Photobioreactor

Abstract

A photobioreactor for growing algae comprises a tank for holding a volume of growth medium. A plurality of light sources are disposed either within the tank or externally to it in a manner to illuminate substantially uniformly the entire volume of growth medium when the tank is in operation. At least one draft tube is disposed within the tank, above the floor or bottom of the tank, and a diffuser for diffusing a gas stream is disposed near the bottom of the tank so that gas bubbles released from the diffuser rise to the surface of the liquid within the draft tube, thus causing fluid flow upward within the draft tube and downward outside of it, imparting a mixing or agitating motion to algae strains growing within the tank.

1 . A photobioreactor for growing algae comprising
 a housing having a bottom and a volume and adapted to contain a liquid growth medium,   a plurality of light pipes disposed within the housing and configured to illuminate substantially the entire volume,   at least one draft tube located within the housing, the draft tube being suspended above the bottom of the housing so that fluid can flow between the draft tube and the remaining volume of the housing,   a diffuser disposed at or near the bottom of the tank such that gas bubbles released from the diffuser rise upward within the draft tube.   
     
     
         2 . The photobioreactor of  claim 1  wherein, in operation, the top of the draft tube is maintained below the surface of the liquid growth medium within the housing, such that the rising gas bubbles entrain the growth medium and cause fluid flow between the growth medium within draft tube and the growth medium in the housing outside the draft tube. 
     
     
         3 . The photobioreactor of  claim 1  wherein the at least one draft tube is a plurality of draft tubes. 
     
     
         4 . The photobioreactor of  claim 1  wherein the tank is circular when seen in plan view. 
     
     
         5 . The photobioreactor of  claim 1  wherein the tank is rectangular when see in plan view. 
     
     
         6 . The photobioreactor of  claim 1  wherein the draft tubes are spaces formed by baffles. 
     
     
         7 . A photobioreactor comprising
 a tank having at least one clear wall and adapted to contain a volume of growth medium,   a plurality of light sources attached to the exterior of the at least one clear tank wall to illuminate substantially the entire volume,   at least one draft tube disposed within the tank, and   at least one diffuser disposed under the at least one draft tube to cause fluid flow in the growth medium when the tank is filled with growth medium.