Abstract
A multi-wavelength based optical density sensor unit was designed, developed, and evaluated to monitor microalgae growth in real time. The system consisted of five main components including: (1) laser diode modules as light sources; (2) photodiodes as detectors; (3) driver circuit; (4) flow cell; and (5) sensor housing temperature controller. The sensor unit was designed to be integrated into any microalgae culture system for both real time and non-real time optical density measurements and algae growth monitoring applications. It was shown that the sensor unit was capable of monitoring the dynamics and physiological changes of the microalgae culture in real-time. Algae biomass concentration was accurately estimated with optical density measurements at 650, 685 and 780 nm wavelengths used by the sensor unit. The sensor unit was able to monitor cell concentration as high as 1.05 g·L−1 (1.51 × 108 cells·mL−1) during the culture growth without any sample preparation for the measurements. Since high cell concentrations do not need to be diluted using the sensor unit, the system has the potential to be used in industrial microalgae cultivation systems for real time monitoring and control applications that can lead to improved resource use efficiency.
Highlights
Microalgae have been successfully used as feedstock for the production of pharmaceutical products, nutritional supplements and chemicals [1,2,3,4]
Light absorbance at 780 nm estimates the turbidity of the suspension since the color of microalgae has no effect on the absorbance, whereas, light absorbance at 650 and 685 nm correlates to both intensity of the color and cell concentration
The optical sensor unit prototype demonstrated the capability of estimating cell concentration and changes of the physiological status of the microalgae culture in real-time
Summary
Microalgae have been successfully used as feedstock for the production of pharmaceutical products, nutritional supplements and chemicals [1,2,3,4]. Certain species of microalgae are candidates for the production of biofuels due to their high productivity and high oil content [5,6,7]. Producing sufficient amounts of biomass with controlled quality is the premise of production of microalgae derived products. For large scale microalgae production systems, effective decision making and overall production system management in terms of optimal resource use, harvesting and culture condition optimization (media composition, lighting, temperature, pH, dissolved oxygen levels, etc.) is crucial in order to achieve maximum profit and to prevent or reduce economic losses in case of contamination [8]
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