quiescent 11 and mixing 13 zones is the conversion of biomass into carbon dioxide gas and water the carbon dioxide gas bubbles up through the liquor aiding in the mixing and is collected in dome 7 to be eventually drawn off at the raw gas outlet 15 where it may be separated from the raw gas bottled for sale and or used as a ph control substance and mixing enhancement through line 16 and control valves 17 18 and 19 in the preferred embodiment raw gas separation miller u s pat no 6 291 232 is used to separate the two major gas products methane and carbon dioxide for ph control otherwise other chemical feed may be substituted at line 16 similarly in the preferred embodiment raw gas separation permits a certain amount of methane gas to be injected at 20 in lieu of a base chemical the use of methane gas in mixing greatly enhances the action of methane fermentation to the point that basic chemicals are not required in the ph control process methane injected at 20 is fed into the process through control valves 21 22 and 23 where it not only controls the ph and stability of the process but markedly improves mixing liquor drawn off at zone outlets 24 25 and 26 is circulated by diffusion pumps 27 28 and 29 through uplift nozzles 30 31 and 32 resulting in the flow patterns shown in fig2 valve arrangement 23 33 and 34 provide the possibility to provide a bacteria feedback loop to the process as may be required control valves 36 37 and 38 permit sampling of the phases and emergency drains in the preferred embodiment which incorporates vacuum.