In an anaerobic digestion (AD) process, the hydrolysis phase is often limited when substrates with high concentrations of solids are used. We hypothesized that applying micro-aeration in the hydrolysis phase and the application of granular activated carbon (GAC) in the methanogenesis phase could make the AD process more efficient. A packed bed reactor (PBR) coupled with an up-flow anaerobic sludge blanket (UASB) was conducted, and its effects on methane generation were evaluated. The micro-aeration rate applied in PBR was 254 L-air/kg-Total solids (TS)-d was compared with a control reactor. Micro-aeration showed that it reduced the hydrolysis time and increased the organic matter solubilization as chemical oxygen demand (COD) increasing 200%, with a volatile fatty acids (VFAs) increment higher than 300%, compared to the control reactor (without aeration). Our findings revealed that the implementations of microaeration and GAC in the two-phase AD system could enhance methane production by reducing hydrolysis time, increasing solid waste solubilization.

This paper reviews the chemical hydrolysis processes of dairy manure fiber to make its sugar accessible to microorganisms during anaerobic digestion and identifies obstacles and opportunities. Researchers, so far, investigated acid, alkali, sulfite, and advanced oxidation processes (such as hydrogen peroxide assisted by microwave/ultrasound irradiation, conventional boiling, and wet oxidation), or their combinations. Generally, dilute acid (3–10%) is less effective than concentrated acid (12.5–75%), which decrystallizes the cellulose. Excessive alkaline may produce difficult-to-degrade oxycellulose. Therefore, multi-step acid hydrolysis (without alkaline) is preferred. Such processes yielded 84% and 80% manure-to-glucose and -xylose conversion, respectively. Acid pretreatment increases lignin concentration in the treated manure and hinders subsequent enzymatic processes but is compatible with fungal cellulolytic enzymes which favor low pH. Manure high alkalinity affects dilute acid pretreatment and lowers glucose yield. Accordingly, the ratio of manure to the chemical agent and its initial concentration, reaction temperature and duration, and manure fineness need optimization because they affect the hydrolysis rate. Optimizing these factors or combining processes should balance removing hemicellulose and/or lignin and increasing cellulose concentrations while not hindering any subsequent process. The reviewed methods are neither economical nor integratable with the on-farm anaerobic digestion. Economic analysis and energy balance should be monolithic components of the research. More research is required to assess the effects of nitrogen content on these processes, optimize it, and determine if another pretreatment is necessary.

Valorizing fruit and vegetable residues as renewable sources of bioactive compounds (BCs) is critical for advancing sustainable biotechnology. This review (i) assesses the occurrence, diversity and functionality of BCs in 20 edible plant residues; (ii) compares and classify them by botanical family and residue type; (iii) reviews and evaluates the efficiency of conventional and green extraction and characterization techniques for recovering phytochemical and isolating phenolics (e.g., flavonoids and anthocyanins), carotenoids, alkaloids, saponins, and essential oils; and (iv) examines the BCs’ environmental, medical, and industrial applications. It synthesizes current knowledge on the phytochemical potential of these crops, highlighting their role in diagnostics, biomaterials, and therapeutic platforms. Plant-derived nanomaterials, enzymes, and structural matrices are employed in regenerative medicine and biosensing. Carrot- and pumpkin-based nanoparticles accelerate wound healing through antimicrobial and antioxidant protection. Spinach leaves serve as decellularized scaffolds that mimic vascular and tissue microenvironments. Banana fibers are used in biocompatible composites and sutures, and citrus- and berry-derived polyphenols improve biosensor stability and reduce signal interference. Agro-residue valorization reduces food waste and enables innovations in medical diagnostics, regenerative medicine, and circular bioeconomy, thereby positioning plant-derived BCs as a cornerstone for sustainable biotechnology. The BCs’ concentration in fruit and vegetable residues varies broadly (e.g., total phenolics (~50–300 mg GAE/g DW), anthocyanins (~100–600 mg C3G/g DW), and flavonoids (~20–150 mg QE/g DW)), depending on the crop and extraction method. By linking quantitative food waste hotspots with phytochemical potential, the review highlights priority streams for the circular-bioeconomy interventions and outlines research directions to close current valorization gaps.