This study aimed to cultivate cyanobacteria by an economical method using beet filter cake waste from the sugar industry. The first part included the large-scale production of single-cell protein from S.

platensis using beet filter cake extract (BFCE) as an alternative medium to Zarrouk's medium through optimization cultivation factors. The second part comprised cultivation of another cyanobacterium Leptolyngbya sp.

on BFCE and used crude phycocyanin extract to synthesize selenium nanoparticles, their characterization by various techniques and then applied in the biological sector. Production of single-cell protein S.

platensis occurred through three steps: cultivation of S. platensis by two regimes, the direct cultivation of S.

platensis on different BFCE for one week (batch cultivation) and the second by adaption mode through subjecting S. platensis to a gradual increment in the concentration of BFCE for one month.

From these experiments, it was deduced that higher BFCE significantly decreased protein content, pigments, and dry weight but had a non-significant effect on lipid content. .