Can Anaerobically Digested Food Effluent Support Arthrospira platensis Cultivation in Open Ponds?

The cultivation of Arthrospira platensis (Spirulina) is well-established in applied phycology, but the high cost of conventional media limits large-scale production. Anaerobically digested food effluent (ADFE), rich in nitrogen and phosphorus, offers a cost-effective alternative while mitigating environmental impacts. This study evaluated ADFE as a partial replacement for Zarrouk’s medium, with 37.5%, 50%, and 70% substitutions, the latter two added incrementally. Cultivation was conducted in paddlewheel-driven raceway ponds under outdoor conditions for 22 days during the Australian autumn. The highest biomass productivity (8.83 g m−2 d−1) was achieved with 70% ADFE, significantly outperforming Zarrouk’s medium (p < 0.05). Chlorophyll a content remained unaffected (p > 0.05), and ammonium (N-NH4+) declined to near zero by day 9, indicating efficient nutrient uptake. These findings demonstrate that staged ADFE addition can successfully replace up to 70% of Zarrouk’s medium while maintaining robust A. platensis growth, highlighting its potential as a sustainable alternative for large-scale microalgal cultivation.