BACKGROUNDCyanobacteriae and microalgae industries require large amounts of water for their cultivation. Reusing the Arthrospira platensis culture medium is scarcely evaluated in the literature. This work evaluates coagulation and adsorption as a simultaneous process to treat A. platensis spent medium by applying different concentrations of powdered activated carbon (PAC) and ferric sulfate (S) and by using different contact times (T) to remove organic matter and pigments. RESULTSThe process efficiency was measured by removal of both organic matter and pigments by absorbance at 254 and 440nm, respectively. The highest maximum cell concentration (486364mgL(-1)) and protein content values (60.0 +/- 0.6%) were observed in a medium treated with optimal conditions using PAC = 40.0mgL(-1), S = 32.8mgL(-1) and T = 36.1min. Under such conditions, chlorophyll-a biomass content of 24.5 +/- 0.6mgg dry cell(-1) and chlorophyll-a productivity of 16.8 +/- 0.1mgL(-1) d(-1) were obtained. CONCLUSIONS Coagulation and adsorption as a simultaneus treatment allowing reuse of the spent medium of A. platensis cultivation can diminish not only its production costs but also environmental pollution. The biomass produced in the treated medium contains more protein and chlorophyll than that produced in the standard medium. (c) 2015 Society of Chemical Industry