The activated sludge process is the most widely utilized method for wastewater treatment process due to its relatively low cost and relative ease of operation. The generation of excess sludge is a usual feature in the operation of the activated sludge wastewater treatment process. About 40-60% of the costs of wastewater treatment is associated with the handling, treatment and disposal of the excess sludge.
As a consequence of several factors that include regulatory constraints as well as rising public awareness and sensitivity to sewage sludge disposal issues, sludge management and disposal costs have been rising. There has lately been a renewed interest in technologies focused on fundamentally reducing the generation of sludge in the aeration basin.
Although several methods exist for achieving sludge minimization, the sludge ozonation process has been extensively studied and characterized, and has shown immense promise as a viable method for attaining consistent and reliable reduction of excess sludge. The basic concept is the application of ozone to a side stream containing at a minimum, the equivalent portion of the excess sludge to be eliminated. The application of ozone to this stream causes the bacterial cells that come in contact with ozone to be lysed. Upon lysis, the cellular COD that is contained within the cells is leaked out, and the lysis products are then recycled back to the aeration basin where the bacteria feed on the released COD. The effective reduction in excess sludge is achieved when the COD generated from the lysed VSS (bacterial cells) is bio-oxidized in the aeration basin. The lysis COD when consumed, effectively generate a quantity of excess cells determined by the yield obtained within the wastewater treatment system