Maybe it's a dumb question but how do your suppliers collect the biogas?
It depends per supplier. Dairy farms, wastewater treatment plants and food and beverage biogas producers all produce biogas in anaerobic digesters. The put their manure, biosolids or food waste in the digester and bacteria break down the biosolids into biogas. If they have no use case for the biogas this then gets flared.
At landfills, biogas is produced more naturally and needs to be captured using landfill capture systems.