Special Issue “Bioprocess Engineering: Sustainable Manufacturing for a Green Society”

The transition from linear, resource-intensive production to circular, low-carbon manufacturing currently presents a major challenge. Conventional processes still demand high levels of both raw materials and energy while generating substantial waste, thus contributing to, for example, resource depletion, pollution, and greenhouse gas emissions [1,2,3]. Bioprocess engineering offers a production alternative based on mild operational conditions, selective biocatalysis, and microbial diversity. It is supported by the knowledge gathered in more than a century of industrial fermentation, spanning processes from ethanol and citric acid production to antibiotics and recombinant proteins, and it is further enriched by historical developments in industrial biocatalysis, where enzymes have long been harnessed for selective biotransformation in, e.g., food, pharma and fine chemicals production [4,5,6]. When integrated with biorefinery concepts, bioprocesses can support circular economy strategies and accelerate the transition towards sustainable production of chemicals, fuels, materials, nutraceuticals, and pharmaceuticals [7,8,9]. Seminal literature on biorefineries, biocatalysis, and metabolic engineering underscores the key role of bioprocesses in decarbonized manufacturing [10,11,12,13,14,15,16,17].

This Special Issue of Processes—Bioprocess Engineering: Sustainable Manufacturing for a Green Society—features five contributions that exemplify the transformative potential of the current research in this field to attain sound and sustainable production methods. They include examples of the isolation and screening of new biocatalysts and activities, enzyme immobilization and stabilization, and new applications such as the production of composite materials and analytical methods.

Marine microbiomes provide an underexplored area of biocatalysts. In the study published in this Special Issue, two isolates, Bacillus subtilis HR05 and Shewanella algae HR06, which coexist with the alga Ulva flexuosa, were found to produce xylanases with the highest activities among those isolated [18]. These results are in accordance with the growing evidence for marine biocatalysts usage in biorefineries, food processing, and specialty chemicals, where salinity tolerance and unique catalytic profiles are advantageous [19,20,21]. Industries which could benefit from these xylanases include food industries and pulp and paper production due to their high activity and optimal alkaline pH.

Smith et al. developed natural fiber composites exemplifying the convergence of materials science and bioprocessing [22]. In this study, self-cultured bacterial-retted fibers from hemp were formed into a fiber mat (BGM) and laminated with polylactic acid (PLA) sheets. The 100% biodegradable hemp BFM/PLA composites were not as uniform as desired, but optimization of the fiber-to-matrix ratio can enhance mechanical and thermal performance, positioning these composites as credible alternatives to synthetic fiber-reinforced polymers. This is in accordance with the broader trajectory of bio-based polymers and natural fiber composites reported in the literature, where PLA and lignocellulosic fibers have been shown to enable weight reduction, lower embodied energy, and promote end-of-life compostability [23,24,25,26].

For a given enzyme to be used at production scale, it must be active and stable under highly demanding industrial conditions. Process-ready enzymes depend on architectures that enhance stability, reusability, and synergistic activity. Immobilization of enzymes increases their stability, allows their reuse, facilitates process control and product recovery, and enhances product yield and quality. In the review article of this Special Issue, the authors provide an integrated perspective on (multi)enzyme immobilization, while critically evaluate immobilization methods and carriers and biocatalyst metrics [27]. The impact of key carrier features on biocatalyst performance is discussed, as well as the novel trends towards miniaturization. Illustrative examples that are representative of biocatalytic applications promoting sustainability are presented. In the last two decades, seminal work demonstrating how support chemistry, pore structure, and oriented immobilization modulate mass transfer, activity, selectivity, and stability has been published, resulting in improved catalytic performance [17,28,29,30,31,32,33].

In another study published in the Special Issue, the authors explored triazine-scaffolded solid-phase lead ligands to improve cutinase-related enzymes through affinity-like immobilization [34]. The biomimetic affinity support increased thermal stability of the immobilized cutinase through tailored ligand–protein interactions, and the study extended this concept to multiple lipases and to an invertase from Saccharomyces cerevisiae. These findings complement established strategies for enzyme stabilization, such as immobilization, chemical modification, and medium engineering, and underscore the importance of rational ligand design for robustness at elevated temperatures [35,36,37,38,39].

The advancement of cost-effective analytical platforms for bioprocess monitoring is fundamental to ensuring product quality and regulatory compliance [40]. In one of the Special Issue papers, the authors compared a benchtop Fourier Transform (FT) near-infrared (NIR) spectrometer with a prototype of a portable, miniaturized NIR spectrometer (miniNIR) to detect and quantify (i) biodiesel contaminants and (ii) biodiesel in diesel [41]. Models using principal component analysis–linear discriminant analysis (PCA-LDA) provided good accuracies, suggesting that the low cost, portable device has potential for the preliminary analysis of biodiesel. The work contributes to the maturation of process analytics for biodiesel, complementing standards [42] and fostering applications beyond laboratory settings toward point-of-use and inline controls [43].

Taken together, the manuscripts of the Special Issue address the main challenges in biocatalysis and bioprocess engineering, from enzyme discovery to stabilization, and application and process integration, even in new fields.