Does Reverse Osmosis Remove Ammonia from Water? Let’s Find Out!
Written by: Gene Fitzgerald // Last Updated: Apr 13, 2023
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While the most effective method for complete ammonia removal is water distillation, you may be wondering if reverse osmosis can get rid of it too.
If you figured it might be able to, you’d be half right, though it’s a little more complex than just reverse osmosis leaving the ammonia behind.
Confused yet? I was, too, so let’s try to break it down.
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Key Takeaways
- Polyamide reverse osmosis membranes are capable of removing up to 98% of ammonia from water.
Does Reverse Osmosis Remove Ammonia from Water? How Much?
So, does reverse osmosis remove ammonia from water?
Yes, polyamide (PA) reverse osmosis membranes, also commonly known as TFC or thin-film composite membranes, are capable of removing ammonia from water at a rate of 97-98%.
CTA membranes on the other hand, which were replaced by PA membranes in home reverse osmosis systems several years ago, only remove ammonia at a rate of somewhere between 40 and 55%.
Besides, ammonia in water can be present as ammonium hydroxide (NH3) or as ammonium ions (NH4). When the water pH is below 7, it is NH4 that is present, and when it is above 7, it is mainly NH3.When water passes through a reverse osmosis membrane, its pH usually drops to under 7, and therefore any remaining percentage of ammonia in the water will be ammonium ions, which are easily removed with a cation resin post-filtration step (if you have one).
How Does Reverse Osmosis Remove Ammonia from Water?
Reverse osmosis uses a semipermeable membrane – that means the membrane allows certain substances to diffuse through it but not others – to remove contaminants from water. This also goes for ammonia.
If ammonia-contaminated water enters an RO membrane vessel, the water molecules are pushed through the membrane’s tiny pores under high pressure. Ammonia remains on the feed side of the membrane and is flushed down the drain in a waste water stream.
Further Reading:
Challenges When Trying to Remove Ammonia with Reverse Osmosis
Ammonia is present in many tap waters, as it is a byproduct of the addition of chloramine to municipal water for disinfection. The ammonia remains once water passes through the activated carbon pre-filters of a reverse osmosis system and the chlorine part is removed.
If you are working with a polyamide reverse osmosis membrane, up to 98% of that ammonia will then be removed, and the rest can be dealt with a cation exchange filter (water softener) if you want.
Other Ways to Remove Ammonia from Water
Ion Exchange
Ammonia can be removed by using a cation resin exchange, with sodium replacing the ammonium ions. This works if you have soft water, but not necessarily with hard water, as the cation resin exchange might favor the calcium and magnesium in the hard water.
Cation exchange is what’s used by traditional salt-based water softeners.
Boiling/Distillation
Water boiled for around 20 minutes can reduce free ammonia, but not dissolved or ionized ammonia, but it would be suitable to use the water for drinking.
Distillation, on the other hand, removes more than 90% of ammonia from water, and is highly effective.
Activated Carbon
As mentioned before, chloramine is a mixture of ammonia and chlorine.
Activated carbon removes chlorine from water but is not adequate for ammonia removal, which is left behind in the water.
Zeolite
Zeolite can reduce ammonia by up to 75%, but its effectiveness is decreased when dealing with high concentrations, as it has a limited capacity for binding it.
pH Reduction
Water at a pH lower than seven means that ammonia exists in a less toxic form of ammonium ions.
What Is Ammonia and How Does It Enter Our Water Supplies?
Ammonia is a chemical widely used in the USA, usually for fertilizers or other industrial processes. It also can be found naturally in decomposing organic waste, and it can get into water supplies via runoff from agricultural land or directly from contamination with organic waste. Intensive use of fertilizers has increased the concentration of ammonium in groundwater in recent years.
The World Health Organization states that ammonium concentration in drinking water should be less than 0.2 ppm, which is often surpassed.
Ammonia may also be in our water due to water treatment with chloramine, which is a mix of chlorine and ammonia that extends the length of time that chlorine is effective as a disinfectant.
Health Effects of Ammonia in Water
Drinking extremely high levels of ammonia may lead to poisoning, which can present as nausea, fever, coughing, throat pain, swelling of the lips, severe stomach pain, dizziness, chest pain, vomiting, temporary blindness, confusion, restlessness, difficulty walking and lack of coordination, shock, and collapse.
The main routes of exposure for ammonium poisoning are skin contact, eye contact, and inhalation. Poisoning from drinking water is uncommon.
However, ammonia can be highly toxic to aquatic life, and kill fish, which is why a lot of aquarium setups require reverse osmosis filtration with adequate pre and post-filtration steps.
If you have any thoughts about the question, does RO remove ammonia, please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
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