How Your Treatment Plants Work

Table of Contents

• Steps in the Treatment Process
• Preliminary Treatment Phase
• Micro-Organism Phase
• Final Phase
• The Dirty Side
• The Wastewater Factory

Steps in the Treatment Process

1. Preliminary Treatment Phase - In this stage large objects and rags are removed from the waste system.
2. Micro-organism Phase - Next, a healthy population of micro-organisms is kept alive to feed on incoming waste.  The generic term for these plant micro-organisms is "bugs."
3. Final Phase - Lastly, the water is prepared before being placed into the reclaimed water system.
   

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Preliminary Treatment Phase

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Aerial view of Aerator

In the beginning, raw wastewater is sent to the start of the treatment plant (known as the Headworks), from pumping stations throughout the county.  Bar screens capture rags, sticks, and other large objects, but let the water pass through.  This trash is collected and disposed of in the landfill.  Then the wastewater passes through a grit chamber.  Removal of grit is accomplished in one of two ways, using either a slow moving water or centrifuge process.  With the slow moving water process, the flow of water is decreased, and grit falls naturally to the bottom of the tank where it can be removed.  The centrifuge process uses a procedure similar to the spin cycle on your washing machine.  With spinning, heavy particles of grit are drawn naturally to the bottom where they can be removed.

The Southwest plant also has a series of tanks after the Headworks called primary clarifiers.  These tanks contain large paddles that scrape the surface of the water and the bottom of the tank.  The particles collected from the bottom are sent to the solids handling facility for further treatment.  The surface material contains suspended objects that came through the Headworks of the plant.  This surface material may also contain grease, which can be detrimental to treatment plant operation.  Grease can plug up lines and clog pumps, plus the plant's "bugs" just don't like the taste of them.  A "bug" that will eat waste and grease has yet to be discovered.

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Micro-Organism Phase

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Operator checking Activated Sludge Level

In this phase, air is added to the water so the "bugs" can breathe.  It is similar to maintaining a large fish tank, but we can only see these "fish" with the help of a microscope.  The mixture of oxygen and "bugs" is called activated sludge.  Activated sludge is the heart of the plant.  It is used to consume the organic matter in the wastewater, since the "bugs" continually eat and reproduce.  A certified operator keeps the balance of "bugs" and food in line.  If there are not enough "bugs" to feed on the incoming waste, the quality of water leaving the plant will be poor.  If there are too many "bugs" feeding on the incoming waste, the "bugs" will die from starvation, and the quality of water leaving the plant will be poor.

Next, are the clarifiers, where the water begins its cleaning.  In these tanks, the "bugs" realize that there is no oxygen and stop working.  They settle to the bottom of the tank and are then returned to the head of the aeration tank to continue feeding on incoming waste.  Depending on the data collected by the operators, some of this returned activated sludge is removed and sent to the solids facility.  The water on top of the clarifier is sent to the final phase.

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Final Phase

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Storage ponds provide a safe habitat for migrating white pelicans

Next, Manatee County treatment plants use automatic backwash filters to clean the water.  These filters work using the help of gravity.  Water flows downward through a media that is composed of one layer of sand and one layer of anthracite.  Clean water is pumped upward through the media to clean it.  Another pump removes the dirty water that is pumped upward and sends it back to the Headworks to be treated again.  After flowing through the media, the water goes to the chlorine contact chamber to be disinfected.  Manatee County no longer uses gaseous chlorine for disinfection.  Due to the extreme dangers of handling gaseous chlorine, Manatee County switched over to sodium hypochlorite in 2001.  We were one of the first large treatment plants in the State of Florida to switch to sodium hypochlorite.

The treatment plants generate almost 40 million gallons of reclaimed water a day.  This water has been used for years to irrigate golf courses, parks, and agricultural fields throughout the county.  Reclaimed water is now also used for residential irrigation and fire protection throughout the county.  Use of reclaimed water for irrigation helps the environment in a number of ways:

1. Water quality is improved by eliminating wastewater discharged into our rivers and bays.
2. Less drinking water is used for irrigation.
3. Use of water from wells is reduced.

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The Dirty Side

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Methane gas tanks

Once the water is cleaned we must deal with all of the sludge.  This is where the solids handling facility comes into the picture.  Just as reclaimed water is a by-product of the treatment phase, bio-solids are also a by-product.  In this phase, "bugs" are used to break down the composition of the sludge even further in tanks called digesters.

The Southwest plant operates four anaerobic digesters.  These anaerobic digesters contain "bugs" that require no addition of oxygen.  The "bugs" feed on the sludge and produce methane gas.  This gas is captured, cleaned, and used to power an on-site generator that then provides some power for the treatment plant.  Our two other county plants operate aerobic digesters.  These digesters contain "bugs" that require enormous amounts of oxygen to break down the sludge.  No methane is produced from aerobic digesters.  Engineers and planners spend years designing treatment plants that operate at the highest efficiency.  Thus, some plants have aerobic digestion and others have anaerobic.  Once the sludge has been digested it is sent to a belt filter press.  The press is used to squeeze the water from the sludge.  After going through the press, the sludge comes out in the form of moist dirt.  Trucks haul off these bio-solids to agricultural sites throughout Southwest Florida.

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The Wastewater Factory

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Contact Chamber for disinfection

Manatee County's wastewater treatment plants are actually beneficial water and fertilizer factories for the county.  Our plants produce reclaimed water which saves our local drinking water supply, and the use of our bio-solids provides fertilization for farmers.  Remember, flushing is not the end...it is just the beginning!

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