Ozone Water Treatment Glossary

Below is a list of words commonly used in ozone water treatment discussions. After each word is a brief description of the term and where available, a link to more information.

Advanced Oxidation Processes: Advanced oxidation processes are designed to produce hydroxyl radicals (see description below). These processes are normally a combination of more than one oxidant such a ultraviolet light (UV)/ozone, UV/hydrogen peroxide, ozone/hydrogen peroxide, etc.

Alkalinity: Alkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. In the natural environment carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and presence of carbon dioxide in the atmosphere. Other common natural components that can contribute to alkalinity include borate, hydroxide, phosphate, silicate, nitrate, dissolved ammonia, the conjugate bases of some organic acids and sulfide. Carbonate alkalinity is important in ozone systems because ozone forms hydroxyl radicals under proper conditions of pH, temperature, etc. Hydroxyl radicals react with carbonate, preventing it from reacting with other species which is the objective in advanced oxidation processes.

AOC: The terms refers to Assimilable Organic Carbon. These compounds are readily decomposed biologically. Ozone reacts with more complex molecules to make the more biodegradable. Measurement of AOC is used to determine if the potential exist for regrowth of bacteria in the treated system.

Biological Filtration: Because ozone can form AOC (see above), sometimes biological filters are used to remove this biodegradable form of carbon from the system treated by ozone. Normally, conventional filters (sand or granular activated carbon) are allowed to become biologically active, i.e. biological growth is allowed to form on the filter media. This biology feeds on the AOC breaking it down to carbon dioxide. The filters continue to function as standard filters for the physical removal of suspended solids.

Bromate: The bromate anion, BrO3-, is a bromine-based oxoanion. Compounds containing this ion are called bromates. Bromate can be formed during ozone water treatment if bromide ion is present in the source water at a high enough concentration. Bromate levels are control in drinking water application.

Corona Discharge: sometimes referred to as "silent discharge" this is the principal method of producing ozone in most commercial applications. Air or oxygen is passed through an electric arc where a portion of the oxygen present is converted to ozone. Follow the link How Ozone is Made for more information.

Contact Vessel: Sometimes referred to as the reaction vessel or contactors, this is the vessel or tank where ozone is contact with the water to permit the reaction of ozone with the targeted constituents of water that need to be treated.

CT: The letters stand for Concentration of ozone in water multiplied by the time of exposure. The CT at a given temperature is used to estimate pathogen inactivation. Click on the link to a presentation on the EPA Surface Water Treatment Rule(SWTR) for more information.

Dew Point: The "dew point" or "dewpoint" of a given amount of air is the temperature to which the air must be cooled, at constant barometric pressure, for water vapor to condense into water, called dew. This is an important issue in ozone generation since corona discharge ozone generators are very sensitive to the amount of moisture in the feed gas. Typically, ozone generators need feed gas with dew points of -80 to -100 degrees F.

Dielectric: A dielectric is a nonconducting substance. Although "dielectric" and "insulator" are generally considered synonymous, the term "dielectric" is more often used to describe the insulating material between the metallic plates of a capacitor. A dielectric material is used in the design of corona discharge ozone generators, this is typically a ceramic or glass in most commercial ozone systms.

Disinfection Byproducts: Disinfection byproducts (DBP) are chemical compounds formed during the process of disinfecting water. These compounds are formed by most disinfection processes including ozone disinfection. Ozone can reduce the formation of certain types of DBP, especially those formed with the use of free chlorine.

Disinfection Credits: Log reduction of a specific micro organism allowed to be taken by a drinking water facility if EPA guidelines (such as the long term surface water treatment rules)are met in the treatment process.

Fine Bubble Diffuser: A portion ceramic device for forming small bubbles of ozonated gas for contact with water. A discussion of these fine bubble diffusers for ozonation can be found following this link. These devices are also referred to as stone diffusers and are used in a variety of other applications such as aeration.

Fluence: As used in the application of UV is a measure of the quantity of light or other radiation falling from all directions on the smallest possible three-dimensional object . Fluence is often measured in millijoules per square centi-meter (mJ/cm²).

Intermediate Ozone Application: In drinking water treatment, ozonation of settled water prior to filtration.

Haloacetic Acids (HAA): HAA are carboxylic acids in which a halogen atom takes the place of a hydrogen atom in acetic acid. Thus, in a monohaloacetic acid, a single halogen would replace a hydrogen atom. For example, chloroacetic acid would have the structural formula CH2ClCO2H. In the same manner, in dichloroacetic acid two chlorine atoms would take the place of two hydrogen atoms (CHCl2CO2H). These compounds can be formed by using chlorine in the treatment of water and are regulated in the part per billion range by the US EPA.

Hydroxyl Radicals: A highly reactive chemical species, the neutral hydroxide ion (OH) formed by ozone decomposition via a complex mechanism. They are short lived and non selective in their reactions.

LOX: LOX stands for liquid oxygen. It is used in larger ozone systems as the source of oxygen to form ozone. A discussion on LOX systems can be found by following this link.

Ozone: the triatomic form of oxygen. For more details following the link on what is ozone.

Ozone Demand: With respect to water, the amount of ozone that can be consumed by a particular water sample in mg/l.

Ozone Destroyer: A device for removing ozone from gas, typically the vent gas from a process that uses ozone.

Ozone Dose: The amount of ozone applied to water regardless of how much ozone is actually absorbed.

Ozone Generator: A device that produces ozone. The most common types of ozone generators include corona discharge, electrochemical and UV.

Ozone Residual: The amount of ozone measured in water a particular time.

Ozone Transferred: The amount of ozone that is absorbed by the water or reacted in the water.

Peroxone: The name given to the combination of hydrogen peroxide and ozone, the reaction of which produces hydroxyl radicals (see above).

Pre-ozonation: In drinking water treatment, the ozonation of the raw water prior to rapid-mix.

Pressure Swing Absorption (PSA): In ozone applications a process employing pressure and molecular sieves to remove water and nitrogen from air to concentrate oxygen from air as a feed gas to an ozone generator.

Side Stream Injection: a method of injecting ozone into water that takes a side stream of the main flow to be treated and by means of a booster pump and venturi injects the ozonated gas into the water. For a more detailed description follow the link on side stream injection.

SWTR: Surface Water Treatment Rules promulgated by the US EPA providing guidance on the methods of treating surface water for drinking water use.

Transfer Efficiency: The percentage of the ozone dose that is absorbed by the water. It is a function of ozone demand, temperature, ozone concentration in the gas phase and mixing method. For a more detailed discussion follow the link on transfer efficiency.

Trihalomethanes (THMs): THM are chemical compounds in which three of the four hydrogen atoms of methane (CH4) are replaced by halogen atoms. Many trihalomethanes find uses in industry as solvents or refrigerants. THMs are also environmental pollutants, and many are considered carcinogenic. Trihalomethanes with all the same halogen atoms are called haloforms. Trihalomethanes are formed as a byproduct when chlorine or bromine are used to disinfect water for drinking. They result from the reaction of chlorine and/or bromine with organic matter in the water being treated. The THMs produced may have adverse health effects at high concentrations, and many governments set limits on the amount permissible in drinking water. In the United States, the EPA limits the total concentration of chloroform, bromoform, bromodichloromethane, and dibromochloromethane to 80 parts per billion in treated water. This number is called "total trihalomethanes" (TTHM).

Venturi: A device used to mix a gas with a liquid, in this area of study ozone and water. Follow link to a more detailed description. They are some times referred to as injectors or eductors.

UV - Ultraviolet light (UV) includes the wavelengths between visible light and X-rays in the electromagnetic spectrum. A portion of this spectrum can be used for disinfecting water or destroying ozone.

UV Transmittance - (UV Transmissivity, UVT) is the percentage measurement of UV able to pass through a solution. Pure water has a UVT of 100%.