Microalgae cultivated in Swine Wastewater: Stimulation of Seed Growth and Biopesticide Potential

Abstract

Humanity faces dramatic issues related to water scarcity and its contamination, as well as ex-cessive use of chemical fertilizers and pesticides, to increase agriculture efficiency. Eutrophication, contamination and soil infertility threatens agricultural sustainability and public health, as well as the earth’s ecosystems and biodiversity. Currently, microalgae are revealing themselves as promising on bioremediation of various wastewaters and as sustainable alternative on agriculture. This dissertation pretends to ally bioremediation to agriculture: the microalgae Chlorella proto-thecoides, Chlorella vulgaris, Scenedesmus obliquus e Synechocystis sp. were selected (after screen-ing) for swine wastewater treatment. The resulting biomass of the swine wastewater treatment was tested as germination/growth stimulation of tomato, watercress, cucumber, soy, barley and wheat seeds, and as biopesticide against Fusarium oxysporum. Regarding bioremediation, the four species reduced COD levels in 61-75%, total Kjeldahl nitro-gen in 70-80%, ammonia nitrogen in 93-97% and phosphorus between 94-100%, especially C. proto-thecoides and S. obliquus. In general, the limits imposed by Decree Law 236/98 of Portuguese legisla-tion for wastewater treatment were fulfilled and treated waters could be discharged or reused. The biochemical profiles of microalgae biomass presented protein contents between 34-47%, fatty acids (C12-C18) between 26-84%, and total sugars between 25-33%. The results for growth stimulation trials were positive for all microalgae depending on seed type and light conditions, Synechocystis sp. and C. vulgaris having the more relevant results. On biopesticide trials, Synechocystis sp. and S. obliquus obtained the best results as fungi growth inhibitors. In summary, S. obliquus and C. protothecoides were the most efficient in the wastewater treat-ment, S. obliquus and C. vulgaris, on germination/growth stimulation, and Synechocystis and S. obliquus, for biopesticide potential.