Microbial fuel cells operating with autotrophic microorganisms are known as biophotovoltaic devices. It represents a great opportunity for environmentally-friendly power generation using the energy of the sunlight. The efficiency of electricity generation in this novel system is however low. This is partially reflected by the poor understanding of the bioelectrochemical mechanisms behind the electron transfer from these microorganisms to the electrode surface. In this work, we propose a combination of electrochemical and fluorescence techniques, giving emphasis to the pulse amplitude modulation fluorescence. The combination of these two techniques allow us to obtain information that can assist in understanding the electrical response obtained from the generation of electricity through the intrinsic properties related to the photosynthetic efficiency that can be obtained from the fluorescence emitted. These were achieved quantitatively by means of observed changes in four photosynthetic parameters with the bioanode generating electricity. These are the maximum quantum yield (Fv/Fm), alpha (α), light saturation coefficient (Ek) and maximum rate of electron transfer (rETRm). The relationship between the increases in the current density collected by the bioanode to the decrease of the rETRm values in the photosynthetic pathway for the two microorganisms was also discussed.
In photosynthesis, a very small amount of the solar energy absorbed is transformed into chemical energy, while the rest is wasted as heat and fluorescence. This excess energy can be harvested through biophotovoltaic platforms to generate electrical energy. In this study, algal biofilms formed on ITO anodes were investigated for use in the algal biophotovoltaic platforms. Sixteen algal strains, comprising local isolates and two diatoms obtained from the Culture Collection of Marine Phytoplankton (CCMP), USA, were screened and eight were selected based on the growth rate, biochemical composition and photosynthesis performance using suspension cultures. Differences in biofilm formation between the eight algal strains as well as their rapid light curve (RLC) generated using a pulse amplitude modulation (PAM) fluorometer, were examined. The RLC provides detailed information on the saturation characteristics of electron transport and overall photosynthetic performance of the algae. Four algal strains, belonging to the Cyanophyta (Cyanobacteria) Synechococcus elongatus (UMACC 105), Spirulina platensis. (UMACC 159) and the Chlorophyta Chlorella vulgaris (UMACC 051), and Chlorella sp. (UMACC 313) were finally selected for investigation using biophotovoltaic platforms. Based on power output per Chl-a content, the algae can be ranked as follows: Synechococcus elongatus (UMACC 105) (6.38×10(-5) Wm(-2)/µgChl-a)>Chlorella vulgaris UMACC 051 (2.24×10(-5) Wm(-2)/µgChl-a)>Chlorella sp.(UMACC 313) (1.43×10(-5) Wm(-2)/µgChl-a)>Spirulina platensis (UMACC 159) (4.90×10(-6) Wm(-2)/µgChl-a). Our study showed that local algal strains have potential for use in biophotovoltaic platforms due to their high photosynthetic performance, ability to produce biofilm and generation of electrical power.
We report for the first time a photosynthetically active algae immobilized in alginate gel within a fuel cell design for generation of bioelectricity. The algal-alginate biofilm was utilized within a biophotovoltaics (BPV) device developed for direct bioelectricity generation from photosynthesis. A peak power output of 0.289 mWm-2 with an increase of 18% in power output compared to conventional suspension culture BPV device was observed. The increase in maximum power density was correlated to the maximum relative electron transport rate (rETRm). The semi-dry type of photosynthetically active biofilm proposed in this work may offer significantly improved performances in terms of fuel cell design, bioelectricity generation, oxygen production and CO2 reduction.
The search for renewable energy sources has become challenging in the current era, as conventional fuel sources are of finite origins. Recent research interest has focused on various biophotovoltaic (BPV) platforms utilizing algae, which are then used to harvest solar energy and generate electrical power. The majority of BPV platforms incorporate indium tin oxide (ITO) anodes for the purpose of charge transfer due to its inherent optical and electrical properties. However, other materials such as reduced graphene oxide (RGO) could provide higher efficiency due to their intrinsic electrical properties and biological compatibility. In this work, the performance of algae biofilms grown on RGO and ITO anodes were measured and discussed. Results indicate improved peak power of 0.1481 mWm(-2) using the RGO electrode and an increase in efficiency of 119%, illustrating the potential of RGO as an anode material for applications in biofilm derived devices and systems.
The biophotovoltaic cell (BPV) is deemed to be a potent green energy device as it demonstrates the generation of renewable energy from microalgae; however, inadequate electron generation from microalgae is a significant impediment for functional employment of these cells. The photosynthetic process is not only affected by the temperature, CO2 concentration and light intensity but also the spectrum of light. Thus, a detailed understanding of the influences of light spectrum is essential. Accordingly, we developed spectrally optimized light using programmable LED arrays (PLA)s to study the effect on algae growth and bioelectricity generation. Chlorella is a green microalga and contains chlorophyll-a (chl-a), which is the major light harvesting pigment that absorbs light in the blue and red spectrum. In this study, Chlorella is grown under a PLA which can optimally simulate the absorption spectrum of the pigments in Chlorella. This experiment investigated the growth, photosynthetic performance and bioelectricity generation of Chlorella when exposed to an optimally-tuned light spectrum. The algal BPV performed better under PLA with a peak power output of 0.581 mW m-2 for immobilized BPV device on day 8, which is an increase of 188% compared to operation under a conventional white LED light source. The photosynthetic performance, as measured using pulse amplitude modulation (PAM) fluorometry, showed that the optimized spectrum from the PLA gave an increase of 72% in the rETRmax value (190.5 μmol electrons m-2 s-1), compared with the conventional white light source. Highest algal biomass (1100 mg L-1) was achieved in the immobilized system on day eight, which translates to a carbon fixation of 550 mg carbon L-1. When artificial light is used for the BPV system, it should be optimized with the light spectrum and intensity best suited to the absorption capability of the pigments in the cells. Optimum artificial light source with algal BPV device can be integrated into a power management system for low power application (eg. environment sensor for indoor agriculture system).