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Process Schematic

Hover over different parts of the diagram below to see a description of that part of the process.


alt Clean water is discharged from the plant into Mount Hope Bay via underwater pipeline. The last part of the process is de-chlorination. This is when the hypochlorite residue left in the wastewater is neutralized with the addition of sodium bisulfate. The treated wastewater is not called final effluent. Septage that has been pumped from the septic tanks of homes in surrounding towns is delivered to the facility by truck. It enters the plant at the septage receiving station where two 20,000 gallon tanks hold the waste from aeration and grit removal prior to pumping it through a pipe where it enters the main wastewater stream. Sodium hypochlorite is injected into the wastewater for the purpose of disinfecting, or killing disease causing organisms, the wastewater prior to discharge into Mount Hope Bay. Pump The secondary effluent then passes through a flow measuring device called a “parshall flume” to record how much water is being treated.  The ash is sent to a dumpster for disposal at the landfill. The sludge cake may also be sent to the landfill in dumpsters. “Chlorine contact chambers” are deep and maze-shaped, which causes the flow of the wastewater to slow down while creating a mixing action as the treated wastewater travels through the maze. This creates the necessary contact time for the chlorine to kill harmful bacteria. Skimmers are also present at the end of the contact tanks to remove any floating materials and send them to the scum collection system. The scum that has been collected from various locations is them pumped into gravity thickeners where it is mixed with thickened sludge. It is then incinerated or trucked to the landfill. Pump Four oxygenation tanks allow the wastewater to be biologically treated. The facility cultures a large volume of bacteria and other microorganisms, approximately two million gallons, which is called “mixed liquor.” This enters four large, rectangular, and enclosed “oxygenation basins.” Nearly pure oxygen, which is produced at the plant, is added to the airspace above the liquid at the end of the basin where the mixed liquor is entering. Each basin has three large mixers along its length to keep the activated sludge well mixed with the primary effluent. This also lets oxygen to get to the bacteria, allowing them to respire and break down the organic materials present in wastewater into simpler compounds. The sludge cake is burned in the incinerator. The “Dewatering Building” is where a chemical called “polymer” is added to help bind the sludge solids together and help removal of the water from the sludge. The sludge is then sent to a belt filter press which squeezes more water out of the sludge forming “sludge cake”. The water squeezed out is collected and mixed with the primary effluent for treatment. The “gravity thickeners” allow the sludge collected from the clarifiers to become more concentrated, while also storing the sludge until it can be processed further. Water that overflows from the thickeners is called “thickener overflow” and is sent back, via pipeline, to the primary clarifiers for treatment. The wastewater leaving the primary clarifiers is now called “primary effluent” and is collected in a piping system to direct it to further treatment. “Primary clarifiers” let the flow to slow down, allowing the heavier material to settle to the bottom and the lighter material floating to the top. The lighter material is skimmed off the surface and enters the “scum collection system”. The heavier material, called sludge, settles to the bottom of the clarifiers and is removed from the primary clarifiers by being pumped into three “gravity thickeners.” Wastewater is constantly entering the clarifiers and treated waste water is constantly leaving the clarifiers by overflowing the rim, or the “weirs.” In the “aerated grit chambers,” water is bubbled into the wastewater through air pipes along the bottom of the chamber. This lets lighter organic material to be in suspension while allowing sand and grit to settle out in the wastewater. The sand and grit are mechanically removed from the chambers and washed through a cyclone device to remove organic material. The collected material is then deposited into dumpsters for disposal at the landfill. The wastewater is then returned for treatment in the facility. Materials that float to the surface, like greases, are removed with a skimmer and enter the “scum collection system”. When material first enters the plant, it passes through two “bar screens.” These are closely placed vertical bars used to catch rocks, sticks and other large debris to prevent damage to equipment later in the treatment process. This material is then mechanically removed from the screens and deposited into the landfill. A pump then transports the wastewater to two “aerated grit chambers.” When material first enters the plant, it passes through two “bar screens.” These are closely placed vertical bars used to catch rocks, sticks and other large debris to prevent damage to equipment later in the treatment process. This material is then mechanically removed from the screens and deposited into the landfill. A pump then transports the wastewater to two “aerated grit chambers.

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