Utilization of oil crop residues for enhanced algae based production of lipids, polyunsaturated fatty acids, and protein

Abstract

Microalgae are capable of synthesizing many high value compounds, such as lipids, polyunsaturated fatty acids (PUFAs), and proteins, and therefore considered potential feedstock for production of biodiesel, nutraceuticals, and animal feeds. The synthesis and accumulation of lipids, PUFAs, and proteins are influenced by such factors as microalgae strain, trophic conversion mode of growth, nutrient supply, and light and temperature conditions. Regulation of these factors must take cost issue into account. The goal of this research was to investigate the use of oil crop biomass residue (OCBR), a low-cost material from oil extraction plants, to cultivate specific algae strains for targeted production of lipids, PUFAs, and proteins. The specific objectives of present thesis were: 1) to optimize the conditions for acid hydrolysis of OCBR for best yield and desirable profile of nutrients; 2) to evaluate microalgae growth on different OCBR media; 3) to characterize the chemical compositions especially the lipid, protein and EPA contents in the harvested algal biomass as affected by culture media; 4) to study the effect of temperature and growth phase on algae EPA synthesis.The one-factor-at-a-time experimental design was used to optimize the acid hydrolysis conditions based on the key nutrient level including the total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD) and ammonia nitrogen (NH4-N) in the hydrolysates. The optimal conditions were found to be using 3 % sulfuric acid and hydrolyzing residues at 90 °C for 20 hrs. The hydrolysates (OCBR media) produced under the optimal conditions were used to cultivate two algae strains, namely UM258 and UM268. The results from 5 days of cultivation showed that the best OCBR media supported faster algae growth than artificial media, with maximal algal biomass yield of 2.7 g/L and 3 g/L, respectively. Moreover, the total lipids after 5 days cultivation for UM258 and UM268 were 54 % and 35%, respectively. The OCBR also promoted protein accumulation in UM 268 compared with artificial media. Temperature-time interaction-effect on EPA synthesis was observed. Temperature of 20 °C and time of longer than 6 days of cultivation (after algae reach stationary phase), were found optimal for EPA accumulation for UM258 with EPA reaching 18% in total fatty acids. The results suggest that OCBR media are an excellent alternative for algae growth and have great potential for large scale productions of algae based ingredients for biodiesel, high value foods and animal feeds.