Granules

Aerobic granular sludge

Conventional wastewater treatment typically uses a process called activated sludge. Microorganisms grow as flocs suspended in a tank and degrade organic pollutants. Some process configurations can also be used for removal of nitrogen and phosphorous from the wastewater. After the activated sludge tank, the water and microorganisms flow into secondary settlers. The activated sludge (microbial flocs) settle to the bottom and the treated water is discharged. The flocs are then recirculated back to inlet of the activated sludge tank.

Aerobic granular sludge is a relatively new process that creates conditions that make the microorganisms grow in dense granules instead of flocs. The granules settle very quickle, which means we don't need a lot of space for large secondary settlers. The granules also contain microenvironments with different levels of oxygen. This is beneficial because it means different funcitonal groups of microorganisms can coexist, and we can accomplish complex processes such as nitrogen- and phosphorous removal in one single tank.

We have studied the startup of aerobic granular sludge in a series of laboratory scale studies. Granules are typically formed when we apply selection pressures such as high turbulence, feast-famine regimes, and short settling time. In one study, we asked if the same microbial community composition would develop in three reactors started up in parallel. You can read about the results here.

You can also find more studies about AGS among the papers on my Google Scholar profile.