TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: When digester is partially filled, it is left to digest the slurry completely in a batch run, removing and replacing majority of the slurry volume after digestion. The slurry is mixed in a mixing tank to gravitate particulate matter out of the biomass. The step of flushing the digester includes flushing with exhaust gas from a combustion engine. The generation of biogas includes physically supporting a portion of the digester by providing retaining wall for supporting the digester, where the wall includes an elongate wall formations manufactured predominantly from a plastics material buttress formation connected to each wall formation and connection units at either end of each wall formation for connecting adjacent wall formations to each other; providing a biogas-use device which generates waste heat operating the device fueled with biogas; providing a fluid reticulation system passing in contact with the digester; and exchanging waste heat from the device into the reticulation system for heating biomass contained in the digester. The method also includes re-invigorating the slurry for increased biogas production by pumping out a portion of an elevated, more liquid fraction of the digester contents and pumping it back into a lower, solids-rich region of the digester contents; and extracting digested slurry from the digester at the end of the batch run and leaving a seed quantity in the digester to seed the next batch of biomass and restart the anaerobic digestion.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Material: The battery system further includes gas treatment units consisting of a gas scrubber comprising a tank containing a solution of water and slaked lime and/or calcium carbonate, and unit for delivering the generated biogas into the solution; and a tank containing iron filing and/or shavings, and units for delivering the generated biogas through the filings and/or shavings.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The flexible bag of the digester includes a reinforced polyvinyl chloride membrane. The flexible bag is made from a woven or nonwoven material that is non-permeable to methane and is waterproof.