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"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.
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 in laminar flow. Using Process Controller, we can isolate all parameters of flocculator in order to understand how each parameter affects the process.
The details on Process Controller can be viewed here. Before running an experiment, make sure:
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.
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.
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.
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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