Re:Hacker increased chemical level at Oldsmar's city water s...
by loeg on Tuesday February 09, 2021 @11:52AM
(#26079672)
The steps are similar in Seattle, although I think we filter less. I'm having a hard time finding a concise but also technical description of water treatment steps. We definitely do:
- Ozone disinfection, and removal
- Tolt river supply only: water conditioning by filtering through "granular media." (Cedar river supply is clear enough without this step.)
- UV disinfection
- pH adjustment to avoid corroding pipes
- Flouridation for public health
- Chlorination as a final step as water leaves the treatment plant, and also at some downstream facilities (like a networking repeater; just to maintain chlorine levels that would otherwise have fallen due to distance from the upstream chlorination site)
Tolt: http://www.seattle.gov/utilities/your-services/water/water-s...
Cedar: http://www.seattle.gov/utilities/your-services/water/water-s...
They get filtered, but there is no chlorine directly. Some chlorine dioxide is used at the end, though. Here's the official description of the utility, translated to english:
- Via a raw water pumping station, the dam water first reaches the micro-screening plant. It removes coarse contaminants over 35 ~ µm in diameter through stainless steel mesh filters. This provides special safety in times of mass algae growth or during floods.
- Subsequently, the raw water is de-stabilized with a flocculant; and turbid matter accumulates to form large flocs.
- In filter stage 1, two filter materials of different coarseness are used to remove the flocs.
- Ozone is then added to disinfect the raw water.
- Filter stage 2 is equipped with activated carbon and frees the raw water from the reaction products of ozonation. Excess ozone reacts to form oxygen and is thus removed from the raw water.
- The further filter stage 3 uses natural limestone material over which the water flows. Here the excess carbonic acid in the water is removed. Finally, a small protective disinfection with chlorine dioxide takes place before the drinking water leaves the clean water tank in the direction of <city>.