CO(2) sequestration by propagation of the fast-growing Azolla spp.

Azolla is a group of aquatic floating plants that can achieve very high growth rates compared to other aquatic macrophytes, with a doubling time of 2–5 days under optimal growing conditions. The ability of Azolla to grow at such rapid rates allows for the opportunity of utilizing it as a method to sequester a significant amount of atmospheric CO(2) in the form of biomass, which can be locked away to completely remove the carbon from the active carbon cycle, or which can be used in various applications such as animal feeds, biofertilizers, and biofuel production, which in turn will contribute to reduction in the fossil CO(2) emissions. In this desktop study, the potential use of Azolla for mitigating the annual increase in the atmospheric CO(2) levels was addressed, which were estimated at 18.9 billion tons of CO(2) per year. A theoretical setup of 1-ha ponds was assessed to estimate the total Azolla growing area required for counterbalancing the annual atmospheric CO(2) increase. Each 1-ha pond was found capable of capturing 21,266 kg of CO(2) (C) per year. The calculated required total area to mitigate the total annual increase was estimated to be 1,018,023 km(2) (equivalent to around a fifth of the Amazon forest area). Sensitivity analysis, which was based on the variations in the productivity of Azolla due to growing conditions, indicated that the required area would range between 763,518 and 1,527,036 km(2). This study provides a novel natural method for CO(2) sequestration that has lower environmental impacts compared to conventional sequestration technologies as an alternative green approach for mitigating the effects of fossil fuels. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11356-021-16986-6.