Over time anaerobic digesters can become functionally inert and operationally compromised. Sludge forms solid upper layers that cannot be processed often causing congestion in pipes, sludge drying beds, and ponds. Sludge presses become overloaded and sludge volumes become too great and expensive to dispose of.
Because of the high organic and nutrient content remaining it has been shown that leaching from sludge disposal sites can be a major cause of nutrient inflow into rivers and other bulk water resources.
By achieving more complete digestion, a high liquid fraction is achieved, minimizing solid residues and the need for post-digestion sludge management activities including sludge disposal and desludging of ponds where these are used.