Ashland experiences seasonal increases in manganese in its ground water supply. In Ashland’s water, the manganese is organically bound with an organic molecule such as humic, fulvic or tannic acid. Manganese in such a complex is more difficult to remove because the organic molecule provides a protective shell. Treatment of organically bound manganese leaves increased levels of disinfection byproducts in the finished water.

To address the issue, the Howe Street facility was originally designed to use two ozone generators to oxidize the manganese. Unfortunately, the system was difficult to operate and was taken off line for a couple of years. To bring the ozone generators back on-line, the dielectric modules were cleaned and rebuilt. A number of other improvements were made as well: relocating several valves for easier adjustment and maintenance, installing blow-down valves and drain lines for the degas system, and modifying the degassing and destruct units to vent to the entrained water separator without the need for vacuum pumps. Once the maintenance and upgrades were complete the results were dramatic and the project met the goal of having high quality water.

Ozone offers numerous benefits over chlorine as a primary disinfectant, most importantly, a reduction in the formation of chlorinated organic disinfection by products. These compounds are being more tightly regulated by the EPA in drinking water since they are suspected carcinogens.

The need for cyanide destruction has 
increased over the years due to the growing demand for sustainable solutions to neutralize destructive cyanide in tailings dams as more mining companies voluntarily subscribe to the United Nation’s International Cyanide Management Code (ICMC). The fundamental aim of the code is to manage the use of cyanide throughout the gold beneficiation process, which limits the release of solutions containing cyanide into the environment from spillages and tailings disposal. Although compliance with the code is voluntary, it has been implemented by the world’s major gold producers.

The advantages of using the ozone-based process for cyanide destruction should, however, be a huge driver for mines when considering a cyanide destruction process. 
The advantages associated with using this system include the fact that no adjustment to the tailings stream is required when installing ozone equipment and the reaction is rapid, complete, irreversible and by-product free.

Ozone generators are extremely effective in disinfecting wastewater. In addition they potentially can remove pharmaceuticals and personal care products that can end up in drinking water by way of wastewater discharges. Ozone also helps to oxygenate the water before it is returned to rivers enhancing the overall health of the ecosystem.

Springfield Public Works wants to replace ozone generators at the Southwest Wastewater Treatment Plant. That would increase the facility’s capacity to disinfect from 65 million gallons a day to 100 million gallons a day. The generators are about 30 years old and replacement parts are expensive and difficult to come by. If the city had the new generators, it would likely save $4 million in operating costs in the next 20 years. Despite the increased difficulty to find parts, it is does demonstrate that high quality ozone generators can be expected to give extremely long lived operation.

Meyer said $3 million of the $16.2 million will be federal stimulus funds and the remaining $13.2 million will be a 20-year loan from the state’s revolving fund.

At the Southwest Wastewater Treatment Plant, money from the stimulus funds and state loan will be spent on a 24-month project to build a new ozone generator, expanding the facility’s capacity to disinfect up to 100 million gallons of treated water each day. Currently, the facility is limited to 60 million gallons, Meyer said.

“It’s a significant increase in what we can disinfect and treat,” Meyer said. “It will help up with our wet water flows and our peak flows.”

Seventh grader Otana Jakpor was also concerned about this type of ozone generators after reading an article in Consumer Reports. The article indicated the potential dangers of these devices. While most seventh graders would have left it at that, Otana designed experiments to confirm the issues brought up in the Consumer Reports article.

Her work spanned a period of two years. Some purifiers, she found, emitted ozone levels equal to Stage 3 smog alerts. She provided her findings to the California Air Resources Board at the board’s invitation. Her testimony contributed to the regulations that were put into place to regulate ozone generators for home use.

Otana went on to be awarded the President’s Environmental Youth Award and the Action For Nature’s 2009 International Young Eco-Hero Award in the ages 8 to 16 category. She has met with senators and the head of the U.S. Environmental Protection Agency. She is now a volunteer spokesperson for the American Lung Association and will have her study published in the journal of the American Thoracic Society.

Besides the significant personal accomplishment, Otana research confirms work done by others and provides a warning to homeowners in states that do not regulate ozone generators for home use that they need to be very careful in the purchase decisions and use of these devices.

Spartan Environmental Technologies does not sell ozone generators for residential use.

For air fed systems, refrigeration units on the compressors and desiccant dryers were used in the past. More recently pressure swing absorption (PSA) systems have been adopted. the latter have fewer moving parts and are easier to maintain. They do require higher pressure compressed air, in range of 100 psi to work efficiently. In any event, the goal is to remove the water to the -100 degree F dew point level.

For oxygen systems, PSA systems can also be used. In this case, oxygen is concentrated from air to 90-93% in the system. Water is also captured in this process, so dry oxygen gas is prepared. Alternatively, liquid oxygen can be evaporated as the feed gas. This material is inherently dry.

To insure effective drying, moisture sensors should be employed, especially in larger system. These monitors can directly provide the dew point value. Alarms can alert operators, or computer systems, to take action before moisture levels reach values that can result in damage to the equipment. For smaller system, silica gel moisture indicators are a low cost option to follow moisture changes as a change in color of the gel.

PSA systems can be a source of particulate contamination in the gas stream due to the attrition of the molecular sieves used to absorb nitrogen or water. So the use of particulate filters is important. these filters should be in the range of 0.5 to 1.0 micron in size.

For PSA systems, oxygen sensors can provide the oxygen concentration in the gas feed. an alternative is to follow the pressure of the concentrator since a drop of pressure below the recommended level is also an indication the the output concentration has been compromised.

Both ozone generators and PSA systems can be adversely affected by oil and other hydrocarbons. This can be a severe problem with oil lubricated compressors, but hydrocarbons from the environment can also pass through oil free compressors. In the case of oil lubricated compressors, coalescing filters must be used. It is also recommended to use activated carbon filters to polish the gas stream to remove any remaining hydrocarbon. Such filters cna lower hydrocarbon levels to less than 3 ppm.

The cost of a good gas preparation system is well below the potential damage cost by contaminated gas reaching the generator or explain why the generator is not producing ozone at the design vale.

In terms of gas preparation, the main issues are moisture, hydrocarbons and particulates. Moisture lowers efficiency and can cause corrosion due to the formation of nitric acid in the generator. A good system for drying the gas is critical. For larger systems, it is wise to invest in dew point monitors to measure the level of moisture in the gas. Particulates and hydrocarbons can deposit on the electrodes in the generator impacting efficiency. They can also lead to heating of the electrodes with potential damage to the dielectrics.

If water enters the ozone generator catastrophic damage will be done to the system. So, it is critical that water be prevented from entering the unit during operation or during periods when the unit is not active.

In coming posts we will cover each of these factors impacting reliability in detail.