Evaluation of the slag generated during steel production as a culture medium for the obtaining of Spirulina maxima biomass

Abstract The use of cyanobacteria in the context of biofertilizers allows the strategic valorization of aquatic biomass as a bioinput for application in agriculture, since cyanobacteria have both biofertilizer and biostimulant capacity. Furthermore, the use of a residue such as slag generated during steel production as a culture medium for the growth of these microorganisms and as a component of the formulation of an organomineral fertilizer (cyanobacteria/slag) is promising, due to the inclusion of other minerals that are important to the plant. The objective of this study was to evaluate the use of slag as a culture medium for the growth and biomass production of the cyanobacterium Spirulina maxima and its chemical composition. X-ray Fluorescence Spectrometry (XRF) analyses were performed on PLANTPAR’s Flex Azul and Flex Vermelho mineral fertilizer and slag respectively. Based on the XRF analysis, 9 growth media were prepared, supplemented with sulfur source (S) (Na 2 SO 4 ) at 30%; a chlorine (Cl) source (NaCl) at 68%; and potassium (K) source (K 2 SO 4 ) at 97%. Growth was monitored by dry weight analyses and was interrupted on day 10 due to the end of the exponential growth phase. The results from the experiments with supplemented slag were compared to the control E0 in Schlösser medium (P0), which achieved a final ash-free biomass concentration of 1.098 g/L and a productivity of 0.0998 g/(L·day) over the 10-day cultivation period. The volumetric productivities on day 10 followed the order: P0 (0.0998 g/(L·day)) > PE5 (0.0880 g/(L·day)) > PE11 (0.0755 g/(L·day)) > PE9 (0.0590 g/(L·day)) > PE10 (0.0514 g/(L·day)) > PE8 (0.0499 g/(L·day)) > PE7 (0.0459 g/(L·day)) > PE6 (0.0431 g/(L·day)). The slag cultivation medium supplemented with E5 fertilizer achieved a productivity of 88.18% of the value achieved by the E0 control cultivation medium, confirming the possibility of growing Spirulina maxima using slag as a cultivation medium.