Reduction of the Microbial Load of Digestate by the Cultivation of Galdieria sulphuraria Under Acidic Conditions

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Purpose: Organic waste streams with a high microbial load have been used as nutrient sources in the cultivation of heterotrophic microalgae. However, it remains unclear whether an alga-based organic waste utilization can also result in a reduction of the microbial load, and thus in a combined waste utilization and hygenization process. Methods: The heterotrophic cultivation of the microalga Galdieria sulphuraria at a pH of 2 and 45 °C as hygenization method for digestate, which serves as nitrogen source in algae cultivation, was investigated. Attention has been paid to Salmonella sp. and spores, coming from the organic waste stream digestate and its reduction during hydrolysis and cultivation of G. sulphuraria in the resulting hydrolysate. Results: Digestate contained 0.5 × 106 counts per g material, predominantly formed by aerobic, mesophilic organisms. Salmonella sp., yeast and molds, enterobacteriaceae as well as enterococci were diminished within 24 h of hydrolysis or cultivation. During hydrolysis of digestate and cultivation of G. sulphuraria the counts of aerobic, mesophilic organisms could be subsequently reduced by a log reduction factor of 3. The remaining microorganisms were almost exclusively spore forming ones which were reduced by a log reduction factor of 2 during cultivation under acidic conditions. Conclusion: It is suggested here to include the cultivation of G. sulphuraria in future waste management as hygenization process. Graphical Abstract: [Figure not available: see fulltext.]

Original languageEnglish
JournalWaste and Biomass Valorization
Issue number8
Pages (from-to)2621-2627
Number of pages7
Publication statusPublished - 08.2023

Bibliographical note

Open Access funding enabled and organized by Projekt DEAL. The authors acknowledge the German Federal Ministry of Education and Research for providing funding within the Era-Net Cofund “FACCE SURPLUS” Program (031B0934B).

Publisher Copyright:
© 2023, The Author(s).

    Research areas

  • Algae, Hydrolysis, Salmonella sp, Spores
  • Biology