González Fermoso, FernandoZahedi Díaz, SorayaCaroca Sepúlveda, Eric Nicolás2024-09-052024-09-052024-06-142024-06-14https://hdl.handle.net/10433/21640Programa de Doctorado en Biotecnología, Ingeniería y Tecnología Química Línea de Investigación: Tecnología Química y de Materiales Clave Programa: DBI Código Línea: 112Trace elements (TE) are necessary for anaerobic digestion (AD) since many are essential in the metabolic pathways of microorganisms. However, depending on their concentration, they can also have inhibitory or toxic effects. The digestate, a by-product of AD, can be used as fertilizer but the presence of TE could impede its use due to potential contamination in soil and crops. TE can be present under different species amongst which only the bioavailable ones are responsible for the biological response. Diffusive gradients in thin films (DGT) is a passive sampling technique that quantifies the labile fraction, which can be related to the bioavailable fraction. DGT has been studied in waterbodies, sediments, and solids systems, but its application to anaerobic digestates is not straightforward and the methodology must be carefully adapted. The main objectives of this research were to analyze the impact of the presence of a trace element, Cobalt (Co), in the operation of an anerobic reactor and to evaluate the feasibility of using the DGT technique in anaerobic systems: in digestates and also directly inside a bioreactor. Firstly, the effect of continue addition of different concentrations of Co in an upflow anaerobic sludge bed reactor (UASB) was studied. UASB performance was monitored at three different positions along the reactor: bottom and top sludge, and liquid zone. Co concentration for solid (granules), liquid soluble, and extracellular polymeric substances (EPS) were measured in these samples. Biogas production was affected positively for Co dose lower and equal to 50 µM of Co and negatively for Co dose higher than 100 µM of Co. A general decrease in EPS was observed due to Co dose, which compromised the granular stability. No strong differences were observed in Co profile along the depth in the reactor for solid and liquid soluble fractions. The solid Co concentration was around 1000 times higher than the liquid concentrations, indicating a high accumulation of Co in the granules. However, the Co accumulated was found as inert species. In a second stage, Chelex, Zirconia, and Thiol DGT devices were deployed in two different digestates to evaluate the applicability of the passive sampling technique. Time-series deployments were performed in presence and absence of air to determine whether maintaining anaerobic conditions is mandatory. A theoretically expected linear accumulation profile was observed for some TE only (Fe, Mn, Ni or As(III)), depending on the digestate, whereas other elements were detected without a consistent trend over time (Al, As, and Cu). The labile fraction of Co, Cu, Fe and Mn demonstrated changes over a 72 h period when deployments occurred in the presence of air. In the third stage, DGT devices were deployed inside the UASB under Co stress to assess the feasibility of using DGT directly inside a reactor. Biogas accumulation was observed inside the DGT, which invalidated the device. Different deployment configurations were evaluated to limit the phenomenon. The valid deployment was restricted to a perpendicular flow for a maximum of 4 h in the liquid zone, and 8 h in the sludge zone. Additionally, repeatability problems were observed, which indicates the presence of unidentified problems still to be solved. DGT thus appears applicable to evaluate the labile fraction of some TE in digestates but requires careful verification. Consequently, it is recommended to conduct time-series deployments to identify only the elements displaying a linear accumulation trend. Anaerobic conditions should be maintained during deployment to avoid significant shifts in the labile fraction over time. The direct deployment of DGT in an UASB induced some problems and limitations still to be solved.application/pdfenAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Tecnología de aguas residualesdoctoral thesisopen access