Activated sludge treatment can remove up to 90 percent of pollutants from wastewater in only one step, without going through the trickling filter, clarifier, biodisc, clarifier sequence required by the older plant setup.
New Secondary Treatment Process
The wastewater treatment plant at 303 Hollister Avenue uses both an older Trickling Filter (installed circa 1950) and BioDisc Facility (installed 1980) and a newer Activated Sludge Facility (installed 1998) for accomplishing secondary biological treatment. The “secondary splitter” divides the wastewater flow between the two.
The addition of this newer type of secondary treatment process to its plant, providing an alternate route for the wastewater to move through the cleanup process, increased the amount of sewer water that the DeKalb Sanitary District could treat, which was necessary because of the increase in the population.
Aerobic Bacteria in an Activated State
In the Advanced Secondary Treatment section of the plant, wastewater is combined with bacteria that are kept in suspension with fine air bubbles in tanks called “aeration tanks.” The mixture of nitrifying bacteria and air bubbles is called “Activated Sludge.”
A mixed population of many different kinds of organisms (like those found in nature) use the organic materials in the wastewater as their main food supply. These “aerobic” bacteria need oxygen to do their work, and the rich supply of oxygen in the activated sludge facility makes them happier, healthier, and more efficient.
After the bacteria have consumed both organic matter and ammonia nitrogen, the result is carbon dioxide and a bigger population of bacteria. The mixture is separated in clarifiers. Then the wastewater moves on to the next process, while the activated sludge is returned to the head of the aeration tank to begin the feeding process again.