Spent Coffee Grounds Research Articles

Sustainable Activated Carbon from Agricultural Waste: A Study on Adsorption Efficiency for Humic Acid and Methyl Orange Dyes

In this study, porous activated carbon was produced from coffee waste and used as an effective adsorbent for the removal of humic acid (HA) from seawater and methyl orange (MO) dye from aqueous solutions. Phosphoric acid H3PO4 was used as an activating agent for the chemical activation of these agricultural wastes. The characterization of the activated carbon obtained using a scanning electron microscope (SEM), Fourier-transform infrared (FTIR) spectroscopy analysis, X-ray diffraction (XRD) and the Brunauer–Emmett–Teller (BET) method revealed that the activated carbon products exhibited high porosity and the formation of various functional groups. The effects of different parameters were examined using batch adsorption experiments, such as the adsorbent masses, pH, initial pollutant concentration and contact time. The results show that the performance increased with an increased adsorbent mass (up to 0.25 g/L) and decreased initial concentration of the adsorbent tested. On the other hand, this study clearly showed that the adsorption efficiency of the MO on the raw spent coffee grounds (SCGs) waste was around 43%, while no removal was observed for the humic acid. The experiments demonstrated that the activated carbon synthesized from the used coffee grounds (the efficiency was compared with commercial activated carbon (CAC) with a difference of 13%) was a promising alternative to commercially available adsorbents for the removal of humic acid from seawater. To understand and elucidate the adsorption mechanism, various isothermal and kinetic models were studied. The adsorption capacity was analyzed by fitting experimental data to these models. The experimental data for methyl orange dyes were analyzed using Langmuir and Freundlich isothermal models. The Freundlich isotherm model provided a superior fit to the equilibrium data, as indicated by a higher correlation coefficient (R2) than that of the Langmuir model. The maximum adsorption was observed at pH 3. The Freundlich adsorption capacity was found to be 333 mg/g adsorbent. The PAC showed a high adsorption capacity for the MO and HA. The PAC showed the highest adsorption capacities for the HA and MO compared with the other adsorbents used (SCGs and CAC) and would be a good material to increase the adsorption efficiency for humic acid removal in the seawater pretreatment process. In addition, the prepared AC BET surface area was 520.40 m2/g, suggesting a high adsorption capacity. This makes the material potentially suitable for various applications that require a high surface area. These results indicate that high-quality sustainable activated carbon can be efficiently produced from coffee waste, making it suitable for a wide range of adsorbent applications targeting various pollutants.

Microbiome Evolution of Brewer’s Spent Grain and Spent Coffee Ground Solid Sidestreams Under Industrial Storage Conditions

Brewer’s spent grain (BSG) and spent coffee ground (SCG) are solid sidestreams from beverage production increasingly being upcycled into food, feed and other value-added products. These solid sidestreams are prone to microbial spoilage, negatively impacting their upcycling potential. Three samples each of BSG and SCG were obtained from generators and recycling facilities in Singapore, and their chemical, elemental, and microbial composition was characterized. The spoilage mechanisms were investigated during storage under anaerobic and aerobic conditions. Bacterial loads of sidestreams were low from craft brewery and café sources (<1 and 3.53 ± 0.03 log10 CFU/g) and high from recycling facilities (>6 log10 CFU/g). The microbiome of BSG from recycling facilities was dominated by Bacilli, and B. coagulans was identified as the most prevalent species. SCG from recycling facilities was dominated by lactic acid bacteria, with L. panis being the most prevalent species. Storage up to 14 days under anaerobic conditions led to further bacterial proliferation mainly by Bacilli, lactic acid bacteria, and acetic acid bacteria, while aerobic storage led to extensive fungal contamination, including potential aflatoxin-producing Aspergillus flavus. The results shed light on the spoilage mechanisms, while highlighting the short shelf-life and food safety risks of BSG and SCG to inform valorization strategies.

Sustainable Valorisation of Coffee Waste as a Protein Source, Mycelium-Based Packaging Material and Renewable Energy Pellet

This study investigates the valorization of spent coffee grounds (SCGs) through protein extraction and their application in mycelium-based packaging and renewable energy pellets. Three extraction methods—mechanical stirring, ultrasound-assisted, and CO2-assisted extraction—were applied to SCGs. CO2-assisted extraction yielded the highest protein content at 34.24%, followed by mechanical stirring (31.46%) and ultrasound-assisted extraction (28.51%). The total polyphenol content and antioxidant capacity were also highest in the CO2 extracts, suggesting that this method preserves bioactive compounds most effectively. After protein extraction, SCGs were tested as a component in mycelium-based packaging, with results showing an apparent density of 0.551 g/cm3 and compression resistance of 3.354 MPa, indicating its suitability for structural applications. The energy value of SCGs remained high, with a calorific value of 19,887 J/g DW, slightly decreasing after extraction but still sufficient for renewable energy production. These findings highlight the potential of SCGs as a multi-functional resource, contributing to sustainable solutions across various industries.

Development of modified MgO/biochar composite for chemical adsorption enhancement to cleanup fluoride-contaminated groundwater

Fluoride contamination in groundwater has become a global environmental issue. Magnesium oxide (MgO) has demonstrated effectiveness as an adsorbent in treating fluoride pollution in groundwater. However, its use in powder and fine granular form often results in losses during the adsorption process, posing challenges for post-treatment recovery and potentially causing secondary environmental pollution. In this study, two novel fluoride adsorbents [rice husk (RH) and spent coffee grounds (SCG)-based magnesium oxide (MgO) biochar composites (MgO/RH and MgO/SCG)] were developed to cleanup fluoride-polluted groundwater. During the adsorbent synthesis process, RH and SCG biochar were pyrolyzed at 500 °C and modified by calcination using MgO. Both MgO/RH and MgO/SCG surfaces exhibited abundant pore structures and formed MgO crystal phases. Batch experiments results show that when the MgO/RH and MgO/SCG material dosages were 1 g/L, fluoride removal rates reached 80% and 86% respectively. The isotherms and kinetics of fluoride adsorption with MgO/RH and MgO/SCG followed the Langmuir isotherm equation and pseudo-second-order kinetic model. The maximum fluoride adsorption capacities of MgO/RH and MgO/SCG were 63.47 mg/g and 141.98 mg/g, respectively, indicating these materials used mono-layer adsorption mechanism for fluoride adsorption. The addition of MgO into the pores of porous adsorbent materials effectively increased their reactive sites and enhanced the adsorption performance of carbon materials. Particularly, SCG biochar had a richer pore structure than RH biochar, providing a larger contact surface area, facilitating the effective dispersion and doping of MgO into the pores. Therefore, MgO/SCG composite exhibited excellent fluoride adsorption properties in water, indicating the potential for developing a new type of MgO-modified SCG adsorbent material with green prospects. This composite effectively mitigated fluoride contamination, reducing the fluoride concentration in groundwater. Both RH and SCG are agricultural and food waste by-products, thus offering the opportunity to significantly reduce production, operation, and maintenance costs.

Preliminary Physical and Chemical Characterization of By-Products from Cuban Coffee Production

Coffee is one of the most consumed beverages worldwide. Its production generates a large amount of waste, and its use is of vital importance to prevent it from becoming a source of environmental pollution. Cuba is a country with a well-known coffee-growing tradition. Although coffee production has decreased, it is vitally important to use the waste generated in these productions to reduce environmental pollution. To know the possible use or application of coffee waste, it is necessary to know its composition. In this article, three Cuban Arabica coffee wastes (husk, parchment and spent coffee grounds) were characterized using chemical, physical and physicochemical methods. In the characterization of these wastes, SEM and EDX were used to determine their microscopic form and chemical composition. The Chesson–Datta method, ATR and TGA were used to determine whether these materials were lignocellulosic. Ash, pH and density of the waste were determined as characterization methods. The extractive content was determined and a phytochemical screening was performed to determine the groups of the secondary metabolites present.

Characterization and Greenhouse Trial of Zn Bio-Chelates Derived from Spent Coffee Grounds

The conversion of spent coffee grounds (SCG) into hydrochars has been the subject of extensive research in recent years, aimed at evaluating their potential for biofortifying foods and mitigating the plant toxicity linked to SCG. This study aimed to assess the physicochemical characterization and the impact of incorporating both activated (ASCG and AH160) and functionalized SCG (ASCG-Zn), as well as SCG-derived hydrochars (AH160-Zn), on cucumber yield and plant zinc content. The following physicochemical properties were analyzed: specific surface area, pH and electrical conductivity, polyphenols, and nuclear magnetic resonance. The by-products activated and functionalized with zinc were applied to cucumber crops grown in a greenhouse across multiple harvests. The activation of both SCG and H160 reduced the specific surface area of the particles. However, when these by-products were functionalized, their Zn content increased significantly, up to 7400 ppm. Concerning polyphenol content, the activated products showed levels ranging from 3.5 to 4.9 mg GAE/g. Regarding cumulative production, the treatments that showed the highest yields were the by-products activated and functionalized with Zn reaching 25 kg. Incorporating these by-products notably raised the Zn content in cucumbers, reaching 0.1 mg Zn per 100 g of fresh weight. The activated by-products demonstrated the highest Zn utilization efficiency.

Circular Utilization of Coffee Grounds as a Bio-Nutrient through Microbial Transformation for Leafy Vegetables

This study explores the production of bio-nutrients from bioactive compound-rich spent coffee grounds (SCG) and biochar (BC) through composting after inoculation with a biological agent and its impact on the growth performance of garden cress and spinach. The SCG was composted with six doses of BC (0, 5, 10, 15, 20, and 25%). The compost with 10% BC exhibited the best maturity, humification, and phytotoxicity index values of dissolved organic carbon (DOC), humification index (E4/E6), and germination index (GI). A metagenome analysis showed that compost starter enhanced the bacterial community’s relative abundance, richness, and diversity in SCG and BC treatments. This improvement included increased Patescibacteria, which can break down noxious phenolic compounds found in SCG and BC. The BC enriched the compost with phosphorus and potassium while preserving the nitrogen. In plant growth experiments, the total chlorophyll content in compost-treated garden cress and spinach was 2.47 and 4.88 mg g−1, respectively, which was significantly greater (p ≤ 0.05) than in unfertilized plants and similar to the plants treated with traditional fertilizer. Overall, the results show that the compost of SCG + BC was well-suited for promoting the growth of garden cress and spinach, providing adequate nutrients as a fertilizer for these leafy vegetables.

Processes of Metal Oxides Catalyst on Conversion of Spent Coffee Grounds into Rich-Synthesis Gas by Gasification

Spent coffee grounds (SCGs), a waste product of the coffee industry, present a significant untapped resource for fuel production. This study aims to optimize the gasification of SCG using various metal catalysts (NiO, MnO2, Al2O3, and Fe2O3) to maximize syngas yield. SCG samples were gasified at different temperatures (800 °C, 900 °C, 1000 °C) and analyzed using Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TG-DTA), and Fourier Transform Infrared (FTIR) spectroscopy to evaluate catalyst performance and reaction mechanisms. The findings indicated that utilizing mixing techniques for physical contact to introduce catalysts led to a uniform distribution of catalyst particles throughout the sample. The decomposition rate of the gasification experiment after adding the catalyst was 24% faster than that of the pure SCGs. In the gasification experiment, the MnO2 catalyst showed the highest CO production, which was 71% higher than that of NiO under the same conditions. At this temperature, MnO2 generated around 171% more CO than at 800 °C, surpassing the yields observed with other catalysts. The study concludes that Mn emerged as the most promising catalyst, significantly improving both CO and CH4 yields. Selecting the appropriate metal catalyst and optimizing operational temperatures are crucial for enhancing the efficiency of SCG gasification.

Characteristic study of Candida rugosa lipase immobilized on lignocellulosic wastes: effect of support material.

For the first time is reported the comparison of solid biocatalysts derived from Candida rugosa lipase (CRL) immobilized on different lignocellulosic wastes (rice husk, brewer's spent grain, hemp tea waste, green tea waste, vine bark, and spent coffee grounds) focusing on the characterization of these materials and their impact on the lipase-support interaction. The wastes were subjected to meticulous characterization by ATR-FTIR, BET, and SEM analysis, besides lignin content and hydrophobicity determination. Investigating parameters influencing immobilization performance revealed the importance of morphology, textural properties, and hydrophobic interactions revealed the importance of morphology, textural properties and especially hydrophobic interactions which resulted in positive correlations between surface hydrophobicity and lipase immobilization efficiency. Hemp tea waste and spent coffee grounds demonstrated superior immobilization performances (7.20 U/g and 8.74 U/g immobilized activity, 102.3% and 33.5% efficiency, 13.4% and 15.4% recovery, respectively). Moreover, they demonstrated good temporal stability (100% and 92% residual activity after 120days, respectively) and retained 100% of their immobilized activity after five reuses in the hydrolysis of p-nitrophenyl palmitate in hexane. In addition, the study of enzymatic desorption caused by ionic strength and detergent treatments indicated mixed hydrophobic and electrostatic interactions in rice husk, vine bark, and spent coffee grounds supports, while hemp tea waste and green tea waste were dominated by hydrophobic interactions.

Extraction of mannooligosaccharides from spent coffee grounds and its application for functional jelly with improved physical properties and immunomodulatory effect

Extraction of mannooligosaccharides from spent coffee grounds and its application for functional jelly with improved physical properties and immunomodulatory effect

Performance Assessment of a Novel Green Concrete Using Coffee Grounds Biochar Waste

An actual scientific problem in current concrete science is poor knowledge of the problem of modifying concrete with plant waste. At the same time, plant waste benefits from other types of waste because it is a recycled raw material. A promising technological approach to modifying concrete with plant waste is the introduction of components based on the processing of coffee production waste into concrete. This study aims to investigate the use of biochar additives from spent coffee grounds (biochar spent coffee grounds—BSCG) in the technology of cement composites and to identify rational formulations. A biochar-modifying additive was produced from waste coffee grounds by heat treatment of these wastes and additional mechanical grinding after pyrolysis. The phase composition of the manufactured BSCG additive was determined, which is characterized by the presence of phases such as quartz, cristobalite, and amorphous carbon. The results showed that the use of BSCG increases the water demand for cement pastes and reduces the cone slump of concrete mixtures. Rational dosages of BSCG have been determined to improve the properties of cement pastes and concrete. As a result of the tests, it was determined that the ideal situation is for the BSCG ratio to be at a maximum of 8% in the concrete and not to exceed this rate. For cement pastes, the most effective BSCG content was 3% for concrete (3%–4%). The compressive and flexural strengths of the cement pastes were 6.06% and 6.32%, respectively. Concrete’s compressive strength increased by 5.85%, and water absorption decreased by 6.58%. The obtained results prove the feasibility of using BSCG in cement composite technology to reduce cement consumption and solve the environmental problem of recycling plant waste.

Turning Trash to Treasure: The Influence of Carbon Waste Source on the Photothermal Behaviour of Plasmonic Titanium Carbide Interfaces.

Pyrolysis of carbonaceous waste materials has emerged as an effective recycling method to generate value-added products. In addition to producing pyrolytic oil and gas, the thermal degradation process yields solid pyrolytic char, which can be further processed. In this study, local waste materials, birch wood residue, Japanese knotweed stems, spent coffee grounds, tire rubber, and lobster shells were assessed for their potential to form pyrolytic char. After a simple acid treatment, many of these chars were successfully incorporated into solid-state synthesis of plasmonic titanium carbide (TiC) nanoparticles (NPs). Each char exhibited unique physical and chemical properties, which were leveraged to synthesize TiC NPs with distinct characteristics. To evaluate the plasmonic behavior of these TiC samples, solar-driven desalination experiments were performed. Notably, TiC derived from tire rubber demonstrated a high broadband absorbance and achieved a solar-to-vapor generation efficiency of 95%, corresponding to an evaporation rate of 1.40 ± 0.01 kg m-2 h-1 under one-sun illumination. This performance is the highest among all chars tested and ranks among the top reported values in the literature. Additionally, the evaporation interface maintained its performance over multiple cycles and under highly hypersaline conditions.

Environmental impact assessment of alternative technologies for production of biofuels from spent coffee grounds

AbstractIn the strategy to combat climate change that has been caused by the world's overdependence on fossil fuels, current research is focusing on the decarbonisation of the energy sector through the production of renewable cleaner energy, such as biofuels. Spent coffee grounds (SCGs), the waste stream of the coffee brewing industry, are a potential feedstock for the production of valuable products, including biofuels. However, the environmental implications for the valorisation of this valuable waste need to be investigated. This study assesses the environmental impacts of six biomass‐to‐fuel processing technologies using SCGs as a feedstock, with the aim of identifying the most environmentally friendly technology. A cradle‐to‐gate life‐cycle assessment (LCA) was conducted on fast pyrolysis, fermentation, anaerobic digestion (AD), hydrothermal liquefaction (HTL), gasification, and biodiesel production. The mass and energy balances obtained from Aspen Plus simulations served as the life‐cycle inventory data. Using the ReCiPe 2016 midpoint (H) and Eco‐Indicator 99 as the assessment methods, potential environmental impacts were calculated in OpenLCA software. Electricity generation and carbon dioxide emissions were the biggest contributors of environmental impacts. For each category, the maximum result was set to 100% and the results of the other variants were displayed in relation to this result. AD, with the smallest total weighted score (160), was the most environmentally friendly biomass‐to‐fuel processing route, while HTL, with the biggest total weighted score (893), was the worst. A sensitivity analysis indicated that the environmental performance of biofuel production from SCGs was highly influenced by energy input flows and the source of energy generation.

Coffee Biomass-Based Carbon Material for the Electrochemical Determination of Antidepressant in Synthetic Urine

Escitalopram (ESC) is commonly prescribed as an antidepressant to enhance serotonin levels in the brain, effectively addressing conditions such as depression and anxiety. The COVID-19 pandemic, along with ongoing mental health crises, has exacerbated the prevalence of these disorders, largely due to factors such as social isolation, fear of the virus, and financial difficulties. This study presents the enhancement of a glassy carbon electrode (GC) through the incorporation of hydrochar (HDC) derived from spent coffee grounds and copper nanoparticles (CuNPs) for the detection of ESC in synthetic urine. Characterization of the nanocomposite was conducted using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and cyclic voltammetry (CV). The analytical parameters were systematically optimized, and a sensing platform was utilized for the quantification of ESC via square-wave voltammetry (SWV). The established linear range was found to be between 1.0 µmol L−1 and 50.0 µmol L−1, with a limit of detection (LOD) of 0.23 µmol L−1. Finally, an electrochemical sensor was employed to measure ESC levels in synthetic urine, yielding recovery rates ranging from 91.7% to 94.3%. Consequently, the HDC-CuNPs composite emerged as a promising, sustainable, and cost-effective alternative for electroanalytical applications.

Spent coffee grounds as an alternative fertilizer: impact on bioaccessibility of antioxidants and commercial quality of lettuce.

During the processing of spent coffee grounds (SCGs) several residues are obtained, which are mostly disposed of in landfills. There is an urgent need for a comprehensive waste management strategy for these residues. This study evaluates the potential of SCGs as a biofertilizer by assessing their effects on lettuce leaves and the release of antioxidants following in vitro digestion and fermentation. Lettuce plants were grown with different amounts of SCGs (0-150 g kg-1) in the substrate. High SCG concentrations in the soil generated lighter colored tissues, a decrease in the green color, less root development, and lower dry weight of leaves (P < 0.05). The SCG levels also affected the release of antioxidants by the final product. This effect was more pronounced in the digested fraction: applying the Ferric Reducing Antioxidant Power (FRAP) method, the addition of SCGs from 10 g kg-1 to 125 g kg-1 increased the amount of antioxidant from 43.88 ± 4.81 to 105.96 ± 29.09 μmol Trolox g-1 of dry weight (P < 0.05). The Indigo Carmine Reducing Capacity (ICRED) method also showed a similar trend, but in this case the highest value was obtained with 150 g kg-1 of SCGs (16.41 ± 3.93 mmol catechin g-1 of dry weight) (P < 0.05). Moreover, in the fermented fraction a significant increase in the antioxidant released was found with low levels of SCG(P<0.05), while lettuces fertilized with intermediate amounts of SCGs (25 and 50 g kg-1) presented the highest amount of insoluble antioxidant (P < 0.05). A compromise should be found in order to achieve a product with a high antioxidant capacity and an acceptable visual quality. © 2024 Society of Chemical Industry.

Enhancement on Anaerobic Digestion of Food Waste using Spend Coffee Ground Derived Biochar for Biogas Production

In recent, one of the available energy sources is biogas where it is suitable for necessities of the future with the appropriate application of digestion technology. However, the technology used which is anaerobic digestion (AD) faces some challenges especially for food waste including low biogas productivity due to unstable operation efficiency. In order to overcome this shortcoming, spent coffee ground (SCG) derived biochar is introduced as an additive in AD process to enhance the production. To promote the efficiency of the AD, the optimum condition of biochar dosage, the amount of feedstock and pH value were studied. The experimental findings revealed that 13.528ml/g of biogas yield was achieved under optimum condition of 7g of biochar, 500g of feedstock at pH 7 for 14 days. The characterization analysis of biochar showed that, the carbon content and surface area as well as several functional groups of SCG biochar has led to the enhancement of the biogas production during AD process of food waste. The outcomes shows that the addition of SCG biochar can solve the instability issues of AD process yet increase the production of biogas.

Machine learning based prediction and iso-conversional assessment of oxidatively torrefied spent coffee grounds pyrolysis

This research focused on developing a predictive model for mass loss during the pyrolysis of oxidatively torrefied spent coffee grounds (SCG) using machine learning techniques. Four algorithms were employed: artificial neural networks (ANN), k-nearest neighbors (k-NN), random forest (RF), and decision tree (DT), with the RF model demonstrating superior performance (R2 > 0.9981, RMSE <1.346) for both training and testing sets. The pyrolysis behavior, kinetics, and thermodynamics of SCG were also investigated using thermogravimetric analysis (TGA) under an inert atmosphere at different heating rates. Higher heating rates in TGA cause Tpeak values to shift to higher temperatures with increased DTGpeak values, while also resulting in lower Tonset and higher Toffset. Kinetic analysis, using the Flynn-Wall-Ozawa (FWO) method, was identified as the most suitable approach for determining activation energy (Ea), with values ranging from 192.66 to 288.13 kJ mol−1, indicating differences in energy requirements for pyrolysis across samples. Thermodynamic analysis further revealed that both raw SCG and oxidatively torrefied SCG pyrolysis were endothermic reactions. These findings contribute valuable insights into the optimization of biomass conversion technologies, highlighting the potential of machine learning in improving predictive accuracy and efficiency in thermal behavior modeling. This research advances sustainable bioenergy production by promoting the use of SCG, an abundant waste material, as a renewable feedstock in pyrolysis-based processes.

Efficient coproduction of manno-oligosaccharides and fermentable sugars from spent coffee grounds via aqueous ammonia pretreatment and two-step enzymatic hydrolysis

In this work, the co-production of manno-oligosaccharides (MOS) and fermentable monosaccharides from spent coffee grounds (SCG) was achieved through aqueous ammonia pretreatment and enzymatic hydrolysis. Aqueous ammonia was found to improve the conversion yields of mannan and cellulose in SCG to MOS and fermentable sugars. However, the MOS generated during the enzymatic hydrolysis of aqueous ammonia-treated SCG (AA-SCG) strongly inhibited cellulase activity, reducing the efficiency of cellulose conversion to glucose. To address this issue, a two-step hydrolysis process was implemented: mannanase was first used to hydrolyze AA-SCG, resulting in the degradation of 60% of the mannan and a yield of 52.7% MOS. After separating this hydrolysate, cellulase and mannanase were added to further hydrolyze the remaining polysaccharides. The removal of the mannanase hydrolysate alleviated MOS inhibition on cellulase, resulting in the conversion of 90.6% of cellulose in AA-SCG into glucose. Additionally, about 30% of the mannan was further degraded in the second step, achieving an overall mannan degradation rate of 89.4% and a MOS yield of 63.8%.

Life cycle assessment and yield to optimize extraction time and solvent: Comparing deep eutectic solvents vs conventional ones

Deep eutectic solvents (DES) are gaining interest as eco-friendly alternatives for extracting bioactive compounds, but their environmental benefits remain unclear and need further evaluation. In this work, a case study of total polyphenols (TPC) extraction from spent coffee grounds (SCG) was environmentally evaluated using life cycle assessment (LCA). First, the most convenient extraction time (1, 10, 20, or 40 min) for water and acetone 20 % from an environmental perspective was identified. Second, a comparison of different solvents—DES (choline chloride-1,6-hexanediol), water, and ethanol 20 %—under their optimal extraction yield conditions was performed using literature data. Results from the first study revealed that the environmentally optimal extraction time (10 min) was not the one leading to the highest yield. The main contributors to the impacts were the use of acetone and electricity consumption.For the second study, DES performed worse in all studied environmental impact categories compared to both ethanol 20 % and water. Ethanol 20 % was the better option compared to water due to its higher extraction yield (9.2 mg vs. 6.5 mg TPC/g SCG, respectively). The environmental impacts associated with the DES system were primarily attributed to the DES preparation step, which requires virgin raw materials (e.g., dimethyl hexanediol), and the adsorption stage involving the use of resins. A sensitivity analysis was also conducted by optimizing the DES system to the best possible described conditions (90 % reuse of DES and maximum reduction of the macroporous resin used to adsorb the TPC after extraction). Nevertheless, the DES system still performed worse than water or ethanol 20 % systems, in 11 out of 16 impact categories.The study highlights the importance to consider environmental impacts and yield when optimizing extraction processes, especially at the laboratory scale, as the insights gained are valuable for improving eco-efficiency on an industrial scale.

Enhanced photo-oxidation of hormones in water using biomass waste-derived hydrochar composites as photocatalysts

This study introduces a green chemistry approach to enhance the catalytic efficiency of metal oxides in photocatalytic reactions using agro-industrial waste. Specifically, rice husks and spent coffee grounds were utilized as carbon sources to produce hydrochars, which served as sustainable supports for ZnO and ZnFe₂O₄ oxides. This method promotes waste minimization and circularity by repurposing agricultural byproducts, reducing the environmental impact of traditional catalyst production. The hydrochars were synthesized through mild hydrothermal carbonization (250 °C for 4 h) and characterized by various physicochemical analyses. Their photocatalytic performance was evaluated using a 20 mg L−1 solution of conjugated estrogens under ultraviolet light (120 W cm−2) for 30 min. Composites with ZnO exhibited a significant increase in oxidation reaction rates due to enhanced porosity and an oxygen-rich structure. Reactive oxygen species (ROS) analysis revealed hydroxyl radicals (OH) as the primary agents, with photocatalytic efficiencies exceeding 83 % after eleven cycles. In toxicity tests, 4 mL of treated solution was applied to 20 Lactuca sativa (lettuce) seeds, kept in the dark at 25 °C for 7 days. Seeds exposed to treated solutions showed improved radicle elongation and germination rates compared to controls, except for those with coffee hydrochar and ZnO. This indicates effective degradation of toxic estrogens without harmful by-products. Overall, this work highlights the advantages of integrating green chemistry principles and circular economy practices, transforming waste into valuable materials to enhance environmental sustainability and catalytic performance.