In previous posts we have noted work on the use of ozone in ballast water treatment. IMO rules will require ships to treat ballast water to prevent the transport of invasive species across the globe. As an example of invasive species brought to the US via ballast water are zebra mussels.
The new rules will require the use of ozone, UV or other chemicals to treat the water. The US EPA ETV project has already identified ozone and UV as viable technologies. Currently, a few hundred ships have been equipped with such systems including ozone water treatment systems, but in the next decade over 50,000 systems will be needed at a cost of up to $1,000,000.
To be accepted for this application, manufacturers need to pass IMO certification for their systems. An expensive and time consuming process that can cost millions of dollars. Many ozone generator manufacturers and others are aggressively pursing this course.
If ozone becomes the primary biocide for this application, it is likely to be the largest single application for ozone.
Ozone is most efficiently made from oxygen with a small amount of nitrogen. Oxygen exists in the atmosphere at a concentration of about 21% in air we breathe. Using technologies such as pressure swing absorption (PSA).
PSA is a purely physical process; there are no chemical, electrical, or other reactions in our process. Under pressure nitrogen and water are absorbed by a molecular sieve. When the pressure is released the sieve material gives up the water and nitrogen. The process uses two columns, one is absorbing while the other is desorbing. The gas in the absorbing column is concentrated in oxygen to 90-95% and has a dew point of -100 degrees F. This is ideally suited to supply an ozone generator. The picture below shows a schematic of an oxygen concentrator.
PSA Oxygen Concentrator
For certain specific applications, a variation of the PSA process, called the Vacuum Pressure Swing Adsorption (VSA/VPSA) process. The only differences are that VPSA uses a feed blower instead of an air compressor and the absorber vessels are desorbed through a vacuum blower. The net result is a significant decrease in the power consumption of the system as a whole. However, these plants are typically only cost effective for very large oxygen capacities.
Oxygen Generators can eliminate the expense, inconvenience, hazardous handling, and storage problems associated with purchased liquid or the transportation of high pressure oxygen cylinders.
Ozone is often used to reduce the amount of organic compounds in water treatment applications via a process called oxidation. Commonly used measures of organic levels are COD (chemical oxygen demand) and BOD (biological oxygen demand). The first measure uses high temperature and aggressive chemical oxidants to completely oxygenate organic compounds in a test sample and measure the equivalent amount of oxygen required for this to take place, thus the chemical oxygen demand.
The BOD test uses bacterial to oxygenate the sample, the bacteria use oxygen to digest the organic compound and produce carbon dioxide as a waste product. Thus, it indicates the biological oxygen demand of the water over the time it takes to run the test, typically 1-5 days. Because some compounds are not readily oxidized by bacteria, the COD value can exceed the BOD value. The larger the COD:BOD ratio the less biodegradable the organic compounds are.
Ozone tends to work better on compounds that are not biodegradable. In fact, as the ozone oxidation breaks down the organic compound it tends to to form more biodegradable compounds, typically aldehydes, ketones and carboxylic acids. Ozone is considered a specific oxidant, targeting certain molecules and in some cases specific parts of a molecule. In terms of specific parts of molecules, this applies to compounds that create color, odor or taste in water.
The advantage of a specific oxidant is that less oxidant is required since only the target molecules or portions of the target molecules are effected. This characteristic can be used in water treatment to employ ozone as a pretreatment for a biological process, the recalcitrant compounds are made biodegradable and the biological process can deal with them.
When ozone is combined with peroxide or UV light, the ozone is converted to hydroxyl radical, this is an indiscriminate oxidant, it will attack virtually all organic compounds. Processes that make hydroxyl radicals are typically referred to as advanced oxidation processes.
Fracking has created a large application for various water treatment technologies such as ozone and advanced oxidation processes. Both processes have been used to either breakdown organic contaminants in the water, remove Fe and other minerals or for disinfection of the water prior to injection. An advantage of ozone based processes is that the ozone is made from air and after reaction breaks down into oxygen, leaving no dangerous byproducts and simplifying logistics.
The stock market is starting to take notice. Environmental services stock Heckmann Corporation soared nearly 38% on the NYSE after announcing the acquisition of privately held Power Fuels for $125 million in cash and 95 million shares of stocks. Both companies are involved in fracking water treatment. Ecosphere, which uses ozone based processes, is also a public company drawing a lot of attention.
As the use of fracking continues to expand, ozone and advanced oxidation should continue to see increased usage.
Salt lake City uses ozone at two of its facilities: Little Cottonwood (LCW) and Point of the Mountain (POM). LCW has Utah’s first and largest ozone drinking water treatment system, two ozone generators each sized at 3,750 lb/day of ozone. The facility can treat 143 MGD of water. The plant can dose ozone at 3.5 ppm during times when taste and odor control are required or as low as 1 ppm during normal operation. The ozone provide a 0.5 log reduction of Giardia. the system became operational in 2009.
The new POM plant can produce up to 950 lbs/day of ozone delivering an ozone dose of 3 ppm. It is capable of treating 70 MGD. This system also employs a UV disinfection system down stream of the ozone to allow achievement of the LC2ESWT rule as well as stage 2 disinfectants/disinfection byproducts rule. POM thus has a multi-barrier treatment system with complementary technologies.
Both of the improvement projects were part of a $250 MM capital program. The improvements now allow Salt Lake City to meet future regulations while providing its customers with high quality good tasting water. The large financial commitment illustrates the foresight of the water districts leadership.