Wastewater treatment tech should unlock the anaerobic digester

Just spent several minutes trying to figure out why I couldn't find the digester in any of the build menus. Turns out it's because I skipped right over the biofuel tech in the beginning of the game.
For the other buildings like the air separator and mixer, they are unlocked whenever you first research a tech that requires their use, regardless if you skipped an earlier tech that could have unlocked it. The digester should be treated the same.