Chlorella vulgaris and Scenedesmus quadricauda: diversified applications for environmental and agricultural systems

Abstract

The topic of this thesis takes as its guiding principle the multifunctionality of microalgae, focusing on the use of Chlorella vulgaris and Scenedesmus quadricauda as decontaminants of agricultural wastewater, biostimulants for plant growth and for soil fertility. The main objectives of this thesis have been organized into four chapters. The first aim was to evaluate the removal capacity of microalgae with respect to organic and inorganic pollutants from agricultural wastewater. Secondly, the goal was to investigate the biostimulating effect of microalgae extracts on plants of agricultural interest, in particular sugar beet and maize. The third objective was to evaluate the effect of microalgal extracts and living cells on soil biochemical fertility. Finally, the last objective of this thesis was to evaluate the effects on growth of microalgae and tomato plants in a co-cultivation of C. vulgaris or S. quadricauda and tomato plants. The results suggest that it is possible to use cultivation systems of both microalgae to purify agricultural wastewater which contains inorganic compounds and pesticides. The extracts prepared from C. vulgaris and S.quadricauda seem to be promising as biostimulants, both in promoting germination and in the early stages of plant growth in sugar beet. Furthermore, these microalgal extracts were shown to have positive effects on the physiological parameters under investigation of maize plants. With respect to the biochemical fertility of soil, the results highlighted that metabolites of C. vulgaris and S. quadricauda may induce a higher soil biochemical fertility and simultaneously increase tomato plant growth. Finally, the results suggested that the associated cultures of microalgae and tomato plants, in an hydroponic system, may be a cheap and useful way of simultaneously producing a greater quantity of microalgal biomass as well as improved tomato plant growth.