With the pump located near the periphery and the nozzle aimed at a proper angle to the wall, the action of the nozzle will force the blanket to rotate. Once the blanket is mixed, methane gas production will increase. The pump can then be used on an intermittent basis to keep the scum blanket mixed. The action of chopping and conditioning material to reduce particle size is of proven value in sewage treatment plants. If digestible material is in smaller particles, then the surface area of these particles is relatively large in comparison to their volume.
Bacterial action can then be more effective and rapid.
Clarifier Scum Inherent problems with clarifier scum include plugging and air binding. As discussed throughout this article, the chopper pump addresses the plugging problems. However, air binding must be addressed in an indirect manner. The inherent recirculation around the inlet to a chopper pump usually causes enough mixing to keep air binding from occurring in scum pits that have short retention times. If a scum pit has a long retention time, then the scum tends to concentrate and form a blanket on the top.