Publication: Engineering biorefineries of RAS effluents to combine marine aquaculture and algae production
Authors
Perché, Sarah Armelle Lucia
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Escuela Internacional de Doctorado
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Sánchez Vázquez, Francisco Javier ; López Olmeda, José Fernando ; Letelier-Gordo, Carlos Octavio
Publisher
Universidad de Murcia
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DOI
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info:eu-repo/semantics/doctoralThesis
Description
Abstract
La acuicultura actual es uno de los sectores de producción alimentaria con mayor crecimiento mundial, superando a la pesca extractiva. A pesar de su potencial estratégico en la seguridad alimentaria global, su crecimiento acelerado plantea preocupaciones de sostenibilidad, particularmente con relación al uso del agua y su contaminación. Los sistemas de recirculación (RAS) marinos ofrecen una alternativa más eficiente en recursos al reducir y controlar el consumo hídrico y la descarga de efluentes. No obstante, los RAS producen dos efluentes ricos en nutrientes sujetos a estrictas regulaciones: agua de rebose (OW) y lodo. Esta tesis, enmarcada dentro del programa doctoral industrial EASYTRAIN, investiga una tecnología integrada para valorizar los efluentes del RAS mediante un enfoque de biorrefinería, evaluando la combinación de OW y el sobrenadante del tratamiento anaerobio de lodos marinos como sustrato nutritivo adecuado para Ulva sp. (macroalga comercial). Los objetivos fueron optimizar la recuperación de nutrientes, reducir la dependencia de insumos sintéticos y promover la circularidad en RAS marinos. La tesis se basa en cinco objetivos principales: I.Caracterización de nutrientes - Determinación del requerimiento nutricionales de Ulva sp. y evaluación de lodos como sustituto del medio de crecimiento comercial. II.Optimización de biorreactores - Identificación de las condiciones redox óptimas para solubilizar los nutrientes de los lodos y establecer parámetros escalables de biorreactor. III.Potencial de cultivo algal - Evaluación del rendimiento de crecimiento de Ulva sp. con OW solo, con suplementación de sobrenadante derivado de lodo, y con sobrenadante y suplementación química de trazas. IV. Evaluación económica - Comparación del costo operativo del tratamiento de biorrefinería integrada de efluentes marinos frente al proceso de tratamiento convencional. V.Construcción de laboratorio de investigación - Construcción de un laboratorio húmedo en Landing Aquaculture B.V. para facilitar la investigación aplicada en valorización de lodos y cultivo algal. Capítulo I: Recuperación de nutrientes de lodos mediante procesos de tratamiento impulsados por condiciones redox. La digestión anaerobia fue la más efectiva en solubilizar nutrientes (e.g., nitrógeno, fósforo). El subsiguiente sobrenadante de lodo fermentado (FSS) se mezcló con OW y se probó en ensayos de crecimiento de Ulva sp. FSS+OW alcanzó la mayor tasa de crecimiento específico (9,07 ± 1,49 %/día) que OW solo y el tratamiento enriquecido con oligoelementos, demostrando que los efluentes son capaces de sostener el crecimiento algal independientemente de aditivos sintéticos. Capítulo II: Comparación del tratamiento convencional de efluentes, basado en desnitrificación y coagulación química, con el enfoque de biorrefinería propuesto. Mientras que el sistema convencional tiene altos costos operativos anuales (>1,1 millones euros), principalmente debido a insumos químicos, el modelo innovador reduce los costos operativos a menos de 63 500 euros/año y ofrece hasta 17 600 euros/año de ingresos potenciales por biomasa algal y biogás derivado de lodos. Además de ahorrar costos, el modelo elimina el uso de químicos externos y mantiene la circularidad, alineándose con la política de la UE sobre recuperación de nutrientes. Capítulo III: Planificación y construcción con recursos internos de un laboratorio húmedo polivalente de 14 m2 en una instalación existente, con áreas dedicadas a experimentación en digestión de lodos, análisis de agua y crecimiento algal. El laboratorio es una ubicación clave para la colaboración académico-industrial y la investigación aplicada en acuicultura sostenible. En términos globales, esta tesis propone un enfoque novedoso para cerrar los ciclos de nutrientes en RAS marinos. Mediante la integración del cultivo algal con la digestión anaerobia de lodos, el proceso reduce el impacto ambiental y la dependencia química. Aunque se requiere más investigación para evaluar la escalabilidad a largo plazo y las cuestiones regulatorias, la investigación establece las bases para una acuicultura marina circular que apoya la producción de alimentos y bioproductos.
Aquaculture is currently one of the world's fastest-growing food-producing sectors, outproducing capture fisheries. While it holds tremendous potential for playing a role in future global food security, its rapid growth generates real sustainability concerns, particularly regarding water use and nutrient pollution from waste production. Land-based recirculating aquaculture systems (RAS) offer a more controlled and resource-sensitive alternative by reducing water consumption and controlling effluent discharge. However, RAS produce two nutrient-rich effluents: overflow water (OW) and sludge, that are subject to strict discharge regulations.This doctoral research investigates an integrated technology for valorising marine RAS effluents. Specifically, the study explores a biorefinery approach to assess whether the combination of OW and the supernatant from anaerobic treatment of marine sludge is a suitable nutrient substrate for Ulva sp., a commercial relevant macroalgae. Conducted in the EASYTRAIN industrial doctoral program, the project aims to optimize nutrient recovery, reduce reliance on synthetic inputs, and promote circularity in marine RAS.The research is based on five main objectives:I.Nutrient Characterisation - Determine the nutrient requirement of Ulva sp. and assess if marine RAS sludge can be applied as a substitute for commercial growth medium.II.Bioreactor Optimisation - Identify optimum redox conditions (aerobic, anaerobic, or alternating) to solubilise marine RAS sludge nutrients and establish scalable bioreactor parameters.III.Algae Cultivation Potential - Evaluate the growth performance of Ulva sp. with OW alone, OW with sludge-derived supernatant supplementation, and OW with supernatant and trace chemical supplementation.IV.Economic Evaluation - Compare the operating cost to treat marine RAS effluents of the integrated biorefinery process versus the conventional treatment process.V.Research Laboratory Construction - Construct a wet laboratory at Landing Aquaculture B.V. to facilitate applied research on sludge valorisation and seaweed culture.Chapter I explores nutrient recovery from marine RAS sludge through redox-driven treatment processes. Anaerobic digestion was most effective in solubilizing nutrients such as nitrogen, phosphorus, iron, and manganese. The ensuing fermented sludge supernatant (FSS) was blended with OW and tested in Ulva sp. growth trials. The FSS+OW treatment attained the highest specific growth rate (9,07 ± 1,49 %/day) than OW-alone and trace element-enriched treatment, demonstrating that marine RAS effluents are able to support algal growth regardless of synthetic additives.Chapter II compares conventional marine RAS effluent treatment, based on denitrification and chemical coagulation, with the proposed biorefinery approach. While the conventional system has high annual operating costs (>1,1 million euros), mainly due to chemical inputs, the innovative model reduces operating costs to less than 63 500 euros/year and offers up to 17 600 euros/year of potential revenue from seaweed biomass and sludge-derived biogas. Apart from saving costs, the innovative approach eliminates external chemical use and closes circular resource loops aligned with EU policy on nutrient recovery.Chapter III outlines the planning and building of a 14 m2 wet laboratory in an existing facility. Designed to be flexible and built using in-house resources, the facility has dedicated areas for sludge digestion experimentation, water analysis, and algae growth. Despite delays and overspending, the lab is now a key location for industry-academic collaboration and applied research in sustainable aquaculture.Globally, this thesis proposes a novel approach to close nutrient loops in marine RAS. Through integrating seaweed farming with sludge anaerobic digestion, the process reduces environmental impact, operational cost, and chemical dependency. Despite the need for further research to assess long-term scalability and regulatory issues, the research lays the groundwork for circular land-based marine aquaculture to support food and bioproduct production.
Aquaculture is currently one of the world's fastest-growing food-producing sectors, outproducing capture fisheries. While it holds tremendous potential for playing a role in future global food security, its rapid growth generates real sustainability concerns, particularly regarding water use and nutrient pollution from waste production. Land-based recirculating aquaculture systems (RAS) offer a more controlled and resource-sensitive alternative by reducing water consumption and controlling effluent discharge. However, RAS produce two nutrient-rich effluents: overflow water (OW) and sludge, that are subject to strict discharge regulations.This doctoral research investigates an integrated technology for valorising marine RAS effluents. Specifically, the study explores a biorefinery approach to assess whether the combination of OW and the supernatant from anaerobic treatment of marine sludge is a suitable nutrient substrate for Ulva sp., a commercial relevant macroalgae. Conducted in the EASYTRAIN industrial doctoral program, the project aims to optimize nutrient recovery, reduce reliance on synthetic inputs, and promote circularity in marine RAS.The research is based on five main objectives:I.Nutrient Characterisation - Determine the nutrient requirement of Ulva sp. and assess if marine RAS sludge can be applied as a substitute for commercial growth medium.II.Bioreactor Optimisation - Identify optimum redox conditions (aerobic, anaerobic, or alternating) to solubilise marine RAS sludge nutrients and establish scalable bioreactor parameters.III.Algae Cultivation Potential - Evaluate the growth performance of Ulva sp. with OW alone, OW with sludge-derived supernatant supplementation, and OW with supernatant and trace chemical supplementation.IV.Economic Evaluation - Compare the operating cost to treat marine RAS effluents of the integrated biorefinery process versus the conventional treatment process.V.Research Laboratory Construction - Construct a wet laboratory at Landing Aquaculture B.V. to facilitate applied research on sludge valorisation and seaweed culture.Chapter I explores nutrient recovery from marine RAS sludge through redox-driven treatment processes. Anaerobic digestion was most effective in solubilizing nutrients such as nitrogen, phosphorus, iron, and manganese. The ensuing fermented sludge supernatant (FSS) was blended with OW and tested in Ulva sp. growth trials. The FSS+OW treatment attained the highest specific growth rate (9,07 ± 1,49 %/day) than OW-alone and trace element-enriched treatment, demonstrating that marine RAS effluents are able to support algal growth regardless of synthetic additives.Chapter II compares conventional marine RAS effluent treatment, based on denitrification and chemical coagulation, with the proposed biorefinery approach. While the conventional system has high annual operating costs (>1,1 million euros), mainly due to chemical inputs, the innovative model reduces operating costs to less than 63 500 euros/year and offers up to 17 600 euros/year of potential revenue from seaweed biomass and sludge-derived biogas. Apart from saving costs, the innovative approach eliminates external chemical use and closes circular resource loops aligned with EU policy on nutrient recovery.Chapter III outlines the planning and building of a 14 m2 wet laboratory in an existing facility. Designed to be flexible and built using in-house resources, the facility has dedicated areas for sludge digestion experimentation, water analysis, and algae growth. Despite delays and overspending, the lab is now a key location for industry-academic collaboration and applied research in sustainable aquaculture.Globally, this thesis proposes a novel approach to close nutrient loops in marine RAS. Through integrating seaweed farming with sludge anaerobic digestion, the process reduces environmental impact, operational cost, and chemical dependency. Despite the need for further research to assess long-term scalability and regulatory issues, the research lays the groundwork for circular land-based marine aquaculture to support food and bioproduct production.
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