Effect of shear velocity on dark fermentation for biohydrogen production using dynamic membrane

Functional link hybrid artificial neural network for predicting continuous biohydrogen production in dynamic membrane bioreactor

Conventional machine learning approaches have shown limited predictive power when applied to continuous biohydrogen production due to nonlinearity and instability. This study was aimed at forecasting the dynamic membrane reactor performance in terms of the hydrogen production rate (HPR) and hydrogen yield (HY) using laboratory-based daily operation datapoints for twelve input variables. Hybrid algorithms were developed by integrating particle swarm optimized with functional link artificial neural network (PSO-FLN) which outperformed other hybrid algorithms for both HPR and HY, with determination coefficients (R2) of 0.97 and 0.80 and mean absolute percentage errors of 0.014 % and 0.023 %, respectively. Shapley additive explanations (SHAP) explained the two positive-influencing parameters, OLR_added (1.1-1.3 mol/L/d) and butyric acid (7.5-16.5 g COD/L) supports the highest HPR (40-60 L/L/d). This research indicates that PSO-FLN model are capable of handling complicated datasets with high precision in less computational timeat 9.8 sec for HPR and 10.0 sec for HY prediction.

Effect of bioaugmentation using Clostridium butyricum on the start-up and the performance of continuous biohydrogen production

This study aimed to mitigate the instability in the start-up and continuous performance of dark fermentative biohydrogen production using heat-treated sludge by the addition of an exogenous H₂-producing strain. Continuous fermentation augmented with Clostridium butyricum showed the highest average biohydrogen production rate (HPR) as 50.35 ± 2.56 and 58.57 ± 5.03 L/L-d with H₂-producing butyric and acetic acid pathways, whereas the fermenters without bioaugmentation showed the termination of biohydrogen production in 3 days of continuous operation with non H₂-producing lactic acid pathway and H₂-consuming propionic acid pathway. The bioaugmentation blocked the growth of the competitors for hexose such as Streptococcus, Lactobacillus and Megasphaera, and provided H₂-producer dominated microbiome with not only Clostridium butyricum, but also Clostridium puniceum and Clostridium neuense originated from heat-treated sludge. Bioaugmentation of a H₂-producing strain would be a reliable dissemination strategy for dark fermentative biohydrogen production by minimizing the influence of seed sludge population.

Membrane-based technologies for biohydrogen production: A review

Overcoming the existing environmental issues and the gradual depletion of energy sources is a priority at global level, biohydrogen can provide a sustainable and reliable energy reserve. However, the process instability and low biohydrogen yields are still hindering the adoption of biohydrogen production plants at industrial scale. In this context, membrane-based biohydrogen production technologies, and in particular fermentative membrane bioreactors (MBRs) and microbial electrolysis cells (MECs), as well as downstream membrane-based technologies such as electrodialysis (ED), are suitable options to achieve high-rate biohydrogen production. We have shed the light on the research efforts towards the development of membrane-based technologies for biohydrogen production from organic waste, with special emphasis to the reactor design and materials. Besides, techno-economic analyses have been traced to ensure the suitability of such technologies in bio-H₂ production. Operation parameters such as pH, temperature and organic loading rate affect the performance of MBRs. MEC and ED technologies also are highly affected by the chemistry of the membrane used and anode material as well as the operation parameters. The limitations and future directions for application of membrane-based biohydrogen production technologies have been individuated. At the end, this review helps in the critical understanding of deploying membrane-based technologies for biohydrogen production, thereby encouraging future outcomes for a sustainable biohydrogen economy.

Dark fermentation: Production and utilization of volatile fatty acid from different wastes- A review

Volatile fatty acids (VFAs) are the building blocks of the chemical industry, and they are the primary contributors to the planet's organic carbon cycle. VFA production from fossil fuels (mostly petroleum) is unsustainable, pollutes the environment, and generates greenhouse gases. As a result of these issues, there is a pressing need to develop alternate sources for the long-term generation of VFAs via anaerobic digestion. The accessible feedstocks for its sustainable production, as well as the influencing parameters, are discussed in this review. The use of VFAs as a raw material to make a variety of consumer products is reviewed in order to find a solution. It also bridges the gap between traditional and advanced VFA production and utilization methods from a variety of solid and liquid waste sources for economical stability.

High-rate biohydrogen production from xylose using a dynamic membrane bioreactor

This study aimed a high-rate dark fermentative H₂ production from xylose using a dynamic membrane module bioreactor (DMBR) with a 444-μm pore polyester mesh. 20 g xylose/L was fed continuously to the DMBR at different hydraulic retention times (HRTs) from 12 to 3 h at 37 °C. The maximum average H₂ yield (HY) and H₂ production rate (HPR) at 3 h HRT were found to be 1.40 ± 0.07 mol H₂/mol xylose_consumed and 30.26 ± 1.19 L H₂/L-d, respectively. The short HRT resulted in the maximum suspended biomass concentration (8.92 ± 0.40 g VSS/L) along with significant attached biomass retention (7.88 ± 0.22 g VSS/L). H₂ was produced by both butyric and acetic acid pathways. Low HY was concurrent with lactic acid production. The bacterial population shifted from non-H₂ producers, such as Lactobacillus and Sporolactobacillus spp., to Clostridium sp., when HY increased. Thus, xylose from lignocellulose is a feasible substrate for dark fermentative H₂ production using DMBR.

Dynamic membrane bioreactor for high rate continuous biohydrogen production from algal biomass

This study aimed to achieve continuous biohydrogen production from red algal biomass using a dynamic membrane bioreactor (DMBR). The DMBR was continuously fed with pretreated Echeuma spinosum containing 20 g/L hexose. The highest average hydrogen production rate (HPR) of 21.58 ± 1.59 L/L-d was observed at HRT 3 h, which was higher than previous reports for continuous H₂ production from biomass feedstock. Metabolic flux analysis revealed that butyric acid and propionic acid were the major by-products of the H₂-producing and H₂-consuming pathways, respectively, of the algal biomass fermentation. Hydrogen consumption by propionic acid pathway could not be prevented completely by heat treatment. PICRUSt2 analysis predicted that Clostridium sp., Anaerostipes sp., and Caproiciproducens sp. might significantly contribute to the expression of both ferredoxin hydrogenase and propionate CoA-transferase. This study would provide the design and operational information on high-rate bioreactor for continuous hydrogen production using biomass.

Main Hydrogen Production Processes: An Overview

Due to its characteristics, hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution, as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources, both of fossil and renewable origin, and with as many production processes, which can use renewable or non-renewable energy sources. To achieve carbon neutrality, the sources must necessarily be renewable, and the production processes themselves must use renewable energy sources. In this review article the main characteristics of the most used hydrogen production methods are summarized, mainly focusing on renewable feedstocks, furthermore a series of relevant articles published in the last year, are reviewed. The production methods are grouped according to the type of energy they use; and at the end of each section the strengths and limitations of the processes are highlighted. The conclusions compare the main characteristics of the production processes studied and contextualize their possible use.

State-of-the-art technologies for continuous high-rate biohydrogen production

Dark fermentation is a technically feasible technology for achieving carbon dioxide-free hydrogen production. This review presents the current findings on continuous hydrogen production using dark fermentation. Several operational strategies and reactor configurations have been suggested. The formation of attached mixed-culture microorganisms is a typical prerequisite for achieving high production rate, hydrogen yield, and resilience. To date, fixed-bed reactors and dynamic membrane bioreactors yielded higher biohydrogen performance than other configurations. The symbiosis between H₂-producing bacteria and biofilm-forming bacteria was essential to avoid washout and maintain the high loading rates and hydrogenic metabolic flux. Recent research has initiated a more in-depth comparison of microbial community changes during dark fermentation, primarily with computational science techniques based on 16S rRNA gene sequencing investigations. Future techno-economic analysis of dark fermentative biohydrogen production and perspectives on unraveling mitigation mechanisms induced by attached microorganisms in dark fermentation processes are further discussed.

Investigation of the interaction between lighting and mixing applied during the photo-fermentation biohydrogen production process from agricultural waste

To better clarify the effect of lighting and mixing on the hydrogen production from agricultural waste, experiments under diverse constant and dynamic light intensities and mixing speeds were conducted. Cumulative hydrogen yield, hydrogen production rate, OD₆₆₀, pH, reducing sugar concentration were monitored. Results showed that mixing had positive effects on high substrate concentration. The interaction between lighting and mixing was drawn. Higher light intensity (7000 Lux) was suitable for hydrogen production under mixing. Higher light intensity with higher mixing speed (150 RPM) showed the highest cumulative hydrogen yield of 78.1 mL/g TS. Different periods of hydrogen production process required distinct lighting and mixing. Combined with Gompertz model, dynamic lighting and mixing strategies were discussed. Dynamic light intensity (4000-7000-4000 Lux) accompanied with dynamic mixing speed (50-150-50 RPM) was the optimal condition for PFHP. Highest hydrogen yield of 84.7 mL/g TS and highest light conversion efficiency of 36.32% were obtained.