Optical water quality sensor

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March 2002 Sensors & Transducers

Reverse osmosis processes are used to purify water in a variety of industries. It allows water to be recycled, thereby reducing costs associated with water purchases and environmental loading. In the reverse osmosis process, water flows through membrane filters. The final result is clear water that contains no salts, sugars, proteins or other larger solids.

This method has been applied in an eco project in a Finnish dairy. The project's goal is to reduce purchased raw water use by 30% in first phase and 70% in the second phase.

OPTEC-F analysers, which are online optical sensors, were selected as the best to control and monitor the reverse osmosis equipment. The optical sensor determines the quantity of solids in the rinse water before the membrane filters. If the concentration of solids gets too high OPTEC-F opens a valve and dilutes the rinse water to a level suitable for the filters.

An OPTEC-F sensor also monitors and controls the permeate that comes from the filter. The clear water then flows through disinfection units to the collection tanks.

"The optical measurement is excellent because there are no particles or conductive materials in such pure water," said Jarmo Juurinen, environmental engineer at the dairy, "the quality of water cannot be measured with pH or conductivity meters." Only the purest water is reused for different purposes at the plant, the sensor directs water having slightest trace if impurity into the sewer.

In another area the sensors are used to monitor the quality of raw water that is passed through the heat exchangers in a pasteuriser to collection tanks. The water flows directly to the water tanks and from there to normal use at the plant. The OPTEC-F detects and directs any contaminated water to the sewer and alerts the operator that a leak has occurred in the heat exchanger.

Seppo Floman, instrument technician at the dairy, is impressed with the sensitivity of the sensor: "OPTEC-F is very sensitive to even slightest changes in water purity - a drop of something and the sensor value changes instantly." OPTEC-F makes use of a light-scattering and absorption technique. It is used to monitor the concentration of a wide variety of liquids in the food, beverage, chemical, mineral and mining industries.

Herbert Karolius

Atlas Industrial Systems

016 986 2140

[email protected]

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