An internally LED illuminated photobioreactor to increase energy conversion efficiency: Design and operation

• An internally illuminated reactor is designed; • The reactor is operated at steady state conditions with A. obliquus ; • Spectral matching allows to operate in low light, reaching high energy conversion; • Operative conditions, plant location and lamps efficiency affect illumination cost; In this work, a novel internally LED illuminated prototype photobioreactor (IIPBR) was designed, rationalizing the light supply with a hexagonal geometry and matching the light spectrum to the most photosynthetically active wavelengths. The IIPBR was designed and operated to produce the biomass in a continuous mode. In this system, Acutodesmus obliquus was cultivated under different light intensities (100–400 µmol m −2 s −1 ) and residence times (1–1.9 d). At steady state, a maximum productivity of 40.09 ± 1.99 g m −2 d -1 and a photosynthetic efficiency around 22 % were obtained. The data collected were used to carry out a first evaluation of the costs related to illumination, finding that the correct setting of the operative conditions has a great impact on costs, which span from a minimum of 1.82 up to to 20.63 € kg −1 (with electricity supply rated at autumn–winter 2021). The photoconversion efficiency of the lamps and the plant location play an important role and should be taken into account to increase the economic feasibility of the system proposed, thus enlarging the possible fields final applications of the biomass obtained.