By Paulette Scoville

A major concern in providing safe drinking water from well systems is the control of waterborne diseases. Water treatment dealers who provide ozone disinfection services for customers depending on well water should have a basic understanding of the importance of ozone concentrations. Even with continuing technological advancements in computerized controls and remote operations on home systems, the effectiveness of any ozone disinfections system still heavily depends on the people who install and maintain those systems.

 Bacteria, viruses and protozoans -- the three major types of disease-causing organisms -- differ in size and in their resistance to oxidation from ozonation. However, when ozone is properly applied, it destroys all forms of microbes, colloids (organic materials in water) are destabilized by neutralization and dissolved organic materials are oxidized. 

These reactions stem from the fact that ozone is a powerful oxidant and second only to flourine in strength. It has a high chemical reactivity due to an unstable electron configuration that causes it to seek electrons from other molecules.

 Dealers should maintain a key-point checklist that covers the following areas of ozone injection into well water:

[[radical]] ozone output 

[[radical]] transfer capabilities 

[[radical]] diffusion and concentration 

[[radical]] ability to adapt variations in water 

[[radical]] ozonation control and location of the diffuser.

Of the two primary methods of ozone production, the one most often used in residential applications is ultraviolet light. In this process, ambient air passes through an ozone chamber where ultraviolet light disassociates the oxygen molecules so they recombine as highly unstable ozone molecules. 

However, for treating water held in tanks of less than 1,000 gallons, the method of ozone generation is not an issue -- airflow, concentration and output is.

 When you select an ozone system for customer installation, you should know its output in grams per hour, the concentration of the ozone produced and the volume of airflow through the unit. Any one of these bits of information without the other basically renders the other two useless. Unit specifications should include recommended applications, including desired water quality, volume of water to be treated and recommended contact times.

 Ozone has diverse applications as an oxidizer and flocculant. The systems used to dissolve the ozone gas into the liquid phase can vary in type, design and operating conditions. The type of application not only determines the ozone system used but the mixing system for the ozone generator.

 For example, some generators operate with a positive pressure on the output line. This type of generator is best when installed in conjunction with a positive pressure mixing system. Generators operating with a negative pressure or vacuum on the output line are more efficient when installed with negative pressure mixing systems such as aspirating turbines or injectors.

 In well-water settings the two most frequently used methods of putting ozone into water are bubble diffusers and injectors.

Bubble Diffusers

 A bubble diffuser is made from porous material such as ceramic or titanium. The ozone gas from the generator is pushed through the small pores in the diffuser, which is installed at the deepest point of the water vessel.

 This results in the production of minute ozone bubbles emitting from the surface of the diffuser. Many small bubbles provide a larger surface area than fewer, larger bubbles, resulting in an increased mass transfer of ozone.

 Fine bubble diffusers require a positive pressure feed from the ozone system. This type of dissolution system is dependent upon the height of the water column above the diffuser. Water columns close to 20 feet high are required to achieve greater than 90 percent mass transfer of ozone from the gas into the liquid phase.

 Bubble diffusers have no moving parts and provide more efficient mass transfer of ozone with no additional energy requirements. However, they require cleaning and their efficiency relies on water depth.

Injection Systems

 An injector works on the concept of water flowing rapidly through a pipe or a small orifice, creating a venturi effect or partial vacuum that pulls the ozone gas through the orifice and into the water stream. Injectors can use either negative or positive pressure. 

Consider the following variables when selecting injector systems for wells:

* Pressure on the ozone generator output

* Available hydraulic head

* Use of ancillary components that affect hydraulics

* Construction of ozone-resistant materials.

 As with bubble diffusers, injectors have no moving parts and require little or no maintenance. Unlike diffusers, they require a separate energy source.

 Note that a filtration system may also be required in connection with an ozone system for whole-house water treatment. Filtration removes destroyed microorganisms and other matter to maintain stability and water quality.

 Typical filtration is at the 5-micron level. In some cases carbon filtration is combined as a polisher for additional treatment. Ozone filtration systems differ from reverse osmosis (RO) in that there is no reject water. This feature is beneficial to rural and seasonally drought-afflicted homeowners.

 Guidelines for ozone disinfection were established nearly 30 years ago to provide at least 99.99 percent inactivation of viruses and bacteria. A dissolved ozone residual of 0.4 milligrams per liter (mg/L), which is 0.1 mg higher than tested, is needed for a minimum of 4 minutes (see accompanying graph).

 The amount of residual directly affects contact times in the source water. Manufacturer guidelines are of great assistance in determining the most efficient contact times. As with all water disinfection processes, the best results are obtained with optimal conditions and correct operating procedures.

 Dealers who refer to their key-point checklist will have an easier time designing an ozonation system for their customers' well water.

Paulette Scoville is the sales and consumer education coordinator for DEL Industries, San Luis Obispo, CA.