Maja Berden Zrimec

Crude vegetable oils contain, in addition to glycerides, a range of co-extracted compounds whose composition depends strongly on the biological source. Their removal typically requires multi-stage refining, increasing process complexity as well as solvent and energy demands. In this study, a simple preparative chromatographic method was developed to purify crude algal lipid extracts and recover a glyceride-rich fraction. The process employed hexane as the mobile phase and cellulose-based materials as the stationary phase. The underlying separation mechanism was investigated experimentally using paper chromatography, thin-layer chromatography (TLC), and Fourier transform infrared spectroscopy (FTIR), and was further interpreted using Hansen solubility parameters (HSPs). Approximately 50% of the crude lipid extract was recovered as a glyceride-rich, colorless fraction. A secondary fraction enriched in sterols, chlorophylls, and carotenoids were also recovered, highlighting the potential for simultaneous purification and recovery of valuable lipid-associated compounds. To support potential process scale-up, regeneration of the stationary phase was evaluated, with each cycle required 0.225 L of fresh hexane and 0.1 L of fresh methanol. In addition, low-cost cellulose-rich residues, including used paperboard and wood dust, were successfully validated as alternative stationary phase materials. Overall, the proposed process provides a straightforward and potentially scalable approach to refining algal lipid extracts while enabling the recovery of additional value-added fractions and the use of inexpensive cellulose-based materials.

The bioeconomy is a key pillar of the European Green Deal, yet its implementation remains constrained by entrenched linear value chains, fragmented logistics systems, and regulatory uncertainty. This paper examines how practitioners across Europe envision circular bioeconomy transitions, drawing on evidence from 43 harmonised multi-actor workshops conducted in 14 countries with 1,078 participants from primary production, processing industries, technology provision, public authorities, and civil society. Using a structured participatory canvas and comparative thematic analysis, we analyse how stakeholders redesign existing value chains, which innovation pathways they prioritise, and which barriers they encounter in practice. Across agriculture, forestry, aquatic systems and bio-based industries, stakeholders consistently shift the focus from expanding biomass production toward improving the use of existing residues and side-streams. Dominant innovation pathways include residue valorisation, nutrient and water recycling, integrated bioenergy systems, and emerging biomaterials. At the same time, four interlinked barrier domains recur across countries and sectors: high and uncertain costs, immature or inaccessible technologies, weak feedstock logistics and pre-treatment infrastructure, and misaligned or unclear regulatory frameworks—most notably around waste and by-product classification. By providing one of the most extensive cross-country, practitioner-led analyses of circular bioeconomy value chains to date, the study offers granular evidence on how regulatory ambiguity, infrastructure gaps and investment risk constrain implementation on the ground. The findings point to a policy agenda focused on regulatory clarification rather than deregulation, coordinated investment in residue aggregation and pre-treatment infrastructure, and applied context-sensitive research to support scalable circular bio-based solutions.

Efficient inorganic carbon supply is a common limitation in microalgal cultivation, particularly in waste-derived media such as anaerobic digestate. Carbonic anhydrase (CA) accelerates the interconversion of CO₂ and bicarbonate and may therefore enhance carbon utilisation under conditions where inorganic carbon is abundant but not readily available. In this study, crude CA-containing extracts (aCA) were prepared from Scenedesmus-dominated algal biomass, and CA activity was quantified using an esterase assay (EAA). Although EAA activities varied depending on biomass pretreatment (0.15–0.47 U g⁻¹ DW), the physiological response to extract addition was consistent. In batch cultures of Chlorella sorokiniana grown in diluted digestate, aCA supplementation increased the specific growth rate (SGR) by 21–82%. In contrast, stimulation in a mineral medium was minimal, indicating that the benefit of aCA addition is most apparent under reduced inorganic carbon availability. In semi-continuous cultivation, repeated extract addition sustained a higher biomass productivity over time (rather than a specific growth rate). These results demonstrate that crude microalgal extracts containing CA can improve growth performance in digestate-based cultures and may offer a simple, low-cost approach to enhancing inorganic carbon utilisation in waste-integrated algal production systems.

Anaerobic digestion (AD) produces renewable energy but releases biogenic CO₂ and generates digestate requiring management. This paper evaluates four emerging pathways for CO₂ capture and reuse in AD systems: (1) in situ CO₂ conversion to CH₄ via microbial electrolysis cells (MECs), (2) hydrogenotrophic CO₂ methanation using green hydrogen, (3) enzymatic CO₂ capture coupled with autotrophic algae cultivation, and (4) digestate pyrolysis with syngas biomethanation. Each pathway is assessed in terms of technical feasibility, biocatalyst performance, system configuration, and key implementation challenges. Integrated scenarios demonstrate up to 98% CO₂ emission reduction, substantial bioenergy yield improvements, and enhanced nutrient and biomass recovery compared to conventional AD. MEC-based and hydrogenotrophic pathways show the highest energy efficiency, while algae-based systems provide added bioproduct valorization. The remaining limitations include cost, process integration, and scale-up. The study defines development priorities to advance zero-emission AD technologies for the agri-food and waste management sectors.

The European biofuel and bioenergy industry faces increasing challenges in achieving sustainable energy production while meeting carbon neutrality targets. This study provides a detailed analysis of biogenic emissions from biofuel and bioenergy production, with a focus on key sectors such as biogas, biomethane, bioethanol, syngas, biomass combustion, and biomass pyrolysis. Over 18,000 facilities were examined, including their feedstocks, production processes, and associated greenhouse gas emissions. The results highlight forestry residues as the predominant feedstock and expose significant disparities in infrastructure and technology adoption across EU Member States. While countries like Sweden and Germany lead in emissions management and carbon capture through bioenergy production with carbon capture and storage systems (BECCS), other regions face deficiencies in bioenergy infrastructure. The findings underscore the potential of BECCS and similar carbon management technologies to achieve negative emissions and support the European Green Deal’s climate neutrality goals. This work serves as a resource for policymakers, industry leaders, and researchers, fostering informed strategies for the sustainable advancement of the biofuels sector.

Spirulina is a microalga recognized for its nutritional benefits and its potential in sustainable food production. Existing large-scale cultivation produces spirulina of very different quality, taste, and odor. The reason lies in various approaches to the production, which range from the low-technology simple systems to high-end high-quality production for more demanding consumer market. In this chapter, we present challenges and possible solutions to ensure production of high-grade spirulina. We describe the design and crucial demands that have to be assured in the production system. The quality and productivity can be further increased by applying a bioprocess engineering approach based on modeling of the cultivation. Thermal modeling is also presented as an approach to optimize cultivation in the greenhouse systems. A spirulina production in Italy is showcased to pinpoint challenges of spirulina production in Europe. We conclude with an extensive study of regulatory framework for the spirulina production that must be taken into account for the successful algae production.

In a one-and-a-half-year study conducted in the ALS6 region in Europe (Ljubljana, Slovenia), the cultivation of microalgae in anaerobic digestate from food waste, mainly Scenedesmus dimorphus and Scenedesmus quadricauda, was investigated in three ponds (1260 L each) under a greenhouse. The effects of changing digestate quality and quantity as well as seasonal fluctuations on the productivity of the microalgae were investigated in three stages: Learning/Design (SI), Testing (SII), and Verification/Calibration (SIII). A decision support tool (DST) was developed using easy-to-measure parameters such as pH, temperature, electrical conductivity, mineral nitrogen forms and physical, biological parameters (OD, delayed fluorescence intensity). To control optimal pond operation, we proposed the photosynthetic culture index (PCI) as an early indicator for necessary interventions. Flocculation and nitrite levels (above 3 mg NO₂-N L⁻¹) were signals for the immediate remediation of the algae culture. Under optimal conditions in summer SIII, an average algal biomass production of 11 ± 1.5 g m⁻² day⁻¹ and a nitrogen use efficiency of 28 ± 2.6 g biomass/g N-input were achieved with the developed DST. The developed DST tool was, in this study, successfully implemented and used for the cultivation of microalgae consortia predominated by Scenedesmus dimorphus and S. quadricauda with biogas digestate. DST offers the possibility to be modified according to producers’ specific needs, facility, digestate and climate conditions, and as such, could be used for different microalgae cultivation processes with biogas digestate as a food source.

Editorial: Boosting the potential of algae for biomass production, valorisation, and bioremediation

Zoosporic parasites (i.e. fungi and fungi-like aquatic microorganisms) constitute important drivers of natural populations, causing severe host mortality. Economic impacts of parasitic diseases are notable in the microalgae biotech industry, affecting production of food ingredients, biofuels, pharma- and nutraceuticals. While scientific research on this topic is gaining traction by increasing studies elucidating the functional role of zoosporic parasites in natural ecosystems, we are currently lacking integrated and interdisciplinary efforts for effectively detecting and controlling parasites in the microalgae industry. To fill this gap we propose to establish an innovative, dynamic European network connecting scientists, industries and stakeholders to optimize information exchange, equalize access to resources and to develop a joint research agenda. ParAqua aims at compiling and making available all information on the occurrence of zoosporic parasites and their relationship with hosts, elucidate drivers and evaluate impacts of parasitism in natural and man-made aquatic environments. We aim to implement new tools for monitoring and prevention of infections, and to create protocols and a Decision Support Tool for detecting and controlling parasites in the microalgae biotech production. Applied knowledge on zoosporic parasites can feed back from industry to ecology, and we therefore will explore whether the developed tools can be applied for monitoring lakes and reservoirs. Short-Term Scientific Missions and Training Schools will be organised specifically for early stage scientists and managers – with a specific focus on ITC – with the aim to share and integrate both scientific and applied expertise and increase exchange between basic and applied researchers and stakeholders.