Sludge wasting should occur during the idle cycle to provide the highest concentration of mixedliquor suspended solids (MLSS). The plant should be operated on pounds of MLSS and not concentration.
Sludge from the SBR basins can be wasted to a digester and/or holding tank for future processing and disposal. The digester-tank and sludge-holding-tank capacity should be sized appropriately, based on the sludge treatment and disposal method.
Supernatant from the sludge digester and/or holding tank should be returned to the headworks or influent equalization basin so that it will receive full treatment. The facility should be designed so that the supernatant volume and load do not adversely affect the treatment process.
A high-level alarm and interlock should be provided to prevent sludge-waste pumps from operating during high-level conditions in the digester and/or holding tanks.
Controls should be provided to prevent overflow of sludge from digester tanks and/or holding tanks.