The aim of this review is to provide a comprehensive analysis of the membrane-assisted dark fermentation process for bioH₂ production and purification. This review initially analyses the need for and the current state of the art in H₂ production through dark fermentation, evaluating the research landscape and the maturity level of the technology. Key factors influencing the dark fermentation process are then examined, along with emerging research trends in membrane-assisted fermentative H₂ production systems. This review subsequently addresses the challenges inherent to dark fermentation and explores potential opportunities to enhance H₂ production efficiency. Special attention is given to membrane technology as a promising strategy for process intensification in bioH₂ production and recovery. Finally, this review provides an in-depth discussion of inorganic membranes, mixed matrix membranes (MMMs), and thin and ultrathin membranes, evaluating each membrane type in terms of its advantages, limitations, and purification performance. This review offers valuable insights into intensifying the dark fermentation process by leveraging membrane technology to enhance bioH₂ production and purification efficiency.

The use of metal nanoparticles (NPs) to enhance hydrogen production in dark fermentation (DF) has become a pioneering field of interest. In particular, iron-based nanoparticles (FeNPs) play a pivotal role in enhancing the activity of metalloenzymes and optimizing feedstock utilization, resulting in improved hydrogen production. This study investigated the effect of FeNPs (magnetite) supplementation at three different concentrations of 50, 100, and 200 ppm in a continuous dark fermenter for the production of hydrogen from rice straw acid hydrolysate. The highest hydrogen production rate of 2.6 ± 0.3 NL H₂/L-d was achieved with the addition of 100 ppm of nanoparticles, representing a 53% increase compared to the condition without FeNPs addition. This improvement was driven by a microbial community in which Clostridium was the major dominant genus. In addition, increasing the nanoparticle concentration to 100 ppm resulted in an increase in butyrate concentration to 2.0 ± 0.1 g/L, which is 43% higher than the butyrate concentration without FeNPs. However, when the NP concentration was increased to 200 ppm, the hydrogen production rate decreased to 1.6 ± 0.2 NL H₂/L-d. This study can serve as a guideline for future research aimed at evaluating the effects of FeNPs in continuous dark fermentation systems. This work highlights the potential benefits and challenges associated with the use of FeNPs, paving the way for future studies to optimize their application and improve the efficiency of dark fermentation processes.

Anaerobic digestion is a well-established technology for the sustainable production of biogas. However, to be used as a substitute for natural gas or as vehicle fuel, it is necessary to remove carbon dioxide (CO₂) and other contaminants from biogas that can compromise the useful life of combustion engines. Upgraded biogas is known as biomethane (>95% methane content). This work reviews the different technologies used for upgrading biogas, emphasizing microalgae–nanoparticle systems, representing a more sustainable and environmentally friendly system. Parameters affecting these systems performance are discussed, and the trends and areas of opportunity for subsequent work are evaluated through a bibliometric analysis.

A novel gas-phase bioreactor based on cordierite honeycomb monoliths arranged as microchannels to support Taylor flow for enhanced gas-liquid mass transfer was engineered and validated for biogas bioconversion into ectoine. The assessment of the volumetric gas-liquid mass transfer coefficients for (KLa O2) in this novel Taylor flow bioreactor showed values up to 1575.8 ± 119.4 h-1, representing an increase of one order of magnitude over conventional bubble column reactors. The high shear stress imposed by the gas and liquid recirculations required the gradual enrichment of a mixed methanotrophic culture capable of bioconverting methane into ectoine. Methane bioconversion efficiencies and capacities of up to 74% and 45 g m3 h-1, with an ectoine concentration of up to 30 mg gVSS-1, were achieved when operating with a gas residence time of 30 min, and gas and liquid recirculations of 40 L min-1 and 25 L min-1, respectively (corresponding to a KLa O2 of 727 ± 61 h-1). Process performance was supported by a very well-adapted inoculum dominated by Methylophaga, Methylonatrum and Methylotuvimicrobium¸ which accumulated 44% of the relative abundances. Monoliths as microchannels in high gas-liquid mass transfer reactors exhibit a vast potential for industrial applications, but further optimisation of operational parameters is required to intensify ectoine production from methane

A novel gas-liquid multichannel bioreactor based on cordierite honeycomb monoliths was engineered and operated under internal gas and liquid recirculation for methane bioconversion into ectoine. The assessment of the volumetric gas-liquid mass transfer coefficients for O₂ ( [Formula: see text] ) in this novel bioreactor showed values up to 1472.7 ± 111.6 h^-1, representing an increase of one order of magnitude over conventional bubble column reactors. Bubble measurements were consistent with a flow regime compatible with Taylor-flow operation, suggesting that liquid-film renewal was likely a major contributor to mass-transfer enhancement. During diluted-methane bioconversion into ectoine, stable operation at relatively high gas and liquid recirculation rates was achieved after gradual enrichment of the halotolerant mixed methanotrophic culture, potentially because of the associated hydrodynamic shear stress. After inoculum adaptation, methane bioconversion efficiencies and capacities of up to 72.9% and 45 g m³ h^-1, with an ectoine concentration of 32.1 mg gVSS^-1, were achieved when operating with a gas residence time of 30 min, and gas and liquid recirculation of 40 L min^-1 and 25 L min^-1, respectively (corresponding to a [Formula: see text] of 679.5 ± 57.3 h^-1). Process performance was supported by a well-adapted inoculum dominated by Methylophaga, Methylonatrum and Methylotuvimicrobium, which accumulated 44% of the relative abundances. Monoliths as microchannels in high gas-liquid mass transfer reactors represent a promising platform for methane valorisation, but further optimisation of operational parameters is required to intensify ectoine production from methane.

This study evaluated the performance of a non-aerated 22 L column photobioreactor treating synthetic wastewater (SWW) under increasing organic loading rates (SWW x1, x2, and x3) at a hydraulic retention time of 2 days to investigate how purple phototrophic bacteria (PPB) inoculation timing affects operational stability and nutrient removal. Two strategies were compared: supplementing a microalgae–bacteria consortium with PPB after 15 days (Phase I) versus co-inoculation from startup (Phase II). Phase I maintained active photosynthesis, reaching dissolved oxygen (DO) levels of 14.7 ± 3.8 mg L⁻¹ in SWW x2. Conversely, Phase II sustained persistently low DO (<1.5 mg L⁻¹), which correlated with reduced inorganic carbon fixation and raised effluent inorganic carbon to 205.2 mg L⁻¹ under SWW x3. The highest load (SWW x3) also induced orthophosphate accumulation and elevated ammonium levels up to 150 mg L⁻¹ due to nitrogenase suppression. Phase II also exhibited a higher nitrite accumulation (approx. 10 mg L⁻¹) with minimal nitrate (<3 mg L⁻¹), suggesting impaired nitrifying activity. In conclusion, the early PPB co-inoculation strategy established a distinct microbial community trajectory that favored a sub-optimized, dissipative metabolic regime that impaired carbon fixation and resource recovery under high loading rates.