| Summary: | Pig farming generates highly polluting wastewaters which entail serious environmental issues when not adequately managed. Microalgae systems can be promising for cost, energy and environment-efficient treatment of piggery wastewater (PWW). Aside from clean water, the produced biomass can be used as biostimulants and biopesticides contributing to a more sustainable agriculture.Three microalgae (Tetradesmus obliquus, Chlorella protothecoides, Chlorella vulgaris) and one cyanobacterium (Synechocystis sp.) were selected after a preliminary screening in diluted wastewater (1:20) to treat PWW. The nutrient removals were 62-79% for COD (chemical oxygen demand), 84-92% for TKN (total Kjeldahl nitrogen), 79-92% for NH4+ and over 96% for PO43−. T. obliquus and C. protothecoides were the most efficient ones.After treating PWW, the produced biomass, at 0.5 g L−1, was assessed as a biostimulant for seed germination, root/shoot growth, and pigment content for tomato, watercress, cucumber, soybean, wheat, and barley seeds. We observed an overall increase on germination index (GI) of microalgae-treated seeds, owing to the development of longer roots, especially in T. obliquus and C. vulgaris treatments. The microalgae treatments were especially effective in cucumber seeds (75-138% GI increase).The biopesticide activity against Fusarium oxysporum was also evaluated at 1, 2.5 and 5 g L−1 of microalgae culture. Except for Synechocystis sp., all the microalgae tested inhibited the fungus growth, with T. obliquus and C. vulgaris achieving inhibitions above 40% for all concentrations.
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