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INDEPENDENT STUDY Performed by Northern Indiana Power Company, Hammond, Indiana Case Study - Ozone Disinfection of a Residential Swimming Pool Summary Ozone is a powerful purification method of cleaning and disinfecting water. It is more powerful than chlorine and other chemical oxidizers. Ozone kills by attacking the outer cell walls of bacteria, virus and algae, destroying them much faster than other known methods. The purpose of this case study was to examine the use of ozone in a residential swimming pool over a full swimming season. Energy use, chemical costs, and operating hours were all monitored. Additionally, subjective factors such as water clarity, odor and maintenance were also scrutinized. The results of the study are very encouraging. Total costs with the ozone unit were 17% lower than traditional chlorine disinfection and 63% lower than Soft Swim/Baquacil disinfection. Additionally, water clarity was excellent and typical chlorine odors were non-existent. Pool maintenance entailed testing the water weekly and adding 3 chlorine tablets every 3 to 4 days. Study Rationale The subject swimming pool is a 20' x 40' in-ground, with vinyl liner and concrete decking. The pool capacity is approximately 24,000 gallons. Filtration is handled by a 1hp Hayward earth unit. Pool temperature is maintained in the upper 80's with a natural gas fired 15,000 BTU heater and with a 12 mil solar blanket. Prior to introducing ozone, water purity was handled for 5 years by Soft Swim. Standard chlorine was used in the pool when new and until the introduction of Soft Swim. Since ozone will not work with Soft Swim/Baquacil products, the pool had to be converted back to a chlorine base before turning the ozone unit on. This process took 2 weeks and an inordinate amount of chemicals. Once the Soft Swim was effectively removed from the water, ozone was introduced and chlorine use was reduced drastically. All cost comparisons are exclusive of the cost to convert from Soft Swim back to chlorine. A recurring white water mold problem that BioGuard was unable to address with the Soft Swim products would have required a conversion anyway. Traditionally, the filter system was operated 12 hours per day during the swimming season. With the application of ozone, filter operation was increased to 24 hours per day. The reasoning for this increase is the relatively short life of ozone requires another residual oxidizer or longer injection run times. We chose to increase the ozone injection times and hold the residual chlorine at lower levels of .4 PPM or less. While a residual of chlorine was maintained, as can be seen by the following cost charts, use of the chemical was reduced in half. Additionally, the strong "chlorine" odor noticed around most swimming pools was completely eliminated. This swimming pool odor is actually chloramines, or the resulting by-product of chlorine oxidation. Ozone converts chloramines back to free chlorine, eliminating total dissolved solids and odors. Ozone was generated by a Prozone PZII-1 unit. It operates at 110 volts and draws 2.42 amps maximum. The unit directly injects ozone into the return line using a small compressor. Similar units may be installed that use a venturi bypass system to "suck" the ozone into the return stream, eliminating the need for a compressor and reducing overall energy usage. Startup of the ozone system occurred on May 14, 1996. The system was turned off on September 7, 1996. Except for 2 weeks during early June, the system was operated 24 hours per day. Total season operating time was 2358 hours. This contrasts with a normal season operating time of 1308 hours using conventional chemical treatments. These operating times are significant because they contribute directly to total disinfection costs. Electric use for ozone generation was metered an totaled 342 kWh. Overall, users of the pool were very pleased with introduction of ozone. It competes with Soft Swim very well on a cost basis and provides clearer, cleaner water than available with either chlorine or Soft Swim. The lack of odor and eye irritation is consistent with what had been traditionally been expected with the Soft Swim/Baquacil products. Season Operating Costs - OZONE Operating costs for the ozone system include chemicals, ozone generation and increased system filtration operation. Actual costs were:
Season Operating Costs - CHLORINE ONLY Operating costs for chlorine disinfection includes chemicals only.
Season Operating Costs - SOFT SWIM Operating costs for Soft Swim disinfection includes chemicals only. The pool has also battled white water mold over the past 3 seasons. The recommended response to control the mold is triple shocking the pool. This has been done once each season.
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