Imhoff tanks look like pretty old technology that would be probably trivial to adapt for biogas collection:
Advantage here is that Imhoff tanks, being old tech, are probably purchaseable or salvageable. And the design and maintenance parameters, even if you go and build your own, are by now well enough understood, I imagine.
Advantage again, is that the imhoff tank design does not assume any powered components, being powered only by the compressive force of new wastewater entering the upper chamber.
I don't know whether additional cellulose increases or diminishes biogas production in a system like this. The answer to this might inform whether the designer/user of a system like this would be better served with non-tissue/wipe based sanitation methods.
As with Septic Tank systems, care must be taken to not build such a system carelessly - if you live in a Karst region, then you should probably put your faith in a central sewage system (maybe vacuum-powered for maximum environmental safety) to avoid contaminating the complex local groundwater. If you live somewhere with a high water table, or rapidly flowing groundwater, then that needs to be factored carefully also. And if your neighbours have a well...
Also, the system spillway will be pretty rich in free N/P so make sure the local environment won't be harmed by that. Perhaps plant some fruit trees on the spillway, but definitely don't grow salads or low-growing edibles! :)