Polyaluminum Chloride Dosing System Design
Stock
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.
Peristaltic Pump
The peristaltic pump near the Aguaclara desktop computer pumps 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
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.
There is #16 sized tubing running out of the PAC jug and then there is a connector that switches the tubing size to #13 before the pump.
- Note: It can take awhile for the PAC to travel through the first segment of #16 tubing due to its larger diameter. To speed this process along, first separate the #13 tubing from the #16 at the quick disconnect. Then dip the #16 tubing into the PAC as far as possible, plug the top with your thumb and pull it out and place the end of the hose at a lower elevation than the jug (do this over the flocculator so you don't make a mess), continue to do this till you get a flow of PAC then reconnect with the #13 hose and turn on the pump
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. For this reason we can dose our water at the same ratio as the plant. PAC dosage does not vary as greatly as 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.