What happens to the wastewater treatment plant if it is not properly desludged?

If proper maintenance is not performed on the wastewater treatment plant, the first issue to occur will be over-sludging. This manifests as an increase in the concentration of activated sludge in the activation process beyond the optimum (3-4 kg/m3, which corresponds to about 30% of the volume of the sample taken after settling for 30 minutes). As a result, activated sludge will eventually start to escape into the outflow, typically occurring when the sludge concentration exceeds about 60-70%.