When designing an ozone water treatment system, as with any engineering project, there are tradeoffs between cost and performance.  One aspect of design for such systems involves the controls.  Depending on the application, it is entirely possible to design a system with fully manual controls that will function well.  Such systems require operator attention should one of the systems components fail.  It is also to design and build a full automated ozone system that can run unattended and alert n operator should the need arise.

The cost of automation is usually the major reason why client opt for more manual controls, especially for smaller systems where the costs of controls can exceed the cost of the ozone generator.  On the other hand, if the application where ozone is being applied is critical, the use of controls to maintain proper operation, regardless of operator attention is probably justified.

The basic components of an ozone water treatment system are gas preparation, ozone generator and ozone water mixing.  Gas preparation involves the following options: compressing/drying air, concentrating oxygen from compressed air, or feeding purchased oxygen.  Gas feed is critical for proper ozone generator operation in terms of both product quality and ozone generator protection.  Moisture will not only reduce generator efficiency, but also damage the generating cell. 

For new systems, pressure swing absorption (PSA) is used for both air drying and oxygen concentration.  The process is highly reliable since it uses a solid state process with limited moving parts.  Dew point monitors can directly measure the air drying process and oxygen monitors can follow the oxygen concentration process.  These instruments are reliable and are routinely used in large installation on a regular basis.  The instruments are moderately expensive and require periodic calibration. 

An alternative is to use a pressure switch.  A critical parameter in the operation of PSA systems is the feed pressure.  If this drops below a certain level, the process will no longer work properly.  This tends to be a factor is performance problems associated with such systems.  So, a pressure switch is an inexpensive method to monitor the performance of PSA systems.  While by no means fool proof, it can catch major faults allowing for eh shut down of the system before damage is done and alerting operators to a problem.

Another technique that is also relatively inexpensive is to use a silica gel that changes color with changes in moisture content of the gas.  Both air dryers and oxygen concentrators should produce a gas with a dew point of less than -100 degrees F.  The silica materials change color from a blue to red with the presence of moisture.  While not an automated method of control, it can alert and operator to a problem.

If the quality of the feed gas is good, the operation of the ozone generator is usually good as well.  Ozone generators with good feed gas will last for a long time between servicing.  While near terms failures are not likely, they are possible.   In larger installation, monitors follow the concentration of ozone coming out of the generator.  These monitors use UV light to measure ozone.  They are very accurate, but expensive and require periodic calibration by skilled technicians.  In addition to measuring the concentration of ozone in the gas, these systems also follow the flow of the gas.  They can then calculate the production of ozone in g/h or lbs/day and compare the values to the original specifications for the generators. 

The objective of these controls is to insure that the dose of ozone in the water meets the application requirements.  While the gas phase values can predict the amount of ozone in the water, the concentration of ozone in the water is also monitored.  This can be done using a dissolved ozone monitor employing either UV or an electrochemical method.  In both cases highly accurate measurements of ozone dissolved in water can be made.  From a control point of view, one could do without the gas phase measurements since the critical parameter is the dissolved ozone concentration.  While the gas phase measurements would be highly useful tools for assessing why the concentration of ozone in the water is low or detecting the problem before it occurs, it is not a requirement and most small systems do not use gas phase monitors.

The electrochemical dissolved ozone monitors are easily calibrated on site and are relatively inexpensive.  They often come with built in control outputs that allow the monitor to control the power settings on the ozone generator thus controlling the dissolved ozone levels in the water without direct operator intervention.

Other considerations in the design of an ozone water treatment system are the handling of various systems failures.  We already mentioned the potential for failure of gas preparation when compressed air is the feed source using pressure switches.  Another potential failure is the back flow of water from the liquid side of the system to the ozone generator.  Such an occurrence is catastrophic and would result in the destruction of the generator.  As a result, protection must be put into place with back-up.

For small inexpensive systems, mechanical methods alone are popular and workable.  These include liquid traps and check valves.  Another level of protection involves liquid traps with sensors that detect the back flow and can provide a signal to a control panel to close valves, shut down generators and set off alarms.  In systems that use venturi, back flow would also change the pressure in the line from negative to positive.  This could be sensed by a pressure switch.

Leaks of ozone into closed spaces of a building can create potential hazards for people.  Although ozone is easily detected at safe levels by our sense of smell, our olfactory nerves are easily fatigued by ozone.  If the person exposed to ozone ignores the problem, they could unknowingly be expose themselves to dangerous levels.  While there are no records of anyone dying from such exposure, it is not wise to rely on our sense of smell.  The use of ambient monitors is recommended for these situations.  Most monitors come with relays that can be used to shut down the ozone generator. 

Ozone water treatment systems are designed to make ozone and mix it with water.  So the primary thing to measure and control is the amount of ozone in the water.  The next most important factor is to prevent water from backing up into the generator since this will result in the catastrophic failure of the generator.  Finally, it is important to make sure the gas feed meets specifications in terms of oxygen quality or air dryness. 

These objectives can be accomplished with simple manual methods or with sophisticated instruments and PLC.  The decision of which to use has to do with overall system cost and how critical the application is.  Spartan Environmental Technologies can supply ozone systems with a wide range of controls that can meet the specifications and budgets for a variety of applications and clients.

Spartan Environmental Technologies provides ozone water treatment systems for a variety of applications.  As we have mentioned in previous posts, one of the key elements of such systems is gas preparation.  Oxygen or dried air can be used to make ozone.  In this post we are going to discuss oxygen preparation systems for ozone generation.

The use of oxygen for the production of ozone permits higher rates of production for a given machine (80% more production) with higher ozone concentration (2-3% versus 6-10%).  Higher concentration ozone is beneficial since it allows for easier dissolution into water.  On the other hand, producing oxygen is more difficult than simply drying air.  This means that much more air has to be processes to make oxygen than to dry air.  The more compressed air required the larger the compressor and the more energy required.  These costs offset to some extent the benefits of oxygen inside the ozone generator.

Spartan ozone water treatment systems employ oxygen concentrators using pressure swing absorption (PSA).  This process employs two columns filled with molecular sieves, porous ceramic materials that reversibly absorb nitrogen and water from air on the surfaces. 

Compressed air (90 psi pressure and filtered to remove hydrocarbons and particulates) is fed to one of the two columns.  Under pressure nitrogen and water is absorbed on the surfaces of the molecular sieves.  As the nitrogen and water are removed, the concentration of the oxygen is increased to the 90-95% level.  This is enough to significantly increase the efficiency of an ozone generator versus the use of dried air. 

Once the column has been filled with nitrogen and water, it needs to be unloaded.  This is done by purging the column at atmospheric pressure (0 psig) with product gas from the other column that is operating.  This dry oxygen laden gas caries away the nitrogen and water captured on the molecular sieves, making them ready to repeat the process.  So while one column is producing oxygen the second column is being regenerated.

The ratio of air fed into the sieves to the amount of oxygen produced is about 11:1.  So, if we wanted to produce 260 SCFH (4 SCFM) of oxygen, we would need 45 SCFM of air.  The reason for the discrepancy with the natural ratio of oxygen to nitrogen in air (~1:5) is the amount of product gas (two thirds of total oxygen flow from the operating column) used to purge the column being regenerated.  This means that the usable product is only one third of the total flow of oxygen from the operating column.  The schematic above illustrates the process.

The only moving parts in the PSA process are the solenoid valves used to switch the flow of gas through the columns.  Thus the process is highly reliable.  Pressure switches and oxygen analyzers can follow the process and insure proper operation.

Contact Spartan if you are considering an ozone water treatment system.  Spartan supplies complete system including gas preparation, ozone generation and down stream processes.

One of the things that have always intrigued us about the water industry is the number of people that regularly drink bottled water but complain about the cost of water from their local utility.  Why do people pay $1.50/gallon for bottled water, but complain about water from the tap that costs $0.02/gallon?

Now we understand that some tap water can suffer from taste and odor issues, especially water that comes from surface sources such as reservoirs.  Some people feel bottled water is safer to drink than tap water because of chemicals that might be found in the water.  Water utilities can deal with both issues and for a cost that is a lot less than what consumers currently pay for bottled water.  Unfortunately, consumers are resistant to price increases for tap water and political pressure can make water utilities reluctant to ask for increases to improve water quality.

We think consumers should reconsider their preferences for bottled water for several reasons:  First and foremost, tap water is safe.  It is rigorously regulated by state and federal authorities.  Second, tap water is a more environmentally friendly and sustainable source for water versus bottled water.  Bottled water is transported to the consumer via trucks which consume fossil fuels.  Tap water comes to us via an efficient water distribution system.  Bottled water comes in plastic packaging only 24% of which is recycled.  This means that we are consuming petroleum based products and putting the unused containers in landfills.  Tap water comes without packaging.

In terms of taste, odor and chemicals, as we have noted in previous posting in this blog, these problems can be solved by a range of treatment technologies, some of which are supplied by Spartan Environmental Technologies.  Ozone water treatment and other advanced oxidation processes are proven techniques for reducing taste and odor problems in drinking water.  Water utilities in the Dallas Fort Worth area have successfully used ozone to overcome taste and odor problems typical in the summer due to the turnover of their reservoirs.  Their customer complaints about taste and odor dramatically decreased with the implementation of this technology.

Recently, in this blog and elsewhere in the news media there have been articles on the presence of pharmaceuticals and other personal care products in drinking water.  Numerous case studies have shown that ozone, advanced oxidation processes, membranes and activated carbon can remove a significant portion of these compounds.  Given that the presence of these compounds is already at levels considered safe, removal of virtually all of the compounds was achieved.

At most these technologies would add a few pennies per gallon to the cost of water to the consumer and do so in an environmentally sustainable fashion.  Unfortunately, utilities are reluctant spend the money on these technologies.  In some cases the utilities can legitimately claim that their water is safe to drink and does not require these new processes.  In other cases, the utilities cannot raise the capital required to invest in these technologies.  At the same time, however, enormous amounts of money are spent on bottled water for the same benefits.

On the positive side, the drinking water industry continues to make improvements in water quality on their own initiative and due to the regulatory pressure of the US EPA.  The newer water treatment technologies such as the use of ozone and UV will become prevalent.  Hopefully consumers will realize that improving water quality does not justify the costs associated with bottled water except in limited circumstances.

We are continuing our discussion on ozone for odor control applications. Last time we mentioned that ozone can be applied in the gas phase by mixing ozonated gas with contaminated air or that the ozone can be applied using a wet chemical scrubber with the ozone in the liquid phase.



The simplest arrangement is to work in the gas phase. This approach is only viable for low concentrations of odorants. For hydrogen sulfide, a common odor causing chemical, the concentration in the gas phase should be less than 5 ppm. At this level, ozone, normally made from an air fed ozone generator, can be mixed with the contaminated air and fed into a contactor. The contactor is a vessel that provides surface area and time for the ozone to react with the contaminant. The contactor should lower the gas velocity to less than 1 meter per second. In addition, the contactor should provide a high surface area for the reaction to take place. Plastic packing and aluminum screen are two choices for the materials to use to provide the necessary surface area.



When the concentration of contaminants is high, a wet chemical scrubber is a better way to introduce ozone. The picture above shows a schematic of a wet chemical scrubber used for ozone odor control. In the case of an acidic gas such as hydrogen sulfide, an alkaline scrubbing liquid such a dilute sodium hydroxide would be used. The scrubbing liquid would be mixed with ozone and then sprayed over a plastic packing. The design shown in the schematic, the contaminated air is blow across the scrubber in a perpendicular direction to the flow of the scrubbing liquid.



The scrubbing liquid captures the odorant in solution. The ozone then reacts with the odorant to neutralize the odor. The treated air passes through a demister to prevent the scrubbing liquid from leaving the scrubber. The bulk of the scrubbing liquid flows through the packing to the sump where it is circulated through the ozone mixing device and fed back to the scrubber. The concentration of the scrubbing liquid is adjusted as needed. A small portion of the scrubbing liquid is purged. In most cases the solution can be fed to the sewer without any environmental consequences.



There are numerous applications for ozone based odor control systems. These include municipal sewage plants, sewage collection systems including lift stations, rendering plants, exhaust from restaurant hoods, chemical plants, etc. Essentially any applications where the odor compounds can be oxidized.



Ozone based systems use less energy than thermal oxidation systems and don’t require the purchase or storage of chemical as with other chemical oxidants. Ozone is generated on site from air. So they only thing required is electricity.



Spartan Environmental Technologies supplies both types of ozone odor removal systems: gas phase and wet chemical scrubber. Contact us for further information.