Anaerobic co-digestion of municipal sewage sludge and fruit/vegetable waste: effect of different mixtures on digester stability and methane yield

There are different options for the management of fruit and vegetable wastes (FVWs), but the most environmental-friendly is the anaerobic digestion, because it allows an optimum recovery of materials and energy from the two by-products: biogas and digestate. Nevertheless, in many cases there are economic and technical problems that cause the selection of other alternatives. Frequently these wastes are produced in large quantities but only during few weeks of the year. In these cases, this is the most important economic problem, because large digesters that would be used only for short time periods every year would be required. In addition, a close control of the pH of the digester is required for this kind of residues, for which the hydrolysis is usually faster than the methanogenesis, so large concentrations of fatty acids should be prevented to maintain the adequate pH value for anaerobic digestion that should be neutral or slightly alkaline. Both problems can be simultaneously overcome by the co-digestion with other residues that are produced throughout the year. Among the benefits of co-digestion, one of the most important is the improvement in the feedstock characteristics, since it may allow a more equilibrate composition resulting in a better performance of the digester in treatment capacity, and a better quality of biogas and digestate. The co-digestion with other substrates with a complementary composition that are produced throughout the year and that are already managed by anaerobic digestion is probably the optimum management option. For these cases, if the existing anaerobic digester is oversized and allows the introduction of additional volumes of wastes, the mean retention time of the digestate should be maintained. Therefore, the anaerobic co-digestion of fruit and vegetable waste (FVW) and municipal sewage sludge (MSS) under mesophilic condition and a constant hydraulic retention time (20 d) is studied. The effects on digester performance of the FVW:MSS ratio and the organic loading rate (OLR) were examined. The OLR is the mass of volatile solids fed per volume of digestate and day.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Effect of NaHCO3 addition on the anaerobic co-digestion of fruit and vegetable waste and sewage sludge performance

Digestion of FVW residues with sewage sludge is feasible as long as the FVW to sludge ratio fed to the batch digester is not too large. The pH is the main variable determining the reactor performance and can be controlled by NaHCO3 addition.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Co-digestion of mixed sewage sludge and fruit and vegetables wastes effect of different mixtures on biogas yield

Disposal of fruit and vegetable wastes (FVWs) in landfill site cause serious environmental issues such as contamination of soil, air and ground water. These wastes contain large quantities of biodegradable organic fractions, with high moisture that facilitates their biological treatment. One of the best alternatives to landfill disposal of these wastes is the anaerobic digestion. Therefore, it is one of the most widespread stabilization processes of the sludge in municipal wastewater treatment plants (WWTP). Introduction of FVW in WWTP and co-digestion with mixed sludge (MS) could enhance biogas production and plant economic feasibility. A lab-scale experiment for the anaerobic co-digestion of FVW and municipal mixed sludge under mesophilic condition and 20 days hydraulic retention time is investigated. Initially the digester was fed with mixed sludge (MS) from wastewater treatment plants with an average organic loading rate (OLR) of 0.63 (g L–1 d–1). The co-digestion of mixed sludge and FVW was performed at various organic loading ratios (OLRs), between 0.63 and 5.5 (g L–1 d–1). The experimental specific biogas and methane productions are 0.656 L g–1 and 0.340 L g–1 respectively. Alkalinity and pH remains relatively constant regardless the introduction of different proportions of FVW in the mixture. Co-digestion, compared with the digestion of MS as single substrate, improves the biogas and methane production.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Anaerobic co-digestion of pear residues and sewage sludge using a CSTR digester. Influence of the feed procedure

Anaerobic co-digestion of pear residues with sewage sludge is feasible. Important differences are obtained from the two feed regimes tested, with better results for the so-called continuous feed. The organic loading rate (OLR) is the important parameter for the methane productionUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Digestión y Codigestión Anaerobia de Residuos Agrícolas, Ganaderos y Lodos de Depuradora

En este sentido, se evaluó la codigestión de los purines de cerdo (PC) con residuos de fruta (RF). Así, se detectó un incremento en la producción de biogás de 0,48 L L-1d-1 a 3,33 L L-1d-1 y de eliminación de materia orgánica de 49 % a 70 % para una relación RF/PC de 92:8. Asimismo, la relación C/N incrementa de 8,56 a 25,54, lo cual conlleva una dismunición del riesgo de inhibición por amonio o por ácidos grasos volátiles. Por lo tanto, esta opción puede ser una buena alternativa para la mejora del rendimiento energético y de los beneficios económicos y medioambientales de una planta a escala de granja. También se ha explorado el potencial de la codigestión de lodos mixtos municipales (LMM) procedentes de las EDAR con residuos de fruta y verdura (FVW) generados en el mercado central de Málaga. Se investigó el efecto de las diferentes ratios de FVW/LMM y la carga orgánica (COV) a un tiempo de retención hidráulico constante (20 d) y se encontró que el aumento de la proporción de FVW en la mezcla favorece un incremento de la la tasa de producción de biogás pasando de 0,48 L L-1d-1 a 3,10 L L-1d-1 y de eliminación de solidos volátiles de 39 % a 82 %. Además, el digestor se mantuvo estable durante todos los ensayos. Asimismo, en el caso de la codigestión de LMM y FVW, se evaluó el efecto de la estacionalidad sobre el rendimiento y la estabilidad del digestor, observándose que las características de los FVW de diferentes estaciones del año son relativamente similares, incluso para los LMM. Los resultados obtenidos reflejan la estabilidad del digestor con unas escasas diferencias respecto a la producción de biogás, al mismo tiempo que permiten tener una visión general sobre la posibilidad de la introducción de residuos de fruta y verdura junto con los lodos mixtos municipales en los digestores anaerobios de las EDAR.Muchas regiones de España se distinguen por una agricultura altamente productiva y una industria porcina intensiva que generan grandes cantidades de residuos orgánicos. Además, la cantidad de lodo de depuradora se incrementa cada año. En términos de respeto del medio ambiente, ello hace necesaria una buena gestión de estos residuos. A modo de ejemplo, estos residuos pueden ser buenos candidatos para la producción de bioenergía. La digestión anaerobia, por un lado, es una prometedora vía y una sólida alternativa a los tratamientos convencionales y, por otro, este proceso además de reducir el impacto ambiental y la cantidad de residuos orgánicos y permite la producción de metano, pudiendo revalorizarlos como bioenergía. En este trabajo, se ha estudiado el efecto de la carga orgánica volumétrica (COV) y los modos de alimentación (modo discontinuo vs modo continuo) de residuos de pera como monosustrato, evaluando sus impactos sobre la estabilidad del digestor y la producción de biogás. Se observó que la alimentación en continuo presenta muchas ventajas en términos de la cantidad del residuo a tratar (10,5 vs 6 g L-1d-1) y del volumen de biogás producido (23,21 vs 13,71 L d-1), incluso en la estabilidad del digestor. En el caso de purines de cerdo, se evaluó y comparó la digestión anaeróbica de muestras que provienen de diferentes balsas de decantación de granja, así como de muestras pretratadas por sedimentación o centrifugación. Asimismo, se investigó la opción de concentrar los purines de salida de la granja aumentando la fracción sólida y se detectó una mejora en la producción específica de metano de 0,158 Lgsv-1 a 0,249 Lgsv-1. Sin embargo, en el caso de la monodigestión de purines de cerdo, la producción de biogás es baja y existe riesgo de inhibición a causa del amonio. La codigestión anaerobia presenta amplias posibilidades de aplicación puesto que permite el tratamiento conjunto de distintos sustratos

Lichen rehydration in heavy metal polluted environments: Pb modulates the oxidative response of both Ramalina farinacea thalli and its isolated microalgae

Lichens are adapted to desiccation/rehydration and accumulate heavy metals, which induce ROS especially from the photobiont photosynthetic pigments. Although their mechanisms of abiotic stress tolerance are still to be unravelled, they seem related to symbionts' reciprocal upregulation of antioxidant systems. With the aim to study the effect of Pb on oxidative status during rehydration, the kinetics of intracellular ROS, lipid peroxidation and chlorophyll autofluorescence of whole Ramalina farinacea thalli and its isolated microalgae (Trebouxia TR1 and T. TR9) was recorded. A genetic characterization of the microalgae present in the thalli used was also carried out in order to assess possible correlations among the relative abundance of each phycobiont, their individual physiological responses and that of the entire thallus. Unexpectedly, Pb decreased ROS and lipid peroxidation in thalli and its phycobionts, associated with a lower chlorophyll autofluorescence. Each phycobiont showed a particular pattern, but the oxidative response of the thallus paralleled the TR1's, agreeing with the genetic identification of this strain as the predominant phycobiont. We conclude that: (1) the lichen oxidative behaviour seems to be modulated by the predominant phycobiont and (2) Pb evokes in R. farinacea and its phycobionts strong mechanisms to neutralize its own oxidant effects along with those of rehydration

Effect of hydroxylammonium chloride as a reductant for hydrochloric acid leaching of valuable metals from discarded lithium-ion batteries

The use of hydroxylammonium chloride as a reducing agent is proposed to enhance the acid leaching of cathode material from spent lithium-ion batteries. The current study was conducted using real waste from scooter bat- teries. The main metals found in this cathode material are Mn (43.6%), Li (4.2%), Ni (8.3%) and Co (2.6%), expressed as % w/w. The effect of the initial concentrations of the extracting agent (HCl) and the reducing agent (NH3OHCl) on the extraction yields of the target metals is investigated. The presence of NH3OHCl in HCl so- lutions exerts a highly effective influence during the initial 15 min of the leaching process, with a complete solubilization of Mn within that timeframe, in contrast to the 20% achieved in its absence. During that period, over 70% of Li is solubilized, while Ni and Co reach maximum solubilities of 7% and 5%, respectively. Extending the contact time to 24 h between the extracting solution and LIB waste enables nearly complete extraction of Ni and exceeds 60% for Co. An analysis of variance was used to identify significant factors to be included in multivariable regressions to predict extraction yields. These regressions are used to carry out a preliminary economic analysis of the leaching process based on gross profit. The optimum outcome is achieved when the extraction is conducted through two consecutive leaching processes. In the first process, 100% Mn and 75% of Li are recovered, while the second process recovers the remaining Li, 96% of Ni, and 60% of cobalt. Additionally, the stoichiometry of the reduction of manganese(IV) by NH3OHCl is studied through the correlation between the gas volume released during the leaching processes and the Mn solubilization reached. This reduction proceeds through two parallel reactions, resulting in the production of N2O and N2. The first of these reactions pre- dominates, exhibiting an estimated selectivity of 87%.Authors acknowledge the financial support provided by the Euro- pean Union’s Horizon 2020 research and innovation programme through the Marie Skłodowska-Curie grant agreement No. 778045 and by the Spanish Ministry of Science and Innovation and the University of Málaga through the Research Project PID2021-126794OB-100. Authors acknowledge the funding from the University of Malaga (B1-2021_35). Cerrillo-Gonzalez also acknowledges the postdoctoral grant (A.3.1) ob- tained from the University of Malaga. We also acknowledge all the collaboration from LONDON WEEE, S.A for providing the LIBs residues. Funding for open access charge: Universidad de Málaga/CBU