The effect of discontinuous airlift mixing in outdoor flat panel photobioreactors on growth of Scenedesmus obliquus

Design and characterization of a new pressurized flat panel photobioreactor for microalgae cultivation and CO2 bio-fixation

Microalgae-based biorefinery processes are gaining particular importance as a biotechnological tool for direct carbon dioxide fixation and production of high-quality biomass and energy feedstock for different industrial markets. However, despite the many technological advances in photobioreactor designs and operations, microalgae cultivation is still limited due to the low yields achieved in open systems and to the high investment and operation costs of closed photobioreactors. In this work, a new alveolar flat panel photobioreactor was designed and characterized with the aim of achieving high microalgae productivities and CO₂ bio-fixation rates. Moreover, the energy efficiency of the employed pump-assisted hydraulic circuit was evaluated. The 1.3 cm thick alveolar flat-panels enhance the light utilization, whereas the hydraulic design of the photobioreactor aims to improve the global CO₂ gas-liquid mass transfer coefficient (k_LaCO₂). The mixing time, liquid flow velocity, and k_LaCO₂ as well as the uniformity matrix of the artificial lighting source were experimentally calculated. The performance of the system was tested by cultivating the green microalga Acutodesmus obliquus. A volumetric biomass concentration equal to 1.9 g L^-1 was achieved after 7 days under controlled indoor cultivation conditions with a CO₂ bio-fixation efficiency of 64% of total injected CO₂. The (gross) energy consumption related to substrate handling was estimated to be between 27 and 46 Wh m^-3, without any cost associated to CO₂ injection and O₂ degassing. The data suggest that this pilot-scale cultivation system may constitute a relevant technology in the development of microalgae-based industrial scenario for CO₂ mitigation and biomass production.

Aeration and mass transfer optimization in a rectangular airlift loop photobioreactor for the production of microalgae

Effects of superficial gas velocity and top clearance on gas holdup, liquid circulation velocity, mixing time, and mass transfer coefficient are investigated in a new airlift loop photobioreactor (PBR), and empirical models for its rational control and scale-up are proposed. In addition, the impact of top clearance on hydrodynamics, especially on the gas holdup in the internal airlift loop reactor, is clarified; a novel volume expansion technique is developed to determine the low gas holdup in the PBR. Moreover, a model strain of Chlorella vulgaris is cultivated in the PBR and the volumetric power is analyzed with a classic model, and then the aeration is optimized. It shows that the designed PBR, a cost-effective reactor, is promising for the mass cultivation of microalgae.

Biological components and bioelectronic interfaces of water splitting photoelectrodes for solar hydrogen production

Artificial photosynthesis (AP) is inspired by photosynthesis in nature. In AP, solar hydrogen can be produced by water splitting in photoelectrochemical cells (PEC). The necessary photoelectrodes are inorganic semiconductors. Light-harvesting proteins and biocatalysts can be coupled with these photoelectrodes and thus form bioelectronic interfaces. We expand this concept toward PEC devices with vital bio-organic components and interfaces, and their integration into the built environment.