Estimation of Algae Concentration in Water Using Spectrophotometric Measurements and First Derivative of Absorbance


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The occurrence of algae in conventional wastewater treatment plants or aerated lagoons can result in false indications in the final effluent parameters, such as TSS and CBOD5 . Algae plumes create surface scum, poor water clarity, and noxious odors. The presence of algae at very low concentrations in water supplies used to produce drinking water leads to problems in the drinking water treatment process, such as reduced filter runs, increase the disinfection dose and increase the treatment cost. Analytical and chemical methods currently used to determine algal concentration (e,g. algal number and chlorophyll extraction) are time-consuming, require much laboratory preparation, expensive and are inaccurate. Moreover, it is not clear how efficient the chlorophyll extraction is or how its results are related to the actual algal concentration. Therefore, it is clear that there is a need for a reliable system that can achieve real-time detection of algal concentration in different water samples. Recently, the use of real-time and inline spectrophotometric methods at water and wastewater treatment plants to measure different parameters (e.g. C, N) has increased dramatically. These measurements are considered practical, quick, simple, and accurate for these industries. The absorbance of algae in water sample produces a spectrum with a maximum absorbance near the wavelength of green light (540–690 nm). In some types of water and wastewater, water turbidity and the presence of different constituents masks the absorbance response and affect the sensitivity of the measurements. Spectral first and higher-order derivatives have been used by different studies to facilitate the location of the critical wavelength, to reduce low-frequency background noise, and to resolve overlapping spectra. However, it appears that no research work has explored the use of the first derivative of the absorbance spectra to determine the concentration of algae in water. The present work illustrates the use of spectrophotometric measurement and absorbance first derivative to determine the concentration of algae in different water samples. The study also compares the detection limit of the new developed method with the time-consuming chlorophyll extraction method. The relationship between algal concentration and absorbance for three types of water solution (distilled, surface, and wastewater) was established in the 200–800 nm wavelength range, and the effect of using the absorbance first derivative on improving detection limit was estimated. UV absorbance of algal solution shows peaks at 455, 515, and 675 nm, with the maximum absorbance at 695 nm and a strong linear relationship (R2 > 0.97) between concentration and absorbance at 695 nm. Absorbance first derivative improves algal detection limits and reduces the effect of background and spectra overlapping. In the distilled water, the lowest detection limits, using absorbance measurement and the absorbance first derivative, were 0.55 mg TVS/L and 0.47 mg TVS/L, respectively. surface water and wastewater showed a detection limits of 0.56 to 19.6 mg TVS/L, respectively. Higher detection limits were possible with the chlorophyll extraction methods. The method presented here can be used effectively to monitor algal concentration in water samples.

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Journal: TechConnect Briefs
Volume: 2, Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2016
Published: May 22, 2016
Pages: 144 - 147
Industry sectors: Advanced Materials & Manufacturing | Energy & Sustainability
Topic: Biofuels & Bioproducts
ISBN: 978-0-9975-1171-0