aeration where a slightly tighter specification applies | 43.1 Nm³/h |
| 93 % | Aeration and general plant use | 41.6 Nm³/h |
| 94 % | Where a downstream process asks for it | 40.5 Nm³/h |
| 95 % | Top of the OXYBERG® range | 39.1 Nm³/h |
Here the trade-off works differently from a nitrogen generator, and it is worth being precise about it. On a nitrogen machine, purity drives compressed air consumption, so specifying too high a grade doubles the compressor. On OXYBERG® the air factor is 11 at every purity in the range. Compressed air per cubic metre of oxygen does not move at all.
What moves is output, and by more than most specifications assume. Across the range a machine delivers between 10 and 40 % more oxygen at 90 % than at 95 %, and the gain is largest at the smaller sizes: the 1500 in the table gains 14 %, an OXYBERG® 500 gains 40 %. So the question is not what higher purity costs you in air, because the answer is nothing. It is how much capacity you give away by asking for a grade the basin cannot use.
When a rented tank stops being the cheaper answer
A liquid oxygen tank is a good answer to a specific problem. A blower fails, a basin comes out for refurbishment, an unusual load arrives and has to be absorbed. The tank is quick to arrange, needs no capital approval, and it ends when the event ends. For that situation nothing else comes close.
The picture changes when the event stops being an event. If the peaks come back every summer, every time a particular discharger runs a campaign, or every heavy rain, the rental keeps running between them, the price escalation clause keeps applying, evaporation losses continue every night, and the delivery schedule that decides when the tank is full is not yours to set. At that point the plant is paying permanently for something designed to be temporary. Against liquid-gas supply, a Berg PSA generator typically pays for itself within two to three years.
The other comparison worth making is against more blower capacity. If the basin, the diffuser grid and the electrical supply can carry it, more air is often the straightforward route and there is no reason to argue against it. Oxygen becomes the answer when one of those three has no headroom, which is the usual situation on a works that has been extended repeatedly on the same site.
Need sizing for your application?
Send us your consumption profile and operating data. Our engineering team will size the generator and confirm the configuration.
How much oxygen your wastewater plant needs
Start from the load, not the basin
BOD and COD load plus the nitrification demand determine how much oxygen the biology needs. Basin volume tells you about retention time, not about oxygen demand, and two plants with the same basin can sit far apart. Take the figures from your own operating records rather than from a design value nobody has checked since commissioning.
Decide base load or peak
Continuous enrichment and covering occasional peaks are different machines. This single decision moves the size more than anything else in the specification, and it is the one most often left open in an enquiry.
Set the purity from the use
Aeration sits in the lower band. Ozone generation has its own requirements. The table above is the starting point.
Check the compressed air
Flow times the air factor of 11 gives the demand, and because the factor does not change with purity, the calculation is one multiplication. Quality counts as well as quantity: oil carry-over and residual moisture shorten sieve life, so the dryer is not the place to save. OXYBERG® expects compressed air to ISO 8573-1:2010 Class 1.4.1 at 7 bar(g).
OXYBERG® oxygen generators for aeration duty
OXYBERG® covers 18 sizes in total, listed in full on the oxygen generator overview. The selection below spans the range most treatment plants fall into, shown at the two grades that matter for aeration.
| Model | O₂ at 90 % | O₂ at 93 % | Compressed air at 90 % |
|---|---|---|---|
| OXYBERG® 500 | 2.1 Nm³/h | 1.7 Nm³/h | 23.1 Nm³/h |
| OXYBERG® 900 | 9.2 Nm³/h | 8.2 Nm³/h | 101.2 Nm³/h |
| OXYBERG® 1200 | 18.9 Nm³/h | 17.4 Nm³/h | 207.9 Nm³/h |
| OXYBERG® 1500 | 44.6 Nm³/h | 41.6 Nm³/h | 490.6 Nm³/h |
| OXYBERG® 1700 | 65.8 Nm³/h | 62.1 Nm³/h | 723.8 Nm³/h |
| OXYBERG® 2000 | 131.6 Nm³/h | 124.2 Nm³/h | 1,447.6 Nm³/h |
| OXYBERG® 4000 | 197.4 Nm³/h | 186.3 Nm³/h | 2,171.4 Nm³/h |
Which size fits depends on whether the oxygen carries the base load or covers peaks, not on how large the works is. A plant that only needs help during the busiest months lands several sizes below one enriching continuously at the same capacity.
Where there is no suitable compressed air on site, the generator is planned as a complete plant rather than as one machine: compressor station, air treatment, buffer, generator and oxygen storage, engineered as one chain from one source within the BERG Group. The PSA oxygen plant page covers that configuration. Applicable NITROBERG® and OXYBERG® standard generator assemblies are conformity assessed under PED 2014/68/EU using Modules B + D. Engineering and manufacturing are Made in Germany.
Oxygen for ozone generation in wastewater plants
Ozone does a different job in wastewater than it does in drinking water. Here it is used to break down COD that the biology cannot reach and to attack trace substances that pass through a conventional works untouched. Placed ahead of a biological stage it can also make hard-to-degrade compounds accessible to the bacteria that follow. As discharge requirements tighten and trace substances move up the agenda, this is the part of the plant most likely to grow, and it consumes oxygen continuously once it is built.
An ozone generator does not run on air. It needs clean, dry oxygen as feed gas, because feeding it air cuts the ozone yield sharply and produces nitrogen oxides as a by-product. That is why an oxygen supply sits in front of every ozone stage of any size, and it is the supply rather than the ozone generator that becomes the permanent operating cost. Purity and dew point requirements differ between ozone systems, so the oxygen supply is dimensioned around the specification of the generator it feeds rather than around a standard figure.
Ozone used for disinfection, decolourisation and taste and odour control belongs to a different process. That side sits on the page about oxygen for drinking and process water treatment.
What an oxygen generator needs on site
| Parameter | Value |
|---|---|
| Operating pressure | 10 bar |
| Compressed air inlet pressure | 7 bar(g) |
| Compressed air quality | ISO 8573-1:2010 Class 1.4.1 |
| Sound level | 55 to 78 dB(A) |
| Ambient temperature | +5 °C to +40 °C |
The compressed air quality is a requirement on your supply rather than a property of the generator, and it is the item most often underestimated. Oil and moisture reaching the sieve shorten its life, and the cost of that shows up years later as falling output rather than as a fault.
A buffer vessel belongs in the plan even where the average demand looks comfortable, because treatment plants do not draw evenly. The morning load peak, a storm event and the first hours after a basin comes back into service all pull harder than the daily average, and the buffer covers those so the generator does not have to be sized for them. How much reserve supply you hold beyond that is part of your own operational planning, and it is worth settling while a larger buffer is still cheap to add.
Built in Germany, serviced with standard spare parts
Berg develops and builds the generators in its own plant. Engineering and manufacturing are Made in Germany. That matters less as a label than as a practical fact: the drawings, the assembly and the people who sized your configuration sit in one place, so a technical question reaches somebody who can answer it rather than somebody who has to pass it on.
Once the plant runs, support comes through a worldwide service partner network with a direct line back to Germany. Wear parts are standard components you can buy on the open market, which keeps service open to competition for the whole life of the machine. On an installation that has to run for decades and hold its effluent values while it does, that usually weighs more than the difference in purchase price. Warranty runs three years as standard and up to five years with a service contract.
FAQ: oxygen generators in wastewater treatment
In four places. In the biological stage it supplements or replaces blower air, so the bacteria that break down organic load have enough to work with. As peak cover it absorbs load spikes that the installed aeration cannot follow, from industrial dischargers, rain events or seasonal swings. In the collection system it is injected into rising mains and pumping stations to keep conditions aerobic and prevent hydrogen sulphide forming. And it serves as feed gas for ozone generation, where ozone is used against COD and trace substances.
Air is about 21 % oxygen; the rest is compressed, blown through the basin and released again without contributing. Oxygen at 90 to 95 % raises the partial pressure in the bubble, which increases the driving force into the water, so the same dissolved quantity enters with a much smaller gas flow. That is not an argument for replacing working blowers. It is an argument for the situations where the basin, the diffuser grid or the electrical supply has no headroom left and more air is not available.
Normal practice is 1 to 3 mg/L in the aeration basin. Below that, nitrification slows and effluent values suffer; above it, the plant is supplying oxygen the biology is not using. The right value inside that band depends on your load, your temperature and your process, and it is worth taking from your own records rather than from a rule of thumb, because the same setpoint behaves differently in February and in August.
It follows from the load rather than from the size of the works. BOD and COD load plus the nitrification demand set the requirement, and two plants with identical basin volumes can need very different amounts. The second question matters as much as the first: whether the oxygen carries the base load continuously or only covers peaks. That decision moves the machine size further than any other, and it is the one most often left open when an enquiry arrives.
Between 90 % and 93 % in normal operation. Above that the bacteria gain nothing, because partial pressure has long since stopped being the limiting factor. Unlike a nitrogen generator, asking for higher purity here does not cost you compressed air: the OXYBERG® air factor is 11 at every grade in the range. What it costs is capacity. The same machine delivers between 10 and 40 % more oxygen at 90 % than at 95 %, and the gain is largest at the smaller sizes.
Multiply your oxygen flow by 11 and you have the demand, at any purity in the range. That is the whole calculation, and it can be done before anyone quotes hardware. Air quality matters as well as volume, because sieve life depends on it, and an undersized dryer is a more expensive mistake than a slightly undersized compressor. OXYBERG® expects compressed air to ISO 8573-1:2010 Class 1.4.1.
The buffer vessel carries the plant through short interruptions, which is one of the reasons it belongs in the design rather than in the options list. Beyond that, how much reserve you hold is an operational decision that depends on your load, your effluent limits and what an excursion would cost you. It is worth settling at the design stage, when a larger buffer or a cylinder backup is still inexpensive to add.
The generator measures oxygen purity continuously with a zirconium analyser and shows the reading on the HMI, together with a trend display for the running process. Sensor values and operating hours go into long-term storage for later analysis, and alarms carry a time stamp with a full audit trail, so a deviation and the acknowledgment that followed it stay traceable long after the shift that produced them. For a works that has to demonstrate consistent operation to its supervisory authority, that record sits alongside the plant’s own process data rather than arriving separately with a delivery.