The process of wastewater treatment utilizes a variety of processes to provide communities with potable water that is safe to drink and use. Each wastewater plant has its particular buildings and mechanisms; while they vary slightly from location to location, they generally follow the same five-step process. To learn how wastewater treatment plants make water safe, keep reading about each step in the water’s journey from dirty to healthy.
1. Coagulation
The wastewater treatment process starts with coagulation where the water has positively charged chemicals added to it. Many specs of dirt and other dissolved particulates have positive negative charges associated with them, so positive charges neutralize them. Negative and positive charges bind together, so the chemicals and particulates make slightly bigger particles more straightforward to remove later with filtering, draining, settling, and skimming.
2. Flocculation
As water moves through the automation and control systems of a treatment plant, it goes from coagulation to flocculation. In this step, water is gently mixed until it starts forming flocs, which are bigger and heavier particles. More chemicals might be added to facilitate this process. Hydraulic or mechanical mixing paddle the water in ways that help remove sediment or prepare the water for filtration.
3. Sedimentation
This is the part of the process where solids are separated from the water. Given their heavier weight, the previously formed flocs settle at the bottom, and many treatment plants slow the water down to let gravity help pull particulates down. Sedimentation often has a success rate as high as 90% for removing solids, and clear water closer to the surface goes through launder tubes that move it into the next step in the water’s journey.
4. Filtration
While sedimentation might rid water of 90% of flocs and particulates, the fourth step in the wastewater treatment process catches the remaining 10% when everything works. Clear water goes through filters, which have a variety of materials and pore sizes. Charcoal, gravel, and sand remove everything from microorganisms and dust to chemicals and foul odors.
5. Disinfection
Filtered water has chemical disinfectants added to it that kill any remaining bacterial, virus, or parasitic contaminants. Options include chlorine, chlorine dioxide, and chloramine. Treatment plants ensure that exiting water has low levels of these disinfectants that are still present so that they kill germs living in the pipes between the facility and faucets or taps where the water comes out. Ozone and UV light might also be used for disinfection in the plant, but they don’t help keep pipes clean and healthy after the fact.
Various Sources
Before water is turned into drinking water, it has to come from somewhere as it enters the water treatment system. That might be wastewater already used in a community and groundwater or surface water. In cases of surface water, higher treatment levels are necessary because waterways have more sediment, toxins, chemicals, and germs than water from underground. Still, water treatment plants can turn water from local sources into a reliable potable water supply for most communities.
