Finally our cultures are dense enough to begin to extract final products. After toiling over gallons of green, salty water we are finally collecting and storing quantities of it to concentrate and eventually dry. There are several methods for collecting the dry cells that I have thought about. We could filter the water with a 1 micron screen (the cells are ~2 microns so they will stay behind while the water flows through), or we could use a centrifuge. For now, we settled on the neat gadget that is the centrifuge. We fill several conical-bottomed 15 ml vials with suspended algae culture and put them into pairs of slots that form a circle around the center of the machine. When we close the lid, the centrifuge spins the cultures at 4,000 rpm for 4 minutes. When the time is up, the lid opens and reveals eight vials with clear water on top and a layer of green sludge about 4 millimeters thick at the bottom. We pour off the water and use a pipette to suck out the bottom layer. We fill another vial with the pipetted concentrated algae and then in turn centrifuge that. This process repeats until a good amount of green slime has accumulated. It may be tedious, but the result is worth it: it’s good to be able to see the tangible, green and slimy fruit of our labor. This method is only effective, I believe, for making small batches for limited tests. Making more than a few milliliters of concentrated algae would take hours with this method so in the future I think we will find a different method.
An explanation of centrifuging algae: