Abstract
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).
Highlights
Algae are being used in the development of biophotovoltaic devices (BPVs) for bioelectricity g eneration[1]
Excess energy is dissipated as fluorescence and h eat[14], accompanied by a defense mechanism that triggers production of reactive oxygen species (ROS) to prevent photo-oxidative damage to the Photosystem II (PS II) in a process known as photoinhibition, which prevents cellular death[15]
Cultures were grown for 12 days, with measurements for growth, photosynthetic performance and power output taken on days
Summary
Algae are being used in the development of biophotovoltaic devices (BPVs) for bioelectricity g eneration[1]. Radiant energy absorbed by the algal cell drives the splitting of water to release a pair of electrons, which can be transported to the anode in the BPV device, and to the cathode via an external c ircuit[2]. The maximum power density reported far was generated from a two-chamber device using an algae suspension, mediated electron transfer, and a gold-inscribed Nafion membrane[9]. The carbon negative algal BPV device represents a sustainable, environment-friendly technology amenable to low-power applications Irradiance, characterized by both quality and quantity, is a critical factor influencing photosynthetic performance[13]. The composition of pigments in algae defines the irradiance spectrum best suited for its photosynthetic performance This is especially relevant when artificial light is used for cultivation. Chlorophytes are able to utilize blue light more efficiently than cyanobacteria, due to the loss of chl-b in cyanobacterial s pecies[19]
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