Monitoring mi̇croalgal growth via nitrate sensor

Microalgae are new generation feedstocks for the production of various biofuels such as biodiesel, bioethanol and biochar which are alternative for fossil fuels that cause environmental problems such as global warming and acid rains. Besides, microalgae are utilized in different usage areas like food, animal feed, pharmaceutical and cosmetic industry because of their valuable bioactive compounds. Microalgae are microorganisms that can grow only in the optimum conditions. The proportions of macro (nitrogen, phosphorus, carbon) and micro (calcium, iron, silica, sulfur, calcium, magnesium, sodium, potassium and chlorine, some vitamins and trace elements) elements in nutrient solution and pH, temperature, and light intensity are significant parameters for the growth of microalgae. Sensitive measurement of these elements is very important. In recent years, the development of devices and sensors has been studied specifically for sensitive measurement of these parameters during microalgal growth. Chlorella minutissima are fast growing microalgae species used for the production of different biofuels such as biodiesel and bioethanol because of their high lipid and carbohydrate content. In this study, effect of nitrate, carbonate and phosphate levels in the growth medium on biomass yield of microalgae were investigated statistically by using Box-Behnken design method, and optimum conditions are determined for the highest biomass yield of microalgae. An ion selective potentiometric nitrate sensor was specially produced for this study and nitrate concentration in the nutrient medium was measured sensitively during microalgal growth simultaneously. In addition to this, pH, temperature, dissolved oxygen, salinity, conductivity, resistance and total dissolved solids were measured and relationship between these parameters and microalgal growth was evaluated. It was seen that biomass yield increased with the increase in the amounts of nitrate, carbonate and phosphate. Also it was found that, as nitrate amount decreased, dissolved oxygen, salinity, conductivity, and total dissolved solids increased during microalgal growth.