# Optical Camera Communication as an Enabling Technology for Microalgae Cultivation +
## 1 Introduction  
Microalgae culture has gained significant momentum during the last decade, triggered by the necessity of developing new and sustainable resources. They have become a promising alternative source for biofuels and biogas production, human and animal nutrition, cosmetics and bioactive supply for nutraceuticaltical and pharmaceutical applications. Microalgae biomass production is currently carried out using both open ponds (e.g., raceways) and closed photobioreactors [1]. The last ones are preferable at the laboratory and pilot-plant scales since, with the appropriate design, they can optimise growth conditions (nutrient levels, carbon concentration, temperature, acidity, among others). Among these parameters, light radiant energy is a capital factor that affects the photosynthetic efficiency, and therefore the overall productivity [2]. Generally, microalgae production plants are designed to take advantage of the Sun as the primary light source due to cost optimisation. However, the Sun's irradiance dependson several factors, such as weather conditions, latitude and day time. Furthermore, these open-air plants need vast extensions to be profitable since effective biomass production depends on the directly-exposed surface. Nonetheless, artificial lighting can provide advantages in photosynthetic efficiency (custom spectrum and intensity profiles) and the tight control they offer concerning microalgal biochemistry and growth, increasing industrial processes' reliability. Using this type of lighting, biomass production depends no longer on the plant's exposed surface, but on its equivalent volume. Although optimising light quality could considerably reduce energy consumption, another approach concerns how light is delivered to the culture: flashing (pulsed) light instead of continuous illumination. In this context, pulsed illumination could serve as a communication link, enabling the re-utilisation of light sources as effective visible light communication (VLC) transmitters [3]. The low bandwidth transmission channel they provide (attaining the stated frequency restrictions) could be used for online monitoring of the culture's state conditions via deployable sensors within the photobioreactor module. Nevertheless, there are still a few parameters that are either too complex to be measured in situ or imply invasive methods. These parameters are microalgae biomass concentration and its growth phase. In [4; 5], different approaches based on the digital processing analysis of red-green-blue (RGB) images for low cost, fast and accurate quantification of biomass concentration were proposed and experimentally validated. Therefore, cameras could be used as sensing devices for these parameters. On the other hand, the use of cameras as communication receivers for VLC links is a research topic that is receiving significant attention. Furthermore, there is a current standard specification by the working group IEEE 802.15.7 [6], which has finally integrated this new strategy known as optical camera communication (OCC) [7; 8; 9; 10]. These devices are bandwidth-limited compared to traditional photodetectors, such as p-type, intrinsic, n-type (PIN) and avalanche photodiodes (PDs). However, due to the use of image-forming optics [11], cameras can receive light from multiple sources, providing inherent spatial multiplexing capabilities [12; 13; 14], which can be easily exploited for simultaneous monitoring within a microalgae production plant. This work proposes the use of low-cost cameras for both remotely sensing microalgae culture parameters and for establishing a direct communication link with flat-panel photobioreactors. Compared to other radio or wired technologies, the use of OCC has the following advantages. First of all, this technology reuses the light that comes from the photobioreactors and makes better use of this excess of energy that would otherwise be wasted.