1. Field of the Invention
The present invention relates to a method for measuring the turbidity of a liquid media. More particularly, it relates to a turbidimetric method and apparatus which are suitable for determining the concentration of a suspended substance in activated sludge or pulp waste, or the concentration of microorganisms in a fermented solution or waste of fermentation.
2. Discussion of the Background
Various methods exist for measuring the turbidity (concentration) of a liquid media. These methods are based on ultrasounds, radioactive materials, or light. Methods based on light are classified into (1) methods which use transmitted light or (2) methods which use scattered light. With either of the light-based methods, the presence of bubbles in the liquid media greatly limits measurement accuracy. As a matter of fact, no method currently exists for the on-line determination of the concentration of microorganisms in a fermentation process.
A variety of methods have been proposed for removing bubbles. Some of these are:
(1) Adding an antifoaming agent to the liquid to be analyzed;
(2) Applying pressure to the liquid in a sampler;
(3) Using a bubble removal net;
(4) Using a sampler having an inner tube and an outer tube and causing a liquid to flow up the inner tube and down the outer tube so that bubbles rising in the outer tube may be separated from the liquid; or
(5) Drawing a liquid into a sampler by a piston and leaving the liquid at rest so that bubbles rising in the sampler may be discharged through its liquid inlet.
The conventional methods as hereinabove described, however, suffer from the following problems.
(a) All of these methods suffer from measurement inaccuracy due to the presence of bubbles;
(b) The optical systems used are easily contaminated, resulting in measurement inaccuracy; and
(c) Turbidimeters are complicated in construction and easily stained, resulting in contamination by varied germs, especially in fermentations and other cultivations media.
Thus, there is a strongly felt need for a method for accurately measuring the turbidity of liquid media and/or fermentation media, wherein the method does not suffer from the drawbacks outlined above: measurement inaccuracy due to the presence of bubbles in the media or optical system contamination; or media contamination due to turbidimeter design. Likewise, there is a strong need for a method and apparatus for efficiently, quickly and accurately measuring liquid media.