Sludge Dewatering Demonstration

Demonstration Purpose: To show how polymer is used to thicken sludge and demonstrate liquid - solids separation.

Supplies needed:

  • Polymer
  • Isopropyl Alcohol (if making up dry polymer)
  • Filtering device
  • Belt press material cut to fit the filtering device
  • Syringe or pipette
  • Two mixing containers, 250 ml beakers
  • Sludge container

Optional filter device:

The use of a buchner funnel is the more professional way to perform the test, but the Gatorade container explained below is inexpensive and transparent allowing students to see through. Make the filtering device by cutting the bottom from a Gatorade plastic container. Any container will do, as long as it has a design to hold the belt press material. One way to cut the belt press material is by using a gasket cutter. It leaves a small hole in the center, but by pushing the fibers back together you can't tell there was a hole. If you don't have access to either of the above, the sludge can be poured through a sample piece of belt press material, then capture the filtrate in a jar or pan below. Additionally, cheese cloth or nylons can be placed around one end of a PVC pipe to make a filter device.

The picture shows a Gatorade drink container filter device in use. The treated sludge is on the filter and the filtrate is in the beaker below.


Mixing up some polymer: 
If you don't have access to polymer already prepared, you'll need to mix and age some before the talk. Liquid polymer is not a problem to mix. However, dry can be hard to make up if your plant doesn't have any. For dry, make 100ml of 0.5% by putting a container on an analytical balance or top loader, taring the container, and weighing 0.5 grams of dry polymer. To dissolve the polymer, add 1 or 2 mls of isopropyl alcohol as a wetting agent. Next, quickly add 100 mls of water, cap, and shake. The solution will need some attention for the first 10 minutes or so. Just shake a few times to keep the polymer granules suspended. A few granules may stick to the bottom, but they always seem to dissolve. Now grab some sludge, and you are on your way to the talk.


Mix the Polymer and Sludge:
At the talk, measure 200mls of sludge in one of the premarked 250ml mixing beakers. Then draw the polymer in the syringe or pipette (our sludge took 11mls - there is 5mg per ml of polymer - for a dose of 275mg/l) and start pouring the sludge in the other beaker. As you pour, add the polymer as in the picture to the left. Then just mix back and forth (about 10 times). Students will see the polymer reacting with the sludge. Pour it in the filtering device to show separation. That's it.


Weigh up the polymer in advance. The day of the talk, squirt in some alcohol and add 100mls of water. Get some sludge from the lab samples. Throw the stuff in the box, and you are on your way to give the talk.


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