Photobioreactor Design for Improved Energy Efficiency of Microalgae Production

Abstract

Photobioreactor Design for Improved Energy Efficiency of Microalgae Production Alexander BurnsThe objective of this research was to investigate a new photobioreactor (PBR) design for microalgae production that retains the typical advantages of existing tubular PBRs while reducing power consumption by providing simultaneous culture circulation and gas exchange with airlift alone and no centrifugal recirculating pump. Traditional tubular PBR designs feature a compressed air supply and a centrifugal pump for culture circulation and gas exchange. Circulation and gas exchange in a closed-system PBR is necessary to keep the algae suspended and to provide sufficient mass transfer (mainly for the exchange of oxygen and carbon dioxide). In a traditional tubular PBR sparged air keeps the culture well mixed and strips out excess dissolved oxygen in an airlift-column unit, while the centrifugal pump circulates the culture in the tubular stage and decreases the amount of air bubbles traveling into this stage; where most of the photosynthesis occurs. The PBR design proposed herein does away with the usual centrifugal pump. The air blower performs both gas exchange in the airlift columns and system-wide circulation.This builds on a previous tubular PBR design that provides circulation and gas exchange by airlift alone, which was patented by Cathcart in 2011. However, the Cathcart patent does not provide data on mixing, gas exchange, energy consumption, flow regime or biomass productivity. The new design described here builds on the Cathcart design, but includes several unique design features, such as larger diffuser columns which provide airlift-induced flow for a series of vertical PBR tubes. To perform a power consumption v analysis, a pilot-scale prototype of the new PBR design was built and operated. The prototype PBR consisted of two airlift columns attached to 9 m of vertical serpentine tubing connected to the top and bottom by standard 90-degree PVC elbows in a U-bend fashion to each column to make a total working volume of 235 L. The airlift columns were about 1.5 m tall and 30.5 cm ID, while the serpentine tubes were about 0.9 m tall and 7.6 cm ID to make a total of five vertical tubes for every airlift column. Data collected for this prototype design suggest an average overall areal productivity (

Microalgae Culturing To Produce Biobased Diesel Fuels: An Overview of the Basics, Challenges, and a Look toward a True Biorefinery Future

“…A key design parameter for photobioreactors is the illuminated surface area versus total reactor volume or S/ V ratio. 129 The higher the S/V ratio, the higher the biomass yields due to optimized photoefficiency toward algal cell exposures; however, there become limitations to S/V ratios when constructing photobioreactors at a large scale (commercial applications). Some photobioreactors are placed outdoors so that the sun can provide the light needed for the phototrophs while other photobioreactor systems are placed indoors where artificial light sources are used.…”

“…Often times, these systems are designed as long pillows or tubes. 129 The positive aspects of photobioreactors are a high level of system controlling and access to maximize production, an appreciably smaller land process footprint, the opportunity to produce other products within the reactor (such as Omega III fatty acids), and a much easier system for controlling culture integrity (preventing invasive, nonbeneficial microbial cells from being established within the reactor). The key negative aspect is higher cost for the lipids due to the much higher need for manufactured components, increased operational complexity, and difficulty with producing a large-scale system given the small reactor diameters/widths required.…”

“…The use of engineered photobioreactors to concentrate the culturing of microalgae into a less land intensive operation has been the topic of a tremendous amount of work over the past 20 years. , These specially constructed, closed reactors have been proposed using a wide variety of configurations that all provide optimized reactor conditions for the support of much heavier biomass concentrations than are obtainable using open ponds. Reactors of this type are used to culture either photoautotrophs (needs light) or heterotrophic microalgae (does not need light).…”

Decision-support for Digester-Algae IntegRation for Improved Environmental and Economic Sustainability (DAIRIEES)

“…PBRs are closed vessels and, since the environment is artificial, all the operational variables are specifically controlled to promote the growth of phototropic algae. Many different types of PBR systems have been proposed, such as tubular (serpentine, manifold, helical, fence arrangement with manifolds) flat plate (flat alveolar panels, glass) airlift column, vertical sleeve, fermenter-type, and attached growth (Burns 2014).…”

Agitación y transferencia de masa de CO² en fotobiorreactores tipo airlift

“…Debido a la baja solubilidad del CO2 en H2O, esta etapa es considerada como la de mayor resistencia a la transferencia de masa de CO2 para el aprovechamiento por parte de la microalga, por lo que es necesario determinar la transferencia de masa entre las fases gaseosa y líquida a partir del kLa. Este coeficiente indica la concentración de dió xido de carbono disponible para el cultivo, factor que es fundamental en el proceso de producción de microalgas (Burns, 1993).…”