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Authors: S.S. Bjerregaard and P. Fogh. Date: February 2011
Contact: Adept Water Technologies email@example.com
Keywords: drinking water; water disinfection; disinfection by-products; trihalomethane (THM); chemical oxygen demand (COD); chlorination; BacTerminator
BacTerminator is a unit used for disinfection of e.g. drinking water without adding any chemicals to the water. The principle of BacTerminator disinfection is electrolysis, turning salt in the water into hypochloric acid and chlorine, and thereby effectively eliminating bacteria and other microorganisms.
Water disinfection with chlorine is effective for microbial inactivation, but however chlorination of drinking water can form several disinfection by-products (DBPs) when chlorine reacts with organic matter in the water . One of the DBPs that raise concern is trihalomethanes (THMs), including compounds such as chloroform. Several studies have been performed with THMs, investigating their toxicity and carcinogenicity, and it appears that there is a correlation of THM exposure and some types of cancer and, possibly, reproduction problems . Because of the presumed toxicity and carcinogenicity of THMs, the level of permitted in drinking water is restricted in several countries. In the European Union (EU), the maximum THM level permitted in drinking water is generally 100 mg/L. In Norway it is 50 mg/L, and in Denmark it is only 25 mg/L .
Aim of study the scope of this study was to investigate if THMs are formed when disinfecting water with BacTerminator. The correlation between THMs formed and COD during disinfection was also investigated. Disinfection with BacTerminator was compared to regular chlorination in regard to THM formation.
Some of the contents of each tank was used with addition of chlorine for THM determination, and some of the water was run through the BacTerminator unit and samples from the outlet taken for THM determination. Regular chlorination refers to household bleach added to water. These tests were repeated for three different chlorine levels: 0.5 ppm, 1.0 ppm and 2.0 ppm.
Methods, equipment, and reagents for determination of chlorine and THM were obtained from Hach Lange. The standard reference instrument used for colorimetric measurement was the DR2800. Chlorine was determined with the LCK310 cuvettes and THM by the THM Plus method.
Chemical oxygen demand (COD) is a measure of organic matter in water, and COD is correlated with THM formation when chlorine is present. COD was calculated theoretically and measured by the Eurofins laboratory.
Five different tanks were prepared with different amounts of lactose corresponding to COD levels as shown in Table 1. The theoretically calculated values from the oxidation of lactose correlate well with values determined from the Eurofins laboratory.
In general there was no significant difference between the THM level of water disinfected by regular chlorination and water disinfected with BacTerminator. This should however be hold in regard to the fact that BacTerminator is more efficient in eliminating microorganisms, and can thus run with lower chlorine levels then regular chlorination. It should, however, be remembered that the BacTerminator eliminates microorganisms more efficiently, and it can thus run with lower chlorine levels than in regular chlorination. The BacTerminator thus forms less THM than does regular chlorination. There is a significant difference between the amounts of THM formed with 1.0 ppm than with 0.5 ppm chlorine, with about 20 ppm THM formed in water with 1,200 ppm COD (disinfected with 0.5 ppm chlorine), while the same water disinfected with 1.0 ppm chlorine reached a THM level of 50-60 ppm.. There is no visible difference between 1.0 ppm and 2.0 ppm chlorine, which is probably due to the COD level. COD is the limiting factor, thus the THM level will not increase regardless of the chlorine level. If the COD level of the water were higher, the difference between the THM levels at 1.0 and 2.0 ppm would be expected to be greater. BacTerminator's operating window with respect to THM limits was determined by extrapolation of data, and thereby determination of the maximum COD level that BacTerminator can operate at without exceeding the restrictions for THM levels in drinking water (Table 2).
Disinfection of drinking water with BacTerminator leads to formation of THM if there is organic matter in the water. There is no difference in the formation of THM for regular chlorination and BacTerminator disinfection at the same chlorine level, but the efficiency of BacTerminator is higher, so an absolute elimination of microbes is obtained at a lower chlorine level, and hence with a lower level of THM formed.
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