Cultivation of Algae and Its Biorefinery Approach

Introduction

In today's populated and industrialized world, algae are considered a sustainable resource for producing various products to address societies' demands (Bhattacharya and Goswami 2020). Algal biomass production is advantageous in comparison with terrestrial plants. For instance, algae do not require freshwater for cultivation and can grow in various harsh conditions such as wastewater and saline water. They also do not need fertile land, require much less area than terrestrial crops, and are well known for their high photosynthetic rate and the ability for high CO₂ fixation (Xu et al. 2019).

Algae are photosynthetic species that use sunlight, CO₂, nutrients, and water to produce carbohydrates, lipids, and proteins as their main products (Rahimi and Jazini 2021). These species are applicable in several industry sectors such as food, energy, and the environment. For instance, due to the presence of high-value antioxidants, carotenoids, minerals, and vitamins, algae are potential choices for food and feed (Chandra et al. 2019; M. P. Sudhakar et al. 2019). In the energy sector, producing various biofuels such as biodiesel, bioethanol, and biogas using algal species is possible (Chew et al. 2017). Besides, from an environmental point of view, algal species have been considered potential organisms because they consume CO₂, grow on several industrial wastewaters, and simultaneously consume hazardous components (Javed et al. 2019). However, due to the excessive costs of algal biomass processing, their industrial utilization is still doubtful. There are still challenges in both upstream and downstream processing of algal biomass; They require several technological enhancements and optimizations. Upstream processing is related to cultivation and maximizing the biomass concentration, while downstream processing refers to harvesting, cell disruption and extraction, and purification of algal biomass (Alavijeh et al. 2020).

Since algae can produce a wide range of valuable products, one conceivable way for their commercialization could be the utilization of their whole fractions in which no waste remains (Alavijeh et al. 2020). In this regard, they are considered potential bioresources in the biorefinery concept. As defined by the International Energy Agency (IEA), the sustainable processing of biomass into a spectrum of valuable products (biochemicals and biofuels) is known as biorefinery (Chandra et al. 2019). Algae are advantageous over other generations of biorefineries in many ways. For instance, compared to the first-generation biorefineries, they do not compete with the global food supply (del Río et al. 2020). Besides, compared with the second-generation biorefineries, the algal biomass structure is not complex, though the extraction of biomolecules is more convenient (Xu et al. 2019). Because of the high growth rate of algae compared to terrestrial crops, obtaining considerable amounts of algal biomass is faster than crops or lignocellulosic biomass. It is crucial since feedstock availability is essential for a biorefinery process.

This chapter aims to give a broad overview of algal bioprocessing, focusing on biorefinery. Various algal biomass products are discussed in this respect. General information on algal bioprocessing is then provided, emphasizing cultivation and cell disruption. Furthermore, available information on algal biomass harvesting and conversion is presented. Finally, future difficulties and outlooks on algal biorefineries are discussed.