South District Wastewater Treatment Plant

The raw wastewater that comes into the South District Wastewater Treatment Plant first goes through conventional treatment, which consists of the following steps:

Heavy solids are separated from the wastewater stream.
Biological matter is progressively converted into a solid mass by using indigenous, water-borne micro-organisms.

Finally, the biological solids are neutralized and either disposed of or reused. The treated water may be disinfected chemically or physically.
In the case of Miami-Dade County's project, the water will go from secondary treatment through the High-Level Disinfection plant that is under construction.

How water reclamation works:

The first step is microfiltration or ultra-filtration -- a filtration process that removes contaminants from a fluid (liquid and gas) by passage through a micro-porous membrane. A typical microfiltration membrane pore size range is 0.1 to 10 micrometres (µm). (A micrometer is one millionth of a meter. For comparison, a strand of human hair is about 100 µm wide.)

Next, the water goes through reverse osmosis -- basically, a filtration process. It works by using pressure to force a solution through a membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied.

Hydrogen peroxide is now added. It is commonly used to remove pollutants from wastewater and from air. It contests bacterial growth through oxygen addition. It can also be used to treat pollutants that can be easily oxidized such as iron and sulphides and pollutants that are difficult to oxidize such as dissolved solids, gasoline and pesticides.

Ultraviolet disinfection, a common treatment of drinking water that uses ultraviolet radiations to inactivate microorganisms, is then added. Ultraviolet disinfection of water consists of a purely physical, chemical-free process. The radiation initiates a photochemical reaction that destroys the genetic information contained in the DNA. The bacteria lose their reproductive capability and are destroyed. Even parasites such as Cryptosporidia or Giardia, which are extremely resistant to chemical disinfectants, are efficiently reduced. UV can also be used to remove chlorine and chloramines. This process, called photolysis, requires a higher dose than normal disinfection. The sterilized microorganisms are not removed from the water. UV disinfection does not remove dissolved organics, inorganic compounds or particles in the water. However, UV-oxidation processes can be used to simultaneously destroy trace chemical contaminants and provide high-level disinfection. It is currently in use at the reuse plant in Orange County.

When the full-scale reclaimed water plant is complete and operational it will pump 21 million gallons a day of this purified, highly treated water to the moat at Miami Metrozoo, where it will recharge our groundwater. The result will be very pure water whose quality will be near that of distilled water.

Comment

That is 21 million gallons per day that can be saved for drinking water. Apparently there is only a pilot plant open at this time.

Typically, 50% of the water used residentially is used outdoors. If residents install a submeter they will not be charged for that use, whether its for washing the car, the dog, watering the grass, or refilling the pool. A 50% reduction would be significant for most people and the savings could pay for the cost of installing the submeter. Visit www.miamidade.gov/wasd/save_wup.asp or www.miamidade.gov/wasd/save_submeter.asp for more information.