Advanced photobioreactor strategy for chromium phycoremediation with Spirulina platensis

The study investigates the phycoremediation of Cr(VI) by Spirulina platensis under static cultivation (batch system) and a tubular photobioreactor. An inoculum of Spirulina platensis (1.2 g L⁻¹) was exposed to 30 and 60 mg L⁻¹ Cr(VI). Cellular resistance was verified until day seven, after which chromium exposure led to cell growth inhibition and reduced chlorophyll production. Chromium removal was verified through two mechanisms: initial passive biosorption on cell walls, facilitated by functional groups identified via Fourier-transform infrared spectroscopy, followed by active intracellular bioaccumulation, where Cr(VI) was reduced to less toxic Cr(III) via enzymatic activity. Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed the adsorption of chromium on the cell surface. In the static system, final biomass reached 0.65 g L⁻¹ (46 % reduction), while the photobioreactor produced 3.19 g L⁻¹ (18.2 % below control). Total chromium removal efficiencies reached 69.3 % (10 days) and 67.1 % (7 days) in static and photobioreactor systems, respectively.