Earthenware-based biofilter configuration for Spirulina cultivation on nutrients recycled from food-industry waste streams: A preliminary study

This study integrates an earthenware-based biofilter into photobioreactors (PBR), to allow Spirulina growth on organic nutrient sources. The earthenware acted as permeable membrane, enabling the bio-oxidation of soluble organics and the diffusion of mineralised ions to the photobioreactor. When fed with lactic acid fermentation effluents (organic loading rates of 11.1 mg-COD L−1PBR d−1 and 1.7 mg-Total-N L−1PBR d−1), Spirulina growth rate (19.4 mgdry mass L−1 d−1) was up to the mark with respect to a control with Zarrouk medium. However, the protein content was of 34% w/wDM (as compared to 57% in the control), likely due to insufficient mineral-N supply under the tested system-configuration. The dissolved photosynthetic oxygen established a redox potential gradient (300–400 mV) across the membrane, acting as an electron sink towards consistent COD removal rates (9.0 ± 0.7 mg-COD L−1 d−1). Configurations with higher biofilter/photobioreactor volume ratios should be tested, to improve nitrogen supply rates.