Device for detecting algae concentration using first derivative of visible light absorbance

Abstract

Monitoring and detection of algae in surface water and wastewater is of significant importance, yet there is currently no quick and simple method to achieve this. The present work illustrates a new method to determine the concentration of algae in water and wastewater samples using spectrophotometry, the first derivative of absorbance, and a smoothing technique applied to the first derivative of absorbance (e.g. Savitzky-Golay). The relationship between algal concentration and absorbance for three types of water samples (distilled, surface, and wastewater) was determined in the visible wavelength range, and the effect of using the first derivative of absorbance method on improving algal concentration detection limit was established. Using the first derivative of absorbance method improves algal detection limits, reduces the effect of background absorbance and the resolution of overlapping spectra. The presence of algae in water can cause a number of problems, and the method presented here can be used to effectively monitor algal concentration in various types of water samples and provide necessary information for decision making purposes.

Claims

1. A device for detecting algae in water, comprising: (i) a light source to generate light beams of electromagnetic radiation in the visible light spectrum; (ii) a flow cell containing a water sample including windows to allow said light beams to transmit through said flow cell and water sample; (iii) a spectrometer unit that receives said transmitted light beams penetrating said sample in said flow cell, and resolves said incident light beams into a specific visible absorbance spectrum pertaining to said sample; (iv) a processor connected to said spectrometer unit programmed to: a. compute the derivative of the visible absorbance spectrum through said flow cell; b. compute from the derivative spectra the concentration of varying types of algae.

2. A device for detecting algae according to claim 1 wherein said device can be operated to measure the concentration of algae in distilled water, surface water, or wastewater.

3. A device for detecting algae according to claim 1 wherein said processor is programmed to apply a smoothing technique to improve the signal to noise ratio in the visible absorbance spectrum.

4. A device for detecting algae according to claim 3 wherein said smoothing technique is a Savitzky-Golay smoothing technique.

5. A device for detecting algae according to claim 1 wherein samples can be directly placed into said spectrometer unit for analysis with no additional sample preparation requirements.

6. A device for detecting algae according to claim 1 wherein said light source is a tungsten lamp.

7. A device for detecting algae according to claim 1 wherein said light source is an LED based light source.

8. A device for detecting algae according to claim 1 wherein said spectrometer unit is a photodiode array based spectrometer.

9. A device for detecting algae according to claim 1 wherein said spectrometer unit is a monochromator.

10. A device for detecting algae according to claim 1 wherein said device could be immersed in a sample water such that the sample water is free to flow in and out of a substantially open flow cell area.

11. A device for detecting algae according to claim 1 wherein said flow cell allows sample water to flow through either continuously or in successive batches from a sample source to a sample drain.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments will now be described, by way of example only, with reference to the drawings, in which:

(2) FIG. 1 shows the preferred embodiment of the invention, and describes its apparatus.

(3) FIG. 2 shows the absorbance scans of various concentrations of Microcystis aeruginosa CPCC 299 in deionized water.

(4) FIG. 3 shows the Savitzky-Golay first derivative of the absorbance scans of various concentrations of Microcystis aeruginosa CPCC 299 in deionized water.

DETAILED DESCRIPTION

(5) Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. The Figures are not to scale. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.

(6) As used herein, the terms, comprises and comprising are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms, comprises and comprising and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.

(7) As used herein, the term exemplary means serving as an example, instance, or illustration, and should not be construed as preferred or advantageous over other configurations disclosed herein.

(8) As used herein, the terms about and approximately are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. In one non-limiting example, the terms about and approximately mean plus or minus 10 percent or less.

(9) Unless defined otherwise, all technical and scientific terms used herein are intended to have the same meaning as commonly understood to one of ordinary skill in the art.

(10) An embodiment of the invention includes the apparatus described by FIG. 1. A light source (1) provides light of the required wavelengths for detection of the various algae species to be detected in water, generally in the red light region of the visible spectrum. In the preferred embodiment the light source (1) is a broadband light source in the visible light spectrum, where the broadband light source could be a tungsten lamp, or an LED based light source. A light beam (2) from the light source transmits through a flow cell (4) containing the water sample under test (5) to a spectrometer unit (3). The flow cell allows sample water to flow through either continuously or in successive batches. In the preferred embodiment the sample water flows from a sample source (6) to a sample drain (7) continuously. The flow cell (4) contains windows (9) to allow the light to transmit through the flow cell. Note that in another embodiment the system could be immersed in a sample fluid such that the sample water is free to flow in and out of a substantially open flow cell area. The spectrometer unit (3) resolves the incident light into a specific absorbance spectrum of the water sample under test (5) as shown in FIG. 2. A computer system (8) connected to the spectrometer unit (3) has been programmed specifically to compute the first derivative of the measured absorbance spectrum through the flow cell, apply a smoothing technique to the first derivative (such as, but not limited to, the Savitzky-Golay technique as shown in FIG. 3), and to compute the concentration of various types of algae from the first derivative of absorbance spectra.

(11) The foregoing description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated. It is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents.

REFERENCES

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