Ozone Water Treatment Disadvantages
Ozone Water Treatment Disadvantages
Ozone water treatments treat and purify potable water and industrial water treatment systems. Yet, ozone comes with some downfalls, such as its high cost and maintenance, high reactivity and toxicity, and the ability to form carcinogenic byproducts.
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Ozone is a powerful disinfectant, effective over a wide pH range, thus, ozone gas can purify drinking water supplies in water treatment systems, eliminating odors, chlorine, iron, and bacteria.
Before using ozone, you need to understand how it works and the pros and cons.
How Do Ozone Water Treatments Work?
Ozone is an inorganic molecule and unstable form of pure oxygen with the chemical formula O3. Like chlorine, ozone is a strong oxidizing agent, which can kill bacteria and viruses in water. But, as ozone cannot kill large organisms, the water must also be filtered or an alternative method must be used to eliminate them.
Besides removing bacteria and viruses, ozone is used to oxidize iron and manganese to improve or control the color, taste, and odor.
Ozone water treatment units are installed as a point-of-entry system where ozone mixes with the water being treated. Turbulence and bubbles are created, to ensure the ozone treats as much of the water as possible. The greater the water flow, the greater the turbulence, and therefore, the more effective the ozone water treatment.
While ozone has been used commercially as a powerful oxidizing agent for water treatment systems since , there are some downsides to using ozone to disinfect water that you should know.
Disadvantages Of Using Ozone Treatment
Ozone is essential in wastewater and sewage systems that contain carbon-based and organic chemicals and other water pollutants. Even though ozone is more effective than chlorine in eliminating germs and pollutants, there are a few disadvantages that are worth mentioning.
1.Solubility & Activity
When the ozone dosage is too low, some germs and bacteria may survive, which is why higher ozone concentrations are used. Higher concentrations, however, are more difficult to control, but as ozone is 12 times more soluble in water than chlorine, you can reach the maximum disinfectant concentration more quickly.
Furthermore, ozone breaks down extremely fast, particularly at higher temperatures or in alkaline (high pH) conditions. Also, if the water being treated is rich in organic compounds or total suspended solids (TSS) then ozone will decay more rapidly, as it reacts with these contaminants, leaving a reduced amount of ozone to eliminate germs, which is the sole purpose of ozone water treatment systems. This is why ozone is not used to treat wastewater that contains a high amount of TSS and organic compounds, it&#;s just not economically suitable.
2. High Cost
Continuing from the economic side, ozone is more challenging to produce and deliver than chlorine, making it more costly than chlorination methods.
Ozone water treatments involve plant generators with two electrodes, where the electrical current passes through the electrodes, known as corona discharge. During corona discharge, around 85% of the energy is lost via heat waste, making ozone treatment extremely energy-intensive.
Treating water with ozone is also energy-intensive because it requires high-class equipment, expensive technology, and an operator that knows how to work the complicated system. These all add costs, making ozone water treatments more costly than alternative purification methods.
3. Reactivity & Toxicity
Ozone is a fantastic disinfectant as it is highly reactive. But with such reactive strength, comes some disadvantages.
Ozone&#;s reactivity with metals can cause issues in wastewater treatment pipes and containers, therefore corrosion-resistant materials such as stainless steel must be used, which adds to plant construction costs.
Additionally, because ozone is super reactive, it makes it a toxic chemical, so wastewater operators must take extra care and design the plant to ensure that they don&#;t come into contact with any ozone gas escaping from the water. Again, this adds to the cost of the ozone water treatment system.
Also, because of the high toxicity, ozone levels need to be constantly monitored with an ozone analyzer, these are fairly expensive to buy and replace.
4. Reactivity & Byproducts
As ozone reacts with organic compounds in the water, it creates byproducts. For example, if the water contains bromide ions, ozone can react to form brominated compounds (like bromate ions/salts), which can cause human cancers. Therefore, treatment operators must control the pH level inside the water or avoid using ozone if the water contains a high level of bromide salts.
What&#;s more, when chlorine is used in wastewater treatments, there is a residual amount of disinfectant left over, making it easy for operators to keep tabs on how well the water disinfection process was. But, ozone leaves nothing behind; any ozone that doesn&#;t react with the water contaminants is immediately broken down, leaving nothing to monitor after the disinfection process.
Advantages Of Using Ozone Treatment
Despite the disadvantages, ozone water treatment has many benefits.
As mentioned, ozone is highly efficient at killing bacteria, and producing ozonated water doesn&#;t require transportation or storage of dangerous materials as the water is processed on-site.
Ozone water treatments are also used over chlorine disinfection because it produces fewer trihalomethanes (THM) by-products. Additionally, no chlorine or chlorinated disinfection by-products are produced, making dechlorination unnecessary, and simplifying the process.
Ozone water treatment can also assist in filtration by oxidizing sulfates. As ozone disinfects the water, impurities such as iron and manganese are removed.
Another benefit is time. As ozone is 50% stronger than chlorine, less time is required to remove the inorganic and organic impurities than conventional methods such as boiling, filtration, sedimentation, or solar radiation.
Alternatives To Treating Water With Ozone
Ozone is not the only solution to treating drinking water supplies. To purify water, the following methods can also be used:
- Boiling
- Reverse osmosis
- Water chlorination
- Distillation
- Adding iodine
- Solar purification
- Clay vessel filtration
Summary
Ozone is an efficient way to remove bacteria from water supplies. However, its high reactivity, toxicity, and expensive costs and maintenance are a few reasons why other water purification methods are used.
Before purchasing an ozone water treatment device, determine which contaminants are present. This will help you decide if ozone will be effective for your water or if you should use an alternative system.
If you have any questions about ozone or what water testing kits we have, do not hesitate to contact our world-class team at Atlas Scientific.
pH Probes & Sensors
Ozone vs. Chlorine for Water Disinfection
Across the U.S., municipal water treatment agencies are faced with evaluating ozone systems for water treatment to help safeguard against bacteria, viruses, and pathogens. According to the EPA, &#;Disinfection is considered to be the primary mechanism for the inactivation of pathogenic organisms to prevent the spread of waterborne diseases to downstream users and the environment.&#; (See Table 1 for some common micro-organisms found in domestic wastewater and the diseases associated with them.)
TABLE 1: Infectious Agents Potentially Present in Untreated Domestic Wastewater
ORGANISM
DISEASE CAUSED
BACTERIA
Escherichia coli (enterotoxigenic)
Gastroenteritis
Leptospira (spp.)
Leptospirosis
Salmonella typhi
Typhoid Fever
Salmonella (=2,100 serotypes)
Salmonellosis
Shigella (4 spp.)
Shigellosis (bacillary dysentery)
Vibrio cholerae
Cholera
PROTOZOA
Balantidium coli
Balantidiasis
Cryptosporidium parvum
Cryptosporidiosis
Entamoeba histolytica
Amebiasis (amoebic dysentery)
Giarda lamblia
Giardiasis
HELMINTHS
Ascaris lumbricoides
Ascariasis
T. solium
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Taeniasis
Trichuris trichiura
Trichuriasis
VIRUSES
Enteroviruses (72 types, e.g., polio, echo, coxsackie)
gastroenteritis, heart anomalies, meningitis
Hepatitis A
Infectious hepatitis
Norwalk agent
Gastroenteritis
Rotavirus
Gastroenteritis
Source: Adapted from Crites and Tchobanoglous,
Both ozone and chlorine can be used to treat these organisms. So, the question when it comes to comparing ozone vs. chlorine for water disinfection is, &#;Which is better?&#; Chlorine has long been the default choice. It is a powerful oxidizer and is very effective at treating many pathogens. However, factors such as environmental issues, long-term cost, particulate removal effectiveness, and health issues have made ozone the preferred choice for many municipalities.
Ozonated Water Disinfects Better than Chlorine
Ozone, like chlorine, is an oxidizing agent effective at eliminating bacteria in water. It is recognized as among the strongest and fastest commercially available disinfectants and oxidants for water treatment. While chlorine does kill many microorganisms, it cannot treat all water-borne pathogens if used at EPA-approved doses. On the contrary, ozone can remain well within EPA regulations and be effective. When ozone decomposes in water, the free radicals formed, hydroperoxyl (HO2) and hydroxyl (OH), have great oxidizing capacity and play an active role in disinfection. Bacteria are destroyed by protoplasmic oxidation, which results in cell wall disintegration (cell lysis).
The Ozonation Process
Ozone is created using an ozone generator. This exposes a stream of air to either UV light or to a high voltage electrical discharge, the method known as corona discharge. The corona discharge method is typically preferred and takes place by breaking apart the two oxygen atoms of an oxygen molecule (O2) and then charging one of those atoms to another oxygen molecule, thus creating ozone (O3) molecules. Unfortunately, ozone cannot be stored or packaged because of its instability. Its effectiveness will depend on CT, which will be explained later.
In a water treatment application, the raw water passes through a venturi injector, which creates a vacuum and pulls the ozone gas into the water. An alternate method is bubble diffusion, where air bubbles up through the water being treated. Since the ozone will react with other contaminants or metals to create insoluble metal oxides, post filtration is sometimes required.
Ozone CT Explained
CT is the product of residual disinfectant concentration (C) in mg/l and the corresponding disinfectant contact time (T) in minutes. In other words, ozone CT is the dissolved ozone concentration multiplied by the contact time.
Some sanitizing treatments with ozone can be accomplished very quickly, but other treatments will require higher levels of ozone or longer contact time in the water. This contact time is required for the dissolved ozone to oxidize organic contaminants and disinfect the water. This CT value is assumed to be unitless. To ensure a given level of disinfection is obtained, either the ozone concentration can be held constant while the time is varied or vice-versa. For example, the CT value the bottled water industry generally uses is 1.6. This means the dosage rate is 1.6 mg/l minutes. Ozonation can happen at 0.2 ppm for 8 minutes or 0.4 ppm for 4 minutes. Either approach yields a final CT of 1.6.
The CT value is roughly x higher when using chlorine compared to ozone. For example, if a dissolved ozone level of 0.2 ppm for 1 minute (CT=0.2) is needed to inactivate a specific microorganism, you will need 200 ppm of chlorine for 3 minutes (CT=600).
How Bad Is Chlorine?
Chlorine is a powerful, cost-effective disinfecting agent for many applications. It has played a transformative role in bringing clean, safe drinking water to many areas throughout the world. But we are just beginning to assess the overall health impact of chlorine as a disinfectant in our water.
There is an abundance of well-founded concern about chlorine. Studies have shown that when chlorine is added to our water, it combines with other natural compounds to form Trihalomethanes (chlorination by-products), or THMs. These chlorine by-products trigger the production of free radicals in the body, causing cell damage, and they are highly carcinogenic. &#;Although concentrations of these carcinogens (THMs) are low, it is precisely these low levels that cancer scientists believe are responsible forthe majority of human cancers. Breast cancer, which now affects one in every eight women in North America, has recently been linked to the accumulation of chlorine compounds in the breast tissue". A study carried out in Hartford, Connecticut, found that &#;women with breast cancer have 50% to 60% higher levels of organochlorines (chlorination by-products) in their breast tissue than women without breast cancer.&#;
This increased link to cancer-causing compounds is corroborated in another recent study. According to Johns Hopkins University, &#;Toxic and carcinogenic compounds are produced when phenols in drinking water mix with chlorine.&#;
However, it&#;s not just the threat of cancer that is problematic when evaluating chlorine. A study by the American Chemical Society showed that chlorine use in water and sewage treatment may be contributing to antibiotic resistance. Beyond direct human impact, there are potential environmental impacts to microorganisms that may pose little health threat to humans but play a vital role in various ecosystems.
When evaluating this data, chlorine has meaningful risks. But what are ozone's other specific advantages?
Advantages of Choosing Ozone vs. Chlorine
Health Benefits: Chlorine can form chloroforms, linked to cancer, while ozone leaves no harmful by-products and reverts to oxygen if unused.
Effectiveness: Ozone is a stronger and faster disinfectant, purifying water times faster than chlorine. It can treat all water-borne pathogens, including those resistant to chlorine, like protozoa, E. coli, and Giardia.
Convenience: Ozone is generated on-site, eliminating the need for storage and transportation.
Mineral Removal: Ozone helps remove iron, manganese, and sulfur minerals.
No Residual Taste or Smell: Ozone-treated water has no chemical taste or smell.
Gentle on Skin: Low-dose dissolved ozone in water does not irritate skin, nose, or ears.
Efficiency: No rinse steps are needed, saving time and water costs.
Corrosion: Ozone is less corrosive than chlorine, especially compared to salt chlorination.
pH Independence: Ozone is effective across a wide pH range and does not affect the water&#;s pH.
For long-term waterborne disinfection requirements, ozone is clearly the safer, more environmentally friendly, and lower-cost option. If you have any questions about how ozone can provide better results for your needs, please get in touch with us today.
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