Casero-Díaz, TamaraCastro‑Barros, CeliaCarballa Arcos, MartaMauricio Iglesias, MiguelDuarte, Maria Salomé Lira2025-07-112025-07-112025-04-08Casero-Díaz, T., Castro-Barros, C., Carballa, M. et al. Optimizing volatile fatty acids production from fish canning wastewater: the role of feeding strategies and retention time. Biomass Conv. Bioref. (2025). https://doi.org/10.1007/s13399-025-06841-w2190-6815https://hdl.handle.net/10347/42443The transition to a circular economy requires innovative strategies for wastewater valorization, particularly in water-intensive sectors, such as fsh canning. Anaerobic fermentation of fsh canning wastewater to produce volatile fatty acids (VFAs) is a promising alternative to reach this goal. This study evaluated the impact of two bioreactor feeding strategies (continuous (UASB) and sequential batch (SBR)) and two hydraulic retention times (HRT) (6 and 3 days) on VFA yield and product spectrum. The results showed that both feeding modes resulted in high VFA production, exceeding 30 g VFA-COD/L. It can be concluded that the feeding mode has no impact on VFA yield. However, it does exert a signifcant infuence on the product spectrum. Sequential feeding was found to favor butyric acid production, with a 15% higher yield compared to continuous feeding. In contrast, continuous feeding promoted the formation of propionic and valeric acids, with yields 5% and 4% higher, respectively, than those observed under sequential feeding. In contrast, variations in HRT demonstrated no signifcant impact on either yield or product spectrum. These fndings suggest that, for the scaling up of this valorization, the selection of feeding mode should be tailored to the desired objective. Furthermore, a lower HRT (3 days) may lead to financial savings and enhanced productivity without any detrimental impact on yield or product spectrum.eng© The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holderAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/Anaerobic fermentationCarboxylate platformIndustrial wastewaterResource recoveryjournal article10.1007/s13399-025-06841-wopen access