Algae Biomass Conversion Technologies

Introduction

Environmental sustainability and energy crisis caused by overdependence on fossil fuels are the two biggest global challenges confronted by humanity today (Pietrosemoli and Rodríguez-Monroy., 2019). Fossil fuel consumption has caused global warming as a result of the huge amount of greenhouse gases (GHGs) released into the atmosphere (Martins et al. 2019). Therefore, many researchers around the world are focused on finding alternative renewable energy sources. Using first-generation edible feedstocks such as sugarcane and corn for biofuel production has caused the food versus fuel debate. Due to the expansion of biofuels, food prices may continue to rise (Gui et al., 2008). Therefore, lignocellulosic biomass feedstocks such as forest and agricultural residues have been used to produce second-generation biofuels. As a result of this complex structure, pretreatment is intensive and costly before lignocellulosic biomass can be converted into biofuels, limiting its viability (Limayem and Ricke, 2012). Hence, algae can be considered as a possible feedstock for processing third-generation biofuels, which could be a solution to these problems. The pros and cons of different generation of biomass feedstocks have been discussed in Table 1. Through the process of photosynthesis, green algae are able to survive and become the primary microorganism in aquatic environments. The algae biomass has the least utilization of nutrients when compared to biomass productivity. According to Jez et al. (2017), for rapeseed, sunflower and algae cultivation to produce 1 kg biomass per hectare, nitrogen consumption amounts to approx. 40, 45 and 0.003 mg/ha, respectively. This figure is significantly lower for algae cultivation. For rapeseed, sunflower, and algae, the phosphorus requirement is also approx. 25, 56, and 0.002 mg/ha, respectively. A wide range of commercially valuable bioproducts can be produced from algae biomass due to its diverse biochemical composition (carbohydrates, lipids, and proteins). Algal biofuels and biochemicals have been produced simultaneously from algae by integrating downstream biorefineries in recent years. Growing global energy demand could potentially be met by farming algae in aquatic environments, considering the limited agricultural land supply (Li et al., 2008). As a result of recent technological advances in photobioreactor design through integrated algae farming and biorefinery strategies, microalgae biofuel production is has come off age being more cost-effective (Brennan and Owende, 2010). Before being converted to biofuel, algal biomass can be utilized for the production of various macromolecules in the form of lipids, fatty acids, and vital amines. As part of an algae biorefinery system, products of high value includes but is not limited to pharmaceuticals, biofertilizers and biomaterials (Budzianowski, 2017). Through the integration of biofuels and biochemical processing, algae biorefineries have moved closer to becoming a commercial reality.