This article originally appeared in WQP July 2020 issue as "Get in the Zone"
Ozone water treatment technology has been in use commercially for many years as a powerful, non-chemical disinfectant in municipal water treatment facilities and commercial applications. The first drinking water plant utilizing this technology began operations in Nice, France, in 1906.(3)
In the 1970s and 1980s, advancements were made in ozone technology that spurred an increase in the use of ozonation for water treatment. Since then, ozone has rapidly gained public acceptance in the U.S. with U.S. Food and Drug Administration (FDA) acceptance and the introduction of modern ozone generation equipment to control dosage. Many municipalities with surface water supplies containing dangerous cryptosporidium and Giardia, for example, now use ozone water treatment as primary disinfection as chlorine does not penetrate these protozoa and is therefore ineffective in killing them. Additionally, ozone does not create trihalomethanes as a byproduct as can chlorine.
Ozone water treatment in the residential water treatment industry is more recent. There are some excellent uses of this technology that provides solutions to water quality problems that can be difficult to resolve. It may also provide a less expensive alternative in certain circumstances, as well.
Ozone Water Treatment Systems
The formation of oxygen into ozone occurs with the use of energy. In general, an ozone water treatment system includes passing ambient air through a high voltage electric discharge (inside a sealed tube, i.e., corona discharge). The ozone is generated from a circuit board that is mounted inside the system. When the air is exposed to this arcing electrical current, the oxygen in that air (O2) is converted to Ozone (O3), a powerful and rapid acting oxidant. Once the ozone has done its job inside the filtration system, it converts back to oxygen (O2), leaving the effluent water from the filter well oxygenated.(1)
Positive Attributes of an Ozone System
- Ozone water treatment is effective over a wide pH range and rapidly reacts with bacteria, viruses and protozoans (Cryptosporidium, Giardia). It has stronger germicidal properties than chlorination or ultraviolet (UV) light.(2)
- It has a strong oxidizing power with a short reaction time. These systems also have a media bed inside the tank that captures the oxidized minerals then backwashes.
- The treatment process does not add chemicals to the water.
- Ozone can raise pH (under certain conditions).(2)
Practical Uses of Ozone
A common water quality problem experienced in New England, and in many other areas of the country, is hydrogen sulfide. It can create an unbearable rotten egg odor inside the home, is corrosive to metals and can tarnish silver. It can also cause yellow or black staining on fixtures. At lower levels, hydrogen sulfide can often be eradicated with air induction systems, activated carbon, birm, pyrolux or manganese greensand. At higher levels, these methods are often ineffective where the power of ozone prevails.
H2O Care Inc. has experienced situations where air induction had the unintended effect of elevating the odor issues in residences with smells other than hydrogen sulfide related. The air induction increased the oxygen level in the water, enabling those specific forms of bacteria to thrive and produce even greater odor.
Bacterial growth stimulus varies dramatically for different bacterial types. Some thrive in a low oxygen environment while others benefit from it. As a group, bacteria display the widest variation of all organisms in their ability to inhabit different environments.
In situations where a water softener or other types of water filtration equipment are required, ozone water treatment is best installed last in line to kill any bacteria that may be hiding in the plumbing lines or other water treatment equipment.
Correcting Multiple Water Quality Problems
H2O Care Inc. has encountered situations where the water had the following combined issues:
- High iron;
- High manganese;
- Low pH; and
- Strong rotten egg smell.
A standard approach to this situation might be a pH neutralizer with a water softener and then another tank with an odor reducing media. By instead installing an ozone water treatment system, the iron and manganese were reduced to non-detected, while raising pH to the neutral range and eliminating the rotten egg smell.
If the media bed inside the ozone system is carbon based, it is imperative that you test for radon in the water first. The carbon will adsorb the radon and accumulate it over time, causing an eventual health hazard inside the home.
Common Methods for Filtering Minerals & Eliminating Odors
Traditional approaches for eliminating odors and minerals used a combination of greensand media and air pumps (or potassium permanganate) to oxidize minerals and eliminate odors. This requires a separate pump to introduce air or a separate chemical holding tank, which draws potassium permanganate into the system. Also note potassium permanganate is a dangerous chemical. Reading the Material Safety Data Sheet is enough to steer many away from its use in a home environment.
H2O Care Inc. had inherited some service accounts from another organization years ago and slowly converted the customers away from potassium permanganate. Not only did we not want it in their homes, we did not want our employees handling it either for potential health and safety reasons. In contrast, the ozone water treatment system is a self-contained unit with no additional components required to generate oxidization. This eliminates the need for storing chemicals in the home and reduces the amount of equipment required.
Potential Disadvantages of Ozone Water Treatment
Ozonated water may first appear cloudy in a glass due to the increased oxygenation created. The same as any water containing air bubbles, they will rise to the top of the glass and eventually dissipate. Customers should be made aware of this ahead of time.
Ozone is potentially corrosive, thus requiring corrosion-resistant materials to be used in the manufacturing of the system. Some manufacturers have recently converted their standard air system to use ozone generators. If care was not taken by the manufacturer in choosing the materials used to inject the ozone, installing dealers could potentially be dealing with problems and leaks associated with components failing due to ozone deterioration. Check the materials used.
In terms of end user cost, an installed ozone system has approximately the same cost of an air pump with greensand set-up at somewhere in the $2,700 to $3,000 range. The potassium permanganate with greensand would be approximately $500 to $700 less, however, you would have the chemical safety and health issues that accompany it and the on-going added expense of re-filling the storage tank with the potassium permanganate.
In summary, there are specific situations where ozone simply works where other traditional technologies do not. In others, ozone will accomplish what the other approaches will with a simpler, cleaner and potentially less costly result.