What Is a Fluorometer?
Fluorometer is an instrument used to measure the transparency of water flowing through rivers, lakes, marshes, and sewage systems.
A sample is placed in a cylindrical glass container with a mark (marker plate) at the bottom, and the transparency is measured by the amount of water when the marker plate is visible. If the water transparency is high, the marker plate at the bottom can be seen even if the amount of water is high, but if the sample is not so small that it is turbid, the marker plate cannot be seen.
The amount of water is drained from the container until the sign plate is visible, and the amount of water at which the sign plate is clearly visible is read from the scale on the container.
Uses of Fluorometers
Fluorometers are primarily used to measure the clarity of colored water. They measure sewage, rainwater, swimming pools, river water, lake water, and seawater. It is also useful in determining whether industrial wastewater meets standards and in determining the amount of suspended solids in the water.
When a sample contains a large amount of suspended solids, care must be taken because suspended solids may settle to the bottom and cover the bottom markings, which may interfere with the measurement. Also, transparency varies depending on the ambient brightness at the time of measurement. As a general rule, measurements should be taken in daylight.
Principle of Fluorometers
The principle of transparency is to determine the thickness of water by varying the thickness of the water to be measured, so that the double crosses on the sign board can be recognized. By changing the amount of water in the colorimeter, the thickness of the water between the tester’s eyes and the sign board is changed.
The brightness of the environment is important to correctly identify the double-cross on the marker plate. When evaluating water clarity with a Fluorometer, the ambient illumination should be maintained at 1,000 ± 500 lx. This brightness is the same as that of a window with no direct sunlight during a blue day.
Fluorometer Construction
The Fluorometer consists of a Colorimeter, a stand, an outlet, and a sign board.
1. Colorimeter Tube
The container in which the sample is placed is called the colorimeter tube. Colorimeter tubes are available in 30 cm, 50 cm, and 1 m lengths, but the 30 cm tube is the most common.
2. Stand
The stand is equipped with a colorimeter tube, sign board, etc., and has a handle. The bottom of the stand serves as a weight, making it difficult to tip over and allowing water to be collected as it is.
Of course, it is also possible to collect water in a bucket and pour it out, but it is important to pour it out without bubbles.
3. Outlet
A rubber tube with a pinch cock or a siphon type can be used to gradually reduce the amount of water in the color comparison tube.
4. Sign Board
The sign board is a printed double-cross. If the water to be measured is turbid, the double-crosses on the signboard are dimly visible, but as the amount of water is reduced little by little, the double-crosses become visible.
At the amount of water where this sign is clearly visible, stop discharging water from the outlet and read the scale for the height of the water.
Other Information on Fluorometers
1. Digital Fluorometer
The most basic method of measuring fluorometers is by visual evaluation using a sign board, but digital fluorometers are also available. Digital Fluorometers are used in facilities such as water purification plants, water supply and sewage treatment plants, agricultural wastewater treatment plants, and industrial wastewater treatment plants.
Since there is a certain relationship between turbidity and SS and transmissivity, it is possible to estimate turbidity and SS in an applied manner by measuring transmissivity. A handy probe type is also available, in which the detection unit is simply immersed in the sample water for measurement. The most common types use the transmitted light absorption spectrophotometry.
It is important to note that when comparing the results of visual Fluorometers and Digital Fluorometers on an unspecified number of samples, the measurements may not agree. This is due to the influence of the turbidity and hue of the sample water. On the other hand, the digital type has the advantage that there is little variation among the measurers. The disadvantage is that Digital Fluorometers are more expensive than visual Fluorometers.
2. The Standard for Measuring Transparency
The purpose of measuring transparency varies widely from situation to situation. Examples include the evaluation of river water quality, agricultural and industrial wastewater discharged from livestock farms, etc. The Water Pollution Control Law establishes standards for measuring the transparency of wastewater for the purpose of measurement.
When testing wastewater from factories, the Japanese Industrial Standard (JIS-K0102) standardizes the use of a Fluorometer with a height of 30 cm. The permeability is not applicable to drinking water.
Fluorometers with a height of 30 cm are used to evaluate the degree of fluorometer reading from 1 to 30 degrees. If the transparency is 30 degrees or higher, it can be judged so that there is no abnormality in the factory wastewater at the site level.
However, the standards and values that must be met vary depending on the situation, and items other than transparency must also be met. For river water, the height of the Fluorometer used depends on the situation.