Fluid flow and mass transfer in a counter-current gas–liquid inclined tubes photo-bioreactor

Mass Transfer Features of Wavy-Bottomed Cascade Photobioreactors

It has been suggested that the energy-efficient production of microalgae biomass can be more easily obtained in short light path photobioreactors that can be operated at high biomass concentration. On the downside, however, high biomass concentrations also require an efficient gas exchange rate to avoid metabolic growth limitation or inhibition. A cascade photobioreactor featuring a thin liquid layer flowing down a sloping, wavy-bottomed surface can be operated at a biomass concentration that is much higher compared to most usual open-type equipment. Liquid flow, upon investigation, proved to exhibit peculiar “local recirculation” hydrodynamics, potentially conducive to the mixing of superficial and deep zones of the photobioreactor. Mass transfer coefficient represents a useful parameter to optimize the performance of a microalgal photobioreactor and its scale-up. The aim of the present article is to discuss the experimental mass transfer features of this novel type of photobioreactor and highlight expected opportunities and issues entailed by different ways of installing and operating such novel types of photobioreactors.

Microalgae Technology: A Patent Survey

For a long time now, it is known that an infinite number of compounds can be obtained from microalgae due to their promising composition. This fact is used by several companies to produce at medium-scale different high value products such as carotenoids. Furthermore, this last decade research in this topic has significantly increased given the potential solution these microorganisms present to meet World environmental agreements regarding CO2 emissions. However, the culture of large-scale microalgae in order to obtain products which are required in huge quantities (e.g., oil for manufacturing biodiesel) and at the same time removing pollutants appeared as a difficult task due to the great number of variables that must be taken into account. The photobioreactor design for cultivating the microalgae is perhaps the most important task, but there are other bottle-necks, such as the harvesting system, cleaning system, control system, the chosen microalgae, and the extraction of products from the microalgae. This review focuses on around 200 patents covering microalgae technology, from different photobioreactors designs to microalgae applications, in order to construct a perfect large-scale facility removing CO2 in the process.

Combinatorial life cycle assessment to inform process design of industrial production of algal biodiesel

The use of algae as a feedstock for biodiesel production is a rapidly growing industry, in the United States and globally. A life cycle assessment (LCA) is presented that compares various methods, either proposed or under development, for algal biodiesel to inform the most promising pathways for sustainable full-scale production. For this analysis, the system is divided into five distinct process steps: (1) microalgae cultivation, (2) harvesting and/or dewatering, (3) lipid extraction, (4) conversion (transesterification) into biodiesel, and (5) byproduct management. A number of technology options are considered for each process step and various technology combinations are assessed for their life cycle environmental impacts. The optimal option for each process step is selected yielding a best case scenario, comprised of a flat panel enclosed photobioreactor and direct transesterification of algal cells with supercritical methanol. For a functional unit of 10 GJ biodiesel, the best case production system yields a cumulative energy demand savings of more than 65 GJ, reduces water consumption by 585 m(3) and decreases greenhouse gas emissions by 86% compared to a base case scenario typical of early industrial practices, highlighting the importance of technological innovation in algae processing and providing guidance on promising production pathways.