Microalgae and cyanobacteria role in sustainable agriculture: from wastewater treatment to biofertilizer production

Nowadays, one of the major environmental problems at the global level is the fact that the water is polluted by huge loads of organic and inorganic compounds, heavy metals (HMs), and chemicals produced by agricultural, industrial, and human activities. The treatment of these wastewaters (WW) represents a challenge for many countries. Among the various approaches that can be adopted to remediate WWs, an environmentally friendly and costless option is the adoption of biological technologies such as the use of microalgae-based technologies, referred to as phycoremediation. Due to the nature of WWs, microalgae are able to growth and produce biomass by exploiting as nutrients some compounds that can be found in the water. In this way, they reduce the concentrations of such compounds in the WWs. The attractive fact related to the use of microalgae is that these photosynthetic microorganisms can be used in multipurpose environmental applications such as the remediation of WWs and the capture of carbon dioxide, representing at the same time a useful feedstock that can be exploited to produce food, feed, biodiesel as well as fertilizers, biopesticides, and bio-stimulants for the agricultural sector. This review will encompass the direct utilization of microalgal biomass produced by phycoremediation as a valuable feedstock for the production of bio-stimulants, biofertilizers, and biopesticides for the agricultural sector. An analysis of the role played by microalgae-based products as a valid alternative to traditional agrochemicals has been discussed.