Degradación anaerobia de microalgas procedentes del tratamiento del efluente de un reactor anaerobio de membranas sumergidas

La escasez de recursos naturales y el agotamiento de los combustibles fósiles han impulsado un creciente interés en el uso de microalgas, dado que han sido reconocidas como una de las alternativas más sostenibles para suplir la demanda energética global a largo plazo y detener los acusados problemas asociados al cambio climático. Actualmente, la combinación de un tratamiento anaerobio de agua residual y su post-tratamiento mediante un cultivo de microalgas supone una prometedora alternativa, pues permite la obtención simultánea de energía en forma de biogás y un recurso hídrico reutilizable, mientras que los nutrientes son empleados para la producción de una biomasa algal, susceptible de valorización energética mediante digestión anaerobia. El objetivo de esta tesis doctoral ha consistido en estudiar la degradación anaerobia de la biomasa algal, producida en el efluente de un tratamiento anaerobio de agua residual urbana, con el fin de maximizar su valorización energética en forma de biogás. Para ello, se llevaron a cabo dos estrategias basadas en incrementar la biodegradabilidad de las microalgas: (i) mediante un pretratamiento enzimático y (ii) potenciando la actividad hidrolítica de los microorganismos anaerobios. Los resultados obtenidos del pretratamiento enzimático de las microalgas revelaron que su biodegradabilidad anaerobia puede ser incrementada mediante la adecuada combinación de pH, temperatura y dosis de enzima, teniendo una elevada influencia la adaptación del inóculo y el tipo de microalgas que se pretende degradar. Así pues, mediante el pretratamiento enzimático se consiguió incrementar la biodegradabilidad de las microalgas Scenedesmus spp. del 36.7% al 65.7%. Alternativamente a los pretratamientos, la biodegradabilidad de las microalgas puede ser incrementada potenciando la actividad hidrolítica de la propia biomasa anaerobia de dos formas: operando un reactor mesófilo a elevados tiempos de retención celular (TRC) y llevando a cabo la degradación anaerobia de microalgas en condiciones termófilas (55ºC). La operación de un biorreactor anaerobio de membrana (AnMBR) a elevados TRC y bajo condiciones mesófilas (35ºC), favorece el desarrollo de microorganismos con baja tasa de crecimiento e involucrados en la degradación de los componentes que constituyen a las microalgas. De esta forma, se alcanzó una biodegradabilidad de las microalgas Scenedesmus spp. del 70.9%, con la operación del AnMBR a un TRC de 100 días, y una biodegradabilidad del 73.9% de las microalgas Chlorella spp. con un TRC de 140 días. A su vez, el uso de la tecnología de membranas permitió modificar simultáneamente el caudal de tratamiento y la concentración de microalgas en el influente, lo que reduce la concentración de posibles inhibidores así como los costes energéticos asociados al proceso de concentración de microalgas. Además, la elevada biodegradabilidad dio lugar a bajas producciones de fango, lo que reduce los costes de su tratamiento y disposición, y generó un efluente rico en nutrientes que puede ser reutilizado para el cultivo de nueva biomasa algal. Los microorganismos termófilos exhiben una alta actividad hidrolítica que permitió obtener un incremento de la biodegradabilidad de la biomasa algal del 20.4% respecto a su digestión anaerobia a 35ºC, bajo las mismas condiciones experimentales. Sin embargo, se observó que el CSTR termófilo (Continuous Stirred Tank Reactor) no puede trabajar con concentraciones de microalgas que alcancen un valor de DQO de 20000 mgO2·L-1, debido a la liberación de grandes cantidades de amonio al medio que provoca la inhibición del proceso biológico por amoniaco. Así pues, se determinó que la presencia de amoniaco en concentraciones cercanas a 70 mgN-NH3·L-1 provoca el inicio de la inhibición, alcanzando el 30% de inhibición cuando la concentración se incrementa hasta 82 mgN-NH3·L-1. El análisis genómico del AnMBR mesófilo confirmó que su operación a un elevado TRC (100 días) favoreció la biodiversidad microbiana y promovió el desarrollo de una biomasa anaerobia fuertemente hidrolítica, responsable de la elevada biodegradabilidad de las microalgas alcanzada (70.9%). Así mismo, el análisis microbiológico del CSTR termófilo reveló la presencia de microorganismos con una elevada capacidad proteolítica y celulolítica, así como la detección del phylum EM3. A pesar de que la función metabólica de EM3 en digestores anaerobios no está todavía definida, la elevada abundancia relativa de este phylum en el reactor (38.7%) indica que debe estar involucrado en la degradación anaerobia de los compuestos de la biomasa algal en condiciones termófilas. La presente tesis doctoral demuestra que la producción de biogás a partir de la digestión anaerobia de microalgas puede maximizarse sin la necesidad de aplicar costosos pretratamientos, dando lugar a una de las mayores biodegradabilidades de biomasa algal reportada hasta el momento.Depletion of natural resources and fossil fuel reserves have triggered intense attention in the use of microalgae, which have been recognised as sustainable alternative for meeting the global energy demand in the long-term and to mitigate the effects of climate change. Nowadays, the combination of anaerobic wastewater treatment and its post-treatment through microalgae-based technologies can be considered an interesting approach for recovering energy from sewage and water resource. Likewise, mineral nutrients are used to produce microalgal biomass that can be energetically valorised through anaerobic digestion. The main objective of this thesis has been to study the anaerobic degradation of microalgae, which comes from the effluent of a wastewater anaerobic treatment, in order to maximize their energetic valorisation as biogas. For this purpose, two strategies were performed to increase microalgal biodegradability: (i) an enzymatic pretreatment of microalgal biomass and (ii) improving the hydrolytic activity of anaerobic microorganisms. Results retrieved from the enzymatic pretreatment revealed that microalgal biodegradation can be increased through an appropriate combination of pH, temperature and enzyme dose, wherein inoculum adaptation and the type of microalgae used as a substrate have a significant influence on the result. Concretely, enzymatic pretreatment increased Scenedesmus spp. microalgal biodegradability from 36.7 to 65.7%. Alternatively, microalgal biodegradability can be increased by improving the hydrolytic activity of anaerobic biomass in two ways: running the mesophilic anaerobic reactor at high solid retention times (SRT) and operating an anaerobic reactor at thermophilic conditions (55ºC). A mesophilic anaerobic membrane bioreactor (AnMBR) operated at high SRT promote the retention of low growth rate microorganisms involved in microalgal degradation. At 100 days of SRT, Scenedesmus spp. microalgae achieved a biodegradability of 70.9% and at 140 days of SRT Chlorella spp. microalgae achieved a 73.9% of biodegradability. Likewise, the use of membrane technology allows to simultaneously increase the treatment flow rate and decrease microalgal concentration in the influent, which reduces the concentration of possible inhibitors and the energy costs associated with microalgal harvesting. Furthermore, high microalgal biodegradability resulted in low sludge productions, thereby leading to a cost reduction of treatment and disposal of sludge, and produced a nutrient-rich effluent that can be reused as a grown medium for new microalgae culture. Thermophilic microorganisms exhibit high hydrolytic activity that increases microalgal biodegradation in 20.4% in comparison with the mesophilic process under the same operational conditions. However, it has been observed that thermophilic CSTR (Continuous Stirred Tank Reactor) cannot be run with a microalgal COD concentration exceeding 20000 mgO2·L-1 due to a high amount of ammonium released, which causes the biological process inhibition by free ammonia. It was observed that process inhibition started at 70 mgN-NH3·L-1 and achieved a 30% of inhibition when free ammonia concentration increased up to 82 mgN-NH3·L-1. Genomic analyse of mesophilic AnMBR confirmed that high SRT (100 days) promoted high microbial biodiversity, enriched in an anaerobic microorganisms with high hydrolytic activity that are likely responsible for the noticeably microalgal biodegradation (70.9%). Likewise, microbial analyse of thermophilic CSTR revealed a microbial population with high cellulolytic and proteolytic capabilities as well as the detection of EM3 phylum. Although functional role of EM3 remains undefined in anaerobic digesters, the high relative abundance of this phylum (38.7%) indicates that is likely involved in microalgal anaerobic degradation under thermophilic conditions. This thesis has demonstrated that biogas production through anaerobic digestion of microalgal biomass can be maximized without applying costly pretreatments, thereby resulting in one of the highest biogas production currently reported from the anaerobic digestion of raw microalgae grown in wastewater

Thermophilic anaerobic conversion of raw microalgae: Microbial community diversity in high solids retention systems

[EN] The potential of microbial communities for efficient anaerobic conversion of raw microalgae was evaluated in this work. A long-term operated thermophilic digester was fed with three different Organic Loading Rates (OLR) (0.2, 0.3 and 0.4¿g·L¿1·d¿1) reaching 32¿41% biodegradability values. The microbial community analysis revealed a remarkable presence of microorganisms that exhibit high hydrolytic capabilities such as Thermotogae (~44.5%), Firmicutes (~17.6%) and Dictyoglomi, Aminicenantes, Atribacteria and Planctomycetes (below ~5.5%) phyla. The suggested metabolic role of these phyla highlights the importance of protein hydrolysis and fermentation when only degrading microalgae. The ecological analysis of the reactor suggests the implication of the novel group EM3 in fermentation and beta-oxidation pathways during microalgae conversion into methane. Scenedesmus spp. substrate and free ammonia concentration strongly shaped thermophilic reactor microbial structure. Partial Least Square Discriminant Analysis (PLS-DA) remarked the resilient role of minor groups related to Thermogutta, Armatimonadetes and Ruminococcaceae against a potential inhibitor like free ammonia. Towards low-cost biogas production from microalgae, this study reveals valuable information about thermophilic microorganisms that can strongly disrupt microalgae and remain in high solids retention anaerobic digesters.This research work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO, Project CTM2011-28595-C02-02) jointly with the European Regional Development Fund (ERDF), which are gratefully acknowledged. The authors are thankful to Fernando Fdz-Polanco research team (University of Valladolid, Spain) for providing the thermophilic sludge from their pilot plant to inoculate the bioreactor and Llúcia Martínez and Giusseppe D'Aria from FISABIO sequencing service (Valencia, Spain) for their technical support during the Illumina sequencing design.Zamorano-López, N.; Greses-Huerta, S.; Aguado García, D.; Seco Torrecillas, A.; Borrás Falomir, L. (2019). Thermophilic anaerobic conversion of raw microalgae: Microbial community diversity in high solids retention systems. Algal Research. 41:1-9. https://doi.org/10.1016/j.algal.2019.101533S194

Effect of long residence time and high temperature over anaerobic biodegradation of Scenedesmus microalgae grown in wastewater

[EN] Anaerobic digestion of indigenous Scenedesmus spp. microalgae was studied in continuous lab-scale anaerobic reactors at different temperatures (35 degrees C and 55 degrees C), and sludge retention time - SRT (50 and 70 days). Mesophilic digestion was performed in a continuous stirred-tank reactor (CSTR) and in an anaerobic membrane bioreactor (AnMBR). Mesophilic CSTR operated at 50 days SRT only achieved 11.9% of anaerobic biodegradability whereas in the AnMBR at 70 days SRT and 50 days HRT reached 39.5%, which is even higher than the biodegradability achieved in the thermophilic CSTR at 50 days SRT (30.4%). Microbial analysis revealed a high abundance of cellulose-degraders in both reactors, AnMBR (mainly composed of 9.4% Bacteroidetes, 10.1% Chloroflexi, 8.0% Firmicutes and 13.2% Thermotogae) and thermophilic CSTR (dominated by 23.8% Chloroflexi and 12.9% Firmicutes). However, higher microbial diversity was found in the AnMBR compared to the thermophilic CSTR which is related to the SRT. since high SRT promoted low growth-rate microorganisms, increasing the hydrolytic potential of the system. These results present the membrane technology as a promising approach to revalue microalgal biomass, suggesting that microalgae biodegradability and consequently the methane production could be improved operating at higher SRT. (C) 2018 Elsevier Ltd. All rights reserved.This research work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO, Project CTM2011-28595-C02-01/02) jointly with the European Regional Development Fund (ERDF), which are gratefully acknowledged. The authors are thankful to Fernando Fernandez-Polanco for providing the thermophilic sludge to inoculate the reactor.This research work has been financially supported by the Generalitat Valenciana (PROMETEO/2012/029 PROJECT), which is gratefully acknowledged.Greses-Huerta, S.; Zamorano -López, N.; Borrás Falomir, L.; Ferrer, J.; Seco Torrecillas, A.; Aguado García, D. (2018). Effect of long residence time and high temperature over anaerobic biodegradation of Scenedesmus microalgae grown in wastewater. Journal of Environmental Management. 218:425-434. https://doi.org/10.1016/j.jenvman.2018.04.086S42543421

Production of Short-Chain Fatty Acids (Scfas) As Chemicals or Substrates for Microbes to Obtain Biochemicals

[Abstract] Carboxylic acids have become interesting platform molecules in the last years due to their versatility to act as carbon sources for different microorganisms or as precursors for the chemical industry. Among carboxylic acids, short-chain fatty acids (SCFAs) such as acetic, propionic, butyric, valeric, and caproic acids can be biotechnologically produced in an anaerobic fermentation process from lignocellulose or other organic wastes of agricultural, industrial, or municipal origin. The biosynthesis of SCFAs is advantageous compared to chemical synthesis, since the latter relies on fossil-derived raw materials, expensive and toxic catalysts and harsh process conditions. This review article gives an overview on biosynthesis of SCFAs from complex waste products. Different applications of SCFAs are explored and how these acids can be considered as a source of bioproducts, aiming at the development of a circular economy. The use of SCFAs as platform molecules requires adequate concentration and separation processes that are also addressed in this review. Various microorganisms such as bacteria or oleaginous yeasts can efficiently use SCFA mixtures derived from anaerobic fermentation, an attribute that can be exploited in microbial electrolytic cells or to produce biopolymers such as microbial oils or polyhydroxyalkanoates. Promising technologies for the microbial conversion of SCFAs into bioproducts are outlined with recent examples, highlighting SCFAs as interesting platform molecules for the development of future bioeconomy.This article is based upon work from COST Action Yeast4Bio (CA18229), supported by COST (European Cooperation in Science and Technology). Open access funding provided by Swedish University of Agricultural Sciences. CK, NOL, MCV from the BIOENGIN group, are grateful to Xunta de Galicia for its financial support to Competitive Reference Research Groups (ED431C 2021/55). They also thank the Spanish Ministry of Science and Innovation and European FEDER funding (PID2020-117805RB-I00) for financing ongoing research, at the BIOENGIN group, on the topic of this paper. ETP, CGF and SG acknowledge the projects BIOMIO + H2 (PID2020-119403RBC21) funded by MCIN/AEI/http://dx.doi.org/10.13039/501100011033 and OLEOFERM (EraBoBiotech; PCI2021-121936) funded by MCIN/AEI/http://dx.doi.org/10.13039/501100011033 and “European Union NextGenerationEU/PRTR”. ETP also acknowledges the grant RYC2019-027773-I funded by MCIN/AEI/http://dx.doi.org/10.13039/501100011033 and by “ESF Investing in your future”. VP and BM were supported by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas) [grant number 2018–01877]Xunta de Galicia; ED431C 2021/55Suecia. Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas); 2018–0187

Enhancing methane production from lignocellulosic biomass by combined steam‑explosion pretreatment and bioaugmentation with cellulolytic bacterium Caldicellulosiruptor bescii

Background: Biogas production from lignocellulosic biomass is generally considered to be challenging due to the recalcitrant nature of this biomass. In this study, the recalcitrance of birch was reduced by applying steam-explosion (SE) pretreatment (210 °C and 10 min). Moreover, bioaugmentation with the cellulolytic bacterium Caldicellulosiruptor bescii was applied to possibly enhance the methane production from steam-exploded birch in an anaerobic digestion (AD) process under thermophilic conditions (62 °C). Results: Overall, the combined SE and bioaugmentation enhanced the methane yield up to 140% compared to untreated birch, while SE alone contributed to the major share of methane enhancement by 118%. The best methane improvement of 140% on day 50 was observed in bottles fed with pretreated birch and bioaugmentation with lower dosages of C. bescii (2 and 5% of inoculum volume). The maximum methane production rate also increased from 4-mL CH4/ g VS (volatile solids)/day for untreated birch to 9-14-mL CH4/ g VS/day for steam-exploded birch with applied bioaugmentation. Bioaugmentation was particularly effective for increasing the initial methane production rate of the pretreated birch yielding 21-44% more methane than the pretreated birch without applied bioaugmentation. The extent of solubilization of the organic matter was increased by more than twofold when combined SE pretreatment and bioaugmentation was used in comparison with the methane production from untreated birch. The beneficial effects of SE and bioaugmentation on methane yield indicated that biomass recalcitrance and hydrolysis step are the limiting factors for efficient AD of lignocellulosic biomass. Microbial community analysis by 16S rRNA amplicon sequencing showed that the microbial community composition was altered by the pretreatment and bioaugmentation processes. Notably, the enhanced methane production by pretreatment and bioaugmentation was well correlated with the increase in abundance of key bacterial and archaeal communities, particularly the hydrolytic bacterium Caldicoprobacter, several members of syntrophic acetate oxidizing bacteria and the hydrogenotrophic Methanothermobacter. Conclusion: Our findings demonstrate the potential of combined SE and bioaugmentation for enhancing methane production from lignocellulosic biomass

Puesta a punto de una metodología para la calibración de parámetros del modelo de procesos anaerobios

La depuración de aguas residuales requiere del desarrollo de muchos procesos de transformación de forma simultánea o consecutiva que dificultan su estudio. Además, la complejidad de los procesos de depuración va en aumento no sólo por la aparición de requisitos de vertido cada vez más exigentes sino también por las nuevas tendencias hacia el desarrollo sostenible aplicadas a este proceso y centradas fundamentalmente en el ahorro energético y la recuperación de nutrientes de las aguas residuales para mejorar su ciclo de vida. Por este motivo, se hace necesario el uso de herramientas de simulación que tengan en cuenta todos estos procesos mediante un modelo matemático adecuado y que ayuden a determinar y prever el comportamiento de distintos esquemas de tratamiento. Estos simuladores se han convertido en una herramienta necesaria tanto en el diseño como en el control y optimización del funcionamiento de estaciones depuradoras de aguas residuales (EDAR). Con el fin de que un modelo represente fielmente la realidad y de esta manera pueda emplearse para simular distintos procesos, los parámetros de mayor influencia de dicho modelo deben ser calibrados. El objetivo fundamental de este trabajo final de máster es establecer el montaje y el protocolo experimental para llevar a cabo la calibración de los parámetros correspondientes a las bacterias sulfato reductoras (SRB), con el fin de obtener una metodología que permita conocer los parámetros de todos los procesos que tienen lugar en un tratamiento anaerobio. Para ello se han llevado a cabo distintos ensayos en batch, tanto en botellas individuales como en reactores anaerobios a escala de laboratorio, en los que se ha medido el consumo que se produce a lo largo del tiempo de los ácidos grasos volátiles (AGV) y sulfatos. Llevar a cabo una calibración en procesos anaerobios es una tarea compleja puesto que no existe un parámetro tan fiable y fácil de medir como el oxígeno. Por ello, se hace necesario el establecimiento de un protocolo de manipulación de muestras anaerobias y de las técnicas analíticas a emplear. La medición de sulfatos es un problema tener en cuenta pues se altera cuando la muestra entra en contacto con la atmósfera, debido a que los sulfuros presentes se oxidan químicamente. Para lograr una correcta medida del S04- 2 se probaron distintas formas de extraer la muestra, empleando finalmente una sal metálica para precipitar los sulfuros presentes. La validez de esta puesta a punto de la metodología de calibración de bacterias se ha demostrado obteniendo el valor de la constante de semisaturación (KSO4) y el valor del rendimiento de las bacterias sulfato reductoras (YSRB), pudiendo obtener en un futuro otros parámetros de las bacterias SRB como puede ser la velocidad de crecimiento (µSRB-Ac)

Recuperación Natural Monitorizada

El objeto de aprendizaje describe la tecnología de gestión de sedimentos contaminados mediante recuperación natural monitorizadaPachés Giner, MAV.; Greses Huerta, S. (2024). Recuperación Natural Monitorizada. http://hdl.handle.net/10251/20469

Influence of free ammonia extraction in methane production from human urine

Human urine has a high chemical oxygen demand (COD) content which makes anaerobic treatments potentially appropriate for the management of yellow waters, allowing for energy recovery. However, its high N content makes this treatment challenging. The present work studied the viability of performing an anaerobic digestion process for COD valorization on a real (not synthetic) urine stream at laboratory scale. To deal with nitrogen inhibition, two different ammonia extraction systems were proposed and tested. With them, a proper evolution of acidogenesis and methanogenesis was observed. Nitrogen was recovered in the form of ammonium sulphate, which could be used for agriculture, in two different ways: ammonia extraction from the urine stream before feeding the reactor and in situ extraction in the reactor. The first method, which proved to be a better strategy consisted in a desorption process (NaOH addition, air bubbling and acid (H2SO4) absorption column, HCl for final pH adjustment) whereas the in situ extraction in the reactor consisted of an acid (H2SO4) absorption column installed in the biogas recycling line of both reactors. Stable methane production over 220 mL/g COD was achieved and methane content in the biogas was stable around 71%