A state-of-the-art review on the environmental benefits and prospects of Azolla in biofuel, bioremediation and biofertilizer applications

This review paper reports the detailed assessment of biofuel (bio-oil and biodiesel) production capabilities and the potential utilization of Azolla macroalgae in bioremediation and biofertilizer applications. Biodiesel and its blends were utilized in the transportation sector to minimize fossil fuel emissions and greenhouse gas (GHG). Another significant biofuel is bio-oil, which is produced by pyrolysis of biomasses. High energy density combined with easiness of storage and transportation of bio-oil compared to gaseous products, bio-oil is considered a possible source to replace petroleum fuel for power production. The key reason for choosing Azolla species as feedstock for biofuel production is its sustainability, high lipid and energy content. Besides, the Azolla grows in simple wetlands and wastewater, which is efficient and cost-effective. The results from the various literature ensured that the Azolla based biofuels are a better alternative to fossil fuels. The wastewater from the industries and nuclear power plants contains pollutants such as heavy metals and metalloids. Heavy metals cause several damage to the ecosystem. The conventional methods of treating wastewater are expensive and time-consuming, whereas the bioremediation method provides low-cost alternate methods. The removal of heavy metals from wastewater is achieved using Azolla algae, a biological source present in ditches and ponds. Azolla quickly spreads as a dense layer over the water surface and adsorbed heavy metals from the wastewater. The current study critically reviewed the Azolla's potential capacity to be used in the phytoremediation method and remove the heavy metals from wastewater to better environmental conditions. In addition, Azolla is reported as a biofertilizer and green manure in gardens and rice fields due to their high cellulosic content.