Outdoor phycocyanin production in a standalone thermally-insulated photobioreactor.

The operation of solar microalgal photobioreactors requires sufficient cooling and heating to maintain reliable high productivity year-round. These operations are energy-intensive and expensive. Growth characteristics and phycocyanin production of Arthrospira platensis were investigated during the austral winter using a thermally-insulated photobioreactor with photovoltaic panel integration for electricity generation. This was compared with a control photobioreactor under a cycle of heating (13-hour night) and thermostat-regulated cooling, and continuously heated raceway pond. Average temperature in the photovoltaic photobioreactor (21.0 ± 0.03 °C) was similar to that in the heated control. Biomass productivity of Arthrospira in the novel photobioreactor was 67% higher than in the raceway pond but significantly lower than the control. Phycocyanin productivity (16.3 ± 1.43 mgg-1d-1 and purity (1.2 ± 0.03) showed no variation between photobioreactors but was significantly lower in the raceway pond. Electrical energy output of the photovoltaic photobioreactor exceeded mixing energy needs by 75%. These results indicate that the novel photobioreactor offers a reliable, energy-efficient platform for large-scale production of high-value chemicals from microalgae.

Red and blue luminescent solar concentrators for increasing Arthrospira platensis biomass and phycocyanin productivity in outdoor raceway ponds.

Achieving high biomass productivity is critical for establishing a successful large-scale algal facility. Microalgae cultures in raceway ponds are normally light limited. To achieve high biomass productivity, there is a need to develop a system to deliver light into the depth of microalgal cultures in raceway ponds. We investigated red and blue luminescent solar concentrators (LSCs) in outdoor raceway ponds to downgrade the sunlight, re-emit and, deliver it into the depth of Arthrospira platensis culture operated at 21 cm depth. When red LSCs were used, the biomass productivity (12.2 g m-2 d-1) and phycocyanin productivity (8.5 mg L-1 d-1) of A. platensis increased 26% and 44%, respectively. However, using blue LSCs resulted in no significant increase in A. platensis biomass productivity. Therefore, for generating same phycocyanin productivity using red LSCs, 44% less cultivation area would be required. This can lead to a significant reduction in the cost of phycocyanin production.

Sustainable cultivation of microalgae by an insulated glazed glass plate photobioreactor.

Microalgae growth in closed photobioreactors is greatly inhibited by elevated temperatures caused mainly by the infra-red portion of light. Current passive evaporative cooling systems for temperature control in outdoor photobioreactors are neither economical nor sustainable. Here we built a novel flat plate photobioreactor with its illumination surface customized with insulated glazing units (IGP). The IGP design enabled transmission of more than 50% of visible light while blocking 90% of ultraviolet and infrared radiations. The growth and productivity of Nannochloropsis sp. (MUR 267) in the IGP was compared against conventional flat plate photobioreactors subjected to the full spectrum (HLP) and also externally modified spectrum (CLP) of halogen lights. High temperature (up to 42°C) resulted in no growth in the HLP. Biomass productivities of Nannochloropsis sp. grown in the CLP was significantly higher than the IGP due to higher light transmission and lower temperature profiles recorded in the CLP. Lipid content of Nannochloropsis was highest in the CLP (60.23%) while protein was highest in the IGP (42.43%). All photosynthesis parameters were negatively affected in the HLP. The IGP's ability to remove infrared (heat) makes this newly developed photobioreactor a promising and sustainable cultivation system for mass algal production especially for high value products.

Efficient conversion of solar energy to biomass and electricity.

The Earth receives around 1000 W.m(-2) of power from the Sun and only a fraction of this light energy is able to be converted to biomass (chemical energy) via the process of photosynthesis. Out of all photosynthetic organisms, microalgae, due to their fast growth rates and their ability to grow on non-arable land using saline water, have been identified as potential source of raw material for chemical energy production. Electrical energy can also be produced from this same solar resource via the use of photovoltaic modules. In this work we propose a novel method of combining both of these energy production processes to make full utilisation of the solar spectrum and increase the productivity of light-limited microalgae systems. These two methods of energy production would appear to compete for use of the same energy resource (sunlight) to produce either chemical or electrical energy. However, some groups of microalgae (i.e. Chlorophyta) only require the blue and red portions of the spectrum whereas photovoltaic devices can absorb strongly over the full range of visible light. This suggests that a combination of the two energy production systems would allow for a full utilization of the solar spectrum allowing both the production of chemical and electrical energy from the one facility making efficient use of available land and solar energy. In this work we propose to introduce a filter above the algae culture to modify the spectrum of light received by the algae and redirect parts of the spectrum to generate electricity. The electrical energy generated by this approach can then be directed to running ancillary systems or producing extra illumination for the growth of microalgae. We have modelled an approach whereby the productivity of light-limited microalgae systems can be improved by at least 4% through using an LED array to increase the total amount of illumination on the microalgae culture.