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As can be seen from the graph there is a large spike in the pressure readings about 4 hours after beginning the test. The pressure sensor reads a gradually increasing pressure, due to the clogging orifice, until the it builds up enough to "blow out" the clog.
Graph 3: Trial 2 of 24 hour Alum Experiment (Dec. 3. 2009)
Another trial with alum was done over 24 hours (graph 3).
As seen in graph 3, there are spikes in the pressure readings. We are unsure whether or not these represent clogs because the maximum difference in height of the water is at most 0.2cm. This could be in the range of the pressure sensor error.
Possible Sources of Error
The elevated pressure, shown in Graph 2, seems indicative of a clog, but the spike was not repeated at all for the remainder of the experiment. If the clog was "blown out" due to the increase in pressure then it should simply reform after another 4 hour time span, forming a clogging cycle. Yet this cycle of perpetual clogging and clearing of the orifice was not observed. The precipitation and blow out could possibly be more intermittent than one might be able to periodically predict. Because the second experiment had different results, more trials would have to be done to determine whether or not clogging is occurring.
Conclusions/Future Work
The 0.1 cm orifice appeared to clog after 4 hours, indicating that a larger dosing orifice might need to be used. The second 24-hr experiment did not have the same results as the first and thus it is unsure whether or not clogging does occur after four hours. For the Agalteca plant, based off these experimental results and to ensure minimal clogging, we are recommending increasing the diameter of the smallest dosing orifice to 0.152 cm (0.06 inch) to minimize the occurrence of clogs. We used lab grade alum and the one in Honduras could have extraneous material that might clog the small orifices. Further experiments will have to be performed in order to verify that this will indeed increase the time till a clog forms.
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Since lab grade alum was utilized in this experiment and a clog was still presentthe results seem inconclusive, the presence of foreign material, calcium, or carbonates is likely not the main could be a significant cause of the clogs present in the Honduran plants. An inline strainer might could be beneficial to include in future dosing systems but it .It would also be more effective helpful to simply ensure the Honduran operators are cleaning the system regularly and ensuring no foreign matter or excessive concentrations of alum are in the system. It is also recommended that the alum stock tanks are cleaned to prevent the build up of alum precipitates.