Cultivation and safety aspects of Arthrospira platensis (Spirulina) grown with struvite recovered from anaerobic digestion plant as phosphorus source

In this study, the cyanobacterium Arthrospira platensis, commonly known as Spirulina, was cultivated utilizing phosphorus in the form of struvite recovered from effluents of a biogas plant treating municipal and agro-industrial wastes. Under the specific experimental conditions, providing sterilized struvite at about 120 mg/L (or 15 mg-P/L) gave the same results in terms of biomass production and biochemical composition as the control cultures (with KH2PO4 as a P source). Struvite sterilization was found to be an important step because its original microbial load had a negative effect on the biomass production and resulted in biomass with lower value (lower protein and phycocyanin content). P from struvite was almost complete released upon adding it in the cultivation medium after 90 min, where parameters, such as medium pH, struvite particle size and medium reusing cycles had no effect on the kinetics of P release, indicating that P is almost immediately available for cell uptake. Since struvite was generated from effluents of a biogas plant treating municipal and agro-industrial wastes, the potential of its contamination with hazardous compounds was examined in order to assess the safety of the produced biomass. Unwanted compounds like heavy metals, bisphenol A (BPA), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) were calculated to be at levels significantly lower than those of the maximum levels allowed in the European Union regulation for feedstuff safety, while neither veterinary drugs nor Escherichia coli were detected in the struvite. Results suggest that struvite recovered from biogas plants could be used as P source for the cultivation of A. platensis for feed or food quality.