Results and DiscussionsUV Spectrometry Analysis: StandardsThe results obtained from the UV spectrometry test performed in the Hach cadmium test and the micro-phenate test are provided below:Figure 5: UV spectrometry curves for nitrate and nitrite standards.Figure 6: UV spectrometry curves for ammonia standardsWe chose to analyze the nitrate and nitrite standards at 542 λ and the ammonia standards were analyzed at 640 λ because these were the wavelengths with the most observable curves. It should be noted that the cadmium test for nitrate and nitrite had to be run several times on standards before an acceptable linear relationship was determined for the standards. We found that it was important to make sure the timing of each step in the cadmium test was the same from sample to sample in order to achieve accurate results. Acceptable results for the ammonia standards were achieved on the first try. The results of the standards analyzed at of the tests at their appropriate wavelengths are provided below:Figure 7: The linear region of the nitrogen concentration as nitrate and nitrite as determined by tests on prepared standards.Figure 8: The linear region of the nitrogen concentration as ammonia as determined by tests on prepared standards.UV Spectrometry Analysis: SamplesThese linear calibration curves were used to estimate the concentrations of ammonia, nitrate and nitrite in the samples extracted from the reactor.The plant was run with at bulk DO target of 0.5 mg/L with aeration times of 8, 18 and 24 hours. Samples taken from the reactor at the end of these aeration times were analyzed and the results obtained are presented and discussed below.Table 3: Nitrate-nitrogen concentrations at different aeration times for a DO of 0.5 mg/L.Table 4: Ammonia-nitrogen concentrations at different aeration times for a DO of 0.5 mg/L.Table 5: Nitrogen Removal efficiency.At a DO target of 0.5 mg/L, the first aeration cycle was run for 24 hours. At the end of this aeration cycle, the sample taken from the reactor was analyzed for total nitrate and ammonia concentrations. The results obtained indicated a total ammonia concentration of 28.3 mg N-NH3/L and a total nitrate concentration of 4.22 mg N-NO3/L. We know that the initial nitrogen concentration in the tank is 40.9 mg/L, indicating that a total of 8.38 mg/L of Nitrogen was removed by the bacterial process. This corresponds to 20.5% removal of nitrogen.From the 24 hour data, it can be noted that most of the nitrogen remaining is in the form of ammonia. This could indicate to insufficient DO level being maintained in the reactor, a plausible explanation considering the predominant dark color observed in the bio-solids in the reactor during the settling stages. This dark color often serves as an indicator of a predominantly anoxic condition in the reactor. Another plausible explanation could be that we allowed the SND process to extend for far longer than necessary such that the aerobic bacterial population was suffocated in the largely anoxic zones in the reactor and simply ceased to perform effectively anymore. A flaw in our process, in this regard, was our inability to test for viable biomass concentrations in the reactor.Next, we reduced the aeration period to 18 hours, from which we observed a nitrogen removal rate of 13.8%. At the 18-hour aeration cycle, we observed an increase in the residual ammonia-nitrogen concentration to 31.6 mg/L and a decrease in nitrate-nitrogen to 3.64 mg/L.Finally, we achieved 11.7% removal in the 8-hour aeration cycle. However, a much higher percentage of residual nitrogen was in the form of nitrate and nitrite for the 8-hour cycle. The concentration of ammonia for this test was the lowest of the three.The trends in these results are interesting and possibly a bit suspicious. In all cases, the ammonia-nitrogen was in the highest concentration, indicating that anoxic conditions predominated in our tank. However, the nitrogen removal efficiency in the 24-hour and 18-hour tests were high compared to the levels of nitrates in the tank, indicating that denitrification was efficient once nitrogen reached the nitrite or nitrate form. The concentration of nitrates for the 8-hour cycle was very high. This could be an indicator that most of the nitrification is occurring early, but that denitrification does not occur until later. However, the relatively low concentrations of ammonia-nitrogen for this cycle are hard to explain. Ammonia-nitrogen should increase initially, but we expect to see decreasing concentrations of ammonia as nitrogen removal increases. The opposite was observed in our experiment.A possible solution to this problem would have been to run an aeration cycle for 24-hours and to take samples during that same cycle at more frequent intervals. By doing this we would eliminate any variance in the waste feed or bacterial population from one sample to the next, and would be able more accurately show how the nitrogen concentrations in each form change with time. We ran out of Hach cadmium testing materials and were unable to perform this test, but it would be an interesting topic for further investigation.Nutrient Removal ProjectSimultaneous Nitrification and Denitrification ina Sequencing Batch ReactorWill LambertRobert NwaokoroStephen RussoCEE 45312/8/04AbstractNitrogen removal is important part of wastewater treatment, especially in coastalregions where nitrogen loading of oceans and estuaries can cause algal blooms. The mostcommon method of removal uses microbes. Unfortunately, there are several steps toachieve denitrification with an organic nitrogen feed. Many bacteria convert organicnitrogen to ammonia, but only certain anaerobes, namely Nitrobacter and Nitrosomonas,are responsible for the conversion of ammonia to nitrite and nitrate, or nitrification.Furthermore, it is only from the nitrite or nitrate form that anaerobic denitrifying bacteriacan produce nitrogen gas. Therefore, traditional nitrogen removal in waste treatmentplants occurs in first and aerobic stage and then an anaerobic stage. This can either occurin separate tanks or in one tank that is sequenced to go through each state. Recently,further research has been done on simultaneous nitrification and denitrification. It seemsthat at very low levels of dissolved oxygen, anaerobic zones can be produced, allowingboth processes to occur concurrently. The purpose of this research