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Alum dosing has been an important variable throughout flocculation history. It is considered an art form and is generally picked up through practice and experience. At the Cornell Water treatment plant the operators rely on past data and a streaming current director to establish their alum dosing. They also rely on some rules of thumb that are affected by the temperature and the turbidity of the water. It appears that the higher the temperature the less alum is needed. This data is displayed in Table 1.
Table 1. Rule of thumb data used by Cornell University's Water Treatment Plant Operators. || ||

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In an attempt to automate and decrease the mystery behind alum dosing the log relationship equation (Y = A + B*log(NTU)) was used to test its impact on flocculation in the pilot plant flocculator. After the value of A was lowered and the tube settlers stopped clogging there appeared to be good floc formation and clean water being produced in the flocculator. While the third section appeared to break floc ups the alum dosing was sufficient so that by the end of the second section the turbidity was usually around 1 NTU and was almost always below 2 NTU (see Figure 12 and Figure 18). The raw water turbidity coming into the flocculator stayed between 2 and 6 NTU during most tests that were run. While the turbidity is low equation 18 allows good floc formation and for clean water to be produced by AguaClara technology.
Alum dosing was also investigated by watching floc formation in the flocculator at different alum doses. This was done in an attempt to note if it was possible to visually discern when the alum dose needed to be changed. Doses of 0, 5, 20, and 50 mg/L were noted.
Upon observing 0 alum dose, it was very clear that there wasn't any improvement through the tank. In fact the whole way through the flocculator it looked as though there were tiny particles floating along with big particles and this never changed.
When observing 5 mg/L the difference was hard to discern. It appeared that there was improvement through the tank. The last two sections didn't appear to have as many small particles in between some of the larger particles were but the flocs that were seen appeared to be smaller than those observed when using equation 18.
When I raised the alum dose to 20 at first there appeared to be a rush of floc at the beginning that moved up the first section of the tank. It is not clear if this was due to the introduction of the higher alum dose or not. After the initial rush of flocs the water entering the tank didn't seem as dirty as the raw water entering the tank without any alum. The floc formation appears earlier in the tank, after about a third of the first section. They are still small at this point but the improvement over the end of the first section and the middle of the second section is rapid. Most of the particles are in floc and there are not as many particles in between flocs.
When I finally increased the dose to 50 mg/L the water in the first section appeared to have the same small particles in between larger particles as the raw water when there was no alum added.. Through the tank it appeared that there lots of medium to small sized flocs, almost as though there were more medium sized flocs and not any large flocs. It does not look like the flocs are large. They are small and never get bigger throughout the tank. There are a few rare flocs that could be considered large. This is contrary to what I had expected to see, I thought I would see the same type of floc as when the tube settlers were clogging. It appeared almost as though by overdoing it negated the effect of the alum, by creating the reverse charge on the particles which again had a repelling affect.

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