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A three-year test of ozone and direct filtration so convinced the Altoona City Authority (ACA) of its merits that the central Pennsylvania water authority is now installing the technology at six new treatment plants and will retrofit another by 1999. According to the study, preconditioning with ozone will enable ACA to meet tough new EPA drinking water standards and eliminate disease-causing microorganisms. At the same time, ACA's plants, ranging in size from 1 million to 7 million gallons per day (mgd), will cut their chemical consumption, eliminate the need for sedimentation tanks and be able to run their filters at higher rates.
"We found that ozone technology and direct filtration enhances water quality at a fraction of the cost of conventional treatment methods," said David Barr, superintendent of water and wastewater treatment of the ACA. "The ozone/direct filtration treatment technology comes just in time, since amendment provisions to the Safe Drinking Water Act require new treatment facilities for each of our reservoirs. Ozone and direct filtration proved very successful in meeting these regulations. The new system also will give us more flexibility in meeting future EPA water quality requirements."
ACA maintains 13 reservoir sources, one well field and over 350 miles of transmission and distribution main piping. The reservoirs are situated hydrologically to form seven separate systems. The ACA pilot research program was part of a $75 million expansion in collaboration with consulting engineers at Gwinn, Dobson & Foreman, Inc.
The main treatment facility for ACA, the Horseshoe Curve Plant, currently uses chemicals to solidify fine particle matter in the water. Sedimentation and filtration remove the fine particles. Chlorine then disinfects the water. The other surface water sources were not treated except for chlorination before distribution to ACA's 80,000 customers.
"Two ozone treatment plants have been operating since the spring of 1994," said James C. Balliet of Gwinn, Dobson & Foreman. "These produce an average of 2.0 mgd at an ozone system operating cost of $10 per million gallons of treated water."
"Chlorine kills bacteria and viruses, but is not as effective as ozone for Giardia and Cryptosporidium cysts," said Keith Carns, director, EPRI Community Environmental Center.
In the ozone process, an electric current is passed through air oxygen, creating an ozone gas. The resulting bubbles destroy bacteria and viruses and inactivate dangerous organisms such as Giardia and Cryptosporidium cysts. Ozone use also greatly reduces the amount of chlorine needed to treat drinking water. The use of chlorine leads to the formation of certain carcinogens such as trihalomethanes and haloacetic acids, by-products of the union between organic matter and chlorine.
"Using ozone produces better water quality," said Barr.
Joseph Raia of GPU Energy said that the cost of producing ozone is 10 percent of the total cost of operating the entire ozone water treatment system. "Most of the energy used is for the air preparation compressor and off-gas thermal destruct system. Should the ACA need to increase ozone production to meet water quality changes, the impact on energy and operating costs would be small," Raia said.
The ACA has even found that ozone systems require less operator attention and less routine maintenance. In the near future, all facilities will be computer-controlled for automatic operation. Each facility will be operated in a batch mode whereby water is produced to fill the finished-water storage tanks. Depending on the system demands, treatment facilities will operate eight to 14 hours per day.
"A computer control system continuously monitors performance parameters such as turbidity, particle counts, pH, chlorine residual and ozone residual to ensure the quality of finished water," said Balliet.