Photobioreactor for Microalgae Cultivation

The goal of this project is to build a bench scale photo bioreactor for micro algae cultivation. Micro algae is an excellent resource with wide reaching applications, from waste water purification to biodiesel production. We aim to design a system capable of producing micro algae in a cost effective, reliable, and efficient manner.

Background
Photo Bioreactors are devices often used to produce micro algae commercially. Some of the challenges of photo bioreactor design are supplying sufficient light to the micro algae and preventing the micro algae from sticking to the sides of the bioreactor. There are a range of designs currently in use, including open ponds, water filled flexible plastic bags, and long glass tubes. Each of these have issues, either with light penetration, cost, or reliability. A design that solves each of these issues effectively is the goal.

Design Task
Our task is to design a bench scale photo bioreactor for research purposes. It should be designed to maximize efficiency and minimize cost, and thus should be composed of relatively inexpensive materials.

MicroAlgae Requirements
For our project, we needed to be very adaptable with the parameters microalgae need to survive. This is because the PBR needs to grow many different types of algae without major modifications to the physical design. To generalize our PBR’s capabilities, we decided to use a common microalga as a control for all the needed parameters. The Algae we chose to find these parameters is the Chlorella varieties. These species are very common green microalgae found worldwide in all types of water. Most grow best with high ambient light up to 2000 umol/m2s with wavelength of blue and red. They also thrive well in temperatures of 74-80 degrees Fahrenheit, and at a pH between 6.8-7.2. CO2 concentrations should be kept no less than 22 ppm, and greater values are acceptable.



Flow Considerations
Over the development of this project we found that it is hard to find fluid flow models around the sort of system we are working with, involving a bubbling gas flow inducing a liquid flow. We found empirical equations in a book titled "Air-Lift Bioreactors" by M. Y. Chisti. We are currently in the process of creating a math model in TKsolver using these equations to optimize flow velocity and gas holdup. The equations to the right relate these variables to each other.

Design Selection
The problem as it was given to us allowed a lot of room for creativity. There are a variety of possible designs for an air lift reactor, including external loop airlift, flat internal loop, and concentric internal loop.



Our Design
Our design is a concentric internal loop airlift photo bioreactor, composed of two concentric cylinders, where fluid flows up the inner cylinder, or riser, and down the outer cylinder, or downcomer. The flow is driven by a bubble lifter. The bubble lifter also serves to introduce carbon dioxide into the system. Lighting will be provided by tunable RGB LEDs inserted in the wall of the inner cylinder, to provide good light penetration. The cylinders will be made of a clear plastic, and the base will be a separate piece of machined plastic, contoured to reduce the potential for dead spots. Further details will be worked out as we finish calculations and progress in the project.



Construction and Testing
We have created a small prototype of the basic concentric tube airlift design to perform some experimentation with. We hope do a variety of tests with it, including: testing bubble velocity in the riser, using neutrally buoyant beads to test fluid flow rate in the system, and testing the efficiency of different sparger designs.

Matthew Jungert
Currently completing my 5th and final year at the University of Idaho in Biological Engineering. I grew up on a family farm/ranch in Cottonwood Idaho. I currently work in the Lab Animal Research Facility on the University of Idaho campus as a Lab Animal Technician. I plan on going into the fields of precision irrigation or bioenergy.

Sage Pratt
I am a mechanical engineering student from Moscow, Idaho. I chose this educational path due to my general interest in technology and science. I am also enrolled in the Air Force ROTC program, and plan to commission as a 2nd Lieutenant upon graduation and work in space operations. In my free time I attend a bible study at my church, read extensively, and work on metal and woodworking projects in my garage.

Document Archive

 * [[Media:2017_autophyte_prelimdesignrev.pdf|Fall Semester Design Review (Fall 2017)]]