Several hundred people from many countries attended at the Hotel Vancouver. About 40 technical papers were presented and we had a tour of the
Vancouver Aquarium
which uses filtration and ozone to purify the water.
The first ozone system for municipal water supply was built in 1906 in Nice,France.
About 3000 systems are used world wide today.
The use of ozone to treat drinking water in the United States of America has been encouraged by the Evironmental Protection Agency (EPA) regulations.Over 250 U.S. municipal water utilities, serving over 10,000 persons,and about 140 small water plants, currently use Ozone.
The Safe Water drinking act of 1973.
The four Trihalomethanes (THM) chloroform, chlorodibromomethane, bromodichloromethane, and bromoform, have a total
maximum contaminant limit (MCL) of 0.010 milligrams per liter (mg/L)for large utilities (over 10,000 persons).
The safe drinking act amendments of 1986:
The surface water treatment rule, 1987:
Systems serving greater than 10,000 persons required to have primary disinfection of three microorganisms present in surface waters,
Giardia lamblia cysts, enteric viruses, and Legionella bacteria.
Primary meaning in the treatment plant, secondary refers to treated watersin distribution systems.
The CT value was defined
C is the concentration of the disinfectant in milligrams/ Liter (mg/L)T is time in minutes, that the disinfectant is in contact with the water.Table 1 shows CT values to attain 99.9% (3 log) inactivation of Giardia cysts.
The Bromate Ion issue:
Japanese researchers reported that bromate ion is capable of causing kidney carcinomas in rats.
Bromate ion is formed by the oxidation, by ozone, of bromide ion, which is present in the majority of raw waters.
EPA added bromate ion to its list of disinfection byproducts proposed for regulation, MCL 10 micrograms/liter.
Three approaches to minimize formation of bromate ion are:
- conduct ozonation at pH 6.5 or below.
- Add ammonia to water before ozonation.
- Conduct ozonation with minimal levels of dissolved ozone in the water.
For small water treatment systems, an anion pretreatment to remove bromide ion would appear effective in minimizing bromate ion to formduring ozonation.
Cripto
Cryptosporidium parvum, a microorganism cyst, if injested, makes healthy people sick, and can kill people who are immunocompromised.
Milwaukee, Wisconsin had an outbreak in early 1990s.
Filtration to 1 micron can remove many of the organisms, chlorine and chloramine have little effect, ozone and chlorine dioxide are effective for chemical inactivation of C. parvum.
About 3 to 6 times as much ozone is required for cripto as for Giardia.
Gorden Finch, Phd, University of Alberta, Canada is leading a research effort to provide data on Cripto inactivation.
Biologically active filter media:
It is desirable to use a bio-filter after ozonation if the treated water contains organic matter.Ozone is used in water for disinfection and oxidation of organic matter, which produces biodegradable organic matter, which can be removed by biological filtration. Bacteria and other microorganisms colonize sites on the filter media and use for organic matter for growth.
