Polyaluminum Chloride Dosing System Design

Stock

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Polyaluminum Chloride (PAC) solution is stored in a plastic jug near the peristaltic pump. The pump draws solution out of this jug through a tube.

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The peristaltic pump near the Aguaclara desktop computer pumps alum PAC from the plastic jug to the flocculation tank. This pump can be turned on and off, but its speed can be changed only by changing the "PAC dosing" in Process Controller. (See "Starting the alum pump" on the Troubleshooting Start-up page. if you need to know how to do this)

Mixing

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The peristaltic pump sends PAC through a thin tube to the first baffle spacing of the flocculator (which serves as a mixing chamber), where the turbulence from the water entering the flocculator serves to disperse the PAC uniformly.

Process Controller Method

Download the Process Controller method created for PAC dosage here

Setup

PAC is used in much smaller amounts than Alum (less than 6 ml/min) so the Peristaltic Pump is set up with size #13 tubing so that the pump can run at a higher rpm and therefore dose more accurately.

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Make sure all of the variables in process controller are entered correctly, see Troubleshooting Start-up page if you need to know how to do this.

Dosing

At the Cornell Water Filtration Plant PAC is dosed in parts per million (ppm) relative to the amount of water running through the system at the Cornell Water Filtration Plant. For this reason we can dose our water at the same ratio as the plant. PAC dosage does not vary as greatly , so 10 to 15 ppm is a typical range of dosage.

Mixing

The peristaltic pump sends PAC through a thin tube to the first baffle spacing of the flocculator (which serves as a mixing chamber), where the turbulence from the water entering the flocculator serves to disperse the PAC uniformlyas alum so it will remain in a range of 10-30 ppm. With temperature increase during warmer months PAC will likely need to be dosed higher considering that as it gets hotter algae becomes more active. With a higher level of organics, more PAC is needed for floc formation.