Charles U. Ugwu

Influence of irradiance, dissolved oxygen concentration, and temperature on the growth of Chlorella sorokiniana

The growth response of Chlorella sorokiniana to certain irradiance, DO, and temperature demonstrated the possible causes of low productivity with this strain in outdoor cultures. The growth (biomass productivity) and chlorophyll fluorescence (Fv/Fm) were substantially reduced when the dissolved oxygen (above 200 % of air saturation) and temperature were elevated.

Light/dark cyclic movement of algal culture (Synechocystis aquatilis) in outdoor inclined tubular photobioreactor equipped with static mixers for efficient production of biomass

AbstractSynechocystis aquatilis SI-2 was grown outdoors in a 12.5cm diam. tubular photobioreactor equipped with static mixers. The static mixers ensured that cells were efficiently circulated between the upper (illuminated) and lower (dark) sections of the tubes. The biomass productivity varied from 22 to 45g m−2d−1, with an average of 35g m−2d−1, etc which corresponded to average CO2 fixation rate of about 57 g CO2 m−2 d−1. The static mixers not only helped in improving the biomass productivities but also have a high potential to lower the photoinhibitory effect of light during the outdoor cultures of algae.

Design of static mixers for inclined tubular photobioreactors

Static mixers, which improve gas-liquid mass transfer inside tubular photobioreactors and move the cells between the upper and lower parts of the tubes were designed. Each static mixer was equipped with an opening (v-cut slit) at the top (for gas dispersion) and an orifice at the lower part (for liquid circulation). When the static mixers were installed in the riser tube of an inclined tubular photobioreactor, vertical movement of the liquid was induced so that cells were moved between the surface and bottom part of the photobioreactor. The mass transfer rates in the tubular photobioreactor without static mixers decreased sharply when they were scaled up by increasing the tube diameters. However, by installation of static mixers, the mass transfer rates in 12.5-cm diameter tubes were almost as high as those of 3.8-cm tubes without static mixers. The effectiveness of the static mixers in improving the mass transfer characteristics of the tubular photobioreactors was higher in large than small diameter tubes. The ratio of the diameters of the static mixers to the diameter of the tube, the areas of the v-cut slits and the orifice were the important design parameters that affected the mass transfer characteristics. The gas hold up and and kLa were higher when the areas of the slits (v-cut) and the orifice were reduced.

Production of (R)-3-hydroxybutyric acid by fermentation and bioconversion processes with Azohydromonas lata

Feasibility of producing (R)-3-hydroxybutyric acid ((R)-3-HB) using wild type Azohydromonas lata and its mutants (derived by UV mutation) was investigated. A. lata mutant (M5) produced 780 m g/l in the culture broth when sucrose was used as the carbon source. M5 was further studied in terms of its specificity with various bioconversion substrates for production of (R)-3-HB. (R)-3-HB concentration produced in the culture broth by M5 mutant was 2.7-fold higher than that of the wild type strain when sucrose (3% w/v) and (R,S)-1,3-butanediol (3% v/v) were used as carbon source and bioconversion substrate, respectively. Bioconversion of resting cells (M5) with glucose (1% v/w), ethylacetoacetate (2% v/v), and (R,S)-1,3-butanediol (3% v/v), resulted in (R)-3-HB concentrations of 6.5 g/l, 7.3g/l and 8.7 g/l, respectively.

UV mutagenesis of Cupriavidus necator for extracellular production of (R)-3-hydroxybutyric acid.

Aim:  Ultraviolet (UV) mutagenesis was carried out to obtain mutant strains of Cupriavidus necator that could produce (R)‐3‐hydroxybutyric acid [(R)‐3‐HB] in the culture supernatant.

Influence of shading inclined tubular photobioreactor surfaces on biomass productivity of C. sorokiniana

Shading of the tubular photobioreactor (PBR) surfaces that diminished solar irradiance to 70 % led to higher biomass productivity and greater accumulation of total chlorophyll and carotenoids compared to the values obtained when the PBR was completely exposed to full sunlight.

An integrated system of solar light, artificial light and organic carbon supply for cyclic photoautotrophic-heterotrophic cultivation of photosynthetic cells under day-night cycles

An integrated system of solar light, artificial light and organic carbon supply was developed for cyclic photoautotrophic-heterotrophic cultivation of photosynthetic cells. The energy source for the culture is automatically switched to solar light energy (when the weather is sunny), to artificial light energy (during the cloudy period of the day) or to organic carbon source (at night). Thus minimum amount of artificial light is used while ensuring continuous light supply to the culture during the photoautotrophic phase. The α-tocopherol productivity by Euglena gracilis in this system was more than 5 times higher than the value obtained in pure photoautotrophic culture under the same experimental conditions.

Fullerene fine particles adhere to pollen grains and affect their autofluorescence and germination

Adhesion of commercially produced fullerene fine particles to Cryptomeria japonica, Chamaecyparis obtusa and Camellia japonica pollen grains was investigated. The autofluorescence of pollen grains was affected by the adhesion of fullerene fine particles to the pollen grains. The degree of adhesion of fullerene fine particles to the pollen grains varied depending on the type of fullerene. Furthermore, germination of Camellia japonica pollen grains was inhibited by the adhesion of fullerene fine particles.