Abstract
The use of microalgae for biodiesel or solid fuel production is a promising alternative for reducing the dependence on fossil fuel. When converting microalgae into fuels, a large amount of energy is consumed for dewatering and/or drying the microalgae. Pretreatment methods such as thermal treatment, acid or alkali treatment are proven to have positive effects on microalgae drying, e.g. increasing the drying rate, reducing the amount of energy usage, etc. However, there are not too many discussions in literature regarding material losses during the pretreatment processes. Material losses not only reduce the productivity of fuels but also generate impacts to the environment as more waste is produced.
In this paper, experimental and modelling studies documenting the effects of different pretreatment processes on the drying rate and material losses are presented. Samples of microalgae (i.e. chlorella vulgaris) are first centrifuged and filtered before undergoing an alkali (i.e. sodium hydroxide), acid (i.e. sulphuric acid) or hydrothermal treatment. The moisture content, dry weight and compositions (i.e. ultimate analysis) of the samples are measured before and after the treatments. The untreated and pretreated samples are then subjected to thermogravimetric analysis (TGA) to determine their drying rate during the drying process. The drying kinetic is derived from the TGA results.
Findings show that the Page model can be used to represent the drying process with an R2 of 0.99, material losses can be significant for certain cases (as high as 18 %) and changes in elemental analyses after pretreatment e.g. in sulphur, hydrogen and oxygen content occur after pretreatment.
