I started yet another interesting day at office by opening the archives of newsletters and went through all the organized data stored in its annals. I came across some very useful data dealing with various aspects of aeration in a photobioreactor and felt it would be very insensitive of me not to share it with all the wonderful readers of the Oilgae blog. So here is a series of posts dealing with the above-mentioned topic:<\/p>\n
Introduction
\nAeration of cultures serves to keep algae in suspension, to supply the carbon needed for plant growth and pH control, and to strip O2 from the culture media, preventing supersaturation. The aerator system comprises any suitable equipment for:
\n(a) Introducing a carbon dioxide supply into the bioreactor
\n\u2022 Carbon dioxide can be blended with compressed air at a certain percentage (preferably from 0.1% up to 20% of CO2) to provide carbon source for algal photosynthesis.
\n\u2022 In some cases, organic carbon (for example, in the form of acetic acid and\/or glucose) can be added as needed into the culture medium to support algal growth.
\n\u2022 Any suitable source of carbon dioxide can be used, including but not limited to industrial grade, food grade, CO2-rich flue gases emitted from power generators burning coal<\/p>\n
(b) Efficient culture mixing
\n\u2022 To ensure that all algal cells come in contact with the nutrients, CO2 and light for optimum growth.
\n\u2022 To ensure that produced oxygen is removed from the culture systems.
\n\u2022 To maintain effective turbulent flow within the photobioreactor<\/p>\n
Optimum Aeration Condition in a Photobioreactor
\nSeveral studies have characterized the optimized aeration by carbon dioxide gas for microalgal production in a photobioreactor. Air enriched with 5% or 10% (v\/v) CO2 at rates of 0.025-1 vvm (volume of air\/ medium\/time) is found to be cost-effective for mass culture (Zhang et al, 2002). In flat panel photobioreactors, an optimum aeration rate of 0.05 v\/v\/min has been proposed sufficient to improve the mixing and mass transfer (Sierra et al, 2008).<\/p>\n
Types of Aerator Equipments Used in a Photobioreactor
\nThere are different types of equipments that serve aeration purposes. Most common among them include spargers or diffusers. The following details provide the features of a few types of the aerator designs employed in a photobioreactor.
\nSparger is constructed with materials like biopolymers, or perforated metal or sintered glass with varying pore size based on the design and operation requirement. The sparger is connected to the base of the photobioreactor. The bioreactor is aerated by rising CO2enriched air bubbles into the bottom of the photobioreactor via sparger assembly. The bubbles move up the entire photobioreactor column thereby getting dissolved in the culture medium.
\nBubble formation process at the sparger can be separated into 2 stages:
\nIn the first stage, the bubble expands, while staying attached to the nozzle
\nIn the second stage, the buoyancy forces cause the bubble to move away from the nozzle. Bubble growth continues through a narrowing neck connecting the bubble to the nozzle. When this neck closes and the bubble detaches from the nozzle, fluid rushes in to the region of the bubble neck<\/p>\n
There are different types of aerators equipped in a photobioreactor. Some important types are:
\n\uf0d8 Porous Tube Diffuser
\n\uf0d8 Silicone Rubber Diffuser
\n\uf0d8 Sandstone and Stainless Steel Disk for Air Diffusion
\n\uf0d8 Sintered Air Diffuser
\n\uf0d8 Membrane Sparger
\n\uf0d8 Mott Sparger
\n\uf0d8 Ring or Orifice Sparger<\/p>\n
We\u2019ll see in some detail, the characteristics of these aerators in the next blog.<\/p>\n
Some interesting links<\/em><\/p>\n