Abstract

The objective of this study was to evaluate the potential of age Opuntia-derivated digestate (OpDcm) as a nutrient source for photosynthetic microbial consortia (PMC), aiming to reduce dependence on mineral media and promote the valorization of locally available biomass in arid and semi-arid regions. Batch cultures were performed in bubble column photobioreactors (BCPBR) and open raceway (ORPBR) photobioreactors using different proportions of OpDcm and BG110 to assess biomass production, chlorophyll a dynamics, and physicochemical responses of a PMC dominated by Nostoc sp. Chemical characterization showed that OpDcm contained higher levels of K, Ca, Mg, and Mn than BG110, providing a robust ionic matrix for initial growth; however, potential limitations in P, Mg, and Fe were identified. In both BCPBR and ORPBR systems, OpDcm demonstrated nutrient compositions that stimulated biomass production in the PMC at levels comparable to those achieved with BG110 medium. Statistical analyses showed that specific treatments, particularly T1 (10% OpDcm in BCPBR) and T3 (10% OpDcm + 2.5% BG110 in ORPBR), produced biomass yields similar to or higher than those obtained with the conventional BG110 medium. However, chlorophyll a concentration was lower in OpDcm treatments due to limited light transmission and micronutrient constraints. The N–NH4+ dynamics in BCPBR and ORPBR exhibited pronounced variability among the evaluated culture media, spanning from negligible changes (<1 mg L−1) over the entire cultivation period to sustained ammonium production rates of 2–3 mg L−1 day−1. Morphological analysis confirmed a consortium dominated by Nostoc sp., supported by pH values within the optimal range (8–9). Overall, the use of age-Opuntia-derived digestates demonstrated it can serve as a partial or total substitute for a low-cost nutrient source for cyanobacterial cultivation, underscoring their relevance to circular bioeconomy strategies for producing photosynthetic biomass.

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