This review comprehensively examines the advancements and challenges in anaerobic digestion (AD) for biogas production, emphasising technological, microbial, and policy perspectives. It highlights the AD significant potential for valorising diverse organic substrates, including manure, food waste, and microalgae, thereby contributing to renewable energy generation and greenhouse gas mitigation. Key operational factors influencing biogas yield include substrate composition, temperature (preferably mesophilic conditions), pH (6.5–7.5), and the substrate-to-inoculum ratio (SIR), all of which significantly affect microbial activity and process stability. Co-digestion strategies and pretreatments are examined for their roles in enhancing biodegradability and methane yield, respectively. Microbial community dynamics, particularly responses to feedstock heterogeneity and operational parameters, are integral to process optimisation. Advances in metagenomics have provided insights into microbial resilience and adaptation to conditions such as high ammonium levels. This review also discusses various modelling approaches, including kinetic models and machine learning techniques, for predicting and optimising biogas production. Additionally, policy frameworks within regions such as the European Union and Brazil, along with economic incentives and regulatory hurdles, are also considered crucial for scaling up deployment. Challenges such as digestate management and high capital costs persist, underscoring the need for integrated strategies to enhance the sustainability and viability of AD-based biogas projects.

Ecuador is the world’s fifth largest cocoa producer, generating hundreds of tons of residues from this fruit annually. This research generates value from the residual (cocoa pod husk) by using it as raw material to obtain pectin, which is widely used in the food and pharmaceutical industries. Extraction of three different organic acids with GRAS status (safe for use), the citric, malic and fumaric acids, was studied. In addition, two other factors, temperature (70–90 °C) and extraction time (60–90 min), were explored in a central composite design of experiments. We determined the conditions of the experiments where the best yields were garnered for citric acid, malic acid and fumaric acid, along with a ~86 min extraction time. The temperature did not show a significant influence on the yield. The pectin obtained under optimal conditions was characterised, showing the similarity with commercial pectin. However, the equivalent weight and esterification degree of the pectin obtained with fumaric acid led us to classify it as having a high equivalent weight and a low degree of esterification. In these regards, it differed significantly from the other two acids, perhaps due to the limited solubility of fumaric acid.

Pectinolytic enzymes are a group of enzymes widely used in the food industry. They can be obtained through a wide range of by-products and agricultural and agro-industrial waste by the action of fungi, such as Aspergillus spp., by solid-state fermentation (SSF). A wild strain of an Aspergillus sp. isolated in the Universidad Técnica del Norte (UTN) was used to obtain pectinolytic enzymes from dehydrated coffee waste (pulp and husk) derived from coffee cherries cultivated in the Ecuadorian Andean regions. It was possible to find a condition in which the production of pectinases (expressed as Enzymatic Activity (EA)) and the concentration of spores (S) were simultaneously maximized, using the response surface methodology, in a 3-level factorial design, by SSF in simple tray-type bioreactors. After the analysis and optimization of quadratic models, three confirmatory experiments were performed in the unique optimal condition recommended (35 °C and 79% relative humidity), obtaining 29.9 IU/g and 2.64 × 10⁶ #Sp./g for EA and S, respectively; these values coincided with those predicted by the quadratic models, demonstrating their validity. The values obtained in this study are similar to those previously obtained by other authors.

Response surface methodology is a tool for the design of experiments, widely used today to optimize industrial processes, including agro-industrial ones. Since its appearance in the last century’s fifties, hundreds of articles, chapters of books, and books attest to this. In this work, a general overview of this tool’s general practical aspects is made. This statistical tool’s usefulness and popularity, used in the optimization of agro-industrial processes and in making them more efficient and sustainable, is described through multiple examples.

The global citrus-processing industry generates 15–32 million tonnes of waste annually. Lemon-processing residues—peels, seeds, and pomace—constitute 45–55% of fruit mass and harbour high-value bioactive compounds amenable to cascade valorisation. This review (Part I of a two-part series) examines green extraction technologies for recovering bioactive compounds from lemon waste streams. Following bibliometric analysis of 847 publications (2003–2025), this work delineates the compositional heterogeneity of lemon fractions and establishes a hierarchical framework for value-added products encompassing essential oils, pectin, polyphenols, seed oils, citric acid, industrial enzymes, α-cellulose, and nanocrystalline cellulose. Four sustainable extraction methodologies are systematically evaluated: ultrasound-assisted extraction, microwave-assisted extraction, supercritical CO₂ extraction, and enzyme-assisted extraction. Comparative assessment demonstrates yield improvements of 16–112% over conventional approaches, processing-time reductions of 89–98%, and energy savings up to 95%. Critical research gaps include fragmented single-product valorisation, insufficient techno-economic assessment, and limited industrial-scale validation. Integrated cascade biorefineries employing sequential green extraction protocols offer economically viable pathways for transforming lemon waste into diversified revenue streams. Industrial implementation, circular-economy integration, and techno-economic feasibility are addressed in Part II.

Numerous fruits are produced in Ecuador, of which about 40% are never eaten. In addition, fresh goat cheeses are in high demand. However, goat cheese generates goat milk whey with high contamination loads, and, therefore, it must be adequately treated before being discharged into ecosystems. This research aims to use a mixture of tree tomato, common strawberry juices, and goat’s milk whey, to be statically fermented by milk and water kefir grains (WKG) for 48 h. For this, a dual mixture design of L-optimal response surface methodology was carried out to find the conditions that maximized all the responses evaluated (lactic-acid bacteria and yeasts concentrations and the overall acceptability assessed on a 7-point scale). Experiments were carried out in San Gabriel, Ecuador. Temperatures during the day and night were 20.2 ± 0.3 °C and 18.7 ± 0.3 °C, respectively. Three conditions were selected, where the highest response values were reached. Complementary experiments demonstrated the validity of the models. When comparing the results of the present study with similar ones carried out previously, higher values were observed in the concentration of yeasts, which seems related to the presence of the WKG. It is concluded that they could be suitable functional beverage candidates.