Biodiesel from microalgae lipids: from inorganic carbon to energy production

Abstract

Following the United Nations Conference on Climate Change, COP21 (Paris, France), several countries have attempted to reduce their greenhouse gas emissions. In order to reach this objective, microalgae could be used to capture carbon dioxide and transform it into a biomass composed essentially of lipids, carbohydrates and proteins. Moreover, cultivating microalgae does not require arable land, in opposition to several oleaginous plants used to produce biofuels. Despite the fact that microalgae could be transformed into several biofuels such as bioethanol (by fermentation of hydrocarbons) and biomethane (by anaerobic digestion), transforming lipids into biodiesel could allow the reduction of oil-based diesel consumption. However, microalgae biodiesel production costs remain high for a short-term commercialization. The microalgae lipids can be transesterified into biodiesel in the presence of catalysts (homogeneous or heterogeneous). In order to commercialize biodiesel from microalgae, biodiesel physicochemical properties must respect the American Society for Testing and Materials (ASTM) standards. The aim of the study was to describe the current technologies available to produce biodiesel from microalgae. Microalgae compositionMicroalgae are composed of four main components: lipids, carbohydrates, proteins and nucleic acids [37]. CarbohydratesCarbohydrates are structural material, with a metabolic function, of the microalga, which can be found as starch, polysaccharides, monosaccharides (like glucose) and more [38,39]. Concerning biofuels, one of the main interests of carbohydrates is to use microalgal glucose and transform it by fermentation into bioethanol with a yield up to 50 wt% (compared to the total carbohydrates) for Chlorococcum humicola microalgae (a 100%

Algae biofuel: Current status and future applications

“…Algae are generally more efficient converters of solar energy, this is because their cells grow in aqueous suspensions, and they have efficient access to CO2, water, and other nutrients [62]. The oil content of algae in relation to their dry weight made them the ideal renewable fuel and energy source through different conversion processes such as transesterification, anaerobic digestion, hydrotreatment, fermentation, pyrolysis and direct combustion [2,7,12,13,17,39,41,[63][64][65]. However, some of these conversion methods are complex and economically expensive, yet they can be commercially viable if all the by-products are optimally utilized.…”

“…The high content of mannitol in the resultant hydrolysates can stand as a cost-effective organic substrate for algae bioethanol production [63]. Algae bioethanol productivity is two times higher than ethanol's production from sugarcane [65] and five times higher than that of corn. A good source of ethanol from microalgae is Chlorella Vulgaris, due to its high starch content where the ethanol conversion efficiency was recorded up to 65%.…”

“…Fermentation residue could offset the feedstock cost and make up for the whole cost price of the product. Sirajunnisa and Surendhiran [65] suggested that bioethanol from algae could have massive impact and significance in the global renewable and sustainable development without affecting food production and supply. Moreover, with the current research and development aimed at the production of valuable secondary by-products, the economic sustainability of bioethanol could be maximized [84].…”

“…Algae biofuels could play a significant role in the improvement of global transport fuel and at the same time reduce the global emission of GHG [83]. This is because transport fuels are responsible for a quarter of the CO2 emissions [65], which has resulted in the efficiency gains from biofuels as renewable fuel source, that is often used to justify every expansion in the transport and aviation industries with respect to climate change [81].…”

Production of Microalgal Biomass Using Aquaculture Wastewater as Growth Medium

“…Integrating the treatment of aquaculture wastewater with algal cultivation in the Recirculation Aquaculture System (RAS) can bring not only ecological but also economic benefits. Algae obtained in this process can be used in cosmetic and pharmaceutical industries and as a substrate for the production of food, animal feed, and biofuels [16,17], including those from the lipids accumulated in their cells [18]. In this study, we examined whether (1) Chlorella minutissima can grow and (2) promptly remove the nutrients from the wastewater originating from saline aquaculture.…”