Sludge Ozonation

Ozone Sludge Reduction

An emerging application for ozone use in wastewater treatment is the reduction of sludge generation from the activated sludge plants. Sewage plants must dispose of their excess sludge. To do so, additional processing of the sludge is required including filtration and dewatering. In some cases, the sludge must be disposed of in landfills where the plant operator must pay for hauling and disposal costs. Eliminating this excess sludge can be economically interesting depending if the amount of ozone per ton of sludge removed is low enough.

In this process ozone is fed into a side stream of sludge that is be recycled back to the activated sludge tanks.

Ozone Sludge Reduction Process
The ozone attacks the cell walls of the bacteria that make up the activated sludge causing the cells to undergo lysis. Lysis is a process where the cellular wall is breached and the internal materials leak out of the cell.

Ozone Cell Lysis - Initial Cell Structure
Ozone Cell Lysis - Ozone Molecules Attack Cell Wall
Ozone Cell Lysis - Cell Wall Damage Begins
Ozone Cell Lysis - Holes form in Cell Walls Allowing Cellular Materials to Leak
In the activated sludge process this leaked material, or cellular COD, goes back to the activated sludge tank where other bacteria consume the COD. As it turns out this material is very biodegradable. Essentially, the ozone damages certain sludge bacteria so they can be consumed by the rest of the bacteria (biomass or sludge).

This process has been studied extensively and found to work with up to a 60% reduction in excess sludge. Other benefits of the process that have been observed include: elimination of foaming problems, reduction in bulking, improvement in dewatering, improvements in settling and improvement in effluent quality.

Ozone is already used at some sewage treatment plants for disinfection of treated effluent. In this application it has the benefits of improved disinfection, reductions in disinfection byproduct and increasing the oxygen content of the water. Extension of ozone to the activated sludge process may further improve wastewater treatment plant economics and performance.