Entry for May 14, 2008

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.

 

 

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Entry for May 5, 2008

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.

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Entry for May 1, 2008

Most of our discussions regarding ozone have been focused on water treatment.  Ozone is also used in air treatment to reduce or eliminate odors.  Many consumers may be familiar with ozone based systems for cleaning air in the homes, but municipal and industrial applications have also benefited from the use of ozone based odor control systems.  In this post we will briefly discuss the application of ozone and ozone generators for this purpose.

Odor tends to be a nuisance issue for industrial and municipal facilities.  While the facilities may have initially been isolated from the population, the expansion of residential areas may have brought people closer to the plants.  Odors which may initially have gone unnoticed are not a problem with the local population.  Odor control systems become necessary to maintain good relations with the neighboring population.  There are a wide variety of odor control systems for these situations.  We will focus on ozone based systems in this blog.

As we have mentioned before, ozone is powerful oxidizer.  Many odor compounds can be oxidized to a non odorous state.  These compounds include hydrogen sulfide (H2S) and other sulfur containing compounds such as mercaptans that produce the smell of rotten eggs.  Other organic compounds such as amines can also be treated with ozone to reduce or eliminate odors.

Ozone is employed for odor control in two basic ways: First, ozonated air can mixed with the contaminated air in a contact chamber for a gas phase reaction.  The contact chamber will have a packing that will provide surface area for the reaction as well as enough volume to reduce the gas velocity to allow the reaction to take place.  The second approach is to use a wet chemical scrubber.  In this approach a scrubbing liquid is used to capture the contaminant.  Ozone is added to the scrubbing liquid to allow for a liquid phase reaction with the contaminant.  For hydrogen sulfide, the scrubbing liquid would be an alkaline liquid to capture the acidic gas.  The reaction with ozone would convert the sulfide into an odorless sulfate.

The choice of which approach is best depends on the flow rate of the air and the concentration of the contaminant.  Lower flow rates and lower concentrations favor the gas phase treatment method.  Higher concentration of odor compounds favor wet scrubbers.  Ozone based odor control systems offer the following advantages over other systems:

  • Small footprint
  • Low initial capital investment
  • Do not produce any toxic byproducts, ozone breaks down into oxygen
  • Quick start-up

Spartan Environmental Technologies supplies both dry and wet ozone based odor control systems. 

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