by nuclear irradiation to improve growth rate under 15% carbon dioxide in flue gas

Spirulina sp. was mutated by γ-rays from ⁶⁰Co nuclear irradiation to improve growth and CO₂ fixation rate under 15vol.% CO₂ (in flue gas from a power plant). Mutants with enhanced growth phenotype were obtained, with the best strain exhibiting 310% increment in biomass yield on day 4. The mutant was then domesticated with elevated CO₂ concentration, and the biomass yield increased by 500% after domestication under 15vol.% CO₂, with stable inheritance. Ultrastructure of Spirulina sp. shows that the fractal dimension of Spirulina cells decreased by 23% after mutation. Pore size in the cell wall of Spirulina mutant increased by 33% after 15vol.% CO₂ domestication. This characteristic facilitated the direct penetration of CO₂ into cells, thus improving CO₂ biofixation rate.

Enhanced hydrogen production of Enterobacter aerogenes mutated by nuclear irradiation

Nuclear irradiation was used for the first time to generate efficient mutants of hydrogen-producing bacteria Enterobacter aerogenes, which were screened with larger colour circles of more fermentative acid by-products. E. aerogenes cells were mutated by nuclear irradiation of ⁶⁰Co γ-rays. The screened E. aerogenes ZJU1 mutant with larger colour circles enhanced the hydrogenase activity from 89.8 of the wild strain to 157.4mLH₂/(gDWh). The hereditary stability of the E. aerogenes ZJU1 mutant was certified after over ten generations of cultivation. The hydrogen yield of 301mLH₂/gglucose with the mutant was higher by 81.8% than that of 166mL/gglucose with the wild strain. The peak hydrogen production rate of 27.2mL/(L·h) with the mutant was higher by 40.9% compared with that of 19.3mL/(L·h) with the wild strain. The mutant produced more acetate and butyrate but less ethanol compared with the wild strain during hydrogen fermentation.

Growth optimisation of microalga mutant at high CO₂ concentration to purify undiluted anaerobic digestion effluent of swine manure

Growth rate of the microalga Chlorella PY-ZU1 mutated by nuclear irradiation was optimised for use in the purification of undiluted anaerobic digestion effluent of swine manure (UADESM) with 3745 mg L(-1) chemical oxygen demand (COD) and 1135 mg L(-1) total nitrogen content. The problem of accessible carbon in UADESM was solved by continuous introduction of 15% (v/v) CO2. Adding phosphorus to UADESM and aeration of UADESM before inoculation both markedly reduced the lag phase of microalgal growth. In addition, the biomass yield and average growth rate of Chlorella PY-ZU1 increased significantly to 4.81 g L(-1) and 601.2 mg L(-1) d(-1), respectively, while the removal efficiencies of total phosphorus, COD and ammonia nitrogen increased to 95%, 79% and 73%, respectively. Thus, the findings indicate that Chlorella PY-ZU1 can be used for effective purification of UADESM, while the biomass can be safely used as animal feed supplement.