I don't know what the bassist from Mayhem uses,
but my shot at it:
Sansamp Bass Driver DI + maybe an Electro Harmonix Steel Leather.
That will get you into the ballpark.
Take an overdose of the presence control on the Sansamp BDDI.
As far as EQin.... I hear a tad of growl, probably a bit boosted between the 300 to 500 Hz area.
Otherwise I don't feel EQing will get you there.... but you should learn more about EQing regardless of achieving this particular tone. I very much depends on what bass and amp you have.
As for the bass.... go ask in the basses forum what the best bass for metal is, they like that over there.

(joking, don't do that)
I'm guessing anything from and active Jazz bass to a modern active bass would be a logical choice.
But, you as formerly guitarist should probably also know, your instrument choice is very personal, and your choice can't be explained by logic.
You need to find a bass that feels good to you, regardless of what genre you are going to use it for.
For example, I play a fretless precision bass and I play metal. Strange, but it works for me. My favourite bass, the favourite music style I play.
edit: cheap alternative for the Sansamp, the Behringer copy, BDI21
according to some users here it is on par with the Sansamp when it comes to tone quality.
build quality is something else.
Also MXR Blowtorch is something you might want to try out.
It's definately "grit" you're after.
Hard to define that.
Mild metallic overdrive.... I would describe it.