Search

This mini-review is intended to explore the innovative applications of nanoparticles (NPs) in biogas upgrading, emphasizing their capacity to enhance biogas quality. Numerous studies underscore how NPs, when applied during anaerobic digestion, can boost not only the quantity but also the quality of the produced biogas, leading to reduce significantly the concentration of hydrogen sulphide or even to remove it completely. Moreover, NPs are proving to be excellent alternatives as adsorbent materials, achieving up to 400mgH2S g−1 NPs. In addition, new studies are exploring the application of NPs to increase the efficiency of biological treatments thanks to their unique features. This review also emphasizes the potential benefits and addresses the challenges that need to be overcome for these technologies to reach their full potential, ultimately contributing to the development of a sustainable and environmentally friendly energy landscape.

This research delves into a detailed exploration of the thermal decomposition behavior of bio-based polymers, specifically thermoplastic starch (TPS) and polylactic acid (PLA), under varying heating rates in a nitrogen atmosphere. This study employs thermogravimetry (TG) to investigate, providing comprehensive insights into the thermal stability of these eco-friendly polymers. In particular, the TPS kinetic model is examined, encompassing the decomposition of three distinct fractions. In contrast, PLA exhibits a simplified kinetic behavior requiring only a fraction described by a zero-order model. The kinetic study involves a systematic investigation into the individual contributions of key components within TPS, including starch, glycerin, and polyvinyl alcohol (PVA). This detailed analysis contributes to a comprehensive understanding of the thermal degradation process of TPS and PLA, enabling the optimization of processing conditions and the prediction of material behavior across varying thermal environments. Furthermore, the incorporation of different starch sources and calcium carbonate additives in TPS enhances our understanding of the polymer’s thermal stability, offering insights into potential applications in diverse industries.

Multilayer flexible packaging waste (MFPW) represents a critical issue in the field of waste management. The heterogeneous composition of this type of plastic makes its recyclability challenging. In this context, the delamination process appears to be a promising way to recycle the polymers layers separately. However, this process is still limited for a few MFPW. This work propose an innovative way to improve the delamination process using three surface modification techniques (mechanical and laser microperforation (µP), and abrasion) on the MFPW surface in order to accelerate the diffusion of the dissolving agent. The delamination was tested in a 10 % sodium hydroxide solution at 25ºC. Under this study, the mechanical µP and the abrasion gave the best results of delamination compared to the laser µP (total delamination in 25 min vs 45 min, respectively). It was concluded that the distance between the microholes was an important factor in both µP techniques.

The drying of flexible plastic waste is a current industrial problem in the plastic recycling sector. The thermal drying of plastic flakes is considered the most expensive and the most energy-consuming step in the recycling chain, which represents an environmental issue. This process is already present on the industrial scale but not well described in the literature. A better understanding of this process for this material will lead to the design of environmentally efficient dryers with an improved performance. The objective of this research was to investigate the behavior of flexible plastic in a convective drying process at a laboratory scale. The focus was to study the factors affecting this process such as velocity, moisture, size and thickness of the plastic flakes in both fixed and fluidized bed systems and to develop a mathematical model for predicting the drying rate considering heat and mass transfer of convective drying. Three models were investigated: the first one was based on a kinetic correlation of the drying, and the second and third models were based on heat and mass transfer mechanisms, respectively. It was found that heat transfer was the predominant mechanism of this process, and the prediction of the drying was possible. The mass transfer model, on the other hand, did not give good results. Amongst five semi-empirical drying kinetic equations, three equations (Wang and Singh, logarithmic and 3rd-degree polynomial) provided the best prediction for both fixed and fluidized bed systems.

Post-consumer low density polyethylene samples were analysed for PAHs, PCDD/Fs and dioxin-like PCBs content. Subsequently, various treatments were applied to determine a process capable of decontaminating the plastic samples: extraction with polyethylene glycol at different temperatures with and without agitation; extraction using subcritical and hot water at different temperatures in a basic medium; compound degradation by ultraviolet radiation; and compound degradation by advanced oxidation processes using H2O2. The most effective treatment was extraction with polyethylene glycol (agitated) at 120 °C, reducing contamination by 89%, 85% and 95% of PAHs, PCDD/Fs, and dioxin-like PCBs, respectively. The least effective treatments (subcritical and hot water), maximum reductions of 47% and 19% of PAHs were obtained for the temperatures of 160 °C and 90 °C. UV oxidation increased the toxic equivalency of the samples (calculated using the toxicity equivalency factors) by up to 1400%, through the co-formation of the most toxic congeners, e.g., the non-ortho PCBs.

The present study aims to determine the presence of synthetic polymeric microparticles (MPs) in samples of canned tuna. An analysis procedure of these microparticles was developed and tested. Four brands of tuna marketed in Ecuador canned both in water and oil were analysed. A significant presence of MPs was found: 692 ± 120 MPs/100g of tuna in water and 442 ± 84 MPs/100g of tuna in oil. Random samples of the liquid covering the tuna fish in the cans showed 6 MPs/mL in the case of water and 5 MPs/mL in the case of oil-containing samples. A total of 90% of the reported particles presented a size range of 1-50µm. The number of MPs present in canned tuna suggests that the ingredients and inputs of the canning process greatly contribute to micro polymers. The identification of the microparticles using fluorescence and micro-FTIR spectrometry revealed that PET, polystyrene and nylon were the most frequent MPs present in the samples analysed.

In the present work, recycled polyethylene (LDPE) samples of agricultural, post-commercial, post-industrial and post-consumer origin were selected and analysed. The analysis comprised the determination of different contaminants such as metals, polycyclic aromatic hydrocarbons (PAHs), dioxin-like biphenyl polychlorides (PCBs), and polychlorinated-dibenzo-p-dioxins and furans (PCDD/Fs). A comparison with one sample of virgin plastic (unrecycled) was performed. The study aimed at stressing the importance of this type of analysis in recycled plastics. Indeed, such an examination will determine the material’s final destination, and the possible origin of the pollutants analysed is investigated. Black post-industrial and post-consumer samples presented the highest concentration of PCBs and PCDD/Fs, attaining a maximum value of 2.40 pg WHO-TEQ/g, while the least toxic sample (post-commercial) presented a toxicity of 0.38 pg WHO-TEQ/g. PAHs content was also much higher in black samples, reaching 514.41 ng/g, while the lowest concentrations were obtained for the post-commercial plastic sample, which did not exceed 38.98 ng/g. The higher PAHs concentrations in the black samples were related to the carbon black content of the black samples, which was 2.00% for black post-industrial sample and 1.51% for post-consumer sample. The PCDD/Fs congener profile observed in almost all samples was very similar to the profile found in the literature on urban air samples, indicating that the plastic is mainly influenced by the environment. The presence of some metals (mainly copper) showed a slight correlation with PCDD/Fs content. The pollutants analysed were found to be significantly reduced during the cleaning processes that are generally carried out in recycling companies.

Este estudio se ha enfocado en desarrollar un protocolo de análisis de microplásticos (MPs) en varias matrices alimenticias, poniendo énfasis en reducir la cantidad de reactivos utilizados y el efecto sobre la integridad de los MPs. De acuerdo con los resultados obtenidos, se identificó las probables rutas de contaminación en los alimentos analizados, procesados de forma industrial y artesanal. Para lograr este objetivo se evaluaron varias técnicas de extracción propuestas por investigaciones en biota marina e investigaciones incipientes en alimentos. En la primera parte se realiza un estudio del estado del arte de la contaminación con polímeros sintéticos y la generación de MPs por meteorización de los macroplásticos, la definición y acuerdos alcanzados con relación a la conceptualización de los microplásticos y se recoge una pequeña revisión de los riesgos que supone su presencia, así como de las técnicas de análisis e identificación, que se reportan hasta la fecha para matrices marinas, suelos y aire. Seguidamente se desarrolla la experimentación con alimentos líquidos procesados, elegidos para la investigación. La miel, leche, refrescos y cerveza son exponentes fundamentales de los alimentos por su composición líquida y permitieron la inserción en las medidas de estandarización y calidad del protocolo, aplicando técnicas de degradación química de la materia orgánica presente en estas matrices. En los alimentos sólidos, cuya composición representa una interferencia de mayor atención en la degradación de la materia orgánica, se detalla el análisis estadístico de la aplicación de técnicas de degradación química y enzimática para fundamentar la elección del protocolo idóneo en estas matrices. Para esta evaluación se utilizan como alimentos de estudio el atún enlatado con dos tipos de líquidos de cobertura, aceite y salmuera y, como representante del reino vegetal, el tomate tipo Cherry, cuyo tipo de cultivo orgánico y convencional permitió analizar la influencia de

Esta tesis estudia el impacto que tienen los COV presentes en los plásticos reciclados para la economía circular. Actualmente, la industria del reciclaje actual no puede cubrir la creciente demanda de plásticos reciclados de alta calidad en los últimos años. Hasta ahora, el reciclaje mecánico es la solución más utilizada a nivel mundial, y su eficacia y fiabilidad han sido demostradas para el tratamiento del residuo plástico post-industrial. Sin embargo, el mismo reciclaje mecánico aplicado a los residuos plásticos post-consumo da lugar a un material reciclado de menor calidad que solamente es apto para aplicaciones de bajo valor añadido, como son las tuberías de riego o cubos de basura. Por ello, esta tesis evalúa la influencia que tienen las sustancias orgánicas que aparecen en los plásticos reciclados post-consumo dentro el sector del plástico.

Multilayer flexible packaging waste is a critical issue in the field of waste management as it is considered a non-recyclable material. One of the solutions to increase its recyclability is the delamination, which allows the recycling of the different polymer layers separately. This study investigated the optimization of the delamination by microperforating this plastic. The diffusion model was described by Fick's first law. The delamination process was tested at three different temperatures (50, 65 and 80 °C) with caustic soda. In addition, the influence of other parameters such as the thickness of aluminium layer, the presence of inks and the use of surfactants was tested. As a result, the microperforation technique improved the delamination rate by decreasing the residence time by 83% at the optimum conditions studied, being the thickness of the metal and the temperature essential factors affecting the process. However, the presence of inks and surfactant had no effect.

In the present study, the photocatalytic activity of carbon nanoparticles (CNPs) in the degradation of methylene blue (MB) using sunlight was analyzed. The CNPs were synthesized by solvent-assisted hydrothermal carbonization (HTC) and were characterized by various spectroscopic techniques: TEM and SEM microscopy, UV-Vis, FTIR, Fluorescence, and XPS. By changing the conditions of the HTC process, the surface chemistry of CNPs was functionalized, thus a great quantity of oxygenated functional groups was generated, which eventually influenced the photocatalytic process. Next, tests were carried out with different types of nanoparticles, varying the concentration of the dye and the type of light used in the irradiation. As a result of this, more than 93% of MB degradation was achieved in 20 min of irradiation using sunlight. This result is promising since it has not been achieved by other nanomaterial. This research can be a potential starting point for the development of new solar photocatalysts.

While the annual European demand for polyolefins is 25 million tonnes, only 3 million tonnes of recycled polyolefins find their place in the market, despite collecting 15 million tonnes of post-consumer polyolefins every year. Brand owners of care products are showing their interest in using post-consumer recycled plastics for their packaging. However, there is a general concern in using these materials, as recycled polymers can contain unwanted substances that may expose the consumer to health risks or make the packaging unattractive. Accordingly, the presence of these contaminants narrows the market opportunity of recycled plastics to applications with low-quality requirements and in which the product is not in direct contact with the consumer. Though mechanical recycling is the most widespread solution presents limitations in terms of decontamination, as only superficial substances are removed. Thereby, the volatile organic compounds (VOCs) migrated to the polymer matrix remain inside. Consequently, there is a need to find a solution to purify recycled plastics and increase their market share. This study focuses on removing VOCs from post-consumer recycled HDPE through two innovative methods applied for the first time in this field, steam stripping and polyethylene glycol (PEG) extraction. The methodology implemented to analyze the volatile organic compounds in HDPE was HS-SPME-GC/MS. Both methods showed a decrease above 70% in the VOCs content compared to extrusion-degassing. Moreover, these were compared to hot air stripping, a new technology developed at an industrial scale for the removal of VOCs. As a result, steam stripping improved efficiency in reducing the overall VOCs compared to hot air stripping. The PEG extraction method lowered the volatile polar compounds further than using hot air stripping. Additionally, none of these technologies modified the HDPE melting flow index.

Hydrochars produced from agro-industrial wastes contain significant amounts of alkali metals and other inorganic elements that lead to different ash-related issues in energy systems. This work aims to modify the composition of hydrochar ash by adding rice hulls and/or mineral additives (i.e., lime, bentonite and kaolin) to improve their fusion behavior. Two series of samples were prepared to analyze the effect that the use of additives before or after the HTC processing of olive mill waste at 225 °C for 2 h had on the hydrochar properties. Hydrochars were then ashed, in agreement with UNE-EN 18122:2016, and the corresponding ashes subsequently characterized through XRF and ash fusion tests to determine their ash composition and ash characteristic fusion temperatures (AFTs), respectively. Among the studied additives, rice hulls led to the best results, as their use increased the initial ash deformation temperature to >1500 °C and resulted in the lowest hydrochar ash content. Using rice hulls before or after the HTC process did not affect the ash behavior, but it did change the hydrochar properties as a fuel. The joint HTC of rice hulls and feedstock led to a less carbonized solid with 13% higher moisture content and 15% lower energy density. Accordingly, the addition of rice hulls to ready-produced hydrochars is recommended to maintain the energy benefits of HTC as possible. The use of rice hulls as a low-cost additive to improve the fusion behavior of hydrochar ash opens new avenues for hydrochars in energy conversion processes with limited ash-related operational problems.

Adsorption represents the most plausible technology for micropollutants removal from water nowadays. Nevertheless, the regeneration of the saturated carbon materials is still an important challenge, being these solids in practice commonly disposed. This work aims at overcoming this issue by using innovative carbon-encapsulated iron nanoparticles (CE-nFe). This material was synthesized by a low-cost and green method viz. hydrothermal carbonization (HTC), using olive mill wastewater as carbonaceous source. The solid was fully characterized by different techniques (magnetic properties, elemental analyses, N2-sorption isotherms, pHPZC, ICP, XRD and TEM). It showed a clear core-shell structure of around 40 nm in diameter. The core was mainly formed by zero-valent iron and the shell by graphitized carbon. Accordingly, it showed an essentially mesoporous structure, with a specific surface area of 169 m2 g−1, and a clear hydrophobic character (pHPZC = 10). Its adsorption performance was investigated using three relevant micropollutants (diclofenac (DCF), sulfamethoxazole (SMX) and metronidazole (MNZ)). A very fast removal of the micropollutants was achieved (30 min at the most, with rate constants in the range of 0.11–0.41 g mg−1 min−1). The adsorption isotherms revealed the vertical packing of the adsorbate molecules onto the adsorbent active centers, being the data successfully described by the GAB model. The saturated adsorbents were effectively regenerated by heterogeneous Fenton oxidation, taking advantage of the iron core of CE-nFe and the opened mesoporous carbon shell. The regeneration efficiency increased with increasing the operating temperature (25–75 °C) and contact time (1–4 h), as well as the H2O2 dose up to 6 g L-1. The micropollutant nature affected the adsorbent regeneration yield in the order: SMX > DCF > MNZ, consistent with their reactivity towards Fenton oxidation.

El sector de los plásticos está experimentando un importante cambio de dirección hacia la sostenibilidad y la innovación. El modelo de Economía Circular como alternativa al modelo tradicional de producción, uso y vertido está generando un gran impacto en nuestra sociedad. La recuperación y reciclaje de materiales se ha convertido en una etapa importante dentro del sector y se prevé que la demanda de productos reciclados aumente en los próximos años. Sin embargo, el sector del reciclaje no está preparado para cumplir la creciente demanda, sobre todo, en cuanto a la calidad de los materiales. En esta tesis se han estudiado los métodos de tratamiento de residuos plásticos desde tres puntos de vista: medioambiental, tecnológico y calidad del producto final. Se ha dedicado un capítulo de la tesis para profundizar en cada uno de estos temas. Para estudiar el impacto medioambiental se ha realizado un análisis de ciclo de vida comparativo entre un proceso de reciclaje innovador alineado con los principios de la Economía Circular y dos métodos de tratamiento de residuos tradicionales. Desde el punto de vista tecnológico, se ha estudiado el proceso de eliminación de agua durante el reciclaje de plásticos flexibles con el objetivo de optimizar parámetros y reducir el consumo de energía. Por último, se llevado a cabo un estudio de las sustancias orgánicas semivolátiles presentes en plásticos reciclados, ya que éstas pueden suponer un riesgo para la salud de los consumidores si se utilizan en aplicaciones de alto valor añadido. Además, se ha realizado un estudio exhaustivo del estado del arte de los sistemas de gestión de residuos plásticos, prestando especial atención a los plásticos flexibles debido a que su tasa de reciclaje se encuentra por debajo de los plásticos rígidos. Como resultado se han identificado los puntos débiles y se han marcado directrices para impulsar la transición hacia la Economía Circular.

Plastic demand is continuously growing and, with it, the amount of plastic waste. The packaging industry is by far the largest source of single-use plastic products that, after use, end up in landfills and oceans. Mechanical recycling is the solution most widely implemented in the global industry and its effectiveness and reliability have been demonstrated for processing post-industrial plastic scrap. The recycling of post-consumer plastic waste, however, requires an upgrade in the current technology to achieve complete decontamination and removal of malodorous substances embedded in the polymer. This review explores the state-of-the-art technology currently employed in the mechanical recycling of plastic waste, focusing on the progress made for the removal of volatile organic compounds emitted from recycled materials. Followed by a review of the analytical techniques that have been applied for the identification of volatile organic compounds, including, in particular, the techniques used for the identification of odor-active substances. Finally, this review gathers from literature all the volatile organic compounds and odor-active substances identified in virgin and recycled polymers, aiming to evaluate whether there is a notable difference between them based on the chemical structure of the emitted VOCs. As a result, 437 volatiles were gathered, which show the difference between post-consumer recycled plastics and the other plastic waste sources. A larger number of volatile organic compounds, especially flavor and fragrances-based substances as well as oxygenates, appear in post-consumer plastic waste compared to virgin and post-industrial plastic scrap.

In this study, carbon nanoparticles (CNP) have been synthetized by the method of hydrothermal carbonization (HTC), which entails low cost, minimum equipment requirement, and less synthesis time. In order to improve the characteristics and the mass yield of CNP, a variation in the HTC process has been developed; which consists in introducing a blend of organic solvent with water into the reactor, instead of only water. The precursor is the glucose and three organic solvents were tested: hexane, toluene, and butyl acetate at different reaction times: 1, 2 and 4 h. The size distribution of the CNP doesn't depend on the synthesis conditions. But, the mass yields of the CNP has an incredibly increase with the variation of process, this phenomenon is observed with all organic solvents at only 1 h of reaction time. With butyl acetate the highest degree of dehydration was achieved according to the Ven Krevelen diagram and the FT-IR spectra. Besides, with this organic solvent, the highest Photoluminescence Quantum Yield was reached.

In this work, the environmental impacts caused by an innovative upcycling process of printed plastic scrap have been assessed through Life Cycle Analysis (LCA) methodology for the first time. The process consists of removing the inks from the plastic surface before extrusion, so that clear high quality pellets are obtained, suitable to be used in high added value applications (such as packaging). The upcycling technology is compared with two traditional waste treatments: conventional recycling (or downcycling) and incineration with energy recovery. Upcycling is considered to be better aligned with Circular Economy principles and its implementation in the industry requires a comprehensive analysis of environmental impacts. Despite the importance of this topic, only a few studies can be found in the literature. Furthermore, the lack of uniformity and consensus in LCA modelling can lead to the conclusion that upcycling causes the biggest environmental burdens. Therefore, downcycling or incineration are shown as preferable options, regardless of the irreversible loss of the plastics’ potential to be recirculated. To avoid this error, we have emphasised the importance of including the market share for recycled products in the LCA modelling and establishing the virgin plastic substitution ratio correctly. Also, we have suggested that in the perspective of the Circular Economy, the energy produced during incineration cannot substitute the energy from fossil fuels.

Patulin (PAT), a mycotoxin found mainly in matured apples, is produced by different species of fungi, mainly Penicillium expansum, and is found in various fruits and vegetables used to produce juice. Little focus has been placed on nano-technological methods for the mitigation of this problem. In this work, carbon-encapsulated nano-zero valent iron (CE-nZVI) particles were synthesized and used as heterogeneous Fenton agents for the degradation of PAT in apple juice. The particles were found to have a spherical shape with a diameter of 130 ± 50 nm. In a heterogeneous Fenton degradation (involving CE-nZVI) process, a concentration of 0.05 g/L CE-nZVI with 0.5 mM H2O2 was used. Since the Fenton oxidation process is pH-dependent, placebo degradation was observed at varying pH conditions with an average percentage of PAT degradation of 27.8%, 87.0%, 98.0%, and 99.75% at pH 6, 5, 4.5, and 3.5 respectively, between 1 min to 4 h in a water matrix. In a juice matrix, at the regular pH of juice (3.6), percentage PAT degradation of 72% and 89% was obtained after a 2-h treatment using heterogeneous Fenton oxidation (CE-nZVI/H2O2) systems, using 0.5 mM H2O2 and 1 mM H2O2, respectively.

The demand for high quality recycled polymers in the European plastic industry is on the increase, likely due to the EU’s Plastic Strategy intended to implement the circular economy model in this sector. The problem is that there is not enough recycled plastic in the market. In terms of volume, post-consumer plastic waste could be key to meet the current and future demand. Nevertheless, a high level of contamination originated during the product’s life cycle restricts its use. The first step to change this must be identifying the undesired substances in post-consumer plastics and performing an effective risk assessment. The acquired knowledge will be fundamental for the development of innovative decontamination technologies. In this study, 134 substances including volatile and semi-volatile compounds have been identified in recycled LDPE and HDPE from domestic waste. Headspace and solvent extraction followed by GC/MS were used. The possible origin of each substance was studied. The main groups were additives, polymer and additives breakdown products, and contamination from external sources. The results suggest that recycled LDPE contains a broader number of additives and their degradation products. Some of them may cause safety concerns if reused in higher added value applications. Regarding recycled HDPE, the contaminants from the use phase are predominant creating problems such as intense odors. To reduce the number of undesired substances, it is proposed to narrow the variety of additives used in plastic manufacturing and to opt for separate waste collection systems to prevent cross-contamination with organic waste.