On-line Instrumentation 2010 - WTW - #19

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For information visit www.WTW.com for a customer care center near you or inside US: call WTW 800 645 5999. N e u t r a l i z a t i o n / P r e c i p i t a t i o n / D e t o x i f i c a t i o n Both in water and wastewater treatment and also in industrial processes pH is of great practical importance. The acidity or alkalinity of a process medium plays a key role in many chemical or biological reactions as well as in mechanical/ physical actions. A number of reactions – in precipitation and detoxification, for example – may only take place if the pH condition is properly controlled. A “misadjusted” pH can cause a variety of serious effects, of which corrosion is the most common. Therefore, at a low or high pH neutralization treatment often is required. In the area of municipal and industrial wastewater treatment extreme pH conditions may result in the following harmful effects: • Microorganisms in biological purification processes are sensitive to acidic and alkaline conditions. Therefore, the pH of the sewage is supposed to be in the neutral range of pH 7. At pH levels of less than 5 or larger than 10 the activity of the bacteria practically ceases. • pH values of 6.5 and lower result in gradual destruction of metallic materials and mechanical components, and even in damage of the sewer network. • The solubility of many substances varies with the pH level and temperature. Undesirable and obstructive precipitation of solids may be the result. Today’s legislative regulations and environmetal directives in many countries already require that trade effluents may only be discharged into municipal sewer systems if the pH is between 6.5 and 8.5. For this reason, industrial dischargers, for instance, breweries and dairies, often have to pretreat its effluent in a neutralization plant. pH Control System Neutralization, precipitation and detoxification not only require continuous pH measurement but also an efficient pH control system. In less demanding applications, such as stable processes with slowly changing conditions, a simplified 2-point logic control may be adequate. In many cases, however, a proportional control loop is considerably more efficient and also economical with regard to dosing of flocculants or neutralization chemicals. pH measuring t e c h n o l o g y b y WTW WTW`s complete line of pH/ORP instrumentation comprises sensor assemblies, monitors and system components for a wide range of applications. In addition to the well proven SensoLyt® sensor assemblies, which are widely used in wastewater facilities, the product line includes ruggedized sensor assemblies for in-line measurements in industrial processes. The proven monitors of the 170 and 296 series have a PIF control algorithm. A special measuring transducer as well as sensors and accessories are available for use in explosionproof areas (see brochure “Product Details”). The IQ Sensor Net and the IQ sensors open up a whole new realm of technology with features such as an immense degree of flexibility and “sensors which can be pre-calibrated in the laboratory”. 18