Arlington’s tap water is the cleanest among the nation’s big cities, according to a study by a Washington, D.C.-based environmental advocacy group. The Environmental Working Group calculations released this weekend were based on testing conducted since 2004 that found 316 pollutants in U.S. drinking water systems. The rankings that put Arlington No. 1 took into account numbers and percentage of chemicals found in tap water and levels of pollutants compared to legal limits and national averages. Other Texas cities with high ranking include: Fort Worth, third and Dallas 12th. All three cities employ ozone water treatment as part of their overall drinking water treatment program. Another city with a high ranking was Boston which also uses ozone as part of its water treatment program.
With the passage of California SB 790, also known as the Stormwater Resource Planning Act, ozone treatment programs like the one being piloted in Agoura Hills, CA to clean up pollution in local streams could become a popular alternative to building large, expensive water treatment facilities.
The bill, authored by Sen. Fran Pavley (D-Agoura Hills) and recently signed into law, creates a new framework for California cities to deal with storm water issues. Storms carry fast moving water as it races through the streets, picking up trash, oil, and other pollutants and carrying them to the sea.
The bond includes billions of dollars for cleaning up groundwater, recycling and reusing water, improving watershed programs, restoring the L.A. River, and other regional water projects. The bill will allow cities to tap bond funds from the state and use the money for projects that reduce or reuse storm water.
Several months ago we mentioned that Winnipeg was building a water treatment plant that would use ozone to treat their water. Now the start up of that plant is only days away, turning on the taps at a $300-million water-treatment facility.
In the new plant ozone will break down organic chemicals into smaller, more easily destroyed chains. This will improve the look, smell and taste of the water. Fewer organic chemicals in the drinking water means fewer trihalomethanes — potentially carcinogenic compounds created when chlorine comes into contact with organics.
THE WINNIPEG WATER TREATMENT PLANT
Cost: $300 million
Under construction: 2005 to 2009
Capacity: 105 MGD
Benefits: Will reduce summer odor from algae, improve water clarity and reduce the amount of potentially carcinogenic compounds called trihalomethanes, which are created when chlorine comes into contact with organic chemicals
New water-treatment processes: Coagulation and flocculation, dissolved air flotation, ozone water treatment and biologically activated carbon filtration
Existing water-treatment processes: Chlorination and ultraviolet-radiation disinfection
An EPA sponsored study has indicated that sonic energy can enhance ozone effectiveness for disinfection. ozone is already widely used for drinking water treatment applications including disinfection. Currently ozone is produced using the corona discharge method and dissolved into the water either using venturi injectors or fine bubble diffusers. The ozonated water is than sent to a contactor where the ozone can act on the micro organisms.
The sonic technology utilizes a mechanically driven resonator to radiate fluids using high-intensity, low-frequency acoustic energy, was evaluated for its ability to enhance ozone disinfection of drinking water. The device consists of an oscillator coupled to an elastic rod or bar. The oscillator drives the elastic member at a resonant bending mode. The vibrations are then transmitted to the fluid where they can be used to promote mixing and mass transport.
The acoustic radiation was evaluated for its ability to enhance ozone disinfection of drinking water, specifically in the treatment of resistant spore and cyst forming protozoan forms such as Cryptosporidium and Giardia. A surrogate microbe had to be used in place of the protozoans. B. subtilis var niger ATCC 9372 endospores were chosen as a reasonable approximation to the protozoan cysts.
There are two ways in which the acoustic energy could enhance the disinfecting power of ozone:
1. The acoustic waves themselves could damage or otherwise compromise the spores to make them more susceptible to ozone;
2. The mixing and mass transfer effects could give better contact between bubbles and spores, as well as enhance the transfer of ozone from the gas into the liquid.
Experiments were conducted to evaluate the effect of acoustic energy alone, ozone alone, and ozone in combination with acoustic energy on the ability to deactivate the spores for short periods of radiation. (5 minutes).
A 5 log colony forming unit (CFU/mL) was used as a starting population for each test. The contactor was 35 liters in capacity. The tests were conducted in sodium bicarbonate buffered deionized water. Samples were taken as a function of time over the challenge period and quenched with sodium thiosulfate immediately. They were serially diluted and analyzed by standard plate counting techniques, with checking by fluorescence microscopy. The reduction in population was expressed in terms of exposure (ozone concentration times length of exposure).
In tests of one hour duration, the acoustic energy, at both high and low intensity, showed no effect on the viability of spores. The ozone challenges, with and without sonics, were conducted at 0.5, 1,5, and 2 mg/L target dissolved ozone concentrations. The decrease in exposure necessary to reach log 2 population and the 5 minute residual population indicated an enhancement of inactivation, related to increased mass transport.
The sonic contactor discussed here is a mechanically simple technology that enhances the utilization of ozone during liquid contacting which could be incorporated into existing facilities.