Stages of Wastewater Treatment Preliminary treatment removes large pieces of debris like trash and branches with bar racks. Smaller debris, such as gravel and coffee grounds, are separated using aerated grit tanks. The separated material is then taken to the landfill for proper disposal. Primary treatment removes smaller solids through settling tanks and skimming devices. At this point 60% of the solids are removed. Additionally at this step, chlorination of the water takes place. Secondary treatment removes up to 85% of the solid material in the wastewater. In this step the water is aerated to stimulate the growth of helpful bacteria and other microorganisms that break down organic nitrogen and impurities converting them into ammonia. After the sludge created by these microorganisms is separated from the wastewater, the water is chlorinated and then released into the Bay. Many treatment plants have upgraded to Tertiary treatment to comply with strict nitrogen limits. This step converts ammonia into N2 gas which is then released out of the system back into the atmosphere. Because ammonia is the easiest form of nitrogen for algae to utilize, it contributes most significantly to the explosion of microalgal blooms in the upper Bay. Source: STB
Stages of Treatment… Save The Bay The new CSO Tunnel -- video
For Next Week Where does your wastewater go? How is it being treated? Are there any ecological impacts – water quality effects, or other issues? Be sure to look in Google “News” as well as the Web. Come to class prepared to hand in a written report and discuss what you found out.