Abstract Description

Microalgal growth and lipid production is highly dependent on cultivation conditions. Due to the diverse response of microalgae to variables such as light intensity, temperature, nutrients etc., deductions when studying data and comparing information from literature make it difficult to draw clear conclusions. Most known microalgae react to environmental factors such as temperature, in a species dependent manner and it is known that parameters optimal for growth may not be optimal for lipid production. In addition to this, the effect of a single environmental factor could change when in combination with other cultivation conditions. A mixed microalgal consortium, including strains of Phormidium spp., Nitzschia spp., Chlorella spp. and Chlamydomonas spp., known for lipid production, was selected for cultivation on sterilized fish cannery effluent to evaluate parameters impacting growth and lipid production. The effect of temperatures (25 °C, 30 °C and 35 °C) were assessed at pH 7, aeration of 1 vvm and agitation at 200 rpm, with or without illumination. Light:dark (L:D) cycles of 24:0; 18:6; 12:12; 8:16 and 4:20 were evaluated at 300 µmol/m2/s1. The cultivations were also conducted at different pH levels namely, pH 3, 5, 7, 9 and 11. Growth, as well as lipid production and composition were determined. A 10% blend of the algal oil was made with Mosspar 1925 and hydrogenated over a nickel-based catalyst to improve the colour and stability. The blend was tested for appearance, odour, density at 20 °C, Saybolt colour, initial boiling point, 90-Rec, bromine number, kinematic viscosity at 40 °C and cetane number. When the algae were cultivation with illumination, 25 °C yielded the best biomass production, namely, 57.71 g biomass/L with a lipid accumulation of 30.30% (13.73 g lipids/L). The biomass production with continuous illumination (24:0 L:D cycle) was 57.71 g biomass/L, 54.11 g biomass/L with 18:6 L:D cycle and 52.04 g biomass/L with a 12:12 L:D cycle, with a lipid accumulation of 34.51%, 27.24% and 30.96%. The algal consortium showed reduced growth and lipid production at pH values other than pH 7. The algal blend showed compliance for all quality parameters, tested using ASTM D4176, 4052, 156, 2711, 3120, 445 and 613. After analysis of the data obtained for the algal blend, PetroSA, Mossel Bay, SA certified the algal blend to be a functional fuel with good lube oil possibilities, equivalent to conventional diesel and compatible for use in a blend.