JPH02245637A - Sludge densitometer - Google Patents

Abstract

PURPOSE:To achieve a measurement at a high accuracy up to a high density by converging light from a projecting surface to a focal position of a lens in water to be inspected through the lens. CONSTITUTION:An inspection window 2 is provided on the front of a detector case 1 and an optical fiber 3 for projection and optical fibers 4N and 4F for reception are made coaxial at the tip thereof while the tip faces thereof are made flush. One end of an optical fiber 3R for reference is set jointly at the rear end of the optical fiber 3. A convex lens 6 is arranged at the tip faces of the optical fibers 3, 4N and 4F. Light emitting element 7 is disposed on rear end faces of the optical fibers 3 and 3R while photodetectors 8N and 8F are on rear end faces of the optical fibers 4N and 4F respectively as opposed to each other. Then, light leaving the light emitting element 7 passes through the optical fiber 3, the convex lens 6 and the window 2 to be projected so that it is converged to a focus of the convex lens 6 in water W to be inspected while a part thereof is made to enter the optical fiber 3R. When a suspension (x) exists in the water to be inspected at this position, a scattered light is generated and a part thereof is incident into the optical fibers 4N and 4F via the lens 6.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a sludge concentration meter for measuring the sludge concentration of sewage during sewage treatment, wastewater treatment, etc.

80 Summary of the Invention The present invention uses a scattered light comparison method, in particular, a sludge concentration meter that calculates the ratio between the square of the detection output on the nearer light-receiving surface and the detection output on the farther light-receiving surface. By using a coaxial optical fiber with the light emitting part as the central axis in the light receiving part and installing a lens in front of the tip surface before detection, the light emitting part and the light receiving part can be brought closer together to achieve high concentration. This allows for highly accurate measurement of sludge 6 degrees over a wide range of temperatures.

C8 conventional technology The following treatments are carried out at sewage treatment plants:

(1) Sedimentation and removal of suspended matter in wastewater.

(2) Microorganisms oxidize or assimilate dissolved organic matter in wastewater.

Therefore, during sewage treatment, sludge is generated in proportion to the amount of sludge treated, and agglomerations of microorganisms that decompose dirt,
So-called activated sludge will be used, and it is necessary to understand the concentration of sludge during each treatment process.

In addition, in recent years, there has been a trend toward collective treatment of sludge from each sewage treatment plant at a sludge treatment center for the purpose of reducing treatment costs and preventing a foul-smelling environment. In this case as well, it is necessary to measure the concentration of sludge for purposes such as grasping the amount of solids to be fed and switching valves to distinguish between water and sludge.

There are two types of sludge concentration meters currently in use: ultrasonic type and optical type. The ultrasonic method measures sludge concentration from the attenuation rate of ultrasonic waves due to sludge in wastewater flowing between a pair of ultrasonic transmitters and receivers, and can measure up to a high degree of 10%. Since ultrasonic waves are highly attenuated by air, it is difficult or impossible to measure wastewater containing bubbles.

In such cases, a pressure defoaming method, which is a type of sampling method, is used. This is a method in which a sample of a certain length is taken into a pressurized tank and measured after being pressurized by a diaphragm or piston, and can be measured without causing errors due to air bubbles.

However, this is an intermittent measurement.

However, the measurement target that requires pressurized defoaming is concentrated wastewater that contains many air bubbles, and since the concentration changes significantly each time it is withdrawn from the vortex condensation tank, intermittent measurement is inappropriate. In addition, in the case of sludge that tends to settle, accurate measurement may not be possible because the sludge begins to settle at the point where pressure defoaming is completed.

D1 Problems to be Solved by the Invention On the other hand, optical sludge: a degree meters include transmitted light type, scattered light comparison type, etc. Its advantage is that it is relatively unaffected by fine bubbles, and its disadvantage is that it is difficult to measure high concentrations.

First, in the case of the transmitted light method, the Lambert-Beer law is applied to its measurement principle.

Now, as shown in Figure 4, liquid tank 4! A test water 43 containing floating matter 42 is put in the water, and the intensity is measured from the light source 44! . When a luminous flux of decreases to

This transmitted light intensity I is expressed by the following equation.

1-1oaxp(-Kl-a-s)...-cx)
However, K is a constant, Q is the width of the liquid tank, and S is the sludge concentration.

Therefore, if we take the logarithm of equation (1) and transform it, we get
The sludge concentration S is determined.

By the way, the transmitted light intensity in equation (1)! The relationship between S and concentration S is illustrated in Figure 5, and as the concentration S of sludge increases, the permeation intensity! decreases exponentially.

For this reason, a sufficient amount of light cannot be obtained on the high concentration side, and when a measurement system is configured, the signal is buried in the dark current of the light receiving element, amplifier drift, offset change, or noise, making measurement impossible. The upper limit of the measurement range using this measurement principle depends on the width of the liquid tank, but is generally 5000xy/
It is said to be around 12. Furthermore, since colored soluble components reduce transmitted light according to Beer-Lambert's law, there is a problem that the error becomes large in sludge from dyeing wastewater treatment.

In FIG. 4, 45 is a light receiving element that detects transmitted light, and 46 is an amplification/output section.

Next, when using scattered light, unlike the transmitted light described above, the characteristics related to the degree of scattered light intensity are not monotonically decreasing (or increasing) functions, so a pair of emitter and receiver can be used over a wide range. Since it is not possible to measure the concentration range, a scattered light comparison method is generally sought in which scattered light is received at two points, near and far, and compared.

The measurement principle is as follows.

That is, as shown in FIG.
! ; [Two light receiving elements 62N at different distances from 61,
62P, each light receiving element 62N
.

Amplifiers 1Q3N and 63F are connected to 62P and i;, and their outputs are given to the calculation/output section 64.

Now, when light is incident from the light source 61 through the detection window 65 into the test water 67 containing sludge particles 66, scattering occurs by the sludge particles 66, and the light is scattered by the light receiving element 62N.

Scattered light having intensities shown by equations (3) and (4) are received by 62F, respectively.

III! α*5eexp(-βm-5) ・”(3)
! −・−α・S −axp(−β −・・
(4) where, IN: Scattered light intensity at a position near the light source I2: Scattered light intensity at a position far from the light source α: Constants related to light source intensity βN, βF: Between the light source and the light receiving element Constant S related to the distance between and the color of sludge: sludge concentration Therefore, when formula (3) is divided by formula (4) and the logarithm is taken, = (βr - β tone) S ... (5),
Output proportional to concentration can be obtained. However, in the actual measurement system! Considering that the value of r is a relatively small value over the entire concentration range, a constant term remains in equation (5) in order to make the relative amplification factor larger than the output nearer on the circuit. For this reason, it generally becomes a linear equation that does not pass through the origin, and requires zero correction in a subsequent amplifier.

By the way, when equations (3) and (4) are illustrated, they become xlQ in FIG. 7. As can be seen from each formula and figure, when the concentration S becomes large, these values decrease exponentially, so as mentioned in the transmitted light formula, they are no longer extracted as meaningful signals, making it difficult to measure high concentrations. become unable to do so.

Generally, it is said that the limit is about 500019/(l).

Therefore, in order to measure high concentrations, each light-receiving element must be moved closer to the light source so that it has the characteristics shown by the dotted line in Figure 7, or only the farthest light-receiving element must be brought closer to the light source.
I'm the solid line characteristic,! ? shall be the characteristic of the dotted line.

However, in the former case, when the zero-order approximations of equations (3) and (4) are taken, both become linear equations that pass through the origin for the density S. Each of these single characteristics is the principle of a scattered light turbidity meter, and depending on how it is used, it can measure up to 2 to 3000 my/(l).In other words, these scattered light characteristics vary with respect to the concentration on the low concentration side. This indicates that the value changes approximately linearly.This means that the calculation on the left side of equation (5) becomes a constant, which means that it does not follow the sludge concentration at all even in this region.

On the other hand, the same can be said for the latter case. In addition, since the parameters are almost functionally similar, f s/I
F becomes a constant value, and low concentration measurements cannot be made.

Even with the scattered light comparison method, it is impossible to create an instrument that can continuously measure from low to high concentrations. In addition, as can be said about the 9-type in general, there is absorption by the colored solution before the light flux reaches the scatterer and after that until it reaches the light-receiving element, and even in the scattered light comparison formula, the future effect is significant. This will result in an error. Furthermore, since a tungsten bulb is used as a light source, it can only emit DC light, so it is affected by external light, which also causes errors. Moreover, this emission spectrum ranges from blue to red and even infrared, and completely overlaps with the absorption band of chlorophyll, so algae may grow on the emission surface, causing errors.

As described above, measurement targets that contain microbubbles and have large concentration fluctuations tend to be unmeasurable, regardless of whether the method is an ultrasonic method or an optical method.

In order to solve the problem described by Moe, the inventors of the present invention
A new calculation method disclosed in No. 45588 was proposed. This method uses the old In and IF, and performs an operation of squaring 011 and dividing by the latter. That is, the following equation is calculated.

=α・5−exp((βF23m)・S)...(7) Here, if the positions of the two light receiving elements are set appropriately,
(βr−2β阿)−〇, and in the end, equation (7) becomes. Therefore, the concentration can be measured without being affected by the color of the sludge. On the other hand, since the term α remains, fluctuations in light source intensity have a first-order effect;
This can be easily corrected as disclosed in No. 436. In Utility Application No. 55-436, the light source is driven by alternating current, and only alternating current scattered light is extracted as a signal component, so
Not affected by external light. In addition, with this calculation method, even if the intensity of each scattered light changes linearly with the concentration in the low concentration region, the v1'n result is = (linear equation passing through point R) (9),
As the scattered light characteristics, the characteristics shown by the dotted line in FIG. 7 can be adopted.

Therefore, there is a sufficient signal level even in high concentration measurements, and it is possible to measure over a wide concentration range with one instrument.

By the way, the device disclosed in Special IJFJ No. 53-45588 has a structure in which the light-receiving element and the light-emitting element are attached directly to the detection surface, so the space between each element cannot be reduced to less than its physical size. However, there are limits to high concentration measurements. Its limit is 20000-30000n/(l).

In order to overcome this limitation due to the size restriction of the detection surface, it has been proposed to use an optical fiber as the detection surface, and examples of its structure are shown in FIGS. 8 and 9. In the figure, 81 is a detector main body, which also serves as a guide for fixing the optical fiber. 82 is an optical fiber for light emission (light projection), 83N and 83F are optical fibers for light reception, and 84 is a spacer.

Each of the optical fibers is coaxial with the light emitting optical fiber 82 as its central axis, and its tip surfaces are on the same plane. For example, the dimensions are as follows.

The normal fMA of the light-emitting optical fiber 82 is 2 um, and it is better to place the closer light-receiving optical fiber 83N as close to the light source as possible, so the inner diameter is set to α of the light-emitting optical fiber 82.
Same as 1 <2RR1 The outer diameter B is 2.9 square meters. Using these two as initial values, the farthest light receiving optical fiber 8
The optimum value for the position of 3F was determined. This light receiving optical fiber 83■? The outer diameter is 4.1 Im, and the inner aC is 3.5u.
Met. The light emitting area and both light receiving areas were made to be approximately equal.

If the light-receiving optical fiber 83F is positioned inside this range, the output tends to be saturated at high concentrations, as shown in the characteristic ■ in Figure 1O.On the other hand, if it is placed outside, the output tends to be saturated at high concentrations, as shown in the characteristic ■. Since there is a tendency for an abnormal increase, linearity can be maintained up to a high concentration at the above position as shown in characteristic (3).

The condition is that Equation (8) holds true, but if a preemption for detection is obtained, it is necessary for high concentration measurement to bring the light source and the light receiving part (especially the nearby light receiving part) closer together. It is.

However, the shape and size (dimensions A-D) of the detection surface using the optical fiber described above are the dimensions necessary to obtain the light emitted m1 and the received light m required for measurement with the bundle fiber used. Therefore, this shape of bundle fiber (
When a diameter of about 300 μm is used, the measurement limit is, for example, 5 to 6% in concentrated sewage. The distance between the light source and the closer light receiving section is determined by the core diameter of the adjacent optical fiber.

An object of the present invention is to provide a sludge concentration meter that can measure high concentrations with high accuracy.

96 Means for Solving the Problems The present invention has a method for converting light emitted from a light source and scattered by contaminants in sample water to a constant β9. β is received by two light-receiving surfaces whose positions are selected so that 2β, = β, and the ratio of the square of the detection output on the nearer light-receiving surface to the detection output on the farther light-receiving surface is calculated. In a scattered light comparison type sludge densitometer, the light emitting optical fiber whose tip end is the light emitting surface is set as the central axis, and the light receiving optical fiber is attached to the light emitting surface. A light emitting/receiving section is arranged so that two concentric light receiving surfaces are formed around the periphery, and a lens is placed in front of this tip so that the light emitting section and the light receiving section are substantially brought closer together by its optical action. It is characterized by the fact that

The light emitted from the F1 action light projecting section passes through the lens and is projected into the sample water so as to be focused at the lens focal position within the sample sample. If there is a suspended object in the sample water, it causes scattering, and a portion of the scattered light passes through the lens and enters the light receiving surface, travels through the optical fiber, and is detected by the light receiving element. After this, a predetermined calculation is performed using both light reception signals, and the sludge concentration is calculated.

G. Examples Hereinafter, the present invention will be explained in detail based on examples shown in the drawings.

FIGS. 1 and 2 show one embodiment of the present invention.
is a detector case, 2 is a detection window (glass window) provided on the front of this case r, 3 is an optical fiber for light emission (light projection), 4 is
N and 4F are optical fibers for receiving light, and 5 is a spacer. Each optical fiber has at least its distal end portion coaxially shaped as in the case of FIGS. 8 and 9 described above, and its distal end surface is on the same plane. Further, one end of a reference optical fiber 3R is provided at the rear end of the light projecting optical fiber 3.

Reference numeral 6 denotes a convex lens disposed in front of the tip end face of each optical fiber, and has a focal length f such that its focal point is located outside the glass window 2. That is, the focal point is at a distance from the outer surface of the glass window 2 with a thickness of about 100 mm.

Reference numeral 7 denotes a light emitting element (for example, an infrared light emitting diode) arranged to face the rear end surfaces of the Moeki light projecting optical fiber 3 and the reference optical fiber 31, and 8N and 8F oppose the rear end surfaces of the light receiving optical fibers 4N and 4F. 8R is a light receiving element arranged to face the tip of the reference optical fiber 3R, 9N, 9r' and 9 are arranged as shown in FIG.
R is a preamplifier connected to the light receiving elements 8N, 8F, and 8R, IO is a light emitting diode drive circuit, and 11 is a reference value for controlling the self-powered current value of this drive circuit 10, using the output of the preamplifier 9R. Comparator, to compare! 2 is an arithmetic circuit that receives the outputs of the preamplifiers 9N and 9F and performs a predetermined arithmetic operation, and 13 is an output circuit that sends the arithmetic result of the tO1 calculation circuit I2 to the outside as a sludge concentration.

Note that when the light emitting element 7 is caused to emit light in an alternating current manner, the preamplifier 9N is used. An active filter or the like is installed on the 9th floor to extract only the light source emission frequency component, and then performs full-wave or half-wave rectification to remove the influence of relatively low-frequency external light from sunlight, fluorescent lamps, etc.

Next, the operation will be described. The light emitted from the light emitting diode 7 is projected into the sample water W through the light projecting optical fiber 3, the convex lens, etc., and the glass window 2, and a portion of the light is incident on the reference optical fiber 31. In this case, the light is projected into the sample water so as to be focused at its focal point by the action of the convex lens 6. This focal point position is located a little distance ah into the test water from the glass window 2. Therefore, if there is suspended matter X in the sample water at this position, scattered light will occur. A part of this scattered light passes through the glass window 2, passes through the convex lens 6, and passes through the light receiving optical fibers 4N, 41? incident on .

That is, even if the dimensions of the detection surface formed by the optical fiber are as large as necessary for measurement, the provision of the convex lens 6 substantially shortens the distance between the light source and the light receiving section.

The scattered light passes through optical fibers 4N and 4F to light receiving element 8N.
, 8F, and a part of the emitted light passes through the optical fiber 311 and reaches the light receiving element 8R. The signals are then exchanged into electrical signals by each light receiving element and amplified by preamplifiers 9N, 9F and 9R. Amplifier 9N.

The output of 9F is applied to the arithmetic circuit 12, where a predetermined arithmetic operation is performed. This result is output from the output circuit 13 as the sludge concentration.

On the other hand, the output of the amplifier 73911 is compared with a reference value by the comparator 11. Based on this comparison result, the output current of the light emitting diode drive circuit IO is controlled.

In addition, in the above embodiment, the convex lens 6 was placed inside the glass window 2, but as shown in FIGS. 3(a) and 3(b).

As shown in (C), the lens and the glass window may also be used. Figure 3(a) shows the case where a plano-convex lens 6A is used and its flat side is placed in contact with the sample water, Figure 3(b) shows the case where a spherical lens 6B is used, and Figure 3(c) shows the refractive index. This is a case where a distributed type lens 6C is used.

! -■1 Effects of the invention As described above, according to the present invention, an optical fiber is used in the portion of the detection section that becomes the light emitting surface and the scattered light receiving surface, and the lens is placed in front of the tip surface of the optical fiber. The light receiving position can be moved closer to the light source, and the detection signal can be extracted in a range where the signal level is almost unaffected by the drift of the amplifier, etc., and the sludge concentration can be detected over a wide range of sludge concentrations with high precision. becomes measurable. Furthermore, since the detection surface can be of the same size as before, it has the advantage that processing of the optical fiber is easy.

[Brief explanation of drawings]

Fig. 1 is a configuration explanatory diagram showing an embodiment of the sludge concentration meter according to the present invention, Fig. 2 is a sectional view showing the structure of the detection section of the same embodiment, and Figs. 3 (a) to (c) are respectively A cross-sectional view showing a modified example of the detection unit, Fig. 4 is a configuration explanatory diagram that does not show the basic configuration of the transmitted light type sludge densitometer, and Fig. 5 shows the relationship between the sludge concentration S and the transmitted light intensity ■ of the transmitted light type densitometer. FIG. 6 is a configuration explanatory diagram showing the basic configuration of a scattered light comparison type densitometer, and FIG. 7 shows sludge a degree S and scattered light intensity IN, I of a conventional scattered light comparison type densitometer.
A characteristic diagram showing the relationship with P, Fig. 8 is a cross-sectional view showing an example of the structure of the tip of the detection section using an optical fiber, Fig. 9 is a bottom view of the same, and Fig. 10 is a scattering diagram using an optical fiber for the detection section. It is a characteristic diagram showing the relationship between the analysis value and the output value (N″/F) of the optical comparison type densitometer. I...Detector case, 2...Detection window (glass window),
3... Optical fiber for light emission, 3R... Optical fiber for reference, 4 N, 4 F... Optical fiber for light reception,
5... Spacer, 6... Convex lens, 7... Light emitting element, 8N. 8F, 811... Light receiving element, 9N, 9F, 9R...
Preamplifier, 10... Light emitting diode drive circuit, 11
...Comparator, 12...Arithmetic circuit, 13...Output horn circuit, W...Water test, X...Suspended matter. Figure 2 Refined Grain 0 Battle V Length t ω Co Figure 3 Oo Outer Location r) Mugi Evil Threat Lt Howa Chu De Concave Figure 4 No. Figure StI's 4 and force \ skin - pIj mouth 10th figure phantom "ito's vertical 5 in 13 ÷ 1 stop bufu i 1 in 20a MM ri Y (kinibutiku Wonof￥2.s Toni1;
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Claims (1)

[Claims] (1) The light emitted from the light source and scattered by the contaminants in the sample water is divided into two light sources whose distances to the light source are different and whose positions are selected so that the constants β_N and β_F determined by the distances are 2β_N = β_F. In a scattered light comparison type sludge concentration meter, the sludge concentration is calculated by calculating the ratio of the square of the detected output on the nearer light-receiving surface and the detection output on the farthest light-receiving surface. A light-emitting optical fiber whose tip end surface is a light-emitting surface is used as a central axis, and light-receiving optical fibers are arranged around the light-emitting surface so that two concentric light-receiving surfaces are formed. 1. A sludge concentration meter comprising a light receiving section, and a lens is disposed in front of the tip surface so that the light emitting section and the light receiving section are substantially brought closer together by its optical action.