## 5 Potential for Concurrent Production of Biofuels  
Microalgae, through their rapid growth, which goes hand in hand with their high CO\({}_{2}\) sequestration capacity and minimum land requirements, constitute a dynamic energy resource with a positive environmental impact and that does not compete with the food sector. With their capacity to provide biomass with increased amounts of carbohydrates,proteins, and lipids, they can lead to the production of a range of biofuels [32]. The biofuels produced from microalgae biomass are third-generation biofuels and are an evolution of the first generation, which included the production of biofuels from edible crops, and the second generation, produced from lignocellulosic biomass originating from agricultural crop waste and, partly, the organic fraction of municipal solid waste. With the evolution of generations, the advantages and disadvantages mainly related to raw materials are changing. Various microalgae species, such as _Chlorella vulgaris_, _Nannochloropsis_ sp., and _Chlamydomonas reinhardtii_, have been extensively studied for the production of biofuels as they have recorded high growth rates and lipid contents compared to other microalgae species. _Chlorella_, _Chlamydomonas_, _Dunaliella_, _Scenedensmus_, and _Tetraselmis_ have been found to have an increased content of polysaccharides (>40% on a dry basis), and their biomass can be a fermentation medium for bioethanol production. The necessary elements for the growth of microalgae, such as carbon, nutrients, and metals, are found in wastewater in increased quantities, thus ensuring cheap biomass for biofuel production with simultaneous bioremediation of waste. Of the biofuels produced from microalgae biomass (bioethanol, biobutanol, biodiesel, biohydrogen, and biomethane), biodiesel and bioethanol are those studied on larger production scales [33]. The raw materials most used worldwide for biodiesel production are rapeseed oil (59%), soybean oil (25%), palm oil (10%), sunflower oil (5%), and other sources (1%) such as coconuts, peanuts, corn, cooking oil, animal fats, and algae. Some microalgae species grown under optimized growing conditions have the potential to produce 47,000-141,000 L of lipids/ha/year, which represents an oil yield of more than 200 times that of the most productive plants. The predominant problem, however, for the industrial application of microalgae biodiesel production is that more energy is required to increase the energy requirement to increase biomass concentration than the energy produced by microalgae biomass [34]. Several microalgae species contain remarkable lipid amounts. Common microalgae, including _Chlorella_, _Dunaliella_, _Isochrysis_, _Nannochloris_, _Neochloris_, _Phaodactylum_, _Porphyridium_, and _Schizochytrium_, have lipid contents ranging from 20 to 50% dry weight. These values can be increased by appropriate handling of growth factors, optimization of the cultivation and harvesting process, and genetic modifications of the selected strains. Nitrogen deficiency and increased salinity can lead to the induction of fatty acid growth in the majority of microalgae. A fatty acid consists mainly of glycerides, which are esters of glycerol (which has three -OH) with fatty acids, and are therefore called triglycerides (TAG). The fatty acid composition of most microalgae is dominated by the fatty acids C14:0, C16:0, C18:1, C18:2, and C18:3, but the relative composition varies from species to species. Lipids can be converted to fatty acid methyl esters (FAMEs) through transesterification for biodiesel production. Transesterification is the most common technology for the production of biodiesel from biomass, where triglycerides react with short-chain alcohol (e.g., methanol or ethanol) in the presence of alkaline or acid catalysts. The main byproduct of the process is glycerol, which is used in various industrial applications. In addition, residual biomass after oil removal can be used as animal feed [35].