Biofuels have roots since the early days of the automotive industry when Rudolph Diesel tested his first engine using peanut oil. Biofuels are liquid fuels that are made from the biomass of various crops and industrial waste. They have the same variety of applications as fossil fuels but are more advantageous. Based on feedstock and production technologies, biofuels are categorized into four generations. Prior two generations of biofuels were less practical and inefficient since they were primarily based on food crops and municipal waste.
While the fourth generation of biofuels is still in its early stages of technological development, the Algal Biofuels: The Third-Generation Biofuels are emerging as a more practical and eco-friendlier alternative to fossil fuels. This is because, given the current energy scenario, choosing a feedstock that is viable and cost-effective, and sustainable in terms of food security is necessary.
Algae are a large group of photoautotrophic, mixotrophic, and heterotrophic lower plants, which can be subdivided into two major categories based on their relative sizes: macroalgae and microalgae.
Microalgae are single-cell microscopic organisms naturally found in freshwater environments. They are thought to be a potential oleo-feedstock because they need carbon., water, sunshine, phosphates, nitrates, and other (oligo) components for photosynthesis, resulting in the production of lipids.
They can produce a wide variety of sustainable biofuels, such as biomethane, bio-oil, biodiesel, etc. But before we dig deeper into the algal biofuel industry, we must comprehend what sets them apart from other feedstocks.
So, What Makes Algae The Better Feedstock?
1. Rapid Growth Rate
It has been found that microalgae can duplicate their biomass within 24 hours under controlled conditions and are deemed to be 10–20 times more productive than typical biofuel crops. P. Renovo has a doubling time of 2.2 hrs.
2. CO2 Sequestration
Microalgae sequester CO2 from flue gases emitted from fossil fuel-fired power plants and other sources, reducing emissions of a major greenhouse gas (1 kg of dry algal biomass utilizes about 1.83 kg of CO2) and significantly reducing overall emission in the life-cycle analysis.
3. Wastewater Treatment
Algae can efficiently remove the toxic components from the water like NH4 +, NO3 -, PO43-, and even heavy metals from various wastewater sources, e.g., agricultural run-off, concentrated animal feed operations, and industrial and municipal wastewater playing a role in wastewater treatment.
4. Higher Lipid Content
Microalgae have 30%-50% lipid contents by dry weight, which is higher than other sources, including soybeans and palm oils, and this value rises to 85%. Botryococcus braunii is a microalga with 30%-40% hydrocarbon content that can be extracted easily. A few more microalgal species, including some Chlorella species, Dunaliella species, Nannochloris sp., and Parietochloris incisa, have been reported to have the capacity to accumulate large quantities of lipids in cells under favorable conditions.
Additionally, microalgae can produce 30 times the amount of oil per unit area of land compared to oilseed crops, can grow in many environments, including – fresh, brackish, and hypersaline water-over a wide range of pH and temperatures, and are unlikely to interfere with the production of food crops.
Since there are many algae species with different lipid contents, it is essential to comprehend the fundamental production strategy and carefully select which conversion procedure to produce algal biofuels.
Production Method for Algal Biofuels
Source: General production approach of algal biofuels
Some of the critical phases for the conversion of algal biomass into biofuels are listed below:
Transesterification is characterized by the conversion of microalgal biomass to biodiesel and is subcategorized as a chemical changeover of algal biomass. Triglyceride or lipid reacts with mono alcohol with the additive of catalysts in the form of acid, alkali, or enzymes to produce fatty acid methyl ester (FAME) and glycerol.
The breakdown of starch to simple sugars is followed by yeast fermentation to produce bioethanol in this enzymatic process. Numerous factors, including the selection of robust strains, genetic modification, substrate modification, and substrate selection, have also been considered to improve bioethanol production.
3. Anaerobic Digestion
Anaerobic digestion has emerged as a promising and sustainable method for producing biogas from microalgal biomass. It has several benefits, including the reduction of greenhouse gas emissions and the generation of organic manures.
With such undeniable potential, it is surprising that algal biofuels have yet to become a mainstream commodity. The answer is simple: technical problems during the cultivation and harvesting of algae, caused by a lack of infrastructure and well-managed procedures, make the entire process less economical and complex.
Around 30% of the algal biomass is oil, with the remaining 70% being byproducts. If these by-products are used to their full potential, biofuel generation from algae biomass may become commercially viable. Moreover, if high-yielding algae species can be identified with advancements in cultivation and harvesting methods and an integrated biorefinery concept, the cost of production can be significantly reduced.
Given the current state of the art, biofuel cannot replace fossil fuel completely, at least in the short-term; however, in the long run, algal biofuels—the third generation of fuels—could emerge victorious in the energy and biofuel industries.
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