Pilot-scale cultivation of Arthrospira platensis using pretreated anaerobic digestate and geothermal water: A...

In this study, Arthrospira platensis (A. platensis) was cultivated for over 130 days in an experimental greenhouse using open raceway ponds and closed column photobioreactors. A culture medium composed of liquid digestate pretreated with natural zeolite and diluted with geothermal water was evaluated as an alternative to conventional synthetic media for cyanobacteria cultivation. Among the different culture strategies tested, the recirculation of A. platensis inoculum proved unsuccessful, as it prevented the repetition of multiple batches and ultimately led to a complete culture collapse. In contrast, the use of a fresh inoculum enabled stable production across three consecutive batches, despite suboptimal environmental conditions, achieving biomass productivities of 10 ± 3 mg.L^-1.d^-1 in digestate-based cultivation. Throughout most of the cultivation period, ammonium was entirely removed. A nitrogen balance analysis indicated multiple removal mechanisms, with A. platensis assimilation accounting for 7-60 % of nitrogen uptake. The biochemical composition of A. platensis was largely consistent between the control and digestate-based cultures, with proteins (44 ± 6 % DW) as the dominant component, followed by lipids (14 ± 5 % DW) and carbohydrates (9 ± 3 % DW). These findings highlight the potential of digestate-based culture media and emphasize the need for further research to optimize cultivation strategies for sustainable industrial large-scale A. platensis production.