Ozone is expensive, but advocates say the pay-off comes in money saved on chemicals and maintenance. Other advantages include safety for workers. Switching to ozone means less handling of dangerous chemicals, including hazardous chlorine gas. The combination of the technologies effectively disinfects turbid water, colored water, even sludge, without using chemicals or leaving residue. The clouds float the particles to the surface where they are skimmed off.
Additional bubbles work to keep sludge on the surface where it quickly dries out.
Clarified water flowing from the bottom of the tank next enters ozone contactors for primary disinfection. Ozone then kills bacteria and viruses and oxidizes the remaining organic material. Finally, water is filtered and, in some cases, lightly chlorinated. The system is much faster than sedimentation, requires fewer treatment chemicals, and deactivates stubborn parasites. Capital costs are lower, and less space is needed for a DAF tank than for a sedimentation tank.