Abstract This experiment consisted of measuring the turbidities of a variety of samples using the nephelometer .These recorded turbidities were then analyzed and a reasonable explanation for each value is made.
INTRODUCTION Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Turbidity is a measurement of how cloudy water appears. Technically, it is a measure of how much light passes through water, and it is caused by suspended solid particles that scatter light. These particles may be microscopic plankton, stirred up sediment or organic materials, eroded soil, clay, silt, sand, industrial waste, or sewage. Bottom sediment may be stirred up by such actions as waves or currents, bottom-feeding fish, people swimming, or wading, or storm runoff. Clear water may appear cleaner than turbid water, but it is not necessarily healthier. Water may be clear because it has too little dissolved oxygen, too much acidity or too many contaminants to support aquatic life. Water that is turbid from plankton has both the food and oxygen to support fish and plant life. However, high turbidity may be a symptom of other water quality problems.
The method is based upon a comparison of the intensity of light scattered by the sample under defined conditions with the intensity of light scattered by a standard reference suspension. The higher the intensity of scattered light, the higher the turbidity. Readings, in NTU's, are made in a nephelometer designed according tocertain specifications. A primary standard suspension is used to calibrate the instrument. Formazin polymer is used as a primary turbidity suspension for water because it is more reproducible than other types of standards
previously used for turbidity analysis.
EQUIPMENT AND SUPPLIES The turbidimeter shall consist of a nephelometer, with light source for illuminating the sample, and one or more photo-electric detectors with a readout device to indicate the intensity of light scattered at right angles to the path of the incident light. The turbidimeter should be designed so that little stray light reaches the detector in the absence of turbidity and should be free from significant drift after a short warm-up period.
Experimental procedures A. Jackson Turbidimeter 1. Place a clean Jackson turbidimeter tube in the receptacle on the stand. Place a candle in the device and insure that the spring in the candle holder is released and keeping the top of the candle at a distance of 7.6 cm below the bottom of the tube. If the water is relatively clean use the longer tube, otherwise use the shorter tube. 2. Add a small amount of well-mixed sample to the tube and light the candle. Be sure to add a small amount of sample BEFORE lighting the candle to prevent cracking the tube. 3. Add well-mixed sample to the tube until the light field becomes uniform. Note the reading from the side of the calibrated tube.
4. Empty the tube. Extinguish the flame. Mix the sample again, add a few mL to the tube and light the candle. Then add ¾ of the volume of sample added in Step 3. Then add sample slowly until a uniform light field is observed. Record the reading B. Nephelometer 1. Select a standard that compares with the turbidity of the sample. Turn on the unit and select the range corresponding to the standard. Insert the standard and replace the cover. Adjust the calibration knob to provide the correct reading on the meter. Remove the standard. 2. Fill the sample tube about ¾ full of well-mixed sample and wipe the outside of the tube with Kimwipes if any spillage occurred. Insert the tube and replace the cover. If the reading is offscale, switch the range of the meter until the reading is on scale. Record the reading and report it as NTU. 3. If the sample reading is significantly outside of the range in which the meter was calibrated, repeat the exercise calibrating with a standard in the appropriate range.
Results Turbidity: The following data was collected during this experiment: SAMPLE
TURBIDITY(NTU)
Drinking water
1.2
Distilled water
0.8
coffee
78
CaCO3
Error(too high)
Sugar dissolved In water
55(should be between 0-1)
Sand + water
47.3
Soil + water
149
Silt + water
293
DISCUSSION AND CONCLUSION A direct measurement of suspended solids is not usually performed on samples from natural bodies of water or on potable water supplies. The nature of the solids in these waters and the secondary effects they produce are more important than the actual quantity. For such waters a test for turbidity is commonly used.
Sand and water mixture gave less turbidity than that of silt and water which is logical. Silt is a much smaller particle than sand and thus more surface area for pollutants to settle exist leading to higher turbidity. On the other hand, comparing coarse soil and fine sand we see that coarse soil and water had a higher turbidity of 149, this result seems illogical because coarse soil has a larger grain size than the fine sand, yet this result may be due to the fact that coarse particles have more bumps and irregularities resulting in a larger surface area. As for distilled and drinking water, the results obtained are also logical and acceptable. Calcium carbonate gave an error implying that the sample has a very high turbidity that cannot be measured using the Nephelometer .To find the turbidity of this sample we should dilute it by a known ratio, measure the turbidity of the diluted sample and deduce the original’s turbidity.On the other hand, the cold coffee sample gave a turbidity of 78NTU which is larger than that of water . When Coffee cools, its solubility decreases and the coffee precipitates out to become a suspension, and then cause that turbidity we found. From our experiment we conclude that absorption and scattering and thus turbidity are influenced by both size and surface characteristics of the suspended material, and that turbidity is not a direct quantitative measurement of suspended solids .For example a small pebble in a glass of
water would produce virtually no turbidity .If this pebble were crushed into a thousand particles of colloidal size,a measurable turbidity would result even though the mass of solids is still the same.
APPENDIX 1.decribed above 2.Suspended solids absorb light and scatter it leading to a decrease in light intensity and thus the turbidity reading is deacreased.Secondly, Turbidity is not color related, but relates rather to the loss of transparency due to the effect of suspended particulate, colloidal material, or both. A lack of turbidity results in clarity or clearness because it is, in part, the effect of these various suspended materials on light passing through a liquid.The presence of bubbles on the other hand will affect turbidity by scattering light. 3.all three devices rely on the principle of Tyndall or light scattering by colloidal and suspended particles .However these devices differ greatly in their accuracy, where the Jackson turbidity meter is less accurate than the nephelometer because it relies on naked eye sight and no measurable data.
This experiment is prone to many errors of which we list: -Existence of fingerprints and other microorganisms on the external vial walls leading to a fluctuation in the turbidity values. -Air bubbles inside the sample that can be only extracted through de-airing. -The coffee and sugar samples are cold thus solubility is reduced and some particles will settle leading to increased turbidity.
References -Environmental engineering Peavey Row http://www.water-research.net/index.php/stream-water-quality-importance-oftotal-suspended-solids-turbidity
