This process allows solids to accumulate on the bottom of the clarifier tanks where they can be removed in a concentrated form. In secondary treatment, microorganisms convert the remaining dissolved and suspended pollutants into forms which are more easily removed from the wastewater. We have two types of biological systems at the plant. One uses aerobic or airbreathing organisms. These organisms use free oxygen to help break down the pollutants.
Anaerobic digestion is used to stabilize the sludge which is removed from the wastewater.
These organisms convert some solids to methane gas, which is then used as fuel here at the facility. The biological systems, whether aerobic or anaerobic, are truly alive and are highly susceptible to changes in their environment. Other harmless chemicals are also sometimes utilized to enhance treatment. In order to better protect Missoula's precious groundwater, our sole source of drinking water, the City is adding wastewater collection systems to areas which were formerly served by individual on-site septic systems. For more information on S.T.E.P. systems click on the link above.