The study, led by researchers at Universidad Tecnológica del Perú, represents one of the most rigorous attempts to map the full landscape of coffee-waste valorization technologies. Following the PRISMA 2020 guidelines and the PICO framework, the team screened 472 records from Scopus and Web of Science, ultimately including 116 primary studies published between 2020 and 2025. Each study was scored across six methodological quality criteria, from feedstock characterization to techno-economic scalability, ensuring that only high-quality investigations informed the quantitative comparisons that anchor the review’s conclusions.

The findings reveal a striking pattern in how scientists and engineers are approaching coffee waste. Thermochemical routes, dominated by slow pyrolysis, accounted for 27.6 percent of reported technology occurrences, while biochemical pathways led by anaerobic digestion followed closely at 24.1 percent. Other pyrolysis and activation processes, microbial fermentation, composting and vermicomposting, anaerobic co-digestion, and gasification rounded out the portfolio. These technologies are not competing alternatives but complementary tools, each suited to different fractions of the coffee value chain depending on moisture content, carbon-to-nitrogen ratio, and lignin concentration.

The chemistry behind this division of labor is elegant. Coffee pulp and mucilage, which together make up roughly 94 percent of the solid waste generated during wet processing, are rich in soluble carbohydrates and water, making them ideal substrates for microbial digestion and fermentation. In contrast, coffee husks, parchment, and spent grounds contain higher concentrations of carbon and lignin with lower moisture, properties that favor thermochemical conversion. When these dry, recalcitrant fractions are heated to temperatures between 400 and 700 degrees Celsius under inert atmospheres, they yield biochar with thermal stability, low ash content, and remarkable adsorption capacity, recovering between 25 and 40 percent of the initial dry weight as a stable carbon-rich solid.

The environmental payoff from these conversions is quantifiable and substantial. In one life cycle assessment of instant coffee production, integrating a combined cooling, heating, and power system fueled by spent coffee grounds reduced global warming potential from 27.08 to 16.90 kilograms of carbon dioxide equivalent per kilogram of product, a 37.6 percent reduction compared to the baseline scenario. Meanwhile, decentralized pyrolysis units deployed on farms in Ecuador and Brazil demonstrated reductions in thermal drying energy costs ranging from 20 to 35 percent by replacing subsidized fossil fuels with locally produced biochar. Across multiple studies, anaerobic digestion and composting of organic coffee waste were found to mitigate approximately 435 kilograms of carbon dioxide equivalent emissions per ton of treated material.

Beyond energy and climate benefits, coffee-derived biochar is emerging as a versatile environmental workhorse. Studies documented in the review show that biochar produced from coffee husks can reduce the mobility of textile dyes in contaminated alluvial soils by more than 90 percent, while modified biochar adsorbents have removed herbicides and sulfonamide antibiotics from contaminated water with efficiencies exceeding 85 percent. Some researchers have even pushed the technology into unexpected territory, using hydrothermal carbonization to convert spent grounds into hard carbons for battery anodes, achieving specific capacities of 210 to 280 milliampere-hours per gram and offering a sustainable alternative to mined graphite.

The biological pathways are equally impressive in their diversity. Controlled fermentation of coffee pulp and mucilage under anaerobic conditions has yielded ethanol concentrations of up to 8.8 percent by volume, with conversion efficiencies exceeding 80 percent. Dark fermentation of raw coffee silverskin, the thin tegument that separates from the bean during roasting, has produced biohydrogen and acetate without the need for exogenous inoculum. Even kombucha brewed from coffee husk cascara has been reported as a functional beverage enriched with antioxidant phenolic compounds, opening unexpected opportunities in the nutraceutical market.

However, the review is candid about the barriers that stand between laboratory promise and industrial reality. A quantitative capacity analysis revealed that 58.6 percent of the 116 studies operate at laboratory scale below 5 kilograms per hour, while only 13.8 percent reach demonstration or industrial capacity above 50 kilograms per hour. This concentration at small scales limits the assessment of real-world performance and constrains robust techno-economic evaluation. High implementation costs, feedstock heterogeneity, insufficient rural technical training, and a lack of standardized biofertilizer regulations further compound the challenge, particularly in Latin American and African producing countries where the waste streams are most abundant.

The regulatory landscape adds another layer of complexity. In Colombia, agricultural use of organic and digested products is supported by existing standards such as NTC 5167 and Decree 1287 of 2014, but in Ecuador, the literature identifies a more specific gap regarding small-scale thermochemical recovery, with existing energy conversion provisions geared toward larger facilities and insufficient coverage of pyrolysis systems that rural cooperatives could realistically deploy. The authors emphasize that these regulatory barriers are heterogeneous and jurisdiction-specific rather than a generalized absence of rules, meaning that solutions must be tailored to local contexts rather than imposed uniformly.

Despite these hurdles, the researchers identify integrated biorefineries as the most promising pathway forward. By combining pyrolysis, anaerobic digestion, fermentation, and composting within a single facility, these systems can simultaneously produce biochar, biogas, compost, and adsorbents while maximizing resource recovery and minimizing waste. Exergoeconomic analyses cited in the review reported increases of up to 91 percent in overall process energy efficiency alongside reduced operating costs, pointing toward the economic feasibility of such integrated configurations. As the authors conclude, translating laboratory and pilot-scale achievements into sustainable production-scale applications will require strengthening local technical capacities, fostering institutional coordination, and establishing enabling policy frameworks that recognize coffee waste not as a liability but as a strategic resource for the circular bioeconomy.

Subject of Research: Thermochemical and biochemical conversion technologies for valorizing coffee-industry waste residues

Article Title: Thermochemical and biochemical conversion technologies for the valorization of coffee-industry residues: a systematic review

Article References: Yzquierdo-Alejandría, M., Chomlón-Perales, C. A., & Vásquez–Coronel, J. A. (2026). Thermochemical and biochemical conversion technologies for the valorization of coffee-industry residues: a systematic review. Frontiers in Sustainability, 7, Article 1947220. https://doi.org/10.3389/frsus.2026.1947220

Image Credits: AI Generated

DOI: 10.3389/frsus.2026.1947220

Keywords: coffee waste, pyrolysis, anaerobic digestion, biochar, circular economy, biorefinery, biogas, bioethanol, life cycle assessment, sustainability, agro-industrial residues, waste valorization

The research was carried out at the Federal University of Piauí’s Professora Cinobelina Elvas Campus in Bom Jesus, Brazil, using a commercial seed lot of U. brizantha cv. MG-5 from the 2022/2023 crop year. The team, led by Tiago de Oliveira Sousa and Thalesram Izidoro Pinotti, began by characterizing the seed lot’s baseline quality. A tetrazolium viability test, which stains living tissue red and reveals whether embryos are metabolically active, showed that 86 percent of the seeds were alive and met the minimum standards required for commercialization. Yet when the seeds were actually germinated under ideal laboratory conditions, only 55 percent produced normal seedlings, and the first germination count on day seven was a mere 27 percent. That gap between viability and germination is the signature of dormancy, and it is precisely the problem the researchers set out to solve.

Dormancy in Urochloa species is widely attributed to physical barriers. The seeds are wrapped in glumes, lemmas, and paleas, the same bracts that enclose grass florets, and these structures, together with a rigid seed coat, can restrict water absorption and oxygen diffusion, both essential triggers for germination. Uneven inflorescence emergence, asynchronous flowering within racemes, a low proportion of fertile seeds, and natural seed shattering further complicate matters, meaning commercial seed lots can vary widely in quality. Under Brazilian regulations, seed lots of this species must reach at least 60 percent germination to be sold commercially, so lots that fall short represent both an agronomic and an economic liability.

To tackle the physical barrier, the researchers manually removed the glumes, lemmas, and paleas from half of the seeds, a process called scarification. Crucially, the procedure did not touch the seed coat itself, which in Urochloa is known for its rigidity and impermeability, so there was no risk of damaging the embryo. The effect was dramatic. Scarification raised the germination speed index by 73.7 percent, from 5.90 to 10.25, lifted the first germination count from 43 to 66 percent, and increased final germination from 50 to 69 percent, a gain of 19 percentage points. Scarified seedlings also grew longer and accumulated more biomass, with significantly higher root fresh mass, total fresh mass, root dry mass, total dry mass, and total seedling length than their non-scarified counterparts. The likely mechanism is straightforward: removing the coverings accelerates imbibition, the initial uptake of water that kick-starts the metabolic machinery of germination.

The second intervention was biochemical. The team prepared three crude extracts and tested them as seed treatments alongside distilled water and a commercial mineral fertilizer-based product. Two of the extracts came from Trichoderma orientale, a fungus isolated from the ecotone between the Caatinga and Cerrado biomes in Piauí, grown by solid-state fermentation on two agro-industrial residues: orange peel and maize cobs. The third extract was made from leaves of Pereskia aculeata, a plant better known in Brazil as ora-pro-nóbis, a traditional vegetable prized for its unusually high protein content. Using waste materials as fermentation substrates is both economically and environmentally attractive; maize cobs alone account for roughly 18 kilograms of residue for every 100 kilograms of grain harvested, so converting them into value-added products adds revenue and reduces waste.

Biochemical analysis revealed striking differences among the extracts. The orange-peel extract showed the highest proteolytic activity at 200 units per milliliter, far exceeding values previously reported for fungi such as Aspergillus niger, Aspergillus brasiliensis, and various Fusarium strains. The maize-cob extract reached 75.07 units per milliliter, while the Pereskia extract managed only 27.83. However, when activity was normalized to protein content, the two fungal extracts were statistically indistinguishable, at 588.24 and 625.58 units per milligram, both far above the plant extract’s 55.43. The Pereskia extract instead boasted the highest protein concentration, 0.502 milligrams per milliliter, consistent with leaves that contain 23 percent protein on a dry-matter basis. The substrate clearly mattered: orange peel, rich in pectin, cellulose, and easily metabolized sugars, appears to stimulate abundant protease secretion, while maize cobs, dominated by holocellulose and lignin, seem to favor the selective production of a smaller amount of highly efficient enzyme.

When the extracts were applied by soaking seeds for one hour, every treatment outperformed the water control. The germination speed index rose from 5.82 in the control to between 8.30 and 9.42 across the treated groups, with no significant differences among the treatments themselves. First germination counts climbed from 40 percent to between 56 and 62 percent, and final germination increased from 44 percent to between 61 and 67 percent. Notably, all treated seeds cleared the 60 percent germination threshold required for commercial sale, which the untreated lot failed to meet. The commercial fertilizer product and the crude extracts performed comparably on these germination metrics, suggesting that inexpensive, residue-derived extracts could match a conventional product where germination is concerned.

Seedling development told a more nuanced story. The Pereskia aculeata extract produced the highest shoot dry mass and total dry mass of any treatment and, together with the maize-cob fungal extract, the greatest shoot length. Shoot fresh mass was higher in all three extract treatments than in either the water control or the commercial product. Root length, uniquely, depended on an interaction between treatment and scarification: among scarified seeds, the commercial product and the orange-peel fungal extract produced the longest roots, whereas among non-scarified seeds, the commercial product, the maize-cob extract, and the Pereskia extract led. Intriguingly, for the maize-cob and Pereskia treatments, root length did not differ between scarified and non-scarified seeds, implying that these extracts partially compensated for the physical constraint. Seedling vigor index I, which combines germination percentage with seedling length, rose by 47.7 to 59.5 percent under the treatments relative to the control, and scarification alone boosted it by 53.5 percent. Seedling water content, by contrast, was unaffected by any intervention, indicating that the treatments altered growth and biomass accumulation without disturbing tissue hydration.

Perhaps the most scientifically interesting result is what did not correlate. The extract with the highest proteolytic activity was not the one that produced the best seedlings, and the extract with the lowest activity delivered the greatest shoot growth and dry-mass accumulation. A Pearson correlation network built from the morphophysiological data showed that germination traits were tightly interconnected, with the germination speed index correlating at r = 0.99 with the first germination count and r = 0.97 with final germination, while vigor indices correlated strongly with both germination and seedling length. But germination speed was actually negatively correlated with some biomass traits, such as root dry mass, hinting at trade-offs in how seedlings allocate resources when they establish quickly. The authors conclude that seed responses reflect the integrated bioactivity of each crude extract, in which enzymes, proteins, peptides, amino acids, minerals, and soluble carbohydrates act jointly, rather than proteolysis alone. This functional dissociation opens the door to targeted fractionation and heat-inactivation experiments to identify which constituents actually drive the benefit.

The practical implications are considerable. Under laboratory conditions, a one-hour immersion in the extracts lifted final germination from 44 percent to as high as 68 percent, and scarification pushed it to 69 percent while improving seedling length and biomass. Together, the two approaches define complementary intervention points for seed technology: biochemical conditioning with bioactive crude extracts and physical removal of the structures that restrict water and oxygen uptake. The manual scarification used here serves as a proof of concept for developing scalable mechanical procedures, and the extract performance justifies further optimization of application rates, exposure times, formulation stability, and compatibility with seed storage. The authors caution that their results apply to the evaluated cultivar, seed lot, and controlled germination environment, and that validation across seed lots, storage periods, and field-emergence conditions will be needed before these treatments reach commercial protocols. Still, the vision is compelling: turning orange peels and maize cobs into fungal enzyme factories, and a protein-rich leafy vegetable into a seed treatment, to unlock the potential locked inside one of the tropics’ most important pasture grasses.

Subject of Research: Improving seed germination and early seedling development of Urochloa brizantha using scarification and biomolecule-rich fungal and plant extracts

Article Title: Fungal and plant extracts improve germination and early development of Urochloa brizantha

Article References: Sousa, T. D. O., Pinotti, T. I., Costa, T. B., de Sousa Mesquita, A., Gomes, S. O., Santos, A. M. G., & Nascimento, T. P. (2026). Fungal and plant extracts improve germination and early development of Urochloa brizantha. Discover Plants, 3(1), Article 439. https://doi.org/10.1007/s44372-026-00910-8

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00910-8

Keywords: Urochloa brizantha, seed germination, seed dormancy, scarification, Trichoderma orientale, Pereskia aculeata, solid-state fermentation, proteolytic enzymes, agro-industrial residues, forage grass, seed treatment, seedling vigor