Flow Measurements in Sanitary Sewers by Dye
Contents
1. In this mode sewage is continuously pumped through a flow cell installed in the fluorometer via a submersible pump Advantages 1 No cuvette error Standards blanks and samples are all measured with the same cuvette 2 Temperature correction can be made automatically by the Model 10 AU if the optional temperature compensation feature is purchased Anomalies such as rapidly changing flows become obvious If the data are collected with a computer or the optional internal data logger they may be exported to a spreadsheet program This permits the averaging of very large numbers of points for even better accuracy Disadvantages 1 Longer setup time 2 More complicated equipment A three way valve should be used such that the standard and or blank may be poured or siphoned through without disconnection 3 Power A submersible pump that will pump the sewage to the surface from a manhole is necessary This generally implies the availability of 115 VAC 4 Standard preparation requires more time as one ideally should have several gallons usually achieved by multiple use of a 2 liter volumetric flask the largest generally available 5 Not suitable if turbidity is unusually high Note The use of a 10 mm diameter flow cell permits the handling of situations comparable to those using the 13 mm x 100 mm cuvettes The 25 mm Continuous Flow Cuvette System should be used only with quite clean water www turnerdesigns com 9982. Since fluorescence is normally proportional to concentration a more practical form of this equation is 2 Q qxRst D r Where Rst is the reading obtained on your standard r is the reading obtained on your sample D _ is the dilution ratio used to prepare the standard The following discussion of Flow Rate Calculation will be based on equation 2 Sample Readings Sample readings are all net readings If sewage blank was set to zero then the readings obtained for samples are the net readings If the distilled water blank was set to zero subtract the sewage blank reading from all readings to obtain the actual net reading Injection Rate The Injection Rate is normally determined by finding the time it takes to fill a volumetric flask See DYE INJECTION Calibrating the Injector Since volumetric flasks are calibrated in milliliters and elapsed time is most easily measured in seconds we have a conversion problem Two handy numbers are milliliters x 0002642 U S gallons milliliters x 00003532 Cubic feet As an example let s presume that when you tested your dye injector you found that it took 158 seconds to fill a 100 ml volumetric flask This means that the flow rate was 100 divided by 158 or 0 631 milliliters per second or 37 85 milliliters per minute If you wish your final answer to be in mgd then the rate of dye introduced must also be in mgd To convert milliliters per minute to gallons per minute multiply 37 85 b
3. Seal it and if you can t find someone with a drum shaker you must roll the drum repeatedly around on the floor occasionally setting the drum on end to change the flow pattern You can establish how much mixing is required by taking samples from several levels diluting them and reading them in the fluorometer Injection Apparatus The most convenient device is a constant displacement pump A commercially available pump which appears to be nearly ideal for field work is the model RP BG75 2CSY pump made by Fluid Metering Inc and available through Turner Designs This unit features continuously variable flow rate and is self priming Maximum flow rate is 48 ml min 0 012 gallons per minute 2 x 10 mgd Current drain is between 0 06 and 0 1 amperes from a twelve volt battery A very light duty storage battery or a cigarette lighter adaptor for your vehicle may be used Eight size D alkaline flashlight batteries 10 ampere hour 1 5 volts per cell should run the pump for about 100 hours The pump which we have used for field demonstration has shown an excellent reproducibility of 0 1 at maximum rate over a period of 5 years CAUTION These pumps are not explosion proof The dangers of sewer gas explosion must be taken into account A modified chlorine feeder available from Aerofeed Inc P O Box 3203 Chalfont PA 18914 may also be used It is pressurized in the field with a foot or tire pump The flow rate is adjustable from 60
4. Standard Record its reading As in the case of the blank if you wish you may read and average three or more cuvettes of your standard 4 Read and record all samples If any sample is unduly high OVER on the Model 10 AU Fluorometer see High Concentration Measurements following Reading High Concentrations For concentrations between 0 5 and 2 ppm the samples may be read from a calibration curve This is not usually recommended as the curve must be prepared by making at least five dilutions preferably seven or more 0 5 0 75 1 0 1 25 1 5 1 75 and 2 0 ppm For this you need to determine what dilution of your injected dye will give you about 2 ppm and prepare the necessary dilutions to define the curve Under no circumstances should you attempt to carry the curve beyond 2 ppm The curve will be so flat that accuracy will suffer Unless there are a very large number of samples falling slightly above the linear range the fastest and most accurate way to handle high concentration samples is to make a dilution There is no theoretical upper limit to the concentration which can be handled by dilution In fact in unusual situations very high color for example you may wish to deliberately run the concentration very high so that the interference from the color may be diluted out In one instance the author ran the concentration to about 100 ppm and made 1000 fold dilutions The sewer line was opaque with riboflavin and the 1000
5. including the blank sewage till you have calculated all flows and decided the results are reasonable and consistent The ability to recheck your dilutions may well save you from re running the study www turnerdesigns com 998 5107 Revision A Page 11 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution t DESIGNS Reliable Instruments for an Unreliable World PROOF OF PERFORMANCE Significance of Errors It is important to keep in mind the accuracy required If your problem is localizing massive groundwater infiltration then 5 is probably adequate If on the other hand you are calibrating a flowmeter used to decide the ratio of payments between a group of municipalities supporting a single sewage plant then you might require 1 Errors that may result may be estimated as you go through this section on proof of performance So keep your objective in mind It may well reduce test costs significantly Sampling Errors These errors and the steps to take to correct them are discussed in SAMPLING When Should Samples Be Taken and SAMPLING Is Mixing Adequate In addition loss of dye by adsorption on the walls of the flow channel is accounted for when you carry out the tests outlined under SAMPLING When Should Samples Be Taken Such adsorption is limited in its capacity and is reversible It will show up as a slower than normal build up of dye concentration after injection has started and a slower tha
6. injected This was collected when the dye injector was calibrated This dye sample will be used to prepare standards 2 A large sample of sewage 1 gallon to which dye has not been added This will be used to determine BLANK see DEFINITIONS above It will also be used to dilute the dye sample mentioned in 1 above when preparing the calibration standards Samples of sewage taken downstream of the injection point One ounce will be adequate You may wish to take additional samples upstream of the dye injection point to check for variability in the BLANK See 2 above One ounce will be adequate When Should Samples Be Taken If you were to plot dye concentration as a function of time from the start of dye injection you would find 1 A delay time This delay time is almost invariably longer than you would expect from an estimate of velocity It is not unusual to find a delay time of 15 20 minutes for dye to travel 500 feet 2 A period during which the dye concentration rises If the flow is highly turbulent this period will be short If flow is smooth and particularly if there is a reservoir of any kind between the dye injection point and the sampling point this period may be quite long 3 A period of constant dye concentration plateau assuming that flow rate is constant 4 A fall off in concentration of about the same duration as the rise time after the injection is discontinued The time periods involved are a function of trav
7. moving the injection site as well as the sample site 3 Convenience should be considered particularly at the sampling point Certainly the first time around you will wish to take a fair number of samples www turnerdesigns com 998 5107 Revision A Page 5 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution DESIGNS Reliable Instruments for an Unreliable World Calibrating the Injector The accuracy of your final result depends directly on the accuracy of your knowledge of the rate of flow of the dye You will need a stopwatch and a clean dry volumetric flask whose capacity will depend on the type of injection system you are using See PREPARATION OF STANDARDS for information on volumetric flasks When dye flow has stabilized measure the time to fill the volumetric flask then calculate the flow rate See FLOW RATE CALCULATIONS We strongly recommend a flow rate check both before and after a run When using the Fluid Metering Inc pumps a volumetric flask should be chosen that takes at least four minutes to fill This is because the pump makes only 75 strokes per minute It is also the reason that we do not recommend the RP BG 25 series pumps They make only 25 strokes per minute and it takes too long to accurately calibrate them Save the dye collected during calibration of the dye injector See SAMPLING SAMPLING What Samples are Needed Collect the following 1 A sample of the dye being
8. rope and you can close the manhole for the duration of the test 3 Do not attempt to use a long tube at low flow rates from street level The dye flow will surge and the erratic suction on the pump exhaust line will cause erratic results 4 In fact long tubes are to be discouraged from another standpoint Flexible vinyl tubing e g Tygon is convenient but it does adsorb dye reversibly It does have a limited capacity for adsorbing dye and at the concentrations injected equilibrium is rapidly achieved A few feet is no problem A hundred feet is unacceptable Polyethylene polypropylene and unplasticized vinyl tubing do not adsorb but are fairly rigid 5 If you must inject from street level use an appropriate length of PVC pipe with a tee on the top Insert the tube from your injection pump well down the pipe or allow the stream from your dye injector to fall in the top clearly missing the wall until well down Run water from a hose through the tee This is a particularly valuable technique for injecting dye through a pump directly into the bell housing of a pump or for other situations where the desired point of injection is not directly below an opening The PVC pipe is flexible and easily maneuvered The top is easily secured to a ladder laid across the manhole etc 6 If the amount of water added in injecting the dye is substantial compared to the flow being measured consider correcting for the added water In infiltration studi
9. the sewage taken just prior to the start of dye injection For repetitive work i e monthly calibration of a large flowmeter only one standard and one blank will be required When you are just starting up more standards will be required To save repetition the preparation of all standards that you might conceivably need is discussed As you become familiar with the technique you can judge what simplifications can be made Equipment Needed The following is a list of equipment we have found useful If you have a chemist available he or she may well suggest alternatives immediately available to you The equipment which we use was purchased from Scientific Products Equivalent items are available from all major laboratory supply houses 1 ea 1000 ml volumetric flask 6 ea 100 ml volumetric flasks www turnerdesigns com 998 5107 Revision A Page 9 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution DESIGNS Reliable Instruments for an Unreliable World 2ea Volumetric flasks of adequate capacity to calibrate your injector see DYE INJECTION Calibrating the injector 1 case 500 scintillation vials with Polyseal caps see SAMPLE AND STANDARD STORAGE 1 ea 1000 Lil 1 ml Eppendorf pipettor or equivalent and disposable tips They are relatively expensive but are worth it in ease and rapidity of use Under field conditions they frequently prove to be more accurate than conventional pipe
10. to 250 ml min 016 to 066 gallons per minute It features a self contained reservoir with a 9 liter 2 4 gallons capacity The flow is controlled by a special pressure regulator which maintains a constant pressure difference of 5 pounds per square inch cross a metering valve NOTE We know these devices have been used successfully but have not tested them in our laboratory A device frequently mentioned in the literature the Mariotte Vessel is described in a companion monograph entitled A Practical Guide to Flow Measurement While much used in stream gaging it is rarely used in sewer studies Its major advantage the ability to deliver large injection rate without power is not important in sewers There are also numerous precautions and disadvantages see A Practical Guide to Flow Measurement not the least of which is that one small enough to be handled easily by one person is tricky to build and subject to plugging www turnerdesigns com 998 5107 Revision A Page 4 of 17 TURNER TOOGE E DESIGNS Reliable Instruments for an Unreliable World Flow Measurements in Sanitary Sewers by Dye Dilution Things We ve Learned the Hard Way 1 Dye should not be allowed to free fall for more than about one or two feet or splashing and erratic results may occur 2 If you are using a small injection system place reservoir pump and battery in a box with a yoke on it and suspend it by rope from street level Tie a knot in the
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12. 8 5107 Revision A Page 8 of 17 TURNER TOOGE t DESIGNS Reliable Instruments for an Unreliable World Flow Measurements in Sanitary Sewers by Dye Dilution Clear material such as Saran widely used in the kitchen for food storage should never be used These materials adsorb large amounts of the dye 6 A pair of scissors 7 A piece of rod about 3 32 in diameter 3 long A 3 32 Allen wrench with handle is excellent You will need to experiment a little 1 Working from the large end force a tightly wadded piece of glass wool into the stem of the funnel using the 3 32 rod The piece should be large enough so that some forcing is required to end up with a plug of packed fiber in the stem about 3 8 to 1 2 long One eighth inch or more of looser fiber should extend above the stem 2 Place a 13mm x 100 mm cuvette in the test tube rack Place the funnel packed with glass fiber in the cuvette 3 Pour about one ounce of water into the funnel and time how long it takes to fill the cuvette to the label It should take between two and five minutes Adjust your packing procedure until the filtration rate is correct Be prepared in advance Prepare as many filters as needed before handling dye Have a similar number of clean dry 13 mm x 100 mm cuvettes on hand labeled to match your sampling schedule During the study always handle the funnels by the outside near but not at the top Similarly do not touch the rims of the cu
13. IONS will not affect accuracy It should be low enough so that readings are linearly related to dye concentration With the 13 mm x 100 mm Cuvette Holder recommended this final dye concentration should fall between 0 02 and 0 5 parts per million 20 500 ppb for most work In extremely large systems or where multiple measurements are to be made dye costs may make it worthwhile to explore blank variability and aim for a lower final dye concentration Take perhaps 10 blank samples over a one hour period and determine the blank variability If you need only 5 accuracy and dye quantity is a factor then aim for a concentration 20 times the variability of the blank In situations where injection will be at one point and sampling at multiple points as in infiltration studies the flow change may be such that you must exceed 0 5 ppm at the early sample points Up to 4 ppm can be measured with a multi point calibration curve See MEASUREMENT High Concentration Measurements Any concentration can be measured by dilution Simply make a 10 fold or 100 fold dilution and multiply the answer by 10 or 100 You will probably dilute with distilled water and must remember that your blank and standards should be diluted with distilled water in the same ratio So decide on your desired final dye concentration and estimate the flow to be measured Units of course do not matter if they are consistent Call your estimated flow Q The flow rate of your inj
14. TURNER TOOGE E DESIGNS Reliable Instruments for an Unreliable World Flow Measurements in Sanitary Sewers by Dye Dilution FOREWORD Flow in sanitary sewers may be measured to an accuracy of about 1 using fluorescent dye dilution techniques It is the most cost effective method for Quantitating and localizing infiltration Calibrating any type of existing flow meter This monograph based on extensive experience in the United States and in Canada is basically a how to do it manual It complements the more theoretical monograph entitled A PRACTICAL GUIDE TO FLOW MEASUREMENT available at no cost from TURNER DESIGNS It works in surcharged manholes There is no need to crawl a manhole Because this monograph will anticipate unusual situations as well as discuss normal situations the procedure might at first glance seem complicated In practice however in most instances it is straightforward Since there is no need to crawl a manhole the procedure can be done by one person An experienced person can carry out the entire procedure from preparation of dye to calculation of flow in one manhole in about 25 minutes Flows at subsequent manholes downstream simply involve popping the manhole cover dropping a can on a string to collect a sample and a few minutes for the reading of the sample and the calculation Samples may be measured on the spot or if preferred may be taken to the office or a lab and measured at you
15. U 005 CE Field Fluorometer Sample system 25 mm x 13 mm Discrete Sample Holder Set for grab samples OR the 10 mm continuous flow cuvette system for flow through measurements Filters 10 041 Rhodamine Optical Kit CASE select one 10 AU 002 Indoor Case 10 AU 022 Watertight Case CUVETTES 10 031 the 13 mm x 100 mm selected cuvettes for grab samples Other equipment needs are discussed in the sections entitled DYE INJECTION FILTRATION and PREPARATION OF STANDARDS DYE INJECTION Successful dye injection involves several factors Injection must be at a constant concentration at a constant precisely known rate and without surging or splashing Dye Source and Characteristics Rhodamine WT may be ordered from Crompton amp Knowles Corp P O Box 33157 Charlotte NC 28233 3157 Telephone 1 800 323 4383 Turner Designs also supplies the dye in manageable quantities Part Number 10 108 Contact Turner Designs for a more complete list of dye suppliers www turnerdesigns com 998 5107 Revision A Page 2 of 17 TURNER TOOGE t DESIGNS Reliable Instruments for an Unreliable World Flow Measurements in Sanitary Sewers by Dye Dilution Rhodamine WT is supplied as a clear 20 aqueous solution It is very dark red in color somewhat viscous and has a specific gravity of 1 2 The concentrated dye is extremely irritating to the eyes It was specifically developed to have poor dye properties in the conventional sense Thi
16. aining your sewage Standard Record the reading 4 Insert the cuvette containing your sewage Blank Record the reading 5 Subtract reading 4 from reading 3 The net reading obtained in step 5 is the reading due to the dye present in the sewage Divide the net reading from step 5 by the reading from step 2 to get the Recovery Ratio www turnerdesigns com 998 5107 Revision A Page 14 of 17 TURNER TOOGE t DESIGNS Reliable Instruments for an Unreliable World Flow Measurements in Sanitary Sewers by Dye Dilution Reading Samples 1 Remember the only thing that you need is the ratio of Standard to sample 2 Insert the cuvette containing your Blank sewage Record the reading If you wish you may set the sewage Blank to zero However it is useful to know how large the blank is If it is small compared to the standard and samples then you are more confident of the relative accuracy of the test If a small blank varies by a few percent it is negligible If a large one varies the same percentage the error in the answer will be proportionately larger Therefore we recomment that you leave the distilled water set to zero This way you definitely have a record of the magnitude of the blank repeats will always have positive values and you may average three or more cuvettes of your blank for greater accuracy You will always work with the net reading sample or standard minus the blank 3 Insert the cuvette containing your
17. culate material is indicated Since dye is truly removed from the system accurate measurements are not possible under such conditions 2 Dye not adsorbed on particulate materials but filtered sewage appears colored Dissolved colored materials can mask fluorescence just as particulate material can causing low Recovery Ratios To check for this dilute the sewage used for making the Standard until an acceptable Recovery Ratio is obtained Scale up the amount of dye injected by this factor Dilute all samples and blanks and sewage used for making the Standard by this factor with distilled water High precision flow measurements may now be made at the cost of one extra dilution per sample 3 Chemical degradation The dye is slowly destroyed by very high concentrations of residual chlorine much higher than normally encountered in sewage Fresh chlorine however destroys the dye rapidly If the dye goes past a chlorinator the chlorinator must be turned off for the duration of the test Presumably other strong oxidizing or reducing agents could present a problem A series of Recovery Ratios is called for one done as quickly as possible and others at intervals of several hours If degradation is slow satisfactory results may be obtained by making up your Standard at the same time that injection is going on and measuring your samples as quickly as possible Keep the Standard and all samples at the same temperature until measur
18. dye being injected does not need to be accurate As an example the scintillation vials which we recommend for sample storage See Sample and Standard Storage below contain about 2 3 ounce when filled to the bottom of the shoulder This translates to about 0 005 gallons If you have estimated flow to be one mgd and hence need a 0 5 dye concentration it is easy to prepare Fill a scintillation vial to the bottom of the shoulder with concentrated dye Pour this into a plastic one gallon bottle Mix and fill with water to obtain the desired 0 5 dye concentration With the pump recommended the gallon will last about 1 3 hours Mixing the Dye In mixing the dye there are several things to keep in mind 1 If itis not uniformly mixed the results will be inaccurate A completely full container is impossible to mix Leave at least 20 or more air space A container you can pick up and shake is highly recommended Po nN The dye acts like a detergent it foams Never try to add more water or dye after mixing or you will have red foam running down the sides 5 If the container can be picked up mix by swirling the solution inside using a rotary motion then turning it upside down Swirl again and right it Do this 10 times For large drums take a smaller container and use part of the water to pre dilute the dye 20 50 fold Put the rest of the water required in the drum After the foam settles in the pre diluted dye pour it into the drum
19. east three at 1 minute intervals It is not at all unusual to accidentally contaminate a sample If you have only two samples and they disagree you won t know which is right If you have three or more samples and one is wild you can discard it with an easy mind For very accurate calibration of a flow meter you may wish to take 10 samples and average the results SAMPLE AND STANDARD STORAGE Your samples and standards are very stable and may be kept for months for recheck if desired For storage longer than one day they should be protected from strong sunlight The storage container material is important A tin can on a rope is fine for collecting but the samples should not be stored in metal Also some types of ordinary glass jars degrade the sample This degradation may be a pH effect due to traces of lime left on the surface of the glass Rubber and some plastic liners will absorb the dye Potential containers should be tested by filling several with a solution of dye about 0 1 0 3 ppm If the samples are likely to be jostled in transport turn the containers upside down so the lid contact and seal will be tested A few hours later compare dye concentration with the original material stored in your volumetric flask Materials known to be safe are 1 Borosilicate glass such as Pyrex or Kimax Polyethylene polypropylene and polystyrene Polyseal screw caps available for narrow mouth bottles Note If you have trouble with lid
20. ector is q in the same units Assuming you desire a final dye concentration of 0 1 ppm the injected dye concentration should be 0 1 Q q in ppm For example if your estimated flow rate Q is 1000 gpm and your injector delivers 01 gpm q your initial dye concentration should be about 10 000 ppm or 1 Add 1 part of dye to 100 parts of water Two simple guidelines 1 We recommend the use of an RB BG75 2CSY pump for dye injection see below When set for maximum flow it delivers 48 ml min which translates into about 2 x 10 million gallons per day mgd With this injection rate we recommend that you estimate the flow in mgd then multiply by 0 005 to get the desired initial dye concentration For 0 1 mgd use 0 05 dye for 1 mgd use 0 5 dye for 10 mgd use 5 dye etc This will yield a final concentration of about 0 1 ppm which is normally a good concentration to shoot for If your actual flow is one fifth your estimate dye concentration will still be in the linear range If flow is five times higher www turnerdesigns com 998 5107 Revision A Page 3 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution E DESIGNS Reliable Instruments for an Unreliable World than estimated the concentration will still be about 20 times the background normally encountered This is conservatively high as a 20 change in background during the run would result in only a 1 error 2 The concentration of the
21. ed without actually testing the variability in light loss In a crucial meter calibration one might collect several blank samples prepare standards in them and compare readings or simply remove all solids In routine measurements in sewers we normally recommend that you accept up to a 10 loss of light A 10 relative change in turbidity is only a 1 error The quick filtration techniques described below typically reduce turbidity effects to about 2 Overnight settling of sewage usually reduces the effect to near zero Use of Existing Filtration Equipment If measurements are to be made in a laboratory equipped for filtration of samples in reasonable volume then filter But there are several things to avoid 1 Common filter paper should be avoided Glass fiber filter discs or filters such as the Millipore type are O K 2 Cross contamination between one sample and the next must be avoided Rinsing with clear water will not solve the problem since residual clear water will dilute your sample and cause errors Wash down all the area of the filtration apparatus with a small amount of your sample Filter it Swirl the contents of the vessel which receives the filtered sewage Discard Then filter and save for measurement In extreme cases you may wish to wash down and discard two or three times before saving a sample for measurement 3 Cross contamination is easy to check Wash down with water Filter some sewage containing dye a
22. el time between injection and sample sites In a reach of 100 yards in a fast moving stream a 15 minute injection might show a rise time of 1 2 minutes a plateau of 11 12 minutes anda fall off time of 1 2 minutes A mile downstream there might be no plateau at all without longer injection A major advantage of the Model 10 AU Fluorometer is that you can take it into the field and power it from your car battery Cigarette adapters available at any auto parts store will give you instant power By using the fluorometer in the field you can be sure of results Take samples at regular intervals typically one every two minutes and measure them on site until readings stabilize These readings may not be used for final flow measurements but they will enable you to know when to take the sample for flow calculations When the readings are stable you may take the one ounce samples required for final flow determination www turnerdesigns com 998 5107 Revision A Page 6 of 17 TURNER TOOGE t DESIGNS Reliable Instruments for an Unreliable World Flow Measurements in Sanitary Sewers by Dye Dilution Is Mixing Adequate When readings become constant as a function of time as described immediately above take samples across the stream flow If these samples read the same mixing is adequate How Many Samples are Needed Theoretically only one sample is needed taken any time during the plateau period It is good insurance to take at l
23. ements Standards Required When making routine measurements only one standard is required This is a precisely known dilution of the injected dye in raw freshly stirred or mixed sewage The standard must be treated in the same manner as your samples i e allow it to settle or filter it For the first measurement in a new system you will also need a RECOVERY STANDARD This is the same precise dilution made above but with distilled water Actually this recovery standard is very little additional trouble to prepare Until considerable experience is gained it is good practice to prepare it routinely Preparation of Standards Referring to the section on DYE INJECTION Dye Concentration an example was given where a 1 solution was injected with the intent of obtaining a concentration of 0 1 ppm in the sewer Let s continue with this example While there is no theoretical requirement that the standard be 0 1 ppm it can be anywhere from 0 01 0 5 ppm errors are reduced if the standard is near the sample concentration To prepare 0 1 ppm standard we need to dilute a 1 solution 10 000 ppm to 0 1 ppm a 100 000 fold dilution factor This will be done in two steps one dilution of 100 fold and one of 1000 fold Since sewage may contain large particles capable of plugging the tip of the pipettor it is customary to make only the last dilution with sewage all others are with distilled water Since the last dilution should be as near pure fr
24. ements can be made since chemical degradation is sharply temperature sensitive Help From the Manufacturer If you feel that you have a special problem call our Technical Service Department MEASUREMENT Your Model 10 AU Fluorometer should be equipped with the 13 mm x 100 mm cuvette holder and the appropriate filters and lamp from the 10 041 or 10 041R Rhodamine Optical Kit Refer to the Model 10 AU Fluorometer User s Manual for selection and installation instructions The following information describes in general what needs to be done to measure samples Step by step instructions using the Model 10 AU Fluorometer are set forth in A Procedure for the Turner Designs Model 10 AU Digital Fluorometer Flow Measurements in Sanitary Sewers by Dye Dilution Detailed operating instructions for the fluorometer can also be found in the user s manual Sample Handling For precise measurements samples and standards must be at the same temperature since the fluorescence of rhodamine WT has a temperature coefficient of 2 6 per degree centigrade Equipment required is described under FILTRATION A Quick Field Filtration Technique The points that should be remembered are 1 All samples standards and blanks should be poured into clean dry 13 mm x 100 mm cuvettes If you have used the Quick Field Filtration Technique they will already be in such cuvettes www turnerdesigns com 998 5107 Revision A Page 13 of 17 TURNER TOOGE Fl
25. es it will normally be a constant increase in baseline and therefore can be ignored In calibrating a flow meter the added flow should be subtracted from the measured flow for comparison with an upstream flow meter IF the flow meter is downstream there will be no correction as the flow meter is reading the total flow Where Should the Dye be Injected The dye injection and dye sampling points must be considered together The important considerations are 1 The dye must be injected sufficiently far from the sampling point so that it is completely mixed with the sewage before samples are taken This may easily be checked See SAMPLING Is Mixing Adequate The more turbulent the flow the better A pass through a lift pump virtually assures mixing Even under relatively smooth flow conditions expect good mixing 100 to 200 pipe diameters down stream Avoid situations where there is a reservoir between the injection and sampling points It will increase the time required to make a test 2 If flow increases downstream dye dilution techniques measure the total flow at the point where the sample is taken If there is infiltration or a branch entering between the injection and sampling point you will be measuring the total flow at the point where the samples are taken Exfiltration is a special situation Assuming complete mixing prior to loss of flow the flow measured is that prior to the diversion To quantitate such situations requires
26. es prior to the start of measurements Samples Required Experience may allow you to reduce the number of standards but for initial studies you should have 1 Two cuvettes filled with Standard See Preparation of Standards 2 Two cuvettes filled Recovery Standard 3 One cuvette filled with Blank If you are studying Blank variability you may have a number of cuvettes filled with Blanks See DYE INJECTION Dye Concentration 4 One cuvette filled with distilled water 5 Your various samples each in its own cuvette Recovery Ratio Recovery Ratio Tests are important in predicting the precision of your flow measurements and guiding you in improving this precision See PROOF OF PERFORMANCE Recovery Ratio Test Effect of pH Unusual Situations and Help from the Factory 1 Insert the cuvette containing distilled water outside of the cuvette MUST BE dry and suppress the reading to zero blanking procedure in the Calibration section of the user s manual 2 Insert the cuvette containing your Recovery Standard Record the reading on the digital display Note The number you are reading is relative concentration Do not fall into the trap of believing that this is the exact concentration You set up the instrument with a standard of possibly questionable accuracy and definitely at a different temperature You do not need to know the actual concentrations of your samples only the relative concentrations 3 Insert the cuvette cont
27. eshly stirred or mixed sewage as possible it will always be 100 fold or greater As much as 1 clean water present will not cause a significant error In this case it is immaterial whether the 100 fold or the 1000 fold dilution is prepared first though doing the 100 fold first is technically the more correct If you have an adjustable pipettor and desire to make dilutions which are not a factor of 10 keep it simple If for example you would ideally like 38 000 1 make a 40 000 1 dilution One dilution of 0 25 ml 250 LI to 100 and one of 1 ml to 100 gets you 40 000 The nicety of adjusting the standard concentration to be near that of the sample was much more important with meter fluorometers than with digital With the digital fluorometer it is not normally of any particular advantage If you are doing meter calibration it is desirable to avoid the otherwise negligible error of the fluorometer changing from the high to low range or vice versa We cannot emphasize enough the necessity for proper mixing techniques Even when dilutions are accurate if you draw your sample from an inadequately mixed flask your results are invalid Preparation of Recovery Standard Repeat your last dilution with distilled water instead of sewage Insurance Immediately place at least 20 ml about 2 3 fluid ounce of your injected dye and of all dilutions in clean dry marked sample bottles Save these and the remainder of all sewage samples
28. fold dilution allowed measurement to be made with good accuracy It is best to stick to multiples of 10 Prepare a suitable over range standard If your normal dilution factor for the standard was one million make one of 100 000 whatever is needed to give you a standard which when diluted to the same extent as your samples will yield a standard of the optimum concentration about 100 ppb Dilute your samples the new standard and your blank with distilled water If you are running all samples high because of high turbidity or color then prepare a recovery standard in the same manner In the equation for calculating flow D the dilution of the standard is the amount of dilution of the standard above that of the samples Thus if your standard is diluted 10 000 fold then standard blank and samples are diluted another 100 fold this 100 fold should not be counted The purpose of the D is to correct for any dilutions made of the injected solution that are NOT made in the samples FLOW RATE CALCULATION The mathematical equation normally used to calculate flow is 1 Q qClc Where Q isthe flow being measured q is the dye injection rate C is the concentration of the injected dye c is the concentration of dye measured downstream of injection www turnerdesigns com 998 5107 Revision A Page 15 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution E DESIGNS Reliable Instruments for an Unreliable World
29. he pipettor Check that there is no air bubble at the end of the tip apoy Tilt the volumetric flask and insert the pipettor such that the tip is well below any ground portion and is touching the side 6 Gently depress the activating button past the first stop to the second This dispenses the liquid and blows out the last droplet 7 Remove and dispose of the tip by depressing the button to the final eject position Volumetric Flask Fill the flask to the mark with water or raw sewage containing no dye depending on the step in the dilution procedure and type of standard being prepared Use a dropper or clean pipette to add the last bit If you overfill slightly don t worry about it In a typical volumetric flask missing the mark by half an inch leads to an error of www turnerdesigns com 998 5107 Revision A Page 10 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution t DESIGNS Reliable Instruments for an Unreliable World only about 0 7 If you overfill a lot start all over For highest accuracy the bottom of the meniscus should touch the top of the mark Cap the flask and holding the cap tightly in place invert Swirl the flask and right it until the air bubble reaches the top Repeat a total of 10 times You can easily check the precision of your dilution technique Just make several identical dilutions and check the repeatability using the Fluorometer See MEASUREMENT Normal Measur
30. is called for For details refer to the section entitled FILTRATION Effect of pH Dye fluorescence drops off reversibly if your sewage is more acid than pH 4 or more alkaline than pH 10 5 Recovery Ratio will be very low at extreme pH values The pH is easily checked with a pH meter or indicator paper If the pH is low add a pinch of baking soda The amount is not critical since it cannot take the pH too high If the pH is high some dilute acid will have to be added till the pH is correct It is probable not verified that monosodium phosphate could be used to correct high pH in the same way that the baking soda is used for low pH Repeat the Recovery Ratio with pre treated sewage If recoveries are good flow measurements of high accuracy may be made However the pH of all samples blanks and sewage used for making the standards must be adjusted www turnerdesigns com 998 5107 Revision A Page 12 of 17 TURNER TOOGE DESIGNS Reliable Instruments for an Unreliable World Flow Measurements in Sanitary Sewers by Dye Dilution Unusual Standards 1 Dye adsorption on particulate material If there is a large amount of partially burned coal or other similar materials present they will adsorb dye and cause low Recovery Ratios To check for this problem filter the sewage before the dye is added in the process of making up your Standard Recheck the Recovery Ratio If it is significantly better adsorption on parti
31. ke samples downstream of the point where the dye is added This will be discussed under SAMPLING e oO DN On rare occasions a very quick filtration of the sample will be required Elapsed time will be about five minutes and many samples may be filtered at the same time The filtration equipment is so inexpensive that it is usually discarded This will be discussed under FILTRATION 5 Measure the dilution ratio of the dye in your samples This will be discussed under PREPARATION OF STANDARDS and MEASUREMENT Calculate the flow This will be discussed under FLOW RATE CALCULATION 7 Sewage is not all the same so you should run a recovery ratio occasionally This will tell you whether sample processing is really necessary and how effective the processing is This is discussed under PROOF OF PERFORMANCE EQUIPMENT NEEDED For flow measurements in sanitary sewers if you are going to be using only the grab sample method in an area which is reasonably protected from the weather the laboratory fluorometer will be sufficient If however you want to use the grab sample method in less favorable weather or if you wish to use a continuous flow method you will need the field fluorometer If you are also interested in chlorophyll nephelometry turbidity circulation effluent dispersion mixing or outfall location you may wish to contact Turner Designs for the best selection of equipment to meet your overall requirements FLUOROMETER 10 A
32. n normal fall in dye concentration after injection has stopped If a clean plateau of dye concentration can be reached accuracy will not be impaired Recovery Ratio Test The physical and chemical properties of your sewage may interfere with the measurement of the fluorescent dyes A recovery ratio test is used to determine the degree of such interference and the effectiveness of the several simple procedures used to reduce this interference How to make measurements with the Model 10 AU Fluorometer are discussed in the section entitled MEASUREMENTS Details of how to prepare Standards and Recovery Standards are discussed in the section entitled PREPARATION OF STANDARDS To determine a Recovery Ratio 1 Determine the fluorescence due to dye added to distilled water the Recovery Standard 2 Determine the fluorescence due to the same dilution of dye in raw sewage the Standard 3 Divide the number from step 2 by the number from step 1 This is the Recovery Ratio In all cases encountered to date and expected this ratio will be less than one If your recovery ratio is around 0 9 expect accuracy of about 5 If it is around 0 95 expect accuracy of about 2 For highest accuracy all steps possible to obtain a high recovery ratio should be taken The most general cause of low recovery ratios is the masking effect of suspended solids in the sewage To improve the recovery ratio filtration of the Recovery Standard and all unknowns
33. nd save Repeat several times saving each sample Then measure to see how many wash downs are required A Quick Field Filtration Technique We have developed a rapid filtration technique based on very inexpensive disposable items which avoids sample cross contamination and may be used under field conditions The equipment which we use is available through Scientific Products See Laboratory Equipment and Supplies in your telephone directory yellow pages Equivalent items are available from other major supply houses 1 Disposable plastic funnels We have found that Lance 5 5 cm 2 1 4 polystyrene funnels manufactured by Sherwood Medical Industries Inc are excellent They may be rinsed and reused but are brittle and subject to cracking Polypropylene funnels though somewhat more expensive are more durable and a better choice if you wish to rinse and reuse them Pyrex brand wool filtering fiber Corning Catalog 3950 or equivalent A pound will be a lifetime supply A test tube rack for 13 mm x 100 mm culture tubes which may be readily immersed in water A pan which you can place the test tube rack in deep enough so that when partially filled with water cuvettes in place in the test tube rack will be immersed to about 1 1 2 from their tops This is not part of the filtration set up but will be required for measurement 5 Aroll of Parafilm One 4 inch x 125 foot roll is a lifetime supply www turnerdesigns com 99
34. nown dilution of the dye being injected The dilution will be made with sewage collected just prior to the start of dye injection Recovery Standard We will also refer to a recovery standard which will be made by diluting the dye being injected with deionized water distilled water The purpose of the recovery standard is to see whether the reading of a given concentration of dye is the same in both clean water and sewage in other words whether the dye is all recovered in sewage Dilution Ratio This is the entire basis of the technique If you inject dye at a constant rate of 0 01 gpm and find the sewage dilutes it one million fold then the dilution ratio is one million The flow rate in the sewer must then be one million times as great as the injection rate or 10 000 gpm Note that it is not necessary to know the absolute concentration of the dye in either the solution injected or in the sewer only the dilution ratio The instrument will be calibrated with a known dilution of the injected dye solution www turnerdesigns com 998 5107 Revision A Page 1 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution DESIGNS Reliable Instruments for an Unreliable World PROCEDURE OUTLINE Collect about one gallon of sewage immediately prior to injecting dye This will be used for preparing standards e Add dye to the sewage system at a constant rate This will be discussed under DYE INJECTION Ta
35. ow Measurements in Sanitary Sewers by Dye Dilution E DESIGNS Reliable Instruments for an Unreliable World The volume of liquid in the cuvettes should be at least 5 ml This will be assured if they are filled about two thirds or more Do not overfill however as it makes the cuvettes awkward to handle All samples standards and blanks should be in your test tube rack except when being measured The test tube rack should be in a pan of water at room temperature The water level in the pan should be high enough so that it covers the bottom three fourths of the cuvettes 4 lf samples were at about room temperature they should be in the water bath for at least 15 minutes before measurements start If they were at a markedly different temperature allow 30 minutes 5 Measurements should be made rapidly since the instrument is at a higher temperature than the room If a measurement or instrument adjustment cannot be made within 45 seconds the sample should be returned to the test tube rack so that it will return to the correct temperature This is why duplicate Standards are called for See Samples Required below 6 We recommend a minimum of 5 minutes in the test tube rack between one measurement and the next on a single sample 7 The outside of the cuvette MUST BE carefully dried with facial tissue before it is placed in the instrument for measurement 8 The fluorometer should be allowed to warm up for at least ten minut
36. r convenience DEFINITIONS Fluorescent Materials A fluorescent material is one that absorbs light of one color and emits light of a different color For practical purposes the emitted light is always of longer wavelength i e shifted toward the red The fluorescent tracer material under discussion rhodamine WT absorbs green light and emits red light By contrast brighteners which are fluorescent materials added to detergents absorb ultraviolet light and emit blue light Sewage Blank The blank is amount of fluorescent materials occurring naturally in the system expressed as a concentration of the fluorescent material being measured The great value of rhodamine WT lies in the fact that the wavelengths involved are unusually long A high concentration of brightener looks like distilled water to the instrument when it is set up for measuring rhodamine WT A few naturally occurring materials and some industrial materials will fluoresce very weakly at the wavelength of rhodamine WT The highest blank we have encountered in sanitary sewage was equivalent to about 2 parts per billion of the 20 solution of rhodamine WT Most ranged from 0 4 1 5 parts per billion It should be noted that fluctuation of blank during a measurement not the absolute magnitude is the important factor See DYE INJECTION Dye Concentration Sewage Standard A standard is a known concentration of the material of interest In this case the standard will be a k
37. s but not the bottles you can always screw the lid on over a piece of Parafilm Clear material such as Saran widely used in the kitchen for food storage should never be used These materials adsorb large amounts of the dye Containers made of the above materials tend to be more expensive but are indefinitely reusable An inexpensive container of adequate size about 2 3 oz which we have tested is a special low potassium glass scintillation vial with Polyseal caps made by Kimble They are available from Scientific Products and other laboratory suppliers FILTRATION The requirement is that the sample be free enough of suspended solids so that accurate measurements of the fluorescence of the sample may be made In most cases filtration will not be required Whether filtration is necessary and adequacy of the filtration procedure may be easily checked See PROOF OF PERFORMANCE Recovery Ratio Test The Effect of Turbidity Your fluorometer shines green light on the dye to be measured and responds to the red light which the dye emits If these two beams of light are partially obscured then readings will be low Note that the effect is a proportional one not a subtractive one If 10 of the light is lost due to turbid materials then all readings will be reduced by 10 regardless of whether they are high or low Note also that the turbid material must remove light to affect the readings If the particles present do not ab
38. s means that is does not absorb significantly on sediments which would reduce its value as a tracer As a bonus it may be removed from your hands with soap and water though it is not easily removed from clothes Dye Concentration Throughout this manual all guideline concentrations are based on considering the material as purchased to have a concentration of 100 on a basis of volume The fact that the material is supplied as a 20 aqueous solution with a specific gravity of 1 2 is not significant It needs to be mentioned only because much of the technical literature considers dye concentration in terms of active ingredient The concentration of the dye to be injected is governed by three things injection rate estimated flow in the system and final concentration desired As long as the dye injection rate is small compared to the flow being measured it may be independently specified Usually it will be determined by the injection system which you purchase or build We find that injection rates much below 10 ml minute 0 003 gpm are difficult to handle The size of the dye reservoir may set the upper limit of injection rate If for example you are doing infiltration studies on sewer systems where dye injection periods may be several hours long convenience in handling the reservoir may limit the maximum injection rate Dye concentration in the final sample taken should be high enough so that variability in the blank see DEFINIT
39. sorb light but merely deflect it readings will be only slightly affected It is the big dark particles that do the damage The fines which are often very difficult to remove will cause very little error Further we find that the amount of big dark particles is quite variable but the content of fines is low and consistent www turnerdesigns com 998 5107 Revision A Page 7 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution t DESIGNS Reliable Instruments for an Unreliable World There are three methods which may be used to correct or remove errors caused by turbidity 1 Prepare standards with the water of interest Assuming turbidity is constant this automatically corrects for errors 2 Remove the suspended solids to the point where the error is negligible If you are in a hurry filter if you are not in a hurry let them settle 3 Dilute the samples with clean water to the point where turbidity is negligible and multiply the answers by the dilution factor Don t forget that the blank and standards should be similarly diluted Preparation of standards with the water of interest is valid at almost any level of turbidity if the turbidity is constant Even if 50 of the light is lost there will be no error If however the turbidity changes by 10 relative i e from 50 to 45 light loss you now have a 10 error in your results There is no way to predict how much light loss can be tolerat
40. ttes While the 1 ml pipettor and the 100 and 1000 ml volumetric flasks will adequately handle all situations there will be borderline cases where though not strictly necessary it would be nice to have other volumes The pipettors are available in adjustable versions Care of Glassware Technically all glassware should be thoroughly clean and dry before use Cleanliness is however a matter of definition What most chemists would consider very bad practice can be tolerated here Visible dirty spots water marks finger prints etc are not going to cause error unless they contain dye Your primary interest is to see that all previous dye is removed and that the equipment delivers or contains the proper volume of water Volumetric flasks are designed to contain a volume They can be used wet without error providing all dye has been rinsed out Only water above the calibration mark will cause error and this will be trivial unless heavy beading is involved Beading occurs eventually in all glassware due to oils in the air and in the water Occasional washing with a warm mild detergent usually cures this problem Resistant cases can sometimes be cured by rinsing with acetone followed by washing with detergent Severe cases may require soaking in acid cleaning solution After washing or after use all glassware should be rinsed repeatedly with tap water at least three or four times after no dye can be seen followed by one or t
41. vettes This will minimize the chance of any dye on your hands getting into the samples Place the cuvettes in the test tube rack staggered so that when the funnels are in place the funnels do not overlap Pour the sample in When the cuvette is filled to the label remove the funnel and discard Then cover the top of the cuvette with Parafilm Peel the backing paper from the Parafilm keeping fingers off the protected surface Press this clean surface firmly onto the top of the cuvette and fold the excess over the side Your samples are now ready for measurement Overnight Settling On overnight settling most sewage will settle to a clarity not quite as good as a sub micron laboratory filtration but considerably better than the quick filtration To be strictly correct you should prepare your standard dilutions before allowing the solids to settle We have never seen a case in sewage where the solids adsorbed the dye but it could happen If for example the solids contained activated charcoal dye would be adsorbed In filling your cuvettes from settled samples gently pour off anything that has floated to the top then pour the liquid into clean dry labeled cuvettes Cover with Parafilm PREPARATION OF STANDARDS Standards are required to calibrate the fluorometer precisely in terms of the dye that you injected Standards must be prepared for each run using a small portion of the dye actually injected and using a representative sample of
42. wo rinsings with distilled water The latter rinse is a precaution against beading and encrusting with minerals from hard water if the glassware is to air dry It is not necessary if you have soft tap water or intend to reuse the equipment immediately To rinse volumetric flasks fill them about 1 5 full swirl and rapidly invert so that the liquid rinses all inside surface while emptying Rinse the outside neck under the faucet between internal rinsings Cuvettes should be treated like the flasks except that they must be dry for use If they are not dry they should be rinsed several times with the solution to be measured This is not convenient when you are filtering directly into the cuvette Cuvettes should be stored to avoid scratches Minor scratches will not affect accuracy but eventually such treatment will cause errors Dilution Technique It s easy to perform an accurate dilution but there are several points which must be carefully observed Position yourself so you have good light and preferably are facing a light colored wall Pipettor Follow the manufacturer s recommendation with your pipettor Most have three positions of the activating button For these the general instructions are after firmly seating a fresh tip 1 Depress the activating button to the first stop Lower the pipettor till the tip is slightly below the surface of the sample to be pipetted Slowly release the activating button Wait a few seconds and withdraw t
43. y 0002642 yielding 01 gallons per minute or 0 00001440 mgd If you wish your final answer to be in cubic feet per second then convert milliliters per second 0 631 to cubic feet per second by multiplying 0 631 by 00003532 yielding 00002287 cubic feet per second Standard Dilution Ratio You have already selected a Standard Dilution Ratio See PREPARATION OF STANDARDS In the example given it was 100 000 two 100 fold and one 10 fold 100 x 100 x 10 100 000 Example We wish to calculate the flow in mgd q 00 0000144 mgd See Injection Rate Rst 95 4 See Reading Samples r 25 8 See Reading Samples D 100 000 See Standard Dilution Ratio Q 0 0000144 x 95 4 x 100 000 25 8 5 32 mgd or more reasonably stated 5 3 mgd Of course if you are measuring several flows from one injection the obvious thing to do is calculate q Rst D as ris the only variable from sample to sample www turnerdesigns com 998 5107 Revision A Page 16 of 17 TURNER TOOGE Flow Measurements in Sanitary Sewers by Dye Dilution t DESIGNS Reliable Instruments for an Unreliable World ALTERNATIVE OPERATION CONTINUOUS FLOW The grab sample method described above is not the only mode of operation using the Model 10 AU Fluorometer If the sewage is not unusually turbid or colored accuracy may be improved by operating in a continuous flow mode NOTE The Model 10 AU 000 Laboratory Fluorometer cannot perform continuous flow studies
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