Biohydrogen production by mixed culture of Megasphaera elsdenii with lactic acid bacteria as Lactate-driven dark fermentation

Presence of lactic acid bacteria in hydrogen production by dark fermentation: competition or synergy

Dark fermentation in mixed cultures has been extensively studied due to its great potential for sustainable hydrogen production from organic wastes. However, microbial composition, substrate competition, and inhibition by fermentation products can affect hydrogen yield and production rates. Lactic acid bacteria have been identified as the key organisms in this process. On one hand, lactic acid bacteria can efficiently compete for carbohydrate rich substrates, producing lactic acid and secreting bacteriocins that inhibit the growth of hydrogen-producing bacteria, thereby decreasing hydrogen production. On the other hand, due to their metabolic capacity and synergistic interactions with certain hydrogen-producing bacteria, they contribute positively in several ways, for example by providing lactic acid as a substrate for hydrogen generation. Analyzing different perspectives about the role of lactic acid bacteria in hydrogen production by dark fermentation, a literature review was done on this topic. This review article shows a comprehensive view to understand better the role of these bacteria and their influence on the process efficiency, either as competitors or as contributors to hydrogen production by dark fermentation.

Evaluation of individual and combined effect of lactic acid-consuming bacteria on mesophilic hydrogen production from lactic acid effluent from food waste treatment

Lactic acid has been applied as a precursor for hydrogen (H2) production from substrates rich in lactic acid bacteria (LAB), focusing on microbial interactions between producing and consuming LAB tested with model substrates. Therefore, this study evaluated the effect of single and combined lactic acid-consuming bacteria on mesophilic H2 production in batch tests from lactic acid from fermented food waste (FW). Megasphaera elsdenii, Clostridium beijerinckii, and Clostridium butyricum were inoculated at different ratios (v/v). Additionally, thermal pretreated sludge (TPS) was added to the strain mixtures. The highest production was obtained with M. elsdenii, C. beijerinckii, and C. butyricum (17:66:17 ratio), obtaining 1629.0 mL/Lreactor. The optimal mixture (68:32:0 of M. elsdenii and C. beijerinckii) enriched with TPS reached 1739.3 ± 98.6 mL H2/Lreactor, consuming 98 % of lactic acid added. M. elsdenii and Clostridium strains enhance H2 production from lactic acid as they persist in a microbial community initially dominated by LAB.

Biohydrogen production by lactate-driven dark fermentation of real organic wastes derived from solid waste treatment plants

This study evaluated the hydrogen production potential through lactate-driven dark fermentation (LD-DF) of organic wastes from solid waste treatment plants, including the organic fraction of municipal solid waste (OFMSW), mixed sewage sludge, and two OFMSW leachates. In initial batch fermentations, only OFMSW supported a significant hydrogen yield (70.1 ± 7.7 NmL-H2/g-VS added) among the tested feedstocks. Lactate acted as an important hydrogen precursor, requiring the presence of carbohydrates for sequential two-step lactate-type fermentation. The impact of operational pH (5.5-6.5) and initial total solids (TS) concentration (5-12.5 % w/w) was also evaluated using OFMSW as substrate, obtaining hydrogen yields ranging from 6.6 to 55.9 NmL-H2/g-VSadded. The highest yield occurred at 6.5 pH and 7.5 % TS. The LD-DF pathway was indicated to be present under diverse pH and TS conditions, supported by employing a specialized microbial consortium capable of performing LD-DF, along with the observed changes in lactate levels during fermentation.

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.

Impact analysis of hydraulic residence time and dissolved oxygen on performance efficiency and microbial community in N, N-dimethylformamide wastewater treated by an AnSBR-ASBR

Suitable operating parameters are one of the key factors to efficient and stable biological wastewater treatment of N, N-dimethylformamide (DMF) wastewater. In this study, an improved AnSBR-ASBR reactor (anaerobic sequencing batch reactor, AnSBR, and aerobic SBR, ASBR, run in series) was used to investigated the effects of operating conditions such as hydraulic residence time (HRT), AnSBR stirring speed and ASBR dissolved oxygen (DO) for DMF wastewater treatment. When HRT decreased from 24 h to 12 h, the average removal rates of COD by the AnSBR were 34.59% and 39.54%, respectively. Meanwhile, the removal rate of NH4+-N by ASBR decreased from 88.38% to 62.81%. The DMF removal rate reached the best at 18 h and the expression of dehydrogenase was the highest in the AnSBR. The abundance of Megasphaera, the dominant sugar-degrading bacteria in the AnSBR, continued to decline due to the decrease of HRT. The relative abundance of Methanobacterium gradually increased to 80.2% with the decrease of HRT and that hydrotrophic methanogenesis dominated the methanogenic process. The HRT decrease promoted butyrate and pyruvate metabolism in anaerobic sludge, but the proportion of glycolysis and methane metabolism decreased. The AnSBR-ASBR reactor had the best operation performance when HRT was 18 h, AnSBR speed was 220 r/min, and ASBR DO content was 3-4 mg/L. This study provided an effective reference for the reasonable selection of operating parameters in the treatment of DMF-containing wastewater by the AnSBR-ASBR.

Towards industrial biological hydrogen production: a review

Increased production of renewable energy sources is becoming increasingly needed. Amidst other strategies, one promising technology that could help achieve this goal is biological hydrogen production. This technology uses micro-organisms to convert organic matter into hydrogen gas, a clean and versatile fuel that can be used in a wide range of applications. While biohydrogen production is in its early stages, several challenges must be addressed for biological hydrogen production to become a viable commercial solution. From an experimental perspective, the need to improve the efficiency of hydrogen production, the optimization strategy of the microbial consortia, and the reduction in costs associated with the process is still required. From a scale-up perspective, novel strategies (such as modelling and experimental validation) need to be discussed to facilitate this hydrogen production process. Hence, this review considers hydrogen production, not within the framework of a particular production method or technique, but rather outlines the work (bioreactor modes and configurations, modelling, and techno-economic and life cycle assessment) that has been done in the field as a whole. This type of analysis allows for the abstraction of the biohydrogen production technology industrially, giving insights into novel applications, cross-pollination of separate lines of inquiry, and giving a reference point for researchers and industrial developers in the field of biohydrogen production.

Continuous lactate-driven dark fermentation of restaurant food waste: Process characterization and new insights on transient feast/famine perturbations

The effect of hydraulic retention time (HRT) on the continuous lactate-driven dark fermentation (LD-DF) of food waste (FW) was investigated. The robustness of the bioprocess against feast/famine perturbations was also explored. The stepwise HRT decrease from 24 to 16 and 12 h in a continuously stirred tank fermenter fed with simulated restaurant FW impacted on hydrogen production rate (HPR). The optimal HRT of 16 h supported a HPR of 4.2 L H₂/L-d. Feast/famine perturbations caused by 12-h feeding interruptions led to a remarkable peak in HPR up to 19.2 L H₂/L-d, albeit the process became stable at 4.3 L H₂/L-d following perturbation. The occurrence of LD-DF throughout the operation was endorsed by metabolites analysis. Particularly, hydrogen production positively correlated with lactate consumption and butyrate production. Overall, the FW LD-DF process was highly sensitive but resilient against transient feast/famine perturbations, supporting high-rate HPRs under optimal HRTs.

Unrevealing the role of metal oxide nanoparticles on biohydrogen production by Lactobacillus delbrueckii

The positive interaction between Clostridium sp. and lactic acid-producing bacteria (Lactobacillus sp) is commonly seen in various high-rate hydrogen production systems. However, the exact role of the hydrogen production ability of Lactobacillus sp in a dark fermentation production system is rarely studied. Lactobacillus delbrueckii was herein used for the first time, to the best of the author's knowledge, to demonstrate biohydrogen production under anaerobic conditions. At first, the pH condition was optimized, followed by the addition of nanoparticles for enhanced biohydrogen production. Under optimized conditions of pH 6.5, substrate concentration 10 g/L, and 100 mg/L of NiO/Fe₂O₃, the maximum hydrogen yield (HY) of 1.94 mol/mol hexose was obtained, which is 18 % more than the control. The enhanced H₂ production upon the addition of nanoparticles is supported via the external electron transfer (EET) mechanism, which regulates the metabolic pathway regulation with increased production of acetate and butyrate and reduced formation of lactate.

Simultaneous production of hydrogen-methane and spatial community succession in an anaerobic baffled reactor treating corn starch processing wastewater

Corn starch processing wastewater (CSPW) is a high-strength organic wastewater and biological treatment is considered as the dominant process. The present work investigated the effects of pH on the bioenergy production and spatial succession of microbial community in an anaerobic baffled reactor (ABR) treating CSPW. The results showed that above 90.5% of COD removal and above 16.6 L d^-1 of methane were achieved at the influent pHs of 8.0 and 7.0 under organic loading rate of 4.0 kg COD·m^-3·L^-1 condition. Further decreasing the influent pH to 6.0 resulted in the COD removal decreased to 89.7%. Besides, 9.2 L d^-1 of hydrogen and 13.0 L d^-1 of methane were obtained. There was significant difference in the volatile fatty acids profiles during the variation of pH. Illumina Miseq sequencing showed that Clostridium, Ethanoligenens, Megasphaera, Prevotella and Trichococcus with relative abundance of 2.1%∼28.1% were the dominant hydrogen-producing bacteria in C1. Methanogens (Methanothrix and Methanobacterium) dominated in the last three compartments. Function predicted analysis revealed that the abundance of metabolic-related gene families containing carbohydrate, amino acids and energy in the last three compartments were higher than that in C1. A deduced biodegradation model of CSPW in ABR revealed that the anaerobic sludge in C1 mainly produced hydrogen. Microbial population in C3 was responsible for COD removal and methane production. The redundancy analysis revealed that hydrogen production was highly correlated with some hydrogen-producing bacteria in C1, whereas methane production was positively correlated with microbial group in C2∼ C4.

Microalgae-bacterial granular consortium: Striding towards sustainable production of biohydrogen coupled with wastewater treatment

Anthropogenic activities have drastically affected the environment, leading to increased waste accumulation in atmospheric bodies, including water. Wastewater treatment is an energy-consuming process and typically requires thousands of kilowatt hours of energy. This enormous energy demand can be fulfilled by utilizing the microbial electrolysis route to breakdown organic pollutants in wastewater which produces clean water and biohydrogen as a by-product of the reaction. Microalgae are the promising microorganism for the biohydrogen production, and it has been investigated that the interaction between microalgae and bacteria can be used to boost the yield of biohydrogen. Consortium of algae and bacteria resulting around 50-60% more biohydrogen production compared to the biohydrogen production of algae and bacteria separately. This review summarises the recent development in different microalgae-bacteria granular consortium systems successfully employed for biohydrogen generation. We also discuss the limitations in biohydrogen production and factors affecting its production from wastewater.

Effect of Localized Temperature Difference on Hydrogen Fermentation

In a lab-scale bioreactor system, (20 L of effective volume in our study) controlling a constant temperature inside bioreactor with a total volume 25 L is a simple process, whereas it is a complicated process in the actual full-scale system. There might exist a localized temperature difference inside the reactor, affecting bioenergy yield. In the present work, the temperature at the middle layer of bioreactor was controlled at 35 °C, while the temperature at top and bottom of bioreactor was controlled at 35 ± 0.1, ±1.5, ±3.0, and ±5.0 °C. The H2 yield of 1.50 mol H2/mol hexoseadded was achieved at ±0.1 and ±1.5 °C, while it dropped to 1.27 and 0.98 mol H2/mol hexoseadded at ±3.0 and ±5.0 °C, respectively, with an increased lactate production. Then, the reactor with automatic agitation speed control was operated. The agitation speed was 10 rpm (for 22 h) under small temperature difference (<±1.5 °C), while it increased to 100 rpm (for 2 h) when the temperature difference between top and bottom of reactor became larger than ±1.5 °C. Such an operation strategy helped to save 28% of energy requirement for agitation while producing a similar amount of H2. This work contributes to facilitating the upscaling of the dark fermentation process, where appropriate agitation speed can be controlled based on the temperature difference inside the reactor.