The Biological Process within the settling tank

There are three objectives which the microorganisms in the septic tank should accomplish.
 
  The overall anaerobic process occurs in steps that eventually convert organic matter to minerals. The products of biodegradation are gas, clarified effluent and solid. Gases such as H2, H2S, CH4 and CO2 are produced and vented from the tank to the atmosphere. The liquid at the top of the tank should be basically clean and is fed to the adsorption field for furthur degradation and filtration. The solids which enter with the waste settle and are degraded. If the microorganisms can not keep up with the volume of solids, the solids will begin to fill the tank. At that time, a private septic hauler will have to empty the tank