• Energy Research

Research was carried out with the aim of monitoring anaerobic digestion processes using thermal analysis with the aid of mass spectrometry so as to define the stability of the digestate obtained. Three different systems were investigated under varying conditions. The digestion of waste sludge from a pharmaceutical industry (PI) and the digestion of cattle manure (CM) were evaluated under mesophilic conditions. The co-digestion of a mixture of primary sludge (PS) and the organic fraction of municipal solid wastes (OFMSW) was studied under thermophilic conditions. Temperature-programmed combustion tests were carried out to investigate the degree of stabilization of samples throughout the digestion processes. The derivative thermogravimetry (DTG) profiles obtained for the mesophilic digestion of PI waste showed a decrease at low temperatures and an increase at high temperatures in the intensity of the peaks recorded as the stabilization process proceeded. These results are in accordance with those obtained by the present authors in their previous work on the mesophilic digestion of primary sludge and OFMSW. In contrast, the DTG profiles obtained from the stabilization process of CM and thermophilic codigestion of PS and OFMSW showed a reduction in peaks at high temperatures. When the stabilization products obtained from CM by anaerobic digestion and by composting processes were compared, it was observed that the composting process was capable of further decomposing materials readily oxidized at low temperatures and increasing the presence of structurally more complex substances. The evolution of the differential thermal analysis (DTA) signal recorded simultaneously showed considerable similarity to the mass/charge (m/z) signal 44 registered by the mass spectrometer. The use of mass spectrometry helped to clarify the inner workings of the digestion process.

La crisis climática es, desde el punto de vista científico, el mayor desafío que enfrentan las sociedades. Se hace urgente preparar a la ciudadanía para generar cambios de comportamiento a favor del clima en los próximos años. El objetivo específico de este trabajo era evaluar el nivel de desarrollo de la alfabetización climática (AC) antes (fase PRE) y después (fase POS) de la implementación de una intervención sobre el cambio climático (CC), en el alumnado de 3° de ESO pertenecientes a un centro educativo de Castellón, España. Previamente se realizó el diagnóstico de las opiniones y el nivel de conocimiento acerca de la ciencia del clima o AC en los alumnos de 2°, 3° y 4° de la ESO y en el profesorado de este centro. Por tanto, este trabajo de investigación tuvo como meta global ser una contribución a la AC mejorando la comprensión por parte del alumnado de 3° de ESO del tema del calentamiento global antropogénico, o CC, a través de la implementación del programa “cambio climático” diseñado para este fin. La comparativa de resultados antes y después de implementar este programa mostró la existencia de mejoras estadísticamente significativas en algunos de los dominios de conocimiento de la ciencia del clima. Se trasciende que la educación climática es esencial para el desarrollo de visiones del mundo significativas, la comprensión de la ciencia del clima y el compromiso y participación en actividades pro-climáticas. From a scientific perspective, climate crisis is the greatest challenge facing societies. There is an urgent need to prepare citizens for pro-climate changes in the coming years. The specific objective of this study was to evaluate the level of development of climate literacy (CL) before (PRE phase) and after (POS phase) the implementation of an intervention on climate change (CC) in the 3rd grade students in Compulsory Secondary School belonging to an educational centre in Castellón, Spain. Previously, the diagnosis on the opinions and the level of knowledge about climate science or CL of 2nd, 3rd and 4th grade students and teachers at this school was made. Therefore, the overall goal of this research work was to contribute to climate literacy by improving the understanding of 3rd grade students of the topic of anthropogenic global warming, or CC, through the implementation of the "climate change" program designed for this purpose. Comparison of results before and after implementing this program showed statistically significant improvements in some of the climate science knowledge domains. It is transcended that climate education is essential for the development of meaningful worldviews, understanding of climate science and engagement and participation in pro-climate activities.

The potential of using anaerobic digestion for the treatment of poultry blood has been evaluated in batch assays at the laboratory scale and in a mesophilic semi-continuous reactor. The biodegradability test performed on residual poultry blood was carried out in spite of high inhibitory levels of acid intermediaries. The use of activated carbon as a way to prevent inhibitory conditions demonstrated the feasibility of attaining anaerobic digestion under extreme ammonium and acid conditions. Batch assays with higher carbon content presented higher methane production rates, although the difference in the final cumulative biogas production was not as sharp. The digestion of residual blood was also studied under semi-continuous operation using granular and powdered activated carbon. The average specific methane production was 216 ± 12 mL CH4/g VS. This result was obtained in spite of a strong volatile fatty acid (VFA) accumulation, reaching values around 6 g/L, along with high ammonium concentrations (in the range of 6-8 g/L). The use of powdered activated carbon resulted in a better assimilation of C3-C5 acid forms, indicating that an enhancement in syntrophic metabolism may have taken place. Thermal analysis and scanning electron microscopy (SEM) were applied as analytical tools for measuring the presence of organic material in the final digestate and evidencing modifications on the carbon surface. The addition of activated carbon for the digestion of residual blood highly improved the digestion process. The adsorption capacity of ammonium, the protection this carrier may offer by limiting mass transfer of toxic compounds, and its capacity to act as a conductive material may explain the successful digestion of residual blood as the sole substrate.

Thermogravimetric analysis coupled to mass spectrometry (TGA-MS) and Fourier-transform infrared spectroscopy (FTIR) were used to describe the effect of pasteurization as a hygienic pre-treatment of animal by-products over biogas production. Piggery and poultry meat wastes were used as substrates for assessing the anaerobic digestion under batch conditions at mesophilic range. Poultry waste was characterized by high protein and carbohydrate content, while piggery waste presented a major fraction of fat and lower carbohydrate content. Results from anaerobic digestion tests showed a lower methane yield for the pre-treated poultry sample. TGA-MS and FTIR spectroscopy allowed the qualitative identification of recalcitrant nitrogen-containing compounds in the pre-treated poultry sample, produced by Maillard reactions. In the case of piggery waste, the recalcitrant compounds were not detected and its biodegradability test reported higher methane yield and production rates. TGA-MS and FTIR spectroscopy were demonstrated to be useful tools for explaining results obtained by anaerobic biodegradability test and in describing the presence of inhibitory problems.

Anaerobic digestion of livestock wastes with carbon rich residues was studied. Swine manure and poultry litter were selected as livestock waste, and vegetable processing waste was selected as the rich carbon source. A Central Composite Design (CCD) and Response Surface Methodology (RSM) were employed in designing experiments and determine individual and interactive effects over methane production and removal of volatile solids. In the case of swine manure co-digestion, an increase in vegetable processing waste resulted in higher volatile solids removal. However, without a proper substrate/biomass ratio, buffer capacity of swine manure was not able to avoid inhibitory effects associated with TVFA accumulation. Regarding co-digestion with poultry litter, substrate concentration determined VS removal achieved, above 80 g VSL(-1), NH(3) inhibition was detected. Statistical analysis allowed us to set initial conditions and parameters to achieve best outputs for real-scale plant operation and/or co-digestion mixtures design.

Abstract Mesophilic anaerobic digestion of slaughterhouse waste (SHW) and its co-digestion with the organic fraction of municipal solid waste (OFMSW) have been evaluated. These processes were carried out in a laboratory plant semi-continuously operated and two set-ups were run. The first set-up, with a hydraulic retention time (HRT) of 25 days and organic loading rate (OLR) of 1.70 kg VS m −3 day −1 for digestion, and 3.70 kg VS m −3 day −1 for co-digestion, was not successful. The second set-up was initiated with an HRT of 50 days and an OLR of 0.9 kg VS m −3 day −1 for digestion and 1.85 kg VS m −3 day −1 for co-digestion. Under these conditions, once the sludge had been acclimated to a medium with a high fat and ammonia content, it was possible to decrease the HRT while progressively increasing the OLR to the values used in the first set-up until an HRT of 25 days and OLRs of 1.70 and 3.70 kg VS m −3 day −1 , for digestion and co-digestion, respectively (the same conditions of the digesters failures previously). These digesters showed a highly stable performance, volatile fatty acids (VFAs) were not detected and long chain fatty acids (LCFAs) were undetected or only trace levels were measured in the analyzed effluent. Fat removal reached values of up to 83%. Anaerobic digestion was thus found to be a suitable technology for efficiently treating lipid and protein waste.

Abstract The thermophilic anaerobic digestion of cheese whey was evaluated using a single and two stage configuration (H2–CH4) in a sequencing batch reactor (SBR). The single stage process presented stable performance with a specific methane production (SMP) of 314.5 ± 6.6 L CH4 kg−1 CODfeed (Chemical oxygen demand) at a hydraulic retention time (HRT) of 8.3 days. On the contrary, the two stage process presented instabilities at an HRT of 12.5 days with acid accumulation being observed in the methanogenesis phase at an earlier stage. This behaviour was indicative of process inhibition by high concentrations of sodium and potassium ions as a consequence of pH control during the H2 producing stage. In spite of this phenomenon, this condition attained the highest SMP value (340.4 ± 40 L CH4 kg−1 CODfeed). The performance of the anaerobic digestion process was also analysed by means of Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The two stage process showed higher content in triacylglycerol groups probably associated with changes in archaeal lipid complexes as a microbial response to a higher salinity environment.

Anaerobic co-digestion involves the treatment of different substrates with the aim of improving the production of biogas and the stability of the process. In this research, co-digestion of swine manure (SM) and energy crop residues (ECRs) was studied. The mixtures evaluated contained SM combined with maize (Mz), rapeseed (Rs) or sunflower (Sf) residues. Batch and semi-continuous experiments were performed to determine methane (CH4) yields and the behavior of reactors while co-digesting agricultural wastes. Three different proportions of ECRs were tested in batch experiments for co-digestion with SM: 25, 50, and 75% volatile solids (VS). On the basis of the results obtained from batch tests, a mixture with a 50% ECR content was selected for the second stage of the study. Mesophilic reactors with a 3 L working volume were used for semi-continuous experiments. The hydraulic retention time (HRT) was set at 30 days and the reactors were kept under these operational conditions over four HRTs. The addition of ECR to the co-digestion system resulted in a major increase in the amount of biogas produced daily. The highest biogas yield was obtained when co-digesting Rs (3.5 L/day), although no improvement was observed in specific gas production from the addition of the co-substrate.