Culturing Daphnia food

Updated: 28. March 2023.

Chemostats

Chemostats for algae production

Green algae Scenedesmus

Green algae Scenedesmus

Scenedesmus in a counting chamber

Scendesmus in a counting chamber

We grow mainly the green algae Tetradesmus obliquus, formerly called Scenedesmus, in chemostats. The chemostats have a capacity of about 2.5 liters and a flowthrough of about 2 liters per day. We use the following medium, which is routinely produced by mixing 7 stock solutions with TES in deionized (or destilled) water. To produce 20 liter algae medium add to 20 liter water: 2.3 g TES (to buffer the medium)(=0.115 g/L) and 20 ml of each of the 7 stock solutions A - G (in this order!). Afterwards we pump the entire medium through a 0.2 micro-meter filter to sterilize it. (Alternative sterilize in autoclave)

The medium is a modified version of the WC medium (Guillard 1975).

Stock solution Chemical Concentration [g/l]
A CaCl2× 2 H20 36.8
B MgSO4× 7 H2O 37.0
C NaHCO3 12.6
D K2HPO4× 3 H2O 11.4
E NaNO3 85.0
F* Na2SiO3× 5 H2O 21.2
G** NaEDTA 4.360
FeCl3× 6 H2O 3.150
CuSO4× 5 H2O 0.010
ZnSO4× 7 H2O 0.022
CoCl2× 6 H2O 0.010
MnCl2× 4 H2O 0.180
Na2MoO4× 2 H2O 0.006
H3BO3 1.000

* Solution F is not really needed for green algae.

** Solution G contains mainly iron, but also the trace elements. The salt for stock solution G need to be disolved in hot water. The iron may be reduced (even down to 1 g/L) if you have problems with growing bacteria in your cultures).

Some notes on how we run the chemostats:

  • We use LED, placed all around the chemostats (see pictures).
  • The medium in the chemostats is strongly aerated with air from commercial aquaria pumps. The air should be steril filtered, to avoid bringing bacteria into the chemostats.
  • Keep the flow rate high, other wise bacteria take over.
  • We run several chemostats at a time and replace them after about 6 weeks. The algae quality decreases when the chemostats run for much longer.
  • We measure the CO2 concentration in the chemostats and when the pH goes up, we add CO2 to the air. This brings the pH back down. We try to keep the pH between 7 and 7.8. Since we do this, we multiplied the algae production. The entire system works also without controlling the pH by adding CO2, but the production is much lower.
  • When you start a new culture, let it first grow up to a good density, before you run it on full force. The algae need to grow initially slowly (low light, not to low density), before you go into full production.
Chemostats and feeding bottles

Full set of chemostats for algae mass production

Chemostats and feeding bottles

Chemostats with CO2 controller at the right

Chemostats and feeding bottles

Details of chemostats for algae production. Note: the LED panel behind the chemostat are not used in the current setup. The light comes from LEDs placed directly around the chemostats.