Casero Díaz, TamaraCastro Barros, CeliaMauricio Iglesias, MiguelCarballa Arcos, Marta2025-10-172025-10-172025-04Casero-Díaz, T., Castro-Barros, C., Mauricio-Iglesias, M., & Carballa, M. (2025). From dairy waste to butyric acid: Scaling the valorization process. Journal of Environmental Management, 380, 124934. 10.1016/j.jenvman.2025.1249340301-4797https://hdl.handle.net/10347/43131To move towards a circular dairy sector and reduce its environmental impact, sustainable management of its by-products is essential. This study presents a novel approach to valorize milk permeate through the production of butyric acid. Key operating parameters, including hydraulic retention time (HRT) and pH, were tested at a laboratory scale and the best conditions were validated at a pre-industrial scale in a dairy factory. A relatively short retention time (2 d) and pH 5.5 was demonstrated to be appropriate for the conversion of milk permeate into volatile fatty acids (58% yield), likely due to the permeate carbohydrate composition, which is primarily lactose. Furthermore, the acidic pH (5.5) promoted a shift in the product spectrum, increasing the molar fraction of butyric acid from 0.2 to 0.6. These operational conditions resulted in butyric acid productivities of 9.0 g HBut/L·d and 3.1 g HBut/L·d at lab- and pilot scale, respectively. This study represents a significant step towards a promising valorization route for milk permeate at a representative scale, while highlighting the need for process optimization to overcome scale-up challenges to ensure industrial applicability.eng© 2025 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).Attribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Anaerobic fermentationCarboxylate platformIndustrial by-productsResource recoveryVolatile fatty acidsMilk permeatejournal article10.1016/j.jenvman.2025.124934open access