Microalgal biomass production: challenges and realities.

The maximum quantum yield (Φ (max)), calculated from the maximum chlorophyll a specific photosynthetic rate divided by the quantum absorption per unit chlorophyll a, is 8 photons or 0.125 mol C per mol Quanta light energy. For the average solar radiation that reaches the earth's surface this relates to a photosynthetic yield of 1.79 g(dw) m(-2) day(-1) per percentage photosynthetic efficiency and it could be doubled for sunny, dry and hot areas. Many factors determine volumetric yields of mass algal cultures and it is not simply a question of extrapolating controlled laboratory rates to large scale outdoor production systems. This is an obvious mistake many algal biotechnology start-up companies make. Closed photobioreactors should be able to outperform open raceway pond cultures because of the synergistic enhancement of a reduced boundary layer and short light/dark fluctuations at high turbulences. However, this has not been shown on any large scale and to date the industrial norm for very large production systems is open raceway production ponds. Microalgal biomass production offers real opportunities for addressing issues such as CO(2) sequestration, biofuel production and wastewater treatment, and it should be the preferred research emphasis.

Ameliorative role of nitric oxide on H2O2 toxicity to a chlorophycean alga Scenedesmus obliquus.

A concentration-dependent toxicity of hydrogen peroxide (H(2)O(2)) was observed on growth yield, chlorophyll a content and chlorophyll fluorescence characteristics of the green microalga Scenedesmus obliquus under laboratory batch culture conditions. The addition of sodium nitroprusside, a nitric oxide (NO) donor, in combination with H(2)O(2) prevented chlorophyll losses, and the inhibition level of growth yield, maximum quantum yield of photosystem II (PSII) and the light-adapted quantum yield of PSII were significantly reduced. The antioxidant compounds, penicillamine and thiourea also reduced the damage caused by H(2)O(2) exposure. The protective actions of sodium nitroprusside were, however, arrested in cultures where sodium nitroprusside was supplemented in combination with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), a specific scavenger of NO. The NO(3)(-)-grown Scenedesmus depicted less sensitivity to H(2)O(2) toxicity with respect to the quantum yields of PSII as compared to its NH(4)(1)-grown counterpart. The role of NO in providing protection against H(2)O(2) toxicity to the processes under study was discussed.