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.
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.
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