Drying Characteristics of a Microalgae Consortium Developed for Biofuels Production

Abstract

Microalgae are a promising renewable biomass feedstock that can be used to produce a wide range of bioproducts and biofuels. Drying is a critical step in algal biomass production as it improves shelf life, facilitates easier transport and storage, and enhances the extraction efficiency of lipids and other value-added compounds. This article investigated the thin-layer drying characteristics of a robust consortium of green algae consisting of Scenedesmus bijuga, Chlamydomonas globosa, and Chlorella minutissima grown in an open raceway pond. The microalgae consortium samples were harvested with 20% solids content using a centrifuge and were used for conducting thin-layer drying experiments in a convective oven. The change in moisture with time at each selected drying temperature (30°C, 50°C, 70°C, and 90°C) was recorded until the sample reached equilibrium moisture content. A typical drying curve for a microalgae consortium indicated that microalgae drying occurred at a falling rate, and the rate of drying was limited by diffusion. Three thin-layer drying models (Newton, Page, and Henderson-Pabis) were used to fit the microalgae drying data. The Page model fitted well with the drying data with high R2 (0.99) and low RMSE (0.02) values. Effective diffusivity of moisture from the microalgae was determined using the Henderson-Pabis model and increased from 1.94 × 10-10 to 1.74 × 10-9 m2 s-1 with increase in drying temperature from 30°C to 90°C. The low value of moisture diffusion rate from the microalgae samples may be attributed to shrinkage and case hardening of algae cells at the top drying surface. Both the effective diffusivity and the drying constant had significant dependence on drying temperature and were related with Arrhenius-type relationships. Biochemical compositions and fuel characteristics of the dried microalgae consortium were determined, and the dried microalgae can be an attractive feedstock for biofuel production.