Sounds like it needs more attention than a herd of cows.Yes, we recirculate digester contents to mix with the feed, and push it through the macerator. It works well now but needed a lot of development to get it where it is now.
Some digesters work as a two stage process, with a primary tank where mostly acetogenesis happens - breaking down feed materials into volatile fattty acids, and a second methanogenesis stage where the methane is produced. In reality it is never as clear cut as that. Also, some digesters such as those used by Future Biogas have a main digester, then secondary tanks which are mainly for digestate storage but can capture a small amount of gas. These tanks are not heated unlike the main one.
Other big sites can have several systems running in parallel.
We do not have gas scrubbers, these are normally only used when exporting the gas into the gas grid, quite an expensive excercise. We burn our gas in a CHP to give electricity and heat. Some CHPs require an activated carbon filter to remove hydrogen sulphide, but ours does not. We do add ferric hydroxide and run a small amount of oxygen (0.1 to 0.4%) in the tank to reduce the H2S.
We have gas mixing, so instead of mechanical stirrers in the tank, we take some of the gas, compress it and bubble it up through each of 36 pipes in the base of the tank in turn.