Roger A. Binot

Application of light‐emitting diodes in bioreactors: Flashing light effects and energy economy in algal culture (Chlorella pyrenoidosa)

Light‐emitting diodes (LEDs) were used as the sole light source in continuous culture of the green alga Chlorella pyrenoidosa. The LEDs applied show a peak emission at 659 nm with a half‐power bandwidth of 30 nm. Selection of this wavelength range, which is optimal for excitation of chlorophylls a and b in their “red” absorption bands makes all photons emitted potentially suitable for photosynthesis. No need for additional supply of blue light was found. A standardized panel with 2 LEDs cm−2 fully covered one side of the culture vessel. At standard voltage in continuous operation the light output of the diode panel appeared more than sufficient to reach maximal growth. Flash operation (5‐μs pulse duration) enables potential use of higher operating voltages which may render up to three times more light output. Flat airlift fermentor‐type continuous culture devices were used to estimate steady state growth rates of Chlorella pyrenoidosa as a function of the light flux (μmol photons · m−2 · s−1) and the flashing frequency of the light‐emitting diodes (which determines the duration of the dark “off” time between the 5‐μs “on” pulses). At the fixed voltage and turbidostat setting applied a 20‐kHz frequency, which equals dark periods of 45 μs, still permitted the maximum growth rate to become nearly reached. Lower frequencies fell short of sustaining the maximal growth rate. However, the light flux decrease resulting from lowering of the flash frequency appeared to reduce the observed growth rates less than in the case of a similar flux decrease with light originating from LEDs in continuous operation. Flash application also showed reduction of the quantum requirement for oxygen evolution at defined frequencies. The frequency domain of interest was between 2 and 14 kHz. LEDs may open interesting new perspectives for studies on optimization of mixing in mass algal culture via the possibility of separation of interests in the role of modulation on light energy conversion and saturation of nutrient supply. Use of flashing LEDs in indoor algal culture yielded a major gain in energy economy in comparison to luminescent light sources.

Microbial and higher plant biomass selection for closed ecological systems.

A selection of higher plants and microbial strains is presented with its rationale in order to progressively regenerate food from waste in future space and planetary missions.

The proposal for the completely closed system in the Columbus Space Station

Abstract For the European Space Agency, a preliminary investigation has been made on the possibilities of recycling of water in manned space vehicles. One of the purposes was to find a feasible method of water recycling, where 98% of the water is recycled, producing both drinking water and hygiene water of a standard equivalent to the WHO standards for drinking water. Only physical-chemical methods should be used, and the waste should be brought into a storable form. The method must be able to operate under microgravity conditions and must have a low energy requirement. The investigation has shown that no single unit operation alone can produce the required water quality. A system including: Pretreatment with acid and filtration, Acid reverse osmosis, Oxidation with H2O2 and UV light, Neutral reverse osmosis, is recommended for all waste waters other than urine. Urine and reject from acid reverse osmosis are distilled on a centrifugal force vapour compression unit below 60°C. The main chemical and bacteriological problems in the processing are described.

The coming space science programme in animal cell/tissue research.

Between the genotypical potentials and given phenotypical expressions, cell behaviour is hypothesised largely depending on local distributed control mechanisms resulting from delicate mass flux balances involving biochemical (including cytokine, endocrine and paracrine factors) and mechanical signalling pathways. Better knowledge and exogenous control of these mechanisms is a major objective of our ESA programme in biotechnology through the integrated use of natural sciences and engineering sciences. The control of cell potency and differentiation and of cell regulation mechanisms (including apoptosis and migration triggering events) will have a huge impact on regenerative medicine (tissue engineering), and will also improve our understanding of phenomena important in immune diseases, the ageing process, and cancer. A summary is given of current research projects which have in common the understanding of the cell-environment relationship or the development of analytical and processing methods in the discipline of animal cell technology.