Basics on Tube Flocculator

(Fun) Facts about Tube Floc

What is a floc?

"Floc" is the name given to the colloidal aggregates formed during the process of coagulation and flocculation. Small, micron sized particles of dirt and other organic matter exist naturally in rivers and other surface water sources. When there is a high concentration of these suspended particles in the water (as is the case after a storm), the water will look very cloudy and unpleasant to drink. It takes a very very long time (really long if the fluid is not quiescent!) for these suspended particles to settle out. By mixing a coagulant like alum into the water, these suspended particles will begin to stick to one another upon collision. Flocculation is the process of bringing these ever growing aggregates together to form even bigger aggregates which we call flocs. Our goal is to form as many flocs as possible, so that they can eventually settle out by gravity.

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What is a flocculator?

The tube flocculator consists of many segments of plastic tubing joined together into one long coiled unit that is capable to producing flocs. Velocity gradients established by flow in the tube facilitate particle collisions. The tube flocculator allows the team to study how various parameters affect flocculation. Using Process Controller, we can isolate all parameters of flocculator in order to understand how each parameter affects the process.

Checklist for the setup

• Make sure all connections are tight.
• Make sure that there is no clogging in the flocculator and pump tubes
• Get rid of bubbles in the flocculator tube
• Check the pump tube size and the setting on the pump panel
• Check if the tube all goes in the correct direction, especially if you have made changes with the tube setup
• The cables connecting pump and the computer are easily unplugged, so check them out!

Stock preparation

Checklist for Process Controller

The details on Process Controller can be viewed [here]. Before running an experiment, make sure:

• Check the source page
• Check the location of datalog path
• If a new set point has been added in the set point list (and not at the end of the list), check that all rules and states still are referencing the correct set point, and any variable set points are referencing the correct set point too.

Troubleshooting

In this semester, distilled water was used to instead of tap water last semester; however, there was a problem that happened in the connector. In the connector, a kind of solid coagulant formed that influenced the experimental process and results. A hypothesis was that a solid precipitate formed in the push-to-connect junction between the alum dosing and raw water lines. This precipitation could easily occur especially with high raw water turbidities. The precipitate blocked alum flow in combining with the raw water so that the system was not dosed effectively.

What if there are no flocs being formed?

• Always check tube connections and make sure there is no clogging in the connections.
• Check the stock solutions. Make sure that there is no sedimentation occurring in clay and alum stock solutions.
• Check the influent turbidimeter. If it displays lower turbidity, then check the clay stock valve. Check if the valve is properly allowing clay to enter raw water bucket.
• If you suspect that the flow rate for the alum and/or raw water is incorrect, recalibrate the pumps in process controller.
• Check bubbles in the flocculator and settling tubes, especially at the entrance of the settling column. Flocs could get trapped in the bubbles and get broken.

I opened up a Process Controller method, but all the states are gone

This occurs when Process Controller and the same method that you are working on is open on a different computer. Close out of Process Controller on all computers that are using the same method without saving. Open Process Controller and the method again. The states should reappear.

Cleaning Protocol

After running many sets of experiments, the particles get attached and accumulate in the flocculator tubes, so it's harder to observe what's going on in the tubes and this might contribute to a false effluent turbidity reading. Additionally, if the setup sits too long without any action, particles can build up in horizontal pieces of tubing and any connections.

Flocculator Cleaning

The flocculator should be cleaned regularly. Since the tubing is clear, it is visually obvious when the tubes need to be cleaned. Ideally, cleaning can be done between each major experiment, as it is not hard and takes only moments.

1. Turn the Process Controller to the OFF state
2. Prepare a small piece of sponge (cleaning sponge) by the size of tube inner diameter by cutting the sponge with scissors
3. Insert the piece of sponge at the starting point of the tube flocculator (right at the beginning of the clear flocculator tube)
4. Turn the Process Controller ON (State 7 - Calibrate Influent Turbidity)
5. The piece of sponge will move through the flocculator tubing, cleaning the sides of the tubes of any flocs as it moves
6. Turn the Process Controller OFF when it almost reaches the end of tube
7. Clean out the sponge and repeat if the flocculator tubing is excessively dirty

Influent Turbidity Vial

The vial inside the influent turbidimeter accumulates dirty water and does not do adequate self-cleaning. The influent turbidimeter vial should be cleaned just as often as the flocculator, as it contributes to false influent turbidity readings.

1. Turn off the Turbidimeter
2. Twist in the plastic stoppers on the tubing before and after the turbidimeter to stop flow from coming into the turbidimeter
3. Follow the directions on the module to open the top
4. Carefully unscrew the vial
5. Leave the top of the turbidimeter vial in a careful place (facing up) while cleaning the vial
6. Rinse out the vial and fill it with clean water
7. Screw the vial back onto the top
8. Wipe the outside of the vial with a Kimwipe to remove all fingerprints and other blemishes
9. Place the top back into the module and into the lock position, unscrew the plastic stoppers on the tubing and turn the turbidimeter on

Remaking the Stock Buckets

The clay and alum stock solutions can get old after no experiments have been running for quite some time. Because of processes like evaporation that we can not control, we can never be sure that the concentrations in the stocks are the same as we made them. If an experiment is going to be started after a long time from the last experiment, then the stocks should be remade in order to make sure that all parameters are the same across all experiments.
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