With 5:1 ratio this should be the most polluting NG power station in the world, GHG-wise.

Rough calculation - typically NG power stations release 600g CO2/kWh, plus 5 times that (from the associated CO2 released) brings the total to 3,600 g/kWH. This is 4 times more if they burnt coal!

Given that, calling this energy sources "renewable" is a bit ironical, isn't it? And, no it is not serious to expect carbon capture for this project - they don't do that in the West, how could anyone expect Rwanda to do it?! It's ridiculous.

Unfortunately the point is that every now and then the lake spews out a lot of the gas anyway.

So while this isn't "renewable", the CO2 in the lake waters isn't sequestered the way carbon is in coal either.

Burning the methane (or convertin it into fertiliser) and sequestering the CO2 somewhere (or as EP suggests, using it) is the best case scenario, but no the only one...

With 5:1 ratio this should be the most polluting NG power station in the world

And that CO2 would wind up where, in the natural scheme of things?

It occurs to me that this CO2 is produced nearly pure, and would be a perfect feedstock for e.g. algal ethanol/biodiesel systems.  The source will be emitting for thousands of years — it's as renewable as anything else on the timescale of human history.  If it is turned into fuel and burned, it would emit no more CO2 than the natural emissions of the volcanic processes.

Sure, taking that CO2 and injecting it into deep wells would be best for GW abatement.  Sometimes the best is the enemy of the good.