Render isolated object, but still affected by shadows and volume lighting)

Hi

I’m trying to figure out how to render an isolated object, the grid you see in the image below.



I need to render the grid separately, but I still want it to be affected by the volume scattering from the water.
The final grid will look something like this. It is below the surface, but I want it to show through it.
(To illustrate underwater excavation)


Then I’ll compose it over in After Effects.

Any help i appreciated, thanks.

TL;DL
I want to render the grid separately, but still affected by the volumetric water.