Effect of temperature on continuous fermentative hydrogen production from Laminaria japonica by anaerobic mixed cultures

A Review of Biohydrogen Production from Saccharina japonica

Saccharina japonica (known as Laminaria japonica or Phaeophyta japonica), one of the largest macroalgae, has been recognized as food and medicine for a long time in some Asian countries, such as China, South Korea, Japan, etc. In recent years, S. japonica has also been considered the most promising third-generation biofuel feedstock to replace fossil fuels, contributing to solving the challenges people face regarding energy and the environment. In particular, S. japonica-derived biohydrogen (H2) is expected to be a major fuel source in the future because of its clean, high-yield, and sustainable properties. Therefore, this review focuses on recent advances in bio-H2 production from S. japonica. The cutting-edge biological technologies with suitable operating parameters to enhance S. japonica’s bio-H2 production efficiency are reviewed based on the Scopus database. In addition, guidelines for future developments in this field are discussed.

Mathematical modeling of dark fermentation of macroalgae for hydrogen and volatile fatty acids production

A mathematical model of H₂ and volatile fatty acids (VFAs) production via dark fermentation of particulate macroalgal substrates is presented. Carbohydrates, proteins, and lipids in the particulate substrate are convert to H₂, CO₂, and VFAs via disintegration/solubilization, hydrolysis, and acidogenesis. Hydrolysis is modeled using a combined surface-limiting model combined with a first-order reaction model to describe both microbial hydrolysis and physical solubilization. Experimental and published data obtained using Saccharina japonica as the substrate are used to calibrate and validate the model. The model prediction featured a good accuracy, with high R² of 0.912 - 0.976 for all end products. The physical solubilisation accounts for 28.4% of the total hydrolysis. By the model simulation, a H₂ production of 103.2 mL/g-VS and VFA production of 0.41 g/g-VS are found at optimum conditions of 20 g-TS/L (13.2 g-VS/L) of substrate concentration and 7.0 of initial pH.

Hydrogen production from macroalgae by simultaneous dark fermentation and microbial electrolysis cell

Hydrogen production from Saccharina Japonica by simultaneous dark fermentation (DF) and microbial electrolysis cell (MEC), called sDFMEC, was studied. In the novel sDFMEC process, substrates were converted to H₂ and volatile fatty acids (VFAs) by DF in the bulk phase, and VFAs are simultaneously oxidized by the exoelectrogens in the microbial film on anode electrode with further production of H₂ at the cathode. The sDFMEC process was compared with DF and a combined process of DF and MEC in series (DF-MEC) in terms of H₂ production. The overall H₂ production from S. Japonica in sDFMEC process was higher (438.7 ± 13.3 mL/g-TS), than DF (54.6 ± 0.8 mL/g-TS) and DF-MEC (403.5 ± 7.9 mL/g-TS) process, respectively, which is approximately 3-times higher than those reported in the literature.

Understanding the NaCl-dependent behavior of hydrogen production of a marine bacterium, Vibrio tritonius

Biohydrogen is one of the most suitable clean energy sources for sustaining a fossil fuel independent society. The use of both land and ocean bioresources as feedstocks show great potential in maximizing biohydrogen production, but sodium ion is one of the main obstacles in efficient bacterial biohydrogen production. Vibrio tritonius strain AM2 can perform efficient hydrogen production with a molar yield of 1.7 mol H₂/mol mannitol, which corresponds to 85% theoretical molar yield of H₂ production, under saline conditions. With a view to maximizing the hydrogen production using marine biomass, it is important to accumulate knowledge on the effects of salts on the hydrogen production kinetics. Here, we show the kinetics in batch hydrogen production of V. tritonius strain AM2 to investigate the response to various NaCl concentrations. The modified Han-Levenspiel model reveals that salt inhibition in hydrogen production using V. tritonius starts precisely at the point where 10.2 g/L of NaCl is added, and is critically inhibited at 46 g/L. NaCl concentration greatly affects the substrate consumption which in turn affects both growth and hydrogen production. The NaCl-dependent behavior of fermentative hydrogen production of V. tritonius compared to that of Escherichia coli JCM 1649 reveals the marine-adapted fermentative hydrogen production system in V. tritonius. V. tritonius AM2 is capable of producing hydrogen from seaweed carbohydrate under a wide range of NaCl concentrations (5 to 46 g/L). The optimal salt concentration producing the highest levels of hydrogen, optimal substrate consumption and highest molar hydrogen yield is at 10 g/L NaCl (1.0% (w/v)).

Evaluation of system performance and microbial communities of a bioaugmented anaerobic membrane bioreactor treating pharmaceutical wastewater

In this study, a control anaerobic membrane bioreactor (C-AnMBR) and a bioaugmented anaerobic membrane bioreactor (B-AnMBR) were operated for 210 d to treat pharmaceutical wastewater. Both the bioreactors were fed with the pharmaceutical wastewater containing TCOD of 16,249 ± 714 mg/L and total dissolved solids (TDS) of 29,450 ± 2209 mg/L with an organic loading rate (OLR) of 13.0 ± 0.6 kgCOD/m(3)d. Under steady-state condition, an average total chemical oxygen demand (TCOD) removal efficiency of 46.1 ± 2.9% and 60.3 ± 2.8% was achieved by the C-AnMBR and the B-AnMBR, respectively. The conventional anaerobes in the C-AnMBR cannot tolerate the hypersaline conditions well, resulting in lower TCOD removal efficiency, biogas production and methane yield than the B-AnMBR seeded from the coastal shore. Pyrosequencing analysis indicated that marine bacterial species (Oliephilus sp.) and halophilic bacterial species (Thermohalobacter sp.) were only present in the B-AnMBR; these species could possibly degrade complex and recalcitrant organic matter and withstand hypersaline environments. Two different dominant archaeal communities, genus Methanosaeta (43.4%) and Methanolobus (61.7%), were identified as the dominant methanogens in the C-AnMBR and the B-AnMBR, respectively. The species of genus Methanolobus was reported resistant to penicillin and required sodium and magnesium for growth, which could enable it to thrive in the hypersaline environment.

Investigation of intertidal wetland sediment as a novel inoculation source for anaerobic saline wastewater treatment

Biological treatment of saline wastewater is considered unfavorable due to salinity inhibition on microbial activity. In this study, intertidal wetland sediment (IWS) collected from a high saline environment was investigated as a novel inoculation source for anaerobic treatment of saline pharmaceutical wastewater. Two parallel lab-scale anaerobic sequencing batch reactors (AnSBR) were set up to compare the organic removal potential of IWS with conventional anaerobic digested sludge (ADS). Under steady-state condition, IWS reactor (R(i)) showed organic reduction performance significantly superior to that of ADS reactor (R(a)), achieving COD removal efficiency of 71.4 ± 3.7 and 32.3 ± 6.1%, respectively. In addition, as revealed by fluorescent in situ hybridization (FISH) analysis, a higher relative abundance of methanogenic populations was detected in R(i). A further 16S rRNA gene pyrosequencing test was conducted to understand both the bacterial and archaeal community populations in the two AnSBRs. A predominance of halophilic/tolerant microorganisms (class Clostridia of bacteria, genera Methanosarcina, and Methanohalophilus of archaea) in R(i) enhanced its organic removal efficiency. Moreover, several microbial groups related with degradation of hardly biodegradable compounds (PAHs, n-alkenes, aliphatic hydrocarbons, and alkanes, etc.) were detected in the IWS. All these findings indicated that IWS is a promising inoculation source for anaerobic treatment of saline wastewater.

Optimization of volatile fatty acids and hydrogen production from Saccharina japonica: acidogenesis and molecular analysis of the resulting microbial communities

Response surface methodology (RSM) was used to optimize the production of volatile fatty acids (VFAs) and hydrogen from mixed anaerobic cultures of Saccharina japonica with respect to two independent variables: methanogenic inhibitor concentration and temperature. The effects of four methanogenic inhibitors on acidogenic processes were tested, and qualitative microbial analyses were carried out. Escherichia, Acinetobacter, and Clostridium were the most predominant genera in samples treated with chloroform (CHCl3), iodoform (CHI3), 2-bromoethanesulfonate (BES), or β-cyclodextrin (β-CD), respectively. RSM showed that the production of VFAs reached a peak of 12.5 g/L at 38.6 °C in the presence of 7.4 g/L β-CD; these were the conditions under which hydrogen production was also nearly maximal. The quantitative polymerase chain reaction (qPCR) showed that shifts in the bacterial community population correlated with the concentrations of β-CD indicating that this compound effectively inhibited methanogens.

Lichen symbiosis: nature's high yielding machines for induced hydrogen production

Hydrogen is a promising future energy source. Although the ability of green algae to produce hydrogen has long been recognized (since 1939) and several biotechnological applications have been attempted, the greatest obstacle, being the O2-sensitivity of the hydrogenase enzyme, has not yet been overcome. In the present contribution, 75 years after the first report on algal hydrogen production, taking advantage of a natural mechanism of oxygen balance, we demonstrate high hydrogen yields by lichens. Lichens have been selected as the ideal organisms in nature for hydrogen production, since they consist of a mycobiont and a photobiont in symbiosis. It has been hypothesized that the mycobiont's and photobiont's consumption of oxygen (increase of COX and AOX proteins of mitochondrial respiratory pathways and PTOX protein of chrolorespiration) establishes the required anoxic conditions for the activation of the phycobiont's hydrogenase in a closed system. Our results clearly supported the above hypothesis, showing that lichens have the ability to activate appropriate bioenergetic pathways depending on the specific incubation conditions. Under light conditions, they successfully use the PSII-dependent and the PSII-independent pathways (decrease of D1 protein and parallel increase of PSaA protein) to transfer electrons to hydrogenase, while under dark conditions, lichens use the PFOR enzyme and the dark fermentative pathway to supply electrons to hydrogenase. These advantages of lichen symbiosis in combination with their ability to survive in extreme environments (while in a dry state) constitute them as unique and valuable hydrogen producing natural factories and pave the way for future biotechnological applications.