Recent news regarding the algae related water quality problems in Toledo have raised issues about the potential for algae blooms and the release of toxic chemicals from the algae elsewhere in the US and especially in Northwest Ohio.
Celina, another town in Ohio, uses Grand Lake as its water source, which has encountered problems with the algae blooms and the toxins they release since 2009. Celina, however, has updated treatment system to deal with these issues.
The city uses two methods of water treatment to make its water safe, ozone and granular activated carbon treatments. Ozone is a powerful oxidant and highly effective disinfectant. It is a technology that has been in continual commercial use for more than 100 years and has distinct properties that allow disinfection of even heavily compromised water streams.
The GAC treatment is an extremely versatile technology and in many cases has proved to be a cost effective option. GAC absorption is particularly effective in treating low concentration waste streams and in meeting stringent treatment levels. GAC is known to remove a wide variety of toxic organic compounds to non-detectable levels.
As with any water treatment technology, suitability on a specific application normally depends on costs as they relate to the amount of carbon consumed.
The North Texas Municipal Water District (NTMWD) began using ozone as the primary disinfectant at its Wylie Water Treatment Plants in 2014. As a result of the $123 million ozone project, a significant improvement in the taste and odor of the drinking water produced is expected. The NTMWD selected ozone in the treatment process because of changes in US Environmental Protection Agency’s Safe Drinking Water Act.
Now operating the nation’s largest water treatment facility using ozone, the NTMWD implemented extensive planning efforts, modifications, construction and project management at the four Wylie Water Treatment Plants. In addition to the Wylie location, the Bonham and Tawakoni Water Treatment Plants also produce ozonated water. Cumulatively, NTMWD has the capability to treat and deliver 806 million gallons per day of high- quality, safe drinking water to the region served.
Ozone is a good choice for municipal drinking water treatment because it offers multiple benefits to the plant operators. In the case of NTMWD, it allowed them to meet more stringent US EPA regulations for disinfecting drinking water while also improving the waters taste and odor profile. Using another primary disinfectant would have required a second process or chemical to deal with the taste and odor.
The Four Way Special Utility District (SUD) operates multiple potable water plants, including Water Plant Number 3 in Eastern Angelina County, Texas. Plant Number 3 was having problems with Hydrogen Sulfide (H2S) and color due to the presence of tannic acids in the source water. The current process, aeration/chlorination was not successfully treating the problem, so SUD asked their consulting engineer for options. They suggested ozone could resolve all of the problems.
Testing showed that an ozone system would reduce color, taste and odor concerns while avoiding the formation of regulated disinfection by-products. The process design presentation was supported by laboratory testing which confirmed no excessive disinfection by-product formation. In addition to color, taste and odor control that ozone treatment provides, the treatment process enhancement allowed for reduced chlorine dosage and discontinuation of the air stripping process. The ozone system was adopted and is now in operation at Plant Number 3.
The Coquitlam watershed treatment facility in British Columbia provides approximately 370 MLD, a third of the total water supply delivered in Metro Vancouver. The facility uses the process of ozonation as the primary disinfectant, but has added new UV disinfection equipment to complement the existing ozone and chlorination processes. Construction of the new facility started in spring 2011, and the technology cost under 100 million dollars to put in place.
Ultraviolet light at a wavelength of 254 nanometers passes through the water inactivating the micro organisms by disrupting the DNA of microorganisms preventing the organisms from reproducing. Since these organisms have a very short lifetime, without reproduction the population quickly dies away. UV radiation does not change the taste or color of the water.
The facility will continue to use ozone and chlorine as part of its multi barrier approach to disinfection. Each disinfection agent, ozone, UV and chlorine have their own unique advantages. Besides disinfection ozone can remove organic matter that can add color, taste or odor to the water. Ozone also can remove micro pollutants such as pesticides that may be present. UV is very effective against organisms that might require much higher doses of ozone or chlorine such as cryptosporidium. Chlorine provides a persistent residual in the water protecting the water distribution system from developing pathogens.
By employing all three approaches, Coquitlam is offering a significant layers of protection to the people of Vancouver.