Sustainable Bioprocesses: Green Manufacturing & Circular Bioeconomy

Sustainable bioprocesses use biological systems — microorganisms, enzymes, plants, cell cultures — to manufacture chemicals, materials, fuels, and other products with lower environmental impact than conventional petrochemical routes. They are central to the circular bioeconomy: an economic system in which renewable biological resources are used to produce food, feed, materials, and energy, with waste streams recycled back into production. The transition from a fossil-based to a bio-based economy is a defining industrial challenge of the 21st century.

The field draws on industrial biotechnology (fermentation, biocatalysis, downstream processing), metabolic engineering (designing microbial cell factories), and process engineering (bioreactor design, separation processes, process integration). It is enabled by advances in synthetic biology (rapid construction of genetic circuits and pathways), systems biology (multi-omics analysis of cellular physiology), and bioinformatics (mining biological diversity for useful enzymes and pathways).

Hrisana Journal publishes research across the full bioprocess development pipeline, from strain engineering through process development and scale-up to techno-economic and life-cycle analysis. Our interdisciplinary scope reflects the integrated nature of successful bioprocess development.

A biorefinery is the bio-based analogue of a petroleum refinery — a facility that converts biomass into multiple products, maximizing value and minimizing waste. Feedstocks include agricultural residues (corn stover, wheat straw, sugarcane bagasse), forestry residues, dedicated energy crops (switchgrass, miscanthus), municipal solid waste, and algae. Products include fuels (bioethanol, biodiesel, biogas, sustainable aviation fuel), platform chemicals (lactic acid, succinic acid, 1,3-propanediol, ethylene), materials (bioplastics, biofibres), and high-value co-products (nutraceuticals, pharmaceuticals).

Lignocellulosic biorefineries — those using woody or fibrous plant biomass — face the challenge of deconstructing recalcitrant lignocellulose into fermentable sugars. Pretreatment (steam explosion, dilute acid, ammonia fibre expansion, ionic liquid treatment) opens the lignocellulose structure; enzymatic hydrolysis (cellulases, hemicellulases, ligninases) releases sugars; microbial fermentation converts sugars to products. Each step has been the subject of decades of optimization, and integrated approaches that combine pretreatment and saccharification (consolidated bioprocessing) remain an active research frontier.

Algal biorefineries use microalgae or cyanobacteria to convert CO₂ and sunlight into biomass rich in lipids, proteins, and pigments. Potential products include biodiesel, omega-3 fatty acids, animal feed, and high-value pigments such as astaxanthin. Algae can be grown on non-arable land using saline or wastewater, avoiding competition with food crops. Challenges include the dilute nature of algal cultures (requiring energy-intensive harvesting), contamination of open pond cultures, and the economics of downstream processing.

Fermentation — the cultivation of microorganisms or cells in bioreactors to produce target compounds — is the workhorse of industrial biotechnology. Engineered microbial cell factories produce biofuels (ethanol, butanol, biodiesel), platform chemicals (lactic acid, succinic acid, 1,4-butanediol), specialty chemicals (antibiotics, vitamins, flavours), and materials (bioplastics, biosurfactants). The performance of the cell factory — titre, rate, and yield — determines process economics.

Metabolic engineering uses genetic tools to optimize cellular metabolism for production. Pathways can be introduced from other organisms (e.g., introducing the mevalonate pathway for isoprenoid production in E. coli), native pathways can be modified to redirect flux (e.g., knocking out competing pathways), and regulatory networks can be rewired to optimize expression. CRISPR-based tools enable multiplex genome editing, accelerating strain construction. Computational models of cellular metabolism, refined with multi-omics data, guide rational engineering decisions.

Host selection is critical. Escherichia coli and Saccharomyces cerevisiae are workhorses with extensive genetic tools and process knowledge, but they may not be optimal for all products or feedstocks. Alternative hosts — Bacillus, Corynebacterium, Pseudomonas, Yarrowia, Kluyveromyces, oleaginous yeasts, filamentous fungi, microalgae, mammalian cells — offer different metabolic capabilities, tolerance profiles, and product portfolios. Choosing the right host and engineering it effectively is a key research activity.

Biocatalysis — using isolated or whole-cell enzymes to perform chemical transformations — offers high selectivity, mild operating conditions, and renewable catalysts. It enables syntheses that would be difficult or impossible with conventional chemistry, particularly for chiral compounds, complex molecules, and cascade reactions. The integration of biocatalysis with conventional chemistry in hybrid processes often provides the best overall process economics.

Enzyme engineering — through directed evolution, rational design, or computational methods — tailors enzymes for industrial application. Properties engineered include activity (turnover number, catalytic efficiency), stability (thermal, operational, solvent tolerance), substrate specificity, and product selectivity. The development of CRISPR-based directed evolution platforms and machine learning-guided enzyme engineering has accelerated this process dramatically.

Cascade biocatalysis — performing multiple enzymatic steps in a single pot without intermediate isolation — exemplifies green chemistry principles. By avoiding the protection/deprotection steps and isolation/purification operations of conventional synthesis, cascades reduce waste, solvent use, and energy consumption. Multi-enzyme cascades for the synthesis of pharmaceutical intermediates, fine chemicals, and commodity chemicals are being developed and deployed at industrial scale.

A successful bioprocess integrates upstream (strain development, media formulation, inoculum preparation), fermentation (bioreactor operation, process control), and downstream (cell separation, product recovery, purification) operations. Process economics depend on the integration — high-titre fermentation is meaningless if product recovery is prohibitively expensive, and cheap downstream processing cannot rescue a low-titre fermentation. Integrated process design, supported by techno-economic analysis throughout development, is essential.

Scale-up from laboratory to pilot to commercial scale presents challenges in mixing, mass transfer, and heat transfer that are not apparent at small scale. Oxygen transfer in aerobic fermentations, shear sensitivity of cell lines, and product inhibition all change with scale. Computational fluid dynamics, small-scale models that mimic full-scale conditions, and careful pilot-scale evaluation all support successful scale-up. Process analytical technology (PAT) — online monitoring and control — is increasingly important at production scale.

Life-cycle assessment (LCA) and techno-economic analysis (TEA) are essential tools for guiding bioprocess development. LCA quantifies environmental impacts (greenhouse gas emissions, water use, land use) across the full life cycle, identifying hotspots and guiding improvement. TEA quantifies production costs, identifying cost drivers and informing research priorities. Together, they ensure that bioprocesses deliver genuine environmental and economic benefits. Hrisana Journal welcomes submissions that report integrated process development with TEA/LCA.