The Cascada BIO- and AN-water Systems incorporate a Total Organic Carbon (TOC) display in the range 0 to 300 ppb. This provides a measure of organic contamination remaining in the product water and enables users to check that the Cascada Lab Water System is performing satisfactorily and consistently.

Figure 1
TOC Monitor Principle of Operation

Pre-purified water enters the Cascada Lab Water System and passes through the first purification pack, which removes ionic impurities and some organic compounds. The resistivity is then measured at the intermediate water quality sensor (R1). The water passes through a UV lamp chamber where it is exposed to radiation at wavelengths of 185 nm and 254 nm. Absorption of 185 nm radiation results in photo splitting of water to form hydroxyl radicals.

OH radicals are highly effective oxidizing agents, oxidizing virtually all organic compounds. Oxidation produces carboxylic acids and eventually carbon dioxide (carbonic acid). These products have higher conductivity than the original components in the water (all conducting species were removed in the first purification pack). This change in conductivity is detected and measured by the post-UV water quality sensor (R2). The conductivity difference between R2 and R1 is used to calculate the TOC present in the water after the purification. The higher the concentration of TOC, the greater the difference between R1 and R2. Any ionized compounds produced by the UV are removed by the second purification pack.

The monitor was calibrated by challenging it with a range of compounds potentially present in purified water. This data was used to set up the software. The Cascada Lab Water System was then used to purify tanks of organically contaminated water and the readings on the TOC monitor logged along with those from two TOC analyzers - Anatel A100-SE and Sievers 820. Tests were carried out under a wide range of operating conditions. Examples are shown above.