Sequential Production of Lignin, Fatty Acid Methyl Esters and Biogas from Spent Coffee Grounds via an Integrated Physicochemical and Biological Process

Value-Added Products from Coffee Waste: A Review

Coffee waste is often viewed as a problem, but it can be converted into value-added products if managed with clean technologies and long-term waste management strategies. Several compounds, including lipids, lignin, cellulose and hemicelluloses, tannins, antioxidants, caffeine, polyphenols, carotenoids, flavonoids, and biofuel can be extracted or produced through recycling, recovery, or energy valorization. In this review, we will discuss the potential uses of by-products generated from the waste derived from coffee production, including coffee leaves and flowers from cultivation; coffee pulps, husks, and silverskin from coffee processing; and spent coffee grounds (SCGs) from post-consumption. The full utilization of these coffee by-products can be achieved by establishing suitable infrastructure and building networks between scientists, business organizations, and policymakers, thus reducing the economic and environmental burdens of coffee processing in a sustainable manner.

A systems engineering framework for the optimization of food supply chains under circular economy considerations

The current linear "take-make-waste-extractive" model leads to the depletion of natural resources and environmental degradation. Circular Economy (CE) aims to address these impacts by building supply chains that are restorative, regenerative, and environmentally benign. This can be achieved through the re-utilization of products and materials, the extensive usage of renewable energy sources, and ultimately by closing any open material loops. Such a transition towards environmental, economic and social advancements requires analytical tools for quantitative evaluation of the alternative pathways. Here, we present a novel CE system engineering framework and decision-making tool for the modeling and optimization of food supply chains. First, the alternative pathways for the production of the desired product and the valorization of wastes and by-products are identified. Then, a Resource-Task-Network representation that captures all these pathways is utilized, based on which a mixed-integer linear programming model is developed. This approach allows the holistic modeling and optimization of the entire food supply chain, taking into account any of its special characteristics, potential constraints as well as different objectives. Considering that typically CE introduces multiple, often conflicting objectives, we deploy here a multi-objective optimization strategy for trade-off analysis. A representative case study for the supply chain of coffee is discussed, illustrating the steps and the applicability of the framework. Single and multi-objective optimization formulations under five different coffee-product demand scenarios are presented. The production of instant coffee as the only final product is shown to be the least energy and environmental efficient scenario. On the contrary, the production solely of whole beans sets a hypothetical upper bound on the optimal energy and environmental utilization. In both problems presented, the amount of energy generated is significant due to the utilization of waste generated for the production of excess energy.

Monomers, Materials and Energy from Coffee By-Products: A Review

In recent years, the circular economy and sustainability have gained attention in the food industry aimed at recycling food industrial waste and residues. For example, several plant-based materials are nowadays used in packaging and biofuel production. Among them, by-products and waste from coffee processing constitute a largely available, low cost, good quality resource. Coffee production includes many steps, in which by-products are generated including coffee pulp, coffee husks, silver skin and spent coffee. This review aims to analyze the reasons why coffee waste can be considered as a valuable source in recycling strategies for the sustainable production of bio-based chemicals, materials and fuels. It addresses the most recent advances in monomer, polymer and plastic filler productions and applications based on the development of viable biorefinery technologies. The exploration of strategies to unlock the potential of this biomass for fuel productions is also revised. Coffee by-products valorization is a clear example of waste biorefinery. Future applications in areas such as biomedicine, food packaging and material technology should be taken into consideration. However, further efforts in techno-economic analysis and the assessment of the feasibility of valorization processes on an industrial scale are needed.

A shift from anaerobic digestion to dark fermentation in glycol ethylene fermentation

Anaerobic digestion of aqueous glycol ethylene was tested. The process lasted two cycles of 7 days, but after the second cycle, high hydrogen production occurred shift to dark fermentation. The biogas production lasted 14 days, obtaining peak values of hydrogen, and then rapidly stopped. In investigations, the following were checked: dependence of hydrogen, methane and hydrogen sulphide in the process. Mixtures of water with glycol ethylene mass ratio from 0.6 to 0.85 were substrates in experiments. The highest methane production was for water ethylene 0.7 ratio 2.85 L of methane with a yield of 178 mL of methane/g VSS (volatile suspended solids) of glycol ethylene. The optimal ratio of water and glycol ethylene was 0.85 25.5 mL of hydrogen (giving yield 1.71 mL of hydrogen/g VSS of glycol ethylene) and 1.71 mL of hydrogen sulphide emission for a 0.6 ratio. Popular polymer industry wastes, glycol ethylene, can be utilised by anaerobic digestion.

Tuning structure of spent coffee ground lignin by temperature fractionation to improve lignin-based carbon nanofibers mechanical performance

Fabricating lignin-based carbon nanofibers (LCNFs) with the lignin in spent coffee grounds (SCG) as raw material which are disposed as waste amounting to millions tons annual is benefit to promote economy and environmental protection. However, due to the heterogeneity and complex three-dimensional structure, the mechanic property is very poor. In this study, we propose a fractionating pretreatment method to overcome the above problems by regulating the structure of SCG lignin in which high-performance LCNFs were fabricated. On one hand, the linear structure of SCG lignin was optimized to fit the raw material of LCNFs by tuning the content of β-O-4 and C₅-substituted condensed phenolic compounds. On the other hand, the carboxyl as the hydrophilic groups was removed so as to promote the mixing of lignin and polyacrylonitrile (PAN, blending agent) in organic solvents. Additionally, the heterogeneity was reduced by screening large molecular weight SCG lignin with low polydispersity index (PDI). Fortunately, with 1:1 mass ratio of the above fractionated lignin and PAN as substrate, the LCNFs could reach to comparable mechanic properties with those of pure PAN CNFs. This work can provide a new way to not only promote the utilization of SCG lignin but also accelerate the development of LCNFs.

Biorefinery of spent coffee grounds waste: Viable pathway towards circular bioeconomy

The circular bioeconomy plan is an innovative research based scheme intended for augmenting the complete utilization and management of bio-based resources in a sustainable biorefinery route. Spent coffee grounds based biorefinery is the emerging aspect promoting circular bioeconomy. The sustainable circular bioeconomy by utilizing SCG is achieved by cascade approaches and the inclusion of many biorefinery approaches to obtain many bio-products. The maximum energy recovery can be obtained by process integration. The economic analysis of the biofuel production from SCG is dependent on the cost of raw material, transportation, the need of labor and energy, oil extraction operations and biofuel production. The inclusion of new products from already established product can minimize the investment cost when related to the production cost. A positive net present value can be achieved via SCG biorefinery which indicates the profitability of the process.

Desert Palm Date Seeds as a Biodiesel Feedstock: Extraction, Characterization, and Engine Testing

The development of alternative fuels is increasingly important in order to maintain ongoing global economic and technological progress in the face of fossil fuel depletion and increasing environmental damage. Desert palm date seeds have clear potential as feedstock for biodiesel production given their high oil content and availability as food waste that requires no further cultivation. In this study we investigated the optimum production processes and conditions for date seed oil biodiesel, including characterizing the intermediate product and correcting its composition to meet international fuel standards. Four biodiesel blends were prepared (B5, B10, B15, and B20) and tested in a compression ignition engine at engine speeds from 1600 to 3600 rpm (200 rpm increments) and three engine loads (50%, 75%, and 100%). The highest oil yield and biodiesel conversion achieved were 10.74 wt.% and 92%, respectively. The biodiesel properties conformed well with the standards; the values for brake power, brake thermal efficiency, and brake specific fuel consumption were comparable with petrol diesel, though the latter was slightly superior. All blends produced lower levels of CO2, CO, and HC but higher levels of NOx emissions. These results demonstrate the fundamental suitability of date seeds as biodiesel feedstock, deserving of further research.