Abstract Description

High cultivation costs hinder the commercialization of algal oil as biodiesel feedstock. This study evaluated the potential of 19 readily available industrial effluents (autoclaved and non-autoclaved) to support heterotrophic growth and lipid accumulation in six mixed algal cultures. Six oleaginous mixed algal consortia were maintained on Zarrouk mineral medium under fluorescent light and assessed for their ability to produce biomass and lipid production on non-supplemented effluents (autoclave and non-autoclaved) from various industries. Biomass was measured gravimetrically whilst lipids were extracted in chloroform and methylated using trimethyl-sulphonium hydroxide (TMSOH). Fatty acid methyl esters (FAMEs) were analysed using a Varian CP-3800 gas chromatograph with flame ionisation detection. Data were processed using Excel and Stata. Theoretical kinematic viscosity of algal oils was calculated using the equation: Vmix = ΣAc×Vc (Knothe and Steidley, 2011), based on proportional contributions of individual fatty acid esters and their known viscosities. Effluents were analysed for chemical oxygen demand (COD; 5220 D), total Kjeldahl nitrogen (TKN; modified 4500-Norg B), and total phosphorus (TP; 4500-P C) using APHA (2012) standard methods. The average mixotrophic biomass production of 3.27 g biomass/L (autoclaved) on the industrial effluents was significantly higher compared to the photosynthetic growth on the Zarrouk mineral medium (0.19 g biomass/L). The best effluent in terms of biomass and lipid accumulation was the autoclaved fish cannery effluent. On this effluent, the average biomass yield (for the 6 mixed algal consortia) was 31.11 g biomass/L, whilst the highest biomass noted was 53.2485 g biomass/L for the algal consortium TUT2. TUT2 (best isolate) yielding 22.81 g lipids/L. The fatty acid composition of the algal lipids (TUT2) was high in saturated fatty acids (61.76%) leading to acceptable cetane values (67), as well as kinematic viscosity (3.89mm2/s) for biodiesel. These values were found to meet both the European biodiesel standard (EN 14214) and the American biodiesel standard (ASTM D6751). Most effluents tested did not support sufficient growth or lipid accumulation. Growth was primarily influenced by effluent type, with less impact from algal consortia. Lipid profiles were consistent across consortia grown on the same effluent, highlighting the effluent’s dominant role in determining lipid composition. Algal oils generally met biodiesel standards for cetane number and kinematic viscosity. The fish cannery effluent proved to be the best effluent tested, as an affordable cultivation medium, with regards to both biomass and lipid production. Heat treatment of the fish cannery effluent was deemed necessary based on the better performance of the algae on sterilized effluent, specifically the biomass production.