Wednesday, November 20, 2013

Following Water Through a Water Treatment Facility

Water treatment involves taking used and runoff water and making it acceptable for drinking or simply for reintroduction into the environment. Organic and inorganic contaminants are removed through both mechanical and chemical methods. At several designated points along the process, samples are taken and tested to ensure standards are met.

Outlined here is a description of this process in a Middle Georgia water treatment facility that processes surface runoff water.

When water first comes to the facility, it flows into the Influent Pump Station (IPS). Here bar screens take large chunks of organic and inorganic material out of the water and conveyors send them to a landfill. Three main lines bring water from different areas in the city. From here the water is pumped to the next step of the purifying process.

Between the IPS and the next stage is the Switch gear, which houses two sources of power for the plant that back each other up in the event that one fails.

The next step involves the Bar Screen Grit Structure. Here is where smaller particles are removed. The organic matter is agitated into suspension and filtered away. The grit that is retrieved is sent to a landfill. A sampler takes a composite sample that is tested in the facility's laboratory for monitoring purposes.

The Primary Clarifier is the next stage of water treatment. At this location, the solids that settle out are removed and the surface is skimmed. The removed solids are pumped out to the gravity thickeners and then to the digesters. On the way to the next stage, blowers incorporate oxygen into the water.

At the Trickling Filter the flow from the Primary Clarifier is pumped up into the distributor arms and allowed to fall through the filter. Aerobic bacteria located in the media of the filter reduce the ammonia in the water to nitrite.

Next, at the Aeration Basin aerobic bacteria in the water further reduce nitrite to nitrate. A return flow adds water back to the beginning of this step from a later stage to maintain the food value for the bacteria.

The Final Clarifier allows any remaining solids to settle and be filtered out. A portion of the water is sent back to the Aeration Basin.

The majority of the water from the Final Clarifier is sent to the Chlorine Contact Chamber to kill harmful bacteria. Chlorine is added via chlorine injectors and the pH is regulated. Then Sodium bisulfite is added to remove the chlorine before it is pumped into a nearby river.

The solid waste that was removed from the water must be prepped to allow for transport. This is done at the Headhouse Digesters and the Gravity Thickeners. In the thickeners, the collected sludge is thickened through the removal of some excess moisture. In the digesters, the waste solids are stored where anaerobic bacteria break it down, producing methane gas as waste.

The methane gas is used as fuel to heat the digesters so they remain between 85 ºF and 95 ºF, for the bacteria to thrive. This energy is also used to run other equipment at the plant. The solids are then sent to the Secondary Digesters to press out any remaining water and then sent to the a nearby plant.