Estudio de la correlación entre la Dqo de una muestra de agua residual doméstica y su absorbancia en el rango de 250 – 600 nm
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The Chemical Oxygen Demand (COD) determines the amount of oxygen required to oxidize the organic matter contained in a water sample, under specific conditions of oxidizing agent, temperature and reaction time. In order to determine this parameter in a sample of residual water, two methods can be used, one of reflux digestion in the open system and another of digestion in the closed system. However, in both cases, the digestion takes two hours and the measurement, as a whole, at least three hours. This research project seeks to establish a relationship between the COD of a sample of domestic wastewater and its absorbance in the UV / VIS region between 250 and 600 nm. For this, composite samples of wastewater are taken at three different points of the Tunjuelo River, referred to in this study as ‘Makro on Autopista Sur’, ‘Carrera 80 with intersection Río Tunjuelito’ and ‘Río Tunjuelito with intersection Avenida Ciudad de Cali.’ In each of these points the COD was measured by the standard closed system digestion method (SM 5220 CHEMICAL OXYGEN DEMAND) and subsequently the area under the spectral curve, ABC 'in the range 250-600 nm was determined, being, for In all cases, an absolutely linear relationship between these two variables. The spectral measurements were made on a Shimadzu brand spectrophotometer, Model UV 1280, using quartz cells, one centimeter thick. The calibration curves were constructed on dilutions of the original sample, by factors of 10 and, measuring, for each of those diluted samples, the area under the spectral curve in the range 250 to 600 nm. With these data, graphs of ABC ‘vs’ COD were made, obtaining, in most of the trials, linear correlation coefficients close to one.inally, with these curves, prediction exercises were performed, whose deviations were less than 15%. However, it was also found that the predictions fit better when the curves are constructed by concentration ranges. Similarly to what happens with the mass of a substance - there is no balance capable of measuring accurately, from 1.0 milligram to one ton - nor in this case was a calibration curve able to accurately predict the COD of a sample of domestic wastewater, for any concentration range.