Bioreactor

1. Apparatus for use with a collector for receiving sunlight, the apparatus comprising:

a plurality of trays disposed in a stack, each of the trays of the plurality, in use, being in receipt of a respective layer of liquid, the respective layer, in use, having a respective headspace;

light sources which, in use, are disposed in each headspace such that each layer, in use, is substantially fully illuminated throughout the depth of said each layer, the light sources being defined, at least in part, by emitters; and

light tubes coupled to a collector and to the light tubes to carry sunlight from the collector to the emitters.

2. Apparatus according to claim 1 , wherein the light sources are defined in part by lamps which deliver artificially-produced light.

3. A production facility, comprising:

apparatus according to claim 1 ;

apparatus for introducing, into each of the plurality of trays, carbon dioxide, nutrients and water

and for withdrawing, in use, oxygen from each headspace; and

apparatus for withdrawing biosolids and water from each tray.

4. A production facility comprising:

a greenhouse; and

apparatus according to claim 1 disposed within the greenhouse.

5. A facility according to claim 4 , wherein the lamps are LED lights.

6. A facility according to claim 4 , wherein the trays decrease in size as the stack progresses upwardly.

7. A facility according to claim 6 , wherein the trays define a generally conical stack.

8. A facility according to claim 4 , wherein the tray size and spacing is such that, in use, over the course of a sunny day, at least the majority of the surfaces of the layers are exposed to sunlight.