Solar drying technologies for microalgae: impact of cover materials on macromolecules and pigments of Coelastrella sp.

Recent interest in microalgae stems from diverse applications, particularly as dried biomass. This study examined solar drying with various cover materials – polycarbonate, dark polycarbonate, titanium oxide-coated aluminium, glass, and acrylic – as well as conventional oven drying at 50°C, 60°C, and 80°C. Chlorophyll, carotenoid, and protein contents were quantified to assess the effects of the different drying methods on biomolecule stability. Chlorophyll was best retained at lower temperatures, with concentrations of 20.13 mg ml‒1 (electric oven, 50°C) and 17.72 mg ml‒1 (titanium oxide surface, 55.87°C). Carotenoids content remained consistent, ranging between 3.34–4.61 mg ml‒1 across all conditions. Among all drying treatments, the indirect solar dryer equipped with the titanium oxide-coated aluminium cover exhibited the highest protein content (26%). From the perspective of energy utilization during drying, the results reveal a substantial increase in consumption when using electric ovens. Specifically, raising the drying temperature from 50°C to 60°C resulted in a 39% increase in energy consumption, while increasing it to 80°C led to a 106% rise. In contrast, solar dryers use renewable solar energy reducing dependence on conventional energy sources for fossil-fuel-derived electricity. Results showed that solar drying produced microalgae of equal or better quality than electric oven drying. The intended application of the biomass should determine the optimal solar dryer cover material.