EXPERIMENT 2: WATER ANALYSIS COLOUR MEASUREMENT ON SUSPENDED SOLID DETERMINATION 1. Objective This experiment described the method used to measure the presence of suspended solids in water can impair the color measurement. 2. Introduction A Lovibond comparator is used to place the color disc. It has two compartments to hold a sample and distilled water. The samples were places into nessleriser tubes. It is a comparison method without making standard solutions. One of drawbacks of this method is its subjectively. In Spectrophotometer method, an optimum wavelength was chosen. This optimum wavelength ranges between 455 to 465 nm. A series of standard solutions was made and read at a specified wavelength. The respond were then plotted against platinum cobalt solution to produce a calibration graph. The respond from a sample is then determined based on that calibration curve. Most modern equipment incorporated the calibration graph into their equipment. It just needed to calibrate the zero value with distilled water. 3. Theory Color is a very subjective measurement of a water sample. Ones blue color could be a green color to another eye. But in order to be a mentioned standard in drinking water, it has to be measurable or quantify. The earliest method of quantifying color is studied by Hazen. He made a series of standard color solution using a platinum cobalt and gold. The color yield by 1 mg/l of platinum cobalt solution is known as 1 color unit or Hazen unit. The presence of suspended solids can impair our color measurement. The color of water given by unfiltered sample is known as apparent color, while the color given by a filtered sample is referred as true color. Indirectly it is the dissolved color of the sample. The earliest approach by Hazen was by comparing the sample with a series of standard solution. The one that matches the closest to the sample will be the color of that sample. It is tedious and wasteful. Based on the same concept, a color disc is used instead.
4. Apparatus The lists of apparatus are: Nessleriser tubes Color discs Sample vials Spectrophotometer Volumetric flasks, pipettes
5. Procedures A few water samples are given to be analyzed. If the sample out of the color range, then choose a higher color disc or dilute the sample accordingly. Compare the reading obtained from comparator method with spectrophotometer method. a) Firstly, sample is poured into nessleriser tube to the mark and the tube is covered with the lid. Any built up of air bubble in the tube is avoided. The side of the tube is dried with tissue paper. b) Then, the tube is placed in the comparator and the color disc is rotated till the color almost matches the sample. The reading is recorded. c) After that, an aliquot of sample is transferred into a sample vial. d) Next, a spectrophotometer is switched on and color measurement is chosen. The instructed steps are followed. e) Then, the distilled water is placed in and the reading set to zero, once it is ready, the sample cell is placed in and read. f) The reading is recorded.
6. Data recordings Sample A B Lovibond reading 2.5 2.5 Spectrophotometer reading 0.315 0.325
7. Discussion From the data has been recorded, the Lovibond reading and Spectrophotometer reading for sample A were recorded as 2.5 and 0.315 respectively. Well, for sample B the Lovibond reading and Spectrophotometer reading were 2.5 and 0.325. Obviously, there is a discrepancies result in sample A compare to sample B. There are few factors interfere with the readings, the sample vial and turbidity of the sample. Even with a true solution, the sample vial will affect the reading due to its materials. Besides, as discussed before, color was very subjective measurement of water sample. The result could be different to another eye by using a Lovibond comparator. Even though recently with the advancement in optical technology, a better technology is recommended, spectrophotometer. But some minor problems still cannot be avoided. Especially when using spectrophotometer, when the optimum wavelength is applied, the bult of spectrophotometer will affect the color of test sample. That is why a huge discrepancy between both method. In order to reduce it, the best solution is tried to apply a layer of coat on container. 8. Conclusion Comparison between sample A and sample B, obviously sample B presence more suspended solids compare to sample A. But, both results are less sensible due to data obtained. The ideal material for color measurement is quartzite. When the color is over range, a dilution is required. 9. Reference Dr. Chua Kok Hua, 2007. Water and Wastewater Laboratory Practices. College pf Engineering, University Tenaga National. P. Aarne Vesilind, Susan M.Morgan, 2004. Introduction to Environmental Engineering. Second Edition, Thompson Brooks/Cole.
Figure 1: Sample A and sample B is prepared to be test.
Figure 2: Pour the sample into tube and close with the lid to avoid air bubble
Figure 3: Insert color disc to comparator and rotate it till match the color sample.
Figure 4: Lovibond Comparator and color disc
Figure 5: Spectrophotometer comparator
Figure 6: A sample cell in tube is ready to put in spectrophotometer.