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Optimal conditions for maximized H2 yield from a new green algal strain Chlorella sp. KLSc61
(2022-08-01)
Laokua, Natwikar
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Rittiyan, Nutnicha
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Kornrawudaphikasama, Yosita
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Klinsalee, Rachaneekorn
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Tonawut, Yothawut
Hydrogen produced from microalgae is attracting the attention of scientists as a potential new ‘Bio-Circular-Green’ energy source. We screened a selection of naturally occurring algal strains for H<inf>2</inf> yield as a basis for high yield development. The best strain was a new strain of biohydrogen-producing green algae from a fresh water source at King Mongkut's Institute of Technology Ladkrabang, Thailand. Using morphological and 18S rDNA sequencing analyses, this alga was identified and classified as Chlorella sp. KLSc61. When adapted cells in TAP-K medium (with starting pH at 9.0) containing 25 mM ethanol, with 54 μmol photons m−2 s−1 light, and incubated at 35 °C, Chlorella sp. KLSc61 showed a maximum H<inf>2</inf> yield of 9,804 ± 469.5 μmol H<inf>2</inf> mg−1 Chl at day 7. Under these conditions, the cells produced ~ 12.2 times more H<inf>2</inf> gas than without optimization (753.0 μmol H<inf>2</inf> mg−1Chl). Our optimized system also produced H<inf>2</inf> at a rate 11–570 times greater than previously reported microalgae. Thus Chlorella sp. KLSc61 could be a viable strain for biohydrogen production as a clean future energy source.
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Response of green alga Tetraspora sp. CU2551 under potassium deprivation: a new promising strategy for hydrogen production
(2022-04-01)
Pewnual, Totsapon
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Jampapetch, Narirat
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Saladtook, Sathonkorn
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Raksajit, Wuttinun
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Klinsalee, Rachaneekorn
With increasing world energy consumption, renewable energy sources can fulfill the need and many have net zero carbon dioxide emissions. One of these is hydrogen, which is biologically produced molecular hydrogen from organisms. Although many studies have produced hydrogen from green algae and optimized conditions to obtain the highest yield, following our previous works on production optimization from Tetraspora sp. CU2551, we tested deprivation of Fe, Cu, Ca, S, Mg, or K, and surprisingly found that K deprivation showed another promising switch in increased H<inf>2</inf> yield, representing 9.2 ± 0.1 μmol mg−1 DW within 32 h incubation anaerobically. Moreover, longer cell adaptation by aerobic incubation, before production phase, resulted in higher hydrogen yield. Cells adapted in potassium deprivation (TAP-K medium) promoted hydrogen production to a yield of 14.8 ± 0.03 μmol mg−1 DW, or about 3.0 times higher than normal TAP (5.0 ± 0.82 μmol mg−1 DW). The increased yield was caused by (1) lowering PSII activity (direct biophotolysis), resulted in less oxygen being produced, lowering hydrogenase inhibitor levels, and (2) increasing accumulated starch degradation (indirect biophotolysis) (12.2% starch remaining or 7.2 ± 0.9 μg mg−1 DW), increased the flow of electrons to hydrogenase. Our finding makes potassium deprivation conditions as another the promising choice to enhance hydrogen production in biological systems.
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A newly isolated green alga Chlorella sp. KLSc59: potential for biohydrogen production
(2020-10-01)
Sirawattanamongkol, Thanaporn
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Maswanna, Thanaporn
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Maneeruttanarungroj, Cherdsak
Hydrogen production from microalgae has attracted considerable attention due to its high energy content and as a renewable and environmentally friendly energy source. Various strains of microalgae have been reported to produce “biohydrogen”, but screening for new strains is still necessary to discover strains with higher hydrogen yields. A newly isolated hydrogen-producing green alga was screened and labeled Chlorella sp. KLSc59. The effect of extracellular pH, light intensity, external carbon sources, reducing agents, and nutrient deprivation on biohydrogen production of Chlorella sp. KLSc59 were investigated. Hydrogen yield was higher under anaerobic conditions. Under external pH 7.2 with 53.2 μmol photons m−2 s−1 light intensity and using acetate as a carbon source, the optimum hydrogen yield was 281 μmol H<inf>2</inf> mg−1 Chl. Nutrient deprivation reduced the hydrogen yield. Several reducing agents were assessed, and 1 mM ethanol enhanced yield by 3 times for 850 μmol H<inf>2</inf> mg−1 Chl, and 1 mM sodium dithionite increased yield by 2.7 times for 750 μmol H<inf>2</inf> mg−1 Chl. Significantly, our new strain showed higher hydrogen yields ranging from 1.5 to 68 times compared with other microalgae. Thus, Chlorella sp. KLSc59 showed valuable potential for biohydrogen production.
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Improved biohydrogen production by immobilized cells of the green alga Tetraspora sp. CU2551 incubated under aerobic condition
(2020-10-01)
Maswanna, Thanaporn
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Lindblad, Peter
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Maneeruttanarungroj, Cherdsak
The green alga Tetraspora sp. CU2551 was previously investigated and showed enhanced H<inf>2</inf> production under anaerobic (Ar purged) conditions by cells immobilized in a calcium alginate matrix (Maswanna et al., Biomass Bioenergy 111:88–95, 2018). Here, we report successful H<inf>2</inf> production in entrapped cells under aerobic conditions. The most favorable immobilization condition observed was 4% (w/v) final alginate concentration after gelation, 2.80- to 3.35-mm beads, and a biomass content of 0.125 mg DW mL−1 alginate. H<inf>2</inf> production increased when the immobilized cells were incubated in S-deprived media which could be repeated up to six times when using refreshed media. After six cycles, the H<inf>2</inf> production reached 12.8 ± 0.9 mL H<inf>2</inf> 25 mL−1 of medium, corresponding to a rate of 182 ± 20 nmol mg−1 DW h−1, which was significantly higher than previously observed for other microalgae. Thus, our results demonstrate a potential for photobiological H<inf>2</inf> production using immobilized Tetraspora sp. CU2551 cells, grown under ambient aerobic conditions.

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