Screening and optimization of high-efficiency H₂-producing Chlorella strains

Hydrogen (H₂) is a promising clean energy carrier that can be produced from green algae. By screening H₂-producing Chlorella species, Chlorella sp. ChiW1, isolated from a rice paddy field in Chai Nat province, Thailand, exhibited the highest H₂ production rate and yield. The mid-logarithmic phase cells of Chlorella sp. ChiW1 demonstrated the highest H₂ production. Nitrogen deprivation doubled the H₂ production compared to normal conditions, due to increased hydrogenase activity resulting from reduced O₂ evolution. Furthermore, a high concentration of acetic acid in Tris-acetate phosphate medium, combined with increased light intensity, significantly enhanced H₂ production. Under optimal conditions, nitrogen-deprived Chlorella sp. ChiW achieved a maximum H₂ production rate of 31.28 ± 1.73 μmol H₂ mg chl^-1 h^-1 and a total H₂ production yield of 925.32 ± 19.95 μmol H₂ mg chl^-1 after 96 hours of light anaerobic incubation. Compared to other reported Chlorella strains, Chlorella sp. ChiW exhibited significantly higher H₂ production, underscoring its potential for efficient biohydrogen production.