Significance of Use

Turbidity, free and total chlorine, cyanuric acid, pH, iodine, bromine, and low range iron are all critical parameters that can be tested to ensure good water quality in drinking water, wastewater, and water used for pools and spas.

Turbidity is one of the most important parameters used to determine the quality of drinking water. Once considered as a mostly aesthetic characteristic of drinking water, signi˜ficant evidence exists that controlling turbidity is a competent safeguard against pathogens. In natural water, turbidity measurements are taken to gauge general water quality and its compatibility in applications involving aquatic organisms.

Chlorine is one of the most commonly used disinfectants for water treatment. It can be added to in various forms including calcium hypochlorite, sodium hypochlorite, or in some instances, chlorine gas. When added to water, chlorine creates hypochlorous acid (HOCl) which dissociates into hypochlorite ion (OCl-).

HOCl ↔ H+ + OCl-

hypochlorous acid ↔ hydrogen ion + hypochlorite ion

HOCl is the form of chlorine that acts as a stronger disinfectant as compared to OCl-. To ensure the added chlorine is effective at sanitizing, the pH of the water must be taken into account. Around pH 7.5, HOCl and OCl- are present in relatively equal amounts. Below pH 7.5, the equilibrium shifts to favor HOCl; above pH 7.5, the equilibrium shifts to favor OCl-. Depending on the application, addition of chlorine is effective when added to water with a neutral or slightly acidic pH value.

When chlorine is first added to water, it is available as free chlorine. The measurement of free chlorine signifies the amount available for disinfection. Once chlorine begins to sanitize bacteria and pathogens present in the water, it becomes combined chlorine; combined chlorine is no longer available to act as a disinfectant. The measurement of total chlorine signifies the amount of free chlorine and combined chlorine. With both free and total chlorine measurements, a drinking water operator or pool owner can determine if there is enough chlorine available for disinfection.

Cyanuric acid is best known as a stabilizing reagent for chlorine. It is widely applied in swimming pool and spa treatment programs to slow down the decomposition of hypochlorous acid. In outside pool areas, this process is accelerated by the effects of UV rays. When applied properly it can save up to 80% of normal chlorine consumption in pools during peak months.

Bromine is less volatile and more stable than chlorine, making it a good choice as a disinfectant in pools, spas, and hot tubs, and a sanitizing agent in drinking water systems. Like chlorine, excess amounts of bromine in water can be dangerous to health and can cause eye irritation. Daily monitoring of bromine concentration prevents damage to equipment and contributes to the optimization and efficiency of the process while providing for increased user safety.

Iron is naturally present in water in low concentrations, but it reaches high concentrations in wastewater effluents. The iron concentration in water needs to be monitored because it becomes harmful above certain levels. In domestic water, for instance, iron can stain laundry, damage kitchenware, favor the growth of certain bacteria, and unpleasantly alter the taste of water. Iron is also an indicator of ongoing corrosion in water cooling and heating systems. Moreover, iron is normally monitored in mining wastewater to avoid contamination.

Principle of Operation

When measuring turbidity, the light beam that passes through the sample is scattered in all directions. The intensity and pattern of the scattered light is a‰ffected by many variables, such as wavelength of the incident light, particle size and shape, refractive index, and color. The optical system of the HI93102 includes an LED light source and a scattered light detector (90°).

Principle of Operation: Colorimetric Mode

When measuring specific ions in colorimetric mode, a parameter-specific reagent is added to the sample, displaying a color change; the greater the concentration, the deeper the color. The associated color change is then colorimetrically analyzed according to the Beer-Lambert Law. This principle states that light is absorbed by a complementary color, and the emitted radiation is dependent upon concentration. For determination of free and total chlorine, cyanuric acid, pH, iodine, bromine, and low range iron, a narrow band interference filter at 525 nm (green) allows only green light to be detected by the silicon photodetector and omits all other visible light emitted from the light source. As the change in color of the reacted sample increases, absorbance of the specific wavelength of light also increases, while transmittance decreases.