DETERMINATION OF OXYGEN UPTAKE RATES IN ACTIVATED SLUDGE MIXED LIQUOR O by Ronald D. Kooistra AN ABSTRACT Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Civil Engineering 1965 DETERMINATION OF OXYGEN UPTAKE RATES IN ACTIVATED SLUDGE MIXED LIQUOR by Ronald D. Kooistra Continuous measurement of dissolved oxygen in an aqueous solution can be made by a polarographic electrodeo In this thesis a gold-silver polarograph cell has been used to measure dissolved oxygen depletion in mixed liquor samples from the East Lansing Sewage Treatment Plant over short periods of time. A schedule of sampling at 2 hour intervals through- out the day revealed a basic pattern in the variation of the activated sludge activity, kr = milligrams oxygen consumed per gram mixed liquor suSpended solids per hour. The activity increased from a minimum between 7 and 10 AM to a peak value between 2 and 5 PM after which the rate slowly decreased during the evening until at about midnight the rate decreased more rapidly to the minimum value at the following morning. Over the weekend, kr’ was much lower than for a weekday, with Saturday being the period of lowest k.r values while Wednesday was the period of highest kr values. BOD determinations upon the primary effluent taken at the time of the mixed liquor sampling revealed that kr was directly related to both the total and dissolved BOD of the primary effluent. 2 RONALD D. KOOISTRA The aeration system of the sewage treatment plant was analyzed for its capacity by observing the D.O. in the mixed liquor and simultaneously determing rr, the oxygen uptake rate per unit mixed liquor volume. The capacity of the East Lansing aeration system was found to be 20.3 mg/l/hr. while maintaining a D.O. of 1 ppm in the aeration tank at 150C. The slepe of a semilogarithmic plot of the Specific oxygen utilization rate, kr, against temperature, 0C, was found to be 0.0323/00. The activity, as measured by rr, of a starved activated sludge was found to double within one half hour after being fed 500 mg/l glucose. APPROVED DETERMINATION OF OXYGEN UPTAKE RATES IN ACTIVATED SLUDGE MIXED LIQUOR by Ronald D. Kooistra A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Civil Engineering 1965 ACKNOWLEDGEMENTS The author wishes to express his indebtedness and appreciation to Dr. Karl L. Schulze whose generous help and encouragement made this thesis possible. Acknowledgement is made to the Division of Engi- neering Research for its support during the course of this research. I would like to express my sincere gratitude to my wife for her aid and understanding during the years of my education. TABLE OF CONTENTS ACMOWIIEDGEMENTOOOOOOO0.0.00000000000000000000000 LIST OFFIGURESOO 00000 0.0000000000000000000...... LIST OF TABLESOOOOOOOOOOOOOOOOOOOOOOO0.000.00.... LIST OF SMOLSOOOOOOO0.0000000000000000000000000 SECTION ‘ I. INTRODUCTION...OOOOOOOOOOOOOOO00.00.0000 II. LITERATURE REVIEWOOOOOOOOOOOOO0000...... A. Oxygen Electrode.................... B. Activated Sludge Activity........... 1. Effect of D.O. Concentration.... 2. Effect of Temperature........... 3. Effect of Solids Concentration.. 4'. EffeCt Of pHOOOOOOOOOOOOOOOOOOOO 5. Effect of BOD Concentration..... III. EXPERIMENTAL APPARATUS AND MATERIAL..... A0 Material...00°OOOOOOOOOOOOOOOOOOOOOO Bo ApparatuSOO0000.000...0000000000000. l. Polarograph Oxygen E1ectrode.... 20 Air SUPPlYOOOOOOOOOOOO000000.000 3. Magnetic StirrerOOOOOOOOOOOOOOOO IV. EXPERIMENTAL PROCEDURE.................. 1. Electrode Calibration............... 2. Measurement of the Mixed Liquor Oxygen Uptake Rate........... 3 Biochemical Oxygen Demand........... 4: Chemical Oxygen Demand.............. 5. suspended SOlidSOOOOOOOOOOOOOOOOOOOO O pHOOOOOOOOOOOOOOOOOOOOO0..090000000. ii Page vii ix \0 \O \0 \‘lfl0\0\0\ -P- N N I-' SECTION V. EXPERIWNTAL RESULTSOOOOOOOOOOOOOOOOOOOOO A. Mixed Liquor Oxygen Uptake Rate Measurements at the Sewage Treatment PlantOOOOOOOOOOOOOOOOOOO... 1. Between Spring and Summer Terms.. EXperiment No. l ................ Experiment NO. 2 000.000.00.00... Summer Term...................... EXperiment No. 3 ................ Experiment No. 4 ................ Experiment No. 5 ................ Experiment NO. 6 OOOOOOOOOOOOOOO. Experiments No. 7, 8 and 9 ...... Experiment N0. 10 00000000000000. Experiment NO. 11 OOOOOOOOOOOOOO. Experiments No. 12 and 13 ....... Experiments N0. 14 and 15 0000000 Between Summer and Fall Terms.... Experiment No. 16 ............... Experiment NO. 17 ooooooooooooooo Experiment No. 18 ............... Fall TermOOOOOOOOOOOOOOOOOOOOOOO. Experiment No. 19 ............... Experiment No. 20 ............... Peak Oxygen Uptake Rates Over aWeek..OOOOOOOOOOOOOOOOOOOOOOOOO TGSt series N00 1 OOOOOOOOOOOOOOO Test Series No. 2 ............... Determination of the Oxygen Transfer Coefficient, KLa, for the Treatment Plant's Aeration Equipment........o...o.oo.o...... iii Page 24 24 25 25 25 29 29 29 32 34 4O 4O 2% SO SO 50 55 33 59 59 60 64 SECTION V. EXPERIMENTAL RESULTS..................... A. Mixed Liquor Oxygen Uptake Rate Measurements at the Sewage Treatment Plant...................... 1. Between Spring and Summer Terms.. Experiment No. 1 ................ Experiment N0. 2 0.......0...0..0 Summer Term...................... Experiment N00 3 ......00.o..0... Experiment No. 4 ................ Experiment NO. 5 ........0.00.... Experiment N0. 6 .0..0..00..00.00 Experiments No. 7, 8 and 9 ...... Experiment NO. 10 ........0..0... Experiment N00 11 00..00..o..0.0. Experiments No. 12 and 13 ....... Experiments N0. 14 and 15 ....0.. Between Summer and Fall Terms.... Experiment No. 16 ............... Experiment No. 17 ............... Experiment No. 18 ............... Fall TermOO000.00.000.00000000... Experiment No. 19 ............... Experiment No. 20 ............... Peak Oxygen Uptake Rates Over aweekOOOOOOOOOOOOOOOOOO00.0.0000 TeSt series N00 1 00.000000000000 Test Series No. 2 ............... Determination of the Oxygen Transfer Coefficient, KLa, for the Treatment Plant's Aeration EquipmentOOOOOOOOO000000000000... iii Page 24 24 25 25 25 29 29 29 32 34 4O 4O 1% SO SO 50 55 59 59 60 64 SECTION V. EXPERIMENTAL RESULTS CONTINUED B. Other Investigations Upon Sewage- Activated Sludge Mixtures............. l. 2. Temperature Effect................ Effect of Substrate Addition...... VI. DISCUSSION OF RESULTSOOOOOOOOO..0.0.00.00. A. Oxygen Uptake Rates by the Polarographic Oxygen Electrode TGChnique............C......O......... B. Mixed Liquor Oxygen Uptake Rates at the Sewage Treatment Plant......... 1. 2. 3. The Oxygen Uptake Rate Curve overaDay.............0........O. The Oxygen Uptake Rate Curve overaweekend00.................. Relationship of the Specific Respiration Rate, kr, to the Primary Effluent Total and DiSSOlved BODOOO...........0.0.... Measurement of the Capacity of Aeration Equipment Under Operating Conditions.............. VII. CONCLUSIONS......OOO.......0.0.0.0....OOOC BIBLIOGRAPI-IY...0......00000.0.0.0....00000 iv Page 69 72 77 77 80 80 82 84 91 94 96 Figure l. 2. 3. 4. 5. 6. 7. 8. 9. IO. 11. l2. 13. 14. 15. 16. 17. 18. 19. 20. 21. LIST OF FIGURES Cutaway View of the Electrode............ Sample Flask and Oxygen Meter Assembly... Respirometer Assembly.................... Calibration Curve for the Electrode...... Temperature Control of the Respirometer.. Experiment Number 1 ..................... Experiment Number 2 ..................... Experiment Number 3 ..................... Experiment Number 4 ..................... Experiment Number 5 ..................... Experiment Number 6 ..................... Experiments Number 7, 8 and 9 ........... Experiment Number 10 .................... Experiment Number 11 .................... Experiments Number 12 and 13 ............ Experiments Number 14 and 15 ............ Experiment Number 16 .................... Experiment Number 17 .o.................. Experiment Number 18 .................... Experiment Number 19 .................... Experiment Number 20 .................... Page 11 12 13 17 22 26 27 3o 31 33 35 39 41 42 45 48 52 53 S4 57 58 Figure 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33- LIST OF FIGURES CONTINUED Peak Oxygen Demand, rr, Over a Week....... Peak Oxygen Demand, kr, Over a Week....... Determination of the Oxygen Transfer COfoiCient, KLa .........0..............0 Effect of Temperature Upon the Oxygen Uptake Rate of a Mixed Liquor............. Effect of Substrate Addition Using Glucose............0......O0.00.....O..O.. Variation in Oxygen Utilization with Time of Aeration...................0....O. Aging Effect Upon the Electrode senSitiVity....0...0..0.0........0...0.0.. Aging Effect Upon the Electrode senSit1Vity at ZOOCOOOOOO........O........ Mixed Liquor Dissolved Oxygen Depletion Over Time.........0....0.0.0.00. Relationship Between Primary Effluent Total BOD to the Cellular Respiration Rate, kr, Based on MOLQS.S................ Relationship Between Primary Effluent Total and Dissolved BOD to the Cellular Respiration Rate, kr, Based on M.L.V.S.S.. Effect of Aeration Rate Upon Aeration capaCitYOOO.........00..0........0......00 vi Page 62 63 68 71 75 76 78 79 81 89 9O 93 TABLE 1. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 2o. 21. LIST OF TABLES Typical Data Sheet for the Measurement of Oxygen Uptake Rate by the Oxygen EleCtTOGe..........0.................0..0. Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data for Experiment 1 ......... for for for for for for for for for for for for for for for for for for for Experiment Experiment Experiment Experiment Experiment EXperiment Experiment Experiment Experiment Experiment Experiment Experiment Experiment Experiment Experiment Experiment EXperiment Experiment EXperiment vii 2 0........ 3 4 5 6 ......... 7 8 9 IO 11 12 13 14 15 ........ l6 17 18 19 2O 00...... 00...... 00...... Page 21 26 28 3O 31 33 3 5 37 37 38 41 42 44 44 47 47 52 53 54 56 56 TABLE 22. 23. 24. 25. 26. 27. 28. LIST OF TABLES CONTINUED Peak Oxygen Uptake Rate Series No. l ..... Peak Oxygen Uptake Rate Series No. 2 ..... Analytical Data for the Determination of the Oxygen Transfer Coefficient........ Effect of Temperature on Respiration Bate............0..............0....00.... Effect of Substrate Addition Using Glucose................................... Tabulation of the Primary Effluent BOD Data of Experiments 2 through 20 ......... Tabulation of the Primary Effluent BOD Data of Experiments 18, 19 and 20 ........ viii Page 61 61 67 7O 75 86 88 M.L.S.S. M.L.V.S.S. 2.13. 02 u g mg PPm D.O. LIST OF SYMBOLS Biochemical Oxygen Demand 5-day Biochemical Oxygen Demand Oxygen uptake rate per unit volume, mg02/1/hr. or milligrams oxygen consumed per liter per hour Oxygen uptake rate per unit weight of suSpended solids, mgO2/gSS/hr. or milligrams oxygen consumed per gram suSpended solids per hour Mixed liquor suSpended solids Mixed liquor volatile suspended solids Primary effluent Oxygen Micro Grams Milligrams Parts per million Dissolved Oxygen ix SECTION I INTRODUCTION This study has been carried out at the East Lansing Sewage Treatment Plant. This waste treatment plant employs the "biosorption" modification of the activated sludge process for its secondary treatment. The plant treats nearly 100% domestic wastes. The main objective of this study has been to measure the oxygen uptake rates occurring in the aeration tanks. Several 24 hour surveys using two hour sample intervals have been made in order to outline the rate variation according to the day of the week. The four month study has also revealed the effects on the mixed liquor oxygen uptake rates due to changes in the student pOpulation at Michigan State University, which contributes a large portion of the total sewage flow treated by the plant. Other variables measured during the four month survey. were: 1. Primary Effluent BOD (Total and Dissolved) 2. Primary Effluent COD 3. Primary Effluent Suspended Solids 4. Mixed Liquor pH 5. Mixed Liquor SuSpended Solids and Volatile Suspended Solids. SECTION II LITERATURE REVIEW A. Oxygen Electrode _ The drOpping-mercury polarographic electrode was the first polarographic electrode to be used for the deter- mination of dissolved oxygen. There are several advantages of the polarographic technique of D.O. determination over the standard Winkler (1) test. Among the advantages are the rapidity of measurement, the possibility of determining the D.O. "in situ" thereby offering a means of plant control, the feasibility of continuous recorded observations and auto— matic Operating control, the possible use of the sample for other determinations after its D.O. has been determined, and the rapid measurement of D.O. in sludges or suSpensions which makes the measurement of mixed liquor oxygen utili- zation rates feasible. Many workers in the field of waste treatment investi- gated the use of the polarographic technique for D.O. measurement. Ingols (2) and Moore, Morris and Okun (3) concluded from their investigations that the dr0pping mercury electrode was a rapid and accurate instrument for the measurement of D.O. in waste waters. Rand and Heukelekian (4) in their studies of D.O. determination in industrial wastes reported that the drOpping mercury electrode method permitted reasonably accurate determination of D.O. even under conditions which render the standard Winkler method inapplicable. Lynn and Okun (5) reported that the drOpping-mercury electrode suffered the disadvantage of interference with the mercury drOp by the turbulence necessary to keep the activated sludge in suSpension. Furthermore the toxicity of the mercury introduced a serious problem into the measurement of the biological activity of the sludge floc. Lynn and Okun (5) concluded from their investigation that the platinum electrode was not applicable to the determination of D.O. in waste waters due to deleterious effects of impurities in the sample medium. Recent deveIOpments in the field of solid electrodes have over- come the poisoning effects of impurities in the sample medium. Carritt and Kanwish (6) made a very important contribution by developing a temperature-compensated electrode composed of a plastic membrane covered platinum electrode. The plastic membrane is not permeable to the ionic contaminants of the sample solution, but it is permeable to gases. Mancy and Westgarth (7) also made an important contribution by the development of the plastic membrane covered silver-lead galvanic cell oxygen sensitive electrode. Today electrodes based on both the polarographic and galvanic cell principles are commercially produced. The electrodes in general have the desired characteristics of: (a) ability for continuous monitoring of oxygen, (b) ease of Operation and maintenance, (c) long-term stability, and (d) suitability for field use. B. Activated Sludge Activity The concept of dissolved oxygen monitoring for the conservation of power by the prOper pr0portioning Of aeration to oxygen demand and for the early discovery Of sludge activity disturbances is recognized by many sewage treatment plant Operators. Considerable savings may be Obtained by the prOper control of aeration equipment. Greely (8) reports that from 50 to 60 percent of the total power consumption in a sewage treatment plant is used by aeration equipment. A report by the APHA (9) indicated that many plant Operators monitor the aeration tanks by periodically checking the D.O. in the aeration tanks with the minimum permissible D.O. ranging from 0.2 to 2 ppm. However, the activity of the sludge organisms is best evaluated by measuring the rate at which oxygen is utilized by the organisms. Thus there exists a need for a suitable oxygen uptake rate test which can be conducted rapidly and which can serve as an immediate guide in the control Of plant Operation. Several methods have been used for the measurement of mixed liquor oxygen utilization rates. Bloodgood (10) used 4 the Odeeometer and reported that the control of the sludge activity could be accomplished by changing the sewage flow, quantity of air used, or the quantity of mixed liquor solids. Kessler and Nichols (11) used the standard Winkler D.O. test with cupric-sulfamic acid to determine oxygen utilization rates by observing the D.O. depletion over short periods of time. They reported that the oxygen utilization rate, designated Nordell Number, could be used to ascertain the progress Of oxidation of sewage, the sewage strength, and the condition of "activity" of a sludge. Later Kessler (12) using an Odeeometer further studied the Nordell Number and its mathematical relationships with other variables in the activated sludge treatment process. Dawson and Jenkins (13) used both the Barcroft and Warburg manometers for oxygen utilization studies upon mixed liquors. Hoover, Jasewicz and Porges (14) showed that the Magnetic Oxygen Analyzer could be used for the measure- ment Of oxygen utilization rates. Lamb, Westgarth, Rogers and Vernimmen (15) in their studies of industrial waste have reported that the galvanic cell electrode provides a simplified experimental approach for the measurement Of oxygen utilization rates. It is the purpose Of this thesis to demonstrate the application of a polarographic oxygen electrode to the analysis of the mixed liquor oxygen consumption rates at an Operating sewage treatment plant. 1. Effect of Dissolved Oxygen Concentration Smith (16) has reported that no effect on mixed liquor oxygen utilization rates was Observed within a dissolved oxygen range of 0.2 to 6 ppm. The APHA committee (9) reported that a survey of many Operators revealed that the minimum permissible D.O. varied from 0.2 to 2 ppm. The WPCF Manual of Operation (17) recommends that a D.O. of 2 to 4 ppm be maintained in the mixed liquor. 2. Effect of Temperature Activated sludge consists mostly out of micro— organisms and its metabolic rate will therefore be markedly effected by temperature. Bloodgood (10) reported that between 10°C and 30°C each one degree rise increased the oxygen utilization rate by 3 mg02/1/hr. Sawyer and Nichols (18) have reported the oxygen utili- zation rate at 10°, 15°, and 20°C to be 26, 43.5, and 70.5 percent reSpectively of the rate at 25°C. Sawyer and Rohlich (19) have confirmed Sawyer and Nichols results and further observed that winter sludges are adapted to the low temperatures since they have higher oxygen uptake rates at a given low temperature than summer sludges. 3. Effect of Solids Concentration The amount of activated sludge to carry in the aeration tanks is a question upon which few plant Operators will agree. The APHA committee (9) reported that the maintenance of an Optimum solids concentration in a mixed liquor is important but that the Optimum amount at any plant must be determined by the Operators eXperience. Sawyer and Nichols (18) have reported that the oxygen utilization rate is directly pr0portiona1 to the amount of activated sludge solids. Lamb, Westgarth, Rogers and Vernimmen (15) have reported that the oxygen uptake rate is directly pr0portional to the volatile solids concentration and have presented the Specific oxygen uptake rate (mgOZ/gVSS/hr) as being helpful in defining the viability of a sludge in relation to a Specific substrate. 4. Effect of pH Microbiologists have long recognized that pH has a very pronounced effect on microbial growth. In the activated sludge treatment process Keefer and Meisel (20) reported that an effective process range is from pH 6.0 to 9.0 with an Optimum range from pH 7.0 to 7.5. Smith (16) and Eckenfelder and O'Connor (21) maintain the same position. 5. Effect ofgng Concentration Smith (16) has reported that the oxygen uptake rate per unit weight of sludge solids is linearly related 7 to the BOD of the sewage being treated. Eckenfelder and O'Connor (21) maintain the same position but eXpress the relationship a little differently. They reported that the oxygen utilization rate per unit weight of sludge is directly pr0portional to the 5-day BOD removal per unit weight of sludge. In this thesis a new relationship will be introduced namely, that between the oxygen utilization rate and the dissolved 5-day BOD of the sewage being treated. SECTION III EXPERIMENTAL APPARATUS AND MATERIAL A. Material Mixed liquor from the East Lansing, Michigan, Sewage Treatment Plant was used for all the oxygen uptake rate measurements. The sewage treated by this plant is strictly of a residential nature. During the summer months, the plant Operates on a decreased volume because the number of students attending the university is reduced by about two-thirds. The collection system is a combined one, thus during the periods of rain the strength of the waste is reduced considerably. Naturally all of the factors mentioned above have a marked effect on the strength of the primary effluent with reSpect to BOD. During the term of this study the highest primary effluent BOD found was 243 mg/l and the lowest was 36 mg/l based on grab samples taken simultaneously with the mixed liquor samples. B. Apparatus 1. Polarograph Oxygen Electrode The oxygen sensor used to make all Of the oxygen uptake rate measurements was the YSI model 5101 polarographic oxygen probe with model 51 oxygen meter manufactured by the Yellow Springs Instrument Company. Figure 1 shows the details of the polarograph electrode. Figures 2 and 3 Show the sample flask and oxygen meter assembly. The basic components of the reSpirometer consisted of a 250 ml widemouth Erlenmeyer flask, a 1-1/4 inch long by 5/16 inch diameter teflon coated magnetic stirring bar, a number 8 rubber stOpper in which a thermometer, a 1/8 inch diameter glass tube and the electrode were held. The glass tube served as a vent for escaping air and excess liquid when stOppering the flask. A five inch length of lucite tubing was glued with epoxy to the two inch long electrode in order to facilitate the placing of the electrode about 1-1/4 inches above the magnetic stirring bar when the reSpirometer was closed. The polarograph cell consists of a gold ring cathode imbedded in a lucite block, and a silver coil recessed in a central well. The well is filled with 1 N potassium chloride solution. A thin teflon membrane stretched across the end of the cell isolates the cell from its environment with the exception of gases. The membrane is permeable to gases and allows them to make contact with the polarograph cell by diffusion. The correct polarizing voltage across the 10 f x / \\\\\\\\\\\\\\\\\\\\\ 3 .. \\\ LL 1!!!! \\ §IZLL’I'/7 A\\\\ 3. Potassium Chloride, KCl, Solution b. Gold Ring Anode c. Teflon Membrane d. Silver Coil Cathode 9e. NeOprene "0" Ring f. Lucite Block Figure l. Cutaway View of the Electrode. ll Figure 2. Sample Flask and Oxygen Meter Assembly. 12 Thermometer Number 8 rubber stOpper Lead wire to oxygen meter Electrode Glass tube vent, 1/8 inch inner diameter Teflon coated magnetic stirring bar, 1-in. x 5/l6min. diameter 250 m1 Erlenmeyer widemouth flask Figure 3. Respirometer Assembly. 13 cell allows the reduction of molecular oxygen at the gold cathode surface. The oxidation of the silver anode surface supplies the current for the reduction of the oxygen at the cathode. The amount of diffused oxygen reaching the cell is pr0portional to the driving force which is the partial pressure of the oxygen in the sample medium, an aqueous solution in this study. The partial pressure of the oxygen is directly pr0portional to the concentration of the dissolved oxygen. A linear relationship exists between the external oxygen pressure and cell current. 2. Air Supply A small portable air compressor was used to supply compressed air for the aeration of the mixed liquor samples. A quart jar approximately 3/4 full of mixed liquor was aerated at a high rate by forcing compressed air through a 1/2 inch diameter by 1 inch long fritted glass diffuser. Approximately a 200 m1 aliquot of this aerated mixed liquor was used for the oxygen uptake rate determination by observing the oxygen depletion after the air supply had been shut off. 3. Magnetic Stirrer In order not to add any heat to the samples an air driven magnetic stirrer was used, Bronwill Mag— 14 Jet, with a 5/16 inch by lnl/4 inch long teflon covered magnetic stirring bar. The basic factor considered in stirring the sample was to Obtain adequate liquid velocity past the electrode membrane in order to prevent the formation of a stagnant diffusion zone at the membrane surface. The necessary rate of stirring can be easily established by noting the effect of various stirring Speeds upon the current output when the electrode is in a sample of water having a constant D.O.; distilled water is good. The rotation Speed of the stirrer at which no more significant current increase is produced is the Speed to be used for all measurements with the electrode. A pressure regulator was used to obtain the same stirring Speed for each test. This was accomplished by noting the pressure reading, 3 psi, and keeping the needle valve at a constant setting. The air flow was shut off by decreasing the pressure to zero and the correct air flow re~established by increasing the pressure to the control pressure reading. 15 SECTION IV EXPERIMENTAL PROCEDURE 1. Electrode Calibration The current output of the electrode is markedly effected by temperature. This is caused by the fact that the permeability of the plastic membrane is temperature dependent, in the order of 4 per cent per 0C as stated in the instruction pamphlet for the oxygen meter. Mancy and Westgarth (7) have shown that the temperature effect is linear. The linear relationship to the electrode sensitivity to temperature provides a convenient means for calibration of the electrode. The electrode is placed into a sample for which the dissolved oxygen concentration has been previously determined by the standard Winkler test. A minute or two is allowed for stabilization Of the current output., Then the sample is immersed in an ice bath and the current output recorded at 20C intervals. The usual temperature range is from 1000 to room temperature (24°C). The sensitivity, is equal to the microamp output divided by the Winkler D.O. eXpressed as mg per liter. A semi— logarithmic plot of sensitivity versus temperature, as shown in Figure 4, produces a straight line and is called the "calibration curve". Thus a current reading taken at 16 6.0"“ Date - September 9, 1964 Sample — Filtered Red Cedar River Water ? c? L» ‘? sensitivity,microamps/(mg 02/1) N ‘? 1. i 10 20 30 temperature °C Figure 4. Calibration Curve for the Electrode. 17 x 4 x... ._ ~J < a known temperature can easily be converted to mg/l D.O. by dividing the current by the sensitivity obtained from the calibration curve. The current output of the electrode was Observed to be dependent upon the stirring Speed of the magnetic stirring bar at slow Speeds. Mancy and Westgarth (7) have shown that the current output of the galvanic cell oxygen sensor is greatly effected by the stirring of the liquid at slow Speeds. The formation of a stagnant diffusion layer at the membrane surface is prevented at higher Speeds. The current output of the electrode was also observed to be effected by constituents in the aqueous solution other than oxygen. Red Cedar River water filtered through Whatman no. 2 filter paper was used as the calibration reference medium. The calibration curves obtained by this procedure were assumed to be similar to that of sewage. The accuracy of the electrode was checked by making several comparisons between the dissolved oxygen concentration as measured by the electrode and by the standard Winkler test. It was found that the accuracy was in the order of i=0.5 mg/l. 2. Measurement of the Mixed Liguor Oxygen Uptake Rate The sampling point was the center Of the first bay of aeration tank number 2. This point is located approximately 10 feet from both the primary effluent entrance and the return activated sludge entrance. Thus the contact time between the activated sludge and the primary effluent is about one minute. Samples were taken at 2 hour intervals for each survey. The samples were immediately taken to the Michigan State University Sanitary Engineering EXperiment Station located at the plant where they were aerated for 15 minutes. After shutting Off the air supply, an aliquot was immediately poured into the reSpirometer flask for observation of the Oxygen uptake rate by measuring the rate of depletion of the dissolved oxygen over time. Depending upon the magnitude of the oxygen demand rate either 2 or 5 minute current readings were recorded. It was found advantageous to place the electrode in a solution of low D.O. a minute or two prior to the use of the electrode. The supernatant from a settled mixed liquor sample is well suited for this purpose. The advantage of this procedure is that the current ouput will rise when the electrode is placed in the aerated sample. The point of no more rise defines the beginning of equilibrium between the dissolved oxygen concentration and the current output. The initial current reading was taken after the current had fallen from the peak value at least 1 microamp reading. It was endeavored to maintain a constant temperature by placing the reSpirometer into a 600 ml 19 beaker full of fresh primary effluent as shown in Figure 5. A typical data sheet is shown in Table l. The usual temperature rise was about 1°C. The average temperature Of the mixed liquor during the time of this survey was approximately 22°C. The maximum temperature was 25°C and the minimum 14°C. 3. Biochemical Oxygen Demand Primary effluent grab samples were obtained simultaneously with the mixed liquor samples. The standard five day BOD test as described in Standard Methods was used throughout the investigation. In determining the amount of dissolved BOD the primary effluent was filtered through a 0.45'micron Millipore membrane filter. Seeded dilution water as described in Standard Methods (1) was used in determining the BOD of the filtrate. The incubation temperature of 20°C was controlled by means of a water bath in which the bottles were completely submerged. 4. Chemical Oxygen Demand The standard COD test as described in Standard Methods was used for all COD determinations. The digestion process was not catalyzed. 5. SQSpended Solids Mixed liquor suSpended solids were determined by 20 TABLE I TYPICAL DATA SHEET FOR THE MEASUREMENT OF OXYGEN UPTAKE RATE BY THE OXYGEN ELECTRODE Sampling Test Temp. uamps 13.6. A(D.0.) Average 02 Time Time Uptake Rate 1' (min) 00 mg02/1 mgog/i/hr. Example - Thursday, July 23, 1965 6 AM 0 2300 2204 5042 " 15085 5 23.4 17.3 4.12 1.30 10 23.8 12.0 2.79 1.33 8 AM 0 22.8 22.0 5.37 - 15.50 5 22.8 17.5 4.26 1.11 10 23.0 12.3 2.97 1.29 15 23.4 7.0 1.67 1.30 21 Figure 5. Temperature Control of the iespirometer. 22 filtration through a 0.45 micron Millipore membrane filter. The volume filtered was 25 ml for all determinations. Volatile mixed liquor suSpended solids were determined by ignition at approximately 6000C. Primary effluent suSpended solids were also determined by filtration through a 0.45 micron Millipore membrane filter. A constant sample volume of 50 ml was used. 6.3;}; A Beckman model H2, pH meter was used to measure pH of each sample. 23 SECTION V EXPERIMENTAL RESULTS A. Mixed Liquor Oxygen Uptake Rate Measurement at the Sewage Treatment Plant The data have been divided into six groups according to whether they were obtained between terms or during terms. During terms not only the volume but also the strength of the sewage increases significantly. This increased BOD load has marked effects upon the reSpiration rate per unit dry weight of the mixed liquor suSpended solids (kr) as will be shown later. The test procedure consists of taking simultaneously grab samples of mixed liquor and primary effluent at 2 hour intervals. The majority of the test series comprise less than 24 hours. However, test series of 24 hours duration and over weekends are included. The oxygen uptake rate per unit liquid volume is denoted as rr and the oxygen uptake rate per unit weight of suspended solids is denoted as kr' The units are defined as: rr = milligram oxygen consumed per liter mixed liquor per hour, mg02/l/hr. k = milligram oxygen consumed per gram dry weight mixed liquor suSpended solids per hour, mgOZ/gSS/hr. 24 l. Between_§pring and Summer Terms Experiment No. 1: Friday, June 18, 1964 Table 2, Figure 6 This test series was begun at 8:00 AM and ended at 4:00 PM. The oxygen uptake rate was a minimum, rr = 15.6 and k1. = 9.9, at 10:00 AM after which the rate steadily increased until a peak, rr = 31.0 and kr = 19.5, was reached at 2:00 PM. The average temperature of the mixed liquor was 22.50C. The activity of the sludge was relatively low because the majority of the Michigan State University students had left the campus for a vacation break. The BOD concentration of the primary effluent was not determined. Experiment No. 2: Friday, June 26, 1964 Table 3, Figure 7 This test series was begun at 8:00 AM and ended at 8:00 PM. The M.L.S.S. were relatively low because the treatment plant operators were pumping all of the return activated sludge to another aeration tank which was being restarted after a period of repairs. With the exception of a slight dip at 2:00 PM, the oxygen uptake rate increased steadily from 8:00 AM (rr = 12.2 and kr = 8.6) to 4:00 PM (rr = 24.1 and ki = 68.5). Sometime between 3 and 4:00 PM the plant Operators diverted nearly all of the return activated sludge to the newly repaired aeration tank. As 25 TABLE 2 ANALYTICAL DATA FOR EXPERIMENT 1 Sampling Mixed Liquor Time Temp. 02 Uptake Rate 8.8. pH C’C r k mg/l r r 8:00 a.m. 22.5 15.9 11.2 14 0 7.7 10:00 a.m. 23.0 15.6 9.9 15 0 7.7 12:00 p.m. 22.6 26.6 15.2 1750 7.6 2:00 p.m. 23.0 31.0 19.5 1590 7.7 4:00 p.m. 22.6 24.3 14.6 1660 7.8 50 Friday, June 18, 1964 Ar———d3 rr H 40— 0———-O kr £1 \\ a: cm i” 0130— '0 DD 8 2; 20— g H I \R110 c> an E O I I r I I 12 4- 8 12 4 8 12 midnight noon midnight time Figure 6. Experiment Number 1. 26 iwa $9902 5 HO nn\a\mo we 12 midnigh 00 t n O O n time 27 Experiment Number 2. Figure 7. shown in Figure 7 this caused a sudden decrease in M.L.S.S. and surprisingly a massive increase of the kr value from 16.4 to 68.5 mg02 per gram M.L.S.S. per hour. Accordingly the activity of the mixed liquor at 4:00 PM remained rather high, rr = 24.1, in Spite of the loss of cell material. The BOD at this time was at the maximum for the day which apparently offset the expected decrease in r r. TABLE 3 ANALYTICAL DATA FOR EXPERIMENT 2 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate 8.8. pH BOD COD 0C rr kr mg/l mg/l mg/l 8:00 a.m. 21.0 12.2 8.6 1410 7.5 96 222 10:00 a.m. 21.8 18.g 15. 1240 7.4 128 270 12:00 p.m. 22.2 22. 17. 1280 7.4 108 298 2:00 pom. 23.0 21.8 160 1320 7.3 - 205 4:00 p.m. 23.0 24.1 68.5 352 7.4 140 - 7:00 p.m. 22.8 22.3 24.7 905 7.5 120 269 8:00 p.m. 22.8 21.2 21.9 969 7.5 126 217 28 2. Spmmer Term Experiment No. 3: Thursday, July 9, 1964 Table 4, Figure 8 This test series was begun at 6:00 PM and ended at 3:00 PM on the following day. The oxygen uptake rate decreased from a maximum, rr = 22.1 and kr = 12.6, at 12 midnight. The 2:00 AM and 6:00 AM data indicate that the oxygen utilization rate of the cells, kr, remained relatively stable from midnight to 6:00 AM. The oxygen uptake rate then continued to rise throughout the morning and afternoon. The treatment plant was receiving its full summer load as the summer school term had begun several days earlier. The primary treatment facilities were greatly overloaded due to the fact that one of the four primary tanks was closed down for repairs. Experiment No. 4: Thursday, July 16, 1964 Table 5, Figure 9 This test series began at 6:00 AM and ended at 8:00 PM. The oxygen uptake rate rose steadily through- out the day from a minimum, rr = 18.5 and kr = 8.6, at 8:00 AM to a maximum, rr = 34.3 and kr = 21.0, at 4:00 PM after which the rates declined. The temperature of the mixed liquor was quite high in the afternoon, average being 24°C. The afternoon oxygen utilization rates in 29 TABLE 4 ANALYTICAL DATA FOR EXPERIMENT 3 Sampling ‘_ Mixed Liquor Primary Effl. Time Temp. 0 Uptake Rate S.S. pH BOD COD 0 g k: mg/l mg/l mg/l C r 6:00 p.m. 22.0 37.7 20.5 1840 7.4 153 272 7:00 p.m. 22.0 43.9 26.0 1685 7.5 135 230 8:00 p.m. 21.5 31.6 19.1 1655 7.4 132 215 10:00 p.m. 21.5 29.4 15.6 1885 7.4 156 310 12:00 a.m. 21.0 22.1 12.6 1765 7.3 132 253 2:00 a.m. 20.6 23.3 13.6 1720 7.4 117 178 6:00 a.m. 20.5 29.0 12.4 2340 7.4 76 132 8:00 a.m. 21.1 31.8 14.8 2145 7.5 96 200 11:00 a.m. 22.0 31.9 19.3 1650 7.5 162 219 1:00 p.m. 23.5 33.7 20.9 1610 7.5 144 334 3:00 p.m. 23.0 36.1 20.6 1745 7.5 159 245 50 .p O l or mg 02/g SS/hr U) <3 4 Thursday, July 9, 1964 20 d (5 El ’0’,/O——‘O a Cl\\ ,ACk1‘_ ,/Cy :fi T}’ ‘r-CY Q10~ on Io an E 0 I I I I I I 12 , 4 8 12 4- 8 12 noon midnight noon time Figure 8. Experiment Number 3. TABLE ,4 D ANALYTICAL DATA FOR EXPERIMENT 4 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. pH BOD COD 0C Tr kr mg/l mg/l mg/l 6:00 a.m. 20.9 23.4 11.3 2065 7.4 80 136 8:00 a.m. 21.5 18.5 8.6 2160 7.5 68 155 10:00 a.m. 22.5 25.4 13.9 1830 7.5 72 17 12:00 p.m. 23.3 29.3 19.2 1525 7.5 132 19 2:00 p.m. 23.8 31.7 19.9 1590 7.5 122 204 4:00 p.m. 24.3 34.3 21.0 1630 7.3 120 196 6:00 p.m. 24.0 29.9 18.8 1595 7.5 102 186 8:00 p.m. 23.5 28.8 18.1 1585_12i§___150 194_ 50 Thursday, July 16, 1964 . a IQ——1Q Ir {a 40.. 33) 0‘0 R:- an \x 6“ a: 30* {-4 o 5.; 20- \\ .4 \\ cu <3 00 a 10-« 0 I r T I 12 4 8 12 4 12 midnight noon midnight time Figure 9. Experiment Number 4. experiment no. 3 are similar in magnitude to those of eXperiment 4 but the BOD concentration being applied in experiment no. 3 was higher than in no. 4, an average of 150 as compared to 120 mg/l. Expepiment No. 5: Thursday, July 23, 1964 Table 6, Figure 10 This test series began at 6:00 AM and ended at 8:00 PM. The treatment plant was Operating at a reduced sewage flow due to the diversion of the flow of a large sewer main into the Red Cedar River in order to facilitate repair of the sewer main. This diversion took place at a point above the Michigan State University campus and therefore the treatment plant was still receiving all of the Michigan State University flow plus a large portion of the city's flow. The oxygen uptake rate remained stable between 6 and 8:00 AM, rr = 15.5 and kr = 13.4, after which the rate steadily rose until a peak, rr = 33.2 and kr = 28.4, was reached at 2:00 PM; the rate then began to decline. The COD data of experiments 2 and 3 show little correlation to the primary effluent BOD. This may have been caused by the fact that the COD test samples of experiments 2 and 3 were stored overnight in a small portable electric cooler. The data of experiments 4 and 5 where the samples were not stored overnight do 32 TABLE 6 ANALYTICAL DATA FOR EXPERIMENT 5 Sampling Mixed Liquor 2 ,Primary'EffI: Time Temp. 02 Uptake Rate S.S. pH BOD COD 00 r k mg/l mg/l mg/l r r _“___ 6:00 a.m. 23.0 15.9 13.4 1180 7.5 63 118 8:00 a.m. 22.8 15.5 13.4 1155 7.5 78 98 10:00 a.m. 23.2 20.4 15.9 1265 7.6 102 98 12:00 p.m. 23.5 21.0 18.6 1130 7.4 96 110 2:00 p.m. 23.8 33.2 28.4 1170 7.5 156 172 4:00 p.m. 24.0 28.8 22.0 1305 7.4 159 1&3 6:00 p.m. 24.0 27.7 19.2 1495 7.5 201 1 0 8:00 p.m. 23.5 30.7 20.8 1470 7.4 144 139 50 Thursday, July 23, 1964 ,2 £&——£s rr :3 40— 1% C>-C> kr \. (\I C) DID E: 30— S—I O A Q r, 20— \\ (\l C) 00 a 10‘ 0 I 12 4 6 12 4 6 12 midnight noon midnight time Figure 10. Experiment Number 5. ‘13 show some relationship to the BOD for each particular day. Due to these inconsistent results it was decided to discontinue the COD test. Experiment No. 6: Wednesday, July 29, 1964 Table 7, Figure 11 This test series began at 6:00 AM and ended at 12:00 AM. The activity of the sludge, kr, remained unusually stable throughout the day and evening. The average temperature during the day was 23°C and 220C in the evening. The respiration rate, rr, ranged from 26.9 to 34.2 while kr ranged only from 14.6 to 16.3, which are quite small ranges. The BOD at 6, 7 and 8:00 AM averaged about 80 mg/l while the BOD from 10:00 AM to 8:00 PM averaged about 140 mg/l excluding the high 2:30 PM BOD of 192 mg/l. Since the activity of the sludge, kr, remained relatively stable through- out the day, while the BOD ranged from 80 mg/l in the early morning to 140 mg/l in the afternoon, it is assumed that the amount of dissolved BOD probably remained relatively stable throughout the day even though the total BOD varied by 60 mg/l. Since only dissolved BOD is immediately available to the oxidative processes of the cells, this would explain the relative stability of kr’ The reSpiration rate rr in turn remained stable because the M.L.S.S. and kr maintained 34 I L ~&\nnn~\rw»wvm:~ LfiU I IH-\~,I\pruI\:~ TABLE 7 ANALYTICAL DATA FOR EXPERIMENT 6 Sampling Mixed Liqu0r ”Primary Effl. Time Temp. 02 Uptake Rate S.S. pH BOD 0C r k mg/l mg/l r r 6:00 a.m. 23.0 33.8 15.7 2160 7.5 87 7:00 a.m. 22.8 34.2 15.9 2150 7.5 87 8:00 a.m. 22.0 31.4 14.3 2190 7.5 75 10:00 a.m. 23.0 20.8 14.2 2170 7.6 138 12:00 p.m. 23.0 31.2 16.3 1915 7.6 144 2:30 p.m. 23.0 30.1 15.9 1890 7.6 192 4:00 p.m. 23.0 30.9 15.1 2050 7.5 144 6:00 p.m. 23.3 31.2 15.9 1965 7.4 135 8:00 p.m. 22.2 26.9 13.2 2044 7.5 138 10:00 p.m. 22.1 30.0 15.9 1890 7.5 129 12:00 a.m. 22.0 27.4 14.6 1870 7.5 123 50 Wednesday, July 29, 1964 H I' 403 .2 3o— \. co co OD \x 6" g, 20“ X}——— 8 OQG-W/ 0‘0—*"O\\\O///O‘\4C> _§ 10_ ‘\ .4 \\ N 8. 5 O I I I I I 12 4 8 .12 4 8 12 midnight noon midnight time Figure 11. Experiment Number 6. 35 a steady level. Experiments No. 7, 8 and 9: No. 7 - Saturday, August 1, 1964 No. 8 - Sunday, August 2, 1964 No. 9 - Monday, August 3, 1964 Table 8, 9, 10, Figure 12 This weekend survey began at 6:00 AM Saturday and ended at 11:00 PM Monday. On Saturday a definite minimum oxygen uptake rate, rr = 7.4 and kr== 4.9, occurred at 8:00 AM after which the activity of the sludge increased steadily until at 4:00 PM a peak, r1. = 16.4 and k? = 10.4, was reached after which a steady decline in the activity took place during the evening. On Sunday the minimum oxygen uptake rate occurred from 8 to 10:00 AM, the average rr and kr being 11.4 and 6.9 respectively, after which the activity increased steadily until a plateau was reached beginning at 4:00 PM, rr and kr ranged from 21.6 to 22.8 and 12.7 to 14.2 respectively over the plateau which was still maintained at 11:00 PM, the last sample for the day. On Monday the minimum activity occurred from 7:00 to 9:00 AM, average rr and kr being 12.4 and 8.2 respectively, after which the activity suddenly jumped up to r1. = 23.8 and kr== 14.9 and then slowly rose until 36 TABLE 8 ANALYTICAL DATA FOR EXPERIMENT 7 Sampling Mixed Liquor Primary Effl. Time Temp 02 Uptake Rate S.S. pH BOD 0 mg/l mg/l C rr kr 6:00 a.m. 21.0 12.3 7.3 1685 7.4 84 7:00 a.m. 20.8 9.5 5.7 1675 7.4 54 8:00 a.m. 20.8 7.4 4.9 1530 7.4 75 10:00 a.m. 21.2 8.5 5.5 1555 7.5 111 12:00 p.m. 21.8 10.6 7.0 1520 7.3 93 2:00 p.m. 22.5 12.5 7.9 1575 7.4 99 4:00 p.m. 22.8 16.4 10.4 1525 7.5 126 6:00 p.m. 23.4 14.6 9.5 1555 7.5 93 8:00 p.m. 23.2 14.4 9.0 1595 7.5 96 TABLE 9 ANALYTICAL DATA FOR EXPERIMENT 8 Sampling Mixed Liqupr_ _h_____mn__Primary Effl. Time Temp 02 Uptake Rate S.S. pH BOD 0C 1' k mg/l mg/l r r 6:00 a.m. 22.3 13.0 7.3 1776 7.4 45 8:00 a.m. 22.5 11.5 7.0 1640 7.4 51 10:00 a.m. 23.2 11.3 6.8 1660 7.4 45 12:00 p.m. 23.5 12.6 7.8 1620 7.5 60 1:30 p.m. 24.2 15.6 9.1 1710 7.5 75 4:00 p.m. 24.5 22.3 13.4 1670 7.5 111 5:00 p.m. 24.0 21.7 13.8 1570 7.6 - 7:00 p.m. 2405 22.1 13 .4 1648 704 93 9:00 p.m. 24.0 22.8 12.7 1795 7.4 87 11:00 p.m. 23.8 21.6 14 2 1520 7.5 - 37 TABLE 10 ANALYTICAL DATA FOR EXPERIMENT 9 Sampling Mixed Liquor Primary Effl. Time Temp 02 Uptake Rate S.S. pH BOD oC r k mg/l mg/l r r 7:00 a.m. 23.8 12.6 8.3 1495 7.3 69 9:00 a.m. 23.8 12.2 8.2 1490 7.4 60 11:00 a.m. 24.0 23.8 14.9 1600 7.4 126 1:00 p.m. 24.2 23.2 14.6 1592 7.3 117 3‘00 p.m. 24.8 23.4 14.4 1625 7.5 120 5.00 p.m. 25.0 24.5 15.1 1620 7.5 123 7:00 p.m. 24.8 24.5 15.0 1632 7.5 117 9:00 p.m. 24.8 26.7 16.2 1645 7.5 129 11:00 p.m. 24.0 24.5 15.6 1565 7.4 117 an apparent peak was reached at 9:00 p.m., Tr = 26.7 and kr = 16.2 The oxygen uptake rate data indicate that the load on the aeration system was very light on Saturday, a little heavier on Sunday, and still heavier on Monday. A comparison of the BOD data on Saturday and Sunday with reSpect to the reSpective oxygen consumption rates reveals that the organic load on Sunday was more easily oxidized than on Saturday because higher oxygen uptake rates were experienced Sunday, even though the primary effluent BOD values were very similar to those observed on Saturday. The BOD data for Monday show a definite plateau corresponding 38 .m can .m .5 909852 madmafinonxm .NH onsmfim 0.55 _I hwcno: ”LI hwonnm Urn hacnupwm '— pnwmmofia noon pnmfimcas noon pnmfiavaa noon .2 A e _. a ._ a. ._ .1” ._ a . ewma am 9350 an arILq .m pmsmsd .hucqos smsonnp H pmsmsd .hwcnspam o Iom Ice O In sales 9/30 8m 40 IH/T/ZO 3m 39 to the oxygen uptake rate plateau; therefore the characteristics of the organic load must have remained relatively constant. The temperature ranged from 23.800 to 25.000 which is quite high for this treatment plant. Experiment No. 19: Wednesday, August 5, 1964 Table 11, Figure 13 This test series began at 7:00 AM and ended at 11:00 PM. The activity of the sludge increased from a minimum, r1. = 17.6 and kr = 9.9, at 9:00 AM throughout the morning and afternoon until reaching a peak at 3:00 PM, r1. = 31.5 and kr ==18.9. Between 5:00 PM and 11:00 PM both rr and kr remained at plateaus fluctuating about rr = 26.0 and kr = 15.0 reSpectively. The average mixed liquor temperature was 23.00C. Experiment No. 11: Wednesday, August 12, 1964 Table 12, Figure 14 This test series began at 7:00 AM and ended at 11:00 PM. The activity of the sludge increased through- out the morning and afternoon from a minimum at 9:00 AM of rr = 12.5 and kr = 6.2, to a peak at 3:00 PM of r1. = 25.0 and k1. = 11.9. After 3:00 PM the respiration rate per gram cell material remained at a plateau fluctuating about k1. = 11.0. This plateau remained even at 11:00 PM, 40 TABLE 11 ANALYTICAL DATA FOR EXPERIMENT 10 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate 8.5. pH B03 0 mg 1 mg 1 C rr kr 7:00 a.m. 23.5 20.5 11.3 1815 7.4 84 9:00 a.m. 22.2 17.6 9.9 1776 7.5 111 11:00 a.m. 23.0 21.6 13.8 1560 7.6 117 1:00 p.m. 23.2 23.5 14.3 1645 7.6 105 3:00 p.m. 23.0 31.5 18.9 1667 7.6 129 5:00 p.m. 23.2 25.5 15.4 1660 7.5 126 7:00 p.m. 23.0 27.5 16.4 1680 7.6 111 9:00 p.m. 23.0 24.2 13.5 1790 7.6 108 11:00 p.m. 22.0 26.6 15.0 1776 7.5 117 50 Wednesday, August 5, 1964 Ar——{i rr ,1 40- {a I) CF-wD kr (D no an \x 6“ 30— no 8 H O ,3 20— .C‘. \\ I-I \\ N ‘2. 10- a 0 I A I I I 12 4 12 4 8 12 midnight noon midnight time Figure 13. Experiment Number 10. A1 the time of the last sample. The magnitude of the plateau value of k1. (11.0) is rather low for the BOD loading being applied, from 138 to 150 mg/l. For example, in experiment no. 10 a plateau was observed for which the average kr was 15.0 mgO2/gSS/hr. at a BOD of 120 mg/l. Also the average temperature of 20.5°C was lower than the usual 22 to 24°C and this could be partially responsible for the lower activity. Experiment No. 12 and 13: No. 12 - Sunday, August 16, 1964 No. 13 - Monday, August 17, 1964 Table 13, 14, Figure 15 This weekend survey began at 7:00 AM Sunday and ended at 1:00 AM Tuesday. On Sunday the minimum activity of the sludge occurred at 11:00 AM, r = 8.7 and kr = 5.1, after r which the activity steadily rose until reaching a peak at 5:00 PM, rr = 17.8 and k1. = 8.9. The activity of the sludge, kr, remained steady between 7:00 PM and 1:00 AM within a range of 7.9 to 8.0, and the BOD of the primary effluent ranged only from 96 to 108 mg02/1. The steady cellular respiration rate and primary effluent BOD indicate that the plant was receiving a relatively constant type of waste for this period. At 2:00 AM the BOD load and the activity were beginning to decrease. 43 TABLE 13 ANALYTICAL DATA FOR EXPERIMENT 12 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. pH BOD oC r k mg/l mg/l r r 7:00 a.m. 19.8 11.1 6.4 1750 7.4 96 9:00 a.m. 19.2 10.2 5.7 1776 7.5 54 11:00 a.m. 19.8 8.7 5.1 1708 7.5 66 1:00 pom. 20.8 1002 6.2 1744 705 '- 3:00 p.m. 21.2 13.3 7.0 1892 7.5 102 5:00 p.m. 21.0 17.8 8.9 2004 7.4 96 7:00 p.m. 21.0 16.6 8.0 2072 7.5 99 9:00 p.m. 20.8 15.6 7.9 1974 7.5 105 11:00 p.m. 20.8 15.2 7.8 1948 7.4 108 1:00 a.m. 20.5 15.0 7.9 1900 7.4 87 2:00 a.m. 2000 14.0 6.8 1896 704 " TABLE 14 ANALYTICAL DATA FOR EXPERIMENT 13 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. pH BOD °C r k mg/l mg/l r r 7:00 a.m. 20.2 8.8 5.1 1720 7.6 54 9:00 a.m. 20.2 901 5.4 1690 705 66 11:00 a.m. 21.2 1305 7.2 1875 706 66 1:00 pom. 21. 1909 1007 1865 706 "' 3:00 p.m. 21.5 23.8 12.1 1965 7.4 126 5:00 p.m. 21.8 27.6 13.7 2020 7.5 141 7:00 p.m. 21.5 23.1 12.1 1915 7.5 132 9:00 p.m. 21.0 27.2 13.1 2072 7.5 141 11:00 p.m. 21.0 26.2 12.7 2060 7.2 120 1:00 p.m. 20.8 26.5 13.4 1980 7.4 117 44 :3 93 NH 90252 mpnmaflonfim .ma magma T .398: in hwcgm Ammaneaa noon , emmaeeaa noon Ammaqeaa NH 6 «H 6 NH 6 NH 6 ma _ . r _ _ _ _ _ _ O .OH Iom rom am 9:0 up. I 30¢ eema .ma gammsa..emeeo: eema .eH emama< .meeaam om IH/I/ao 3m 45 xu/ss 3/30 3m 40 On Monday the situation was changed. The minimum activity, r = 9.1 and kr = 5.4, occurred at 9:00 AM, 2 r hours sooner. The maximum activity occurred again at 5:00 PM but was much larger, Tr = 27.6 and kr = 13.1. The activity of the sludge, kr, also remained steady between 7:00 PM and 11:00 AM but at a higher range. The kr range was from 12.1 to 13.4. During this period, the primary effluent BOD ranged from 117 to 141 mg02/l. In general the shape of the plots of the sludge activity, kr’ (see Figure 15) for this weekend survey are very similar to the corresponding plots for the previous weekend survey (see Figure 12). Essentially the minimum and maximum oxygen uptake rates occurred at the same time, and the same leveling off at a high plateau during the evening was observed, although the numerical values differed for reasons attributable to differences in the temperature and the BOD load characteristics. Experiment No. 14 and 15: No. 14 - Friday, August 21, 1964 No. 15 - Saturday, August 22, 1964 Table l5, 16, Figure 16 This weekend test survey began at 7:00 AM Friday and ended at 7:00 PM Saturday. The activity of the sludge, fkr, for these two consecutive days showed only small fluctuations over each respective day. On Friday kr 46 TABLE 15 ANALYTICAL DATA FOR EXPERIMENT 14 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. pH BOD °C r k mg/l mg/l r 1' 7:00 a.m. 19.0 20.1 9.3 2144 7.3 60 9:00 a.m. 18.8 14.1 7.3 1925 7.2 36 11:00 a.m. 19.0 15.0 7.2 2090 7.2 51 1:00 p.m. 19.8 18.1 8.3 2175 7.4 66 3:00 p.m. 20.5 20.9 9.3 2250 7.4 99 5:00 p.m. 21.0 16.4 7.4 2210 7.4 93 7:00 p.m. 21.0 19.0 9.2 2064 7.4 93 9:00 p.m. 21.5 20.9 10.0 2092 7.3 108 11:00 p.m. 21.5 21.9 10.1 2188 7.4 87 1:00 a.m. 21.2 20.9 9.9 2108 7.2 87 2:30 a.m. 21.0 20.6 9.3 2200 7.3 72 TABLE 16 ANALYTICAL DATA FOR EXPERIMENT 15 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. pH BOD °C r k mg/l mg/l r r 7:00 a.m. 20.8 14.3 7.5 1895 7.4 72 9:00 a.m. 20.8 15.0 8.0 1885 7.4 54 11:00 a.m. 21.0 14.1 7.5 1865 7.5 57 1:00 p.m. 21.2 14.9 8.0 1868 7.4 75 3:00 p.m. 21.0 17.2 8.7 1964 7.4 84 5:00 p.m. 21.0 13.8 6.6 2076 7.4 42 7:00 p.m. 20.8 13.2 6.4 2092 7.4 45 47 .mH cum S“ 90852 mpnosfinonxm 6H 0.33m T hwcnspwm in hwgam l 3ch35 good panqua noon pnmfiqga NH 8 NH 8 NH 8 NH 8 NH _ _ m _ _ _ _ O nrlw, _ 10.. m 1010. IQGIIQ \O/ -- .Q/ 8 09.996. 8 Q d IOH 0 a/ TL / U. I .8 O J m an Iom 0 3 W um lo.-io a. m .HH I IO.v m eemH .NN Banana .hmenseem ammH .HN emsm64 .mmeHLm 48 ranged from 7.2 to 10.1 while on Saturday kr ranged from 6.4 to 8.7. For each day rr fluctuated widely at times due mainly to fluctuations in the M.L.S.S. concentration. On Friday the minimum activity occurred from 9:00 to 11:00 AM, the average rr and k1. being 14.5 and 7.3 reSpectively, after which the activity reached a plateau beginning at 3:00 PM and lasting through 1:00 AM, for which kr varied only slightly about the 10.0 mg/gSS/hr. level. On Saturday the activity of the sludge, kr, remained at a level of about 8.0 from 7:00 AM until 3:00 PM after which kr began to decrease. 49 3. Between Summer and Fall Terms The week of Monday, August 31 to Friday, September 4, 1964 was final examination week at Michigan State University. During the week some students began leaving the campus and on Friday the campus began closing down. Nearly all of the students had left by the following Monday. With the decrease in student population the mixed liquor at the treatment plant reSponded to the lower BOD load by turning from the dark grey-black color which predominated during the summer term to a light brown color. The mixed liquor was now being sufficiently aerated. The treatment plant data for the time between terms, September 7 to September 28, indicate that the average primary effluent BOD concentration was 100 mg/l which is considerably less than the average summer BOD concentration of about 130 mg/l. No oxygen uptake rate measurements were made during the time of low load, but measurements were taken during the final exam week as shown in Tables 17, 18 and 19 and in Figures 17, 18 and 19. Expegiments No. 16, 17 and 18: No. 16 - Monday, August 31, 1964 No. 17 - Wednesday, September 2, 1964 No. 18 - Friday, September 4, 1964 Tables 17, 18, 19, Figures 17, 18, 19 These three surveys have been grouped together because 50 the conditions at the treatment plant over the week were essentially stable. The average temperature of the mixed liquor for each of the surveys was about 22.0°C and the primary effluent BOD loading was similar for each day although the corresponding oxygen consumption rates differ. On Monday the oxygen uptake rate increased continusouly all day. The range of rr and kr being 8.4 to 24.6 and 5.1 to 14.4 respectively. The rate of increase was much slower in the afternoon and evening than in the morning. The primary effluent BOD did not show any steady rise but fluctuated between 120 andIUHDmgOZ/l. Since the activity of the sludge kr, is assumed to be pr0portiona1 to the amount of dissolved BOD (see Figure 31), the increased activity indicates that the percentage of dissolved BOD increased. The Wednesday survey began at 7:00 AM and ended at 11:00 PM. On Wednesday the oxygen uptake rate increased, from r1. = 18.0 and kr =11.5, until reaching a peak at 3:30 PM, r = 42.1 and kr = 23.4. The rates then declined I‘ to a steady level, r and kr being 35.0 and 19.0 respectively, r from 5 to 11:00 PM. The Friday survey began at 7:00 AM and ended at 11:00 PM. The oxygen uptake rates increased from a minimum at 9:00 AM, r1. = 21.4 and k1. = 15.3, to an average Tr and kr of 35.0 and 20.0 respectively. These values were maintained from 1:00 PM through to the last sample at 11:00 PM. 51 TABLE 17 ANALYTICAL DATA FOR EXPERIMENT 16 52 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. pH BOD o m 1 m 1 C r kr 8/ 8/ 7:00 a.m. 21.0 9.1 5.6 1644 7.3 72 9:00 a.m. 20.8 8.4 5.1 1656 7.4 80 11:00 a.m. 21.5 9.7 6.2 1560 7.5 124 1:00 p.m. 21.5 13.2 8.5 1560 7.5 122 3:00 p.m. 22.0 20.7 12.6 1636 7.5 140 5:00 p.m. 21.8 19.9 11.3 1760 7.5 140 7:00 p.m. 22.0 22.7 13.6 1664 7.5 130 9:00 p.m. 21.8 23.5 13.4 1752 7.4 124 11:00 p.m. 21.5 25.1 14.1 1776 7.4 114 1:00 a.m. 21.2 24.6 14.4 1704 7.5 124 50 —~ — ~ m, Monday, August 31, 1964 . H Pr 2 40-1 \ Q'm-O kr co co Q0 \\ ON cm 30— E $4 0 s3 20— :1 \x H \\ cu c> DD :3 10“ 0 . I I I I I 12 4 12 8 12 4 midnight noon midnight time Figure 17. EXperiment Number 16. TABLE 18 ANALYTICAL DATA FOR EXPERIMENT 17 Sampling Mixed Liquor Primary EffIT- Time Temp. 02 Uptake Rate S.S. pH BOD o 1 m 1 c Tr kr mg/ 8/ 7:00 a.m. 20.2 18.0 11.5 1564 7.4 82 9:00 a.m. 20.5 20.4 13.4 1516 7.5 114 11:00 a.m. 21.0 28.3 16.7 1692 7.4 134 1:00 p.m. 21.2 30.8 17.7 1740 7.5 142 3:30 p.m. 21.8 42.1 23.4 1796 7.5 136 5:00 pom. 2108 34.]. 18.9 1804' 706 '- 7:00 p.m. 21.8 35.5 18.5 1920 7.5 - 9:00 p.m. 22.0 35.5 19.7 1804 7.3 - 11:00 p.m. 21.5 34.0 18.7 1816 7.4 - 50 Wednesday, September 2, 1964 A \ 40fl U.) U) DO \\ cu c> 0.0 a 30‘ LI 0 i. £ 20— H \\ (\l C) no a 10— 0 I l I I I 12 4 8 l2 4 8 12 midnight noon midnight time Figure 18. Experiment Number 17. :2 ANALYTICAL DATA FOR EXPERIMENT 18 TABLE 19 Primary Sampling Mixed Liquor Effl. Time Temp. 02 Uptake Rate S.S. VSS pH BOD OC Tr kI. II18/1 % mg/l 7:00 a.m. 21.8 22.9 15.7 1464 71.5 7.4 94 9:00 a.m. 21.8 21.4 15.3 1392 74.1 7.4 82 11:00 a.m. 22.2 24.6 18.2 1356 73.9 7.4 114 1:00 pom. 22.5 3407 2007 1676 7001 7.4 '- 3:30 p.m. 23.0 35.2 19.2 1832 71.1 7.5 - 5:00 p.m. 22.0 31.6 18.7 1692 72.9 7.5 138 7:00 p.m. 22.5 35.3 20.6 1712 75.0 7.5 122 9:00 pom. 2200 34.9 20.8 1676 7402 7.5 "' 11:00 p.m. 21.8 330]. 19.8 1668 - - - 50 Friday, September 4, 1964 .3 4—4' rr {i 40~ g3 C%——C> kr 0.0 \\ ON a 30- a O .25 _ \‘ 20 H \\ 01 C) 0.0 E 10— 0 I I I I I 12 4 8 12 4 8 12 midnight noon midnight time Figure 19. EXperiment Number 18. 54 4. Fall Term On September 28, 1964 registration began for the fall term at Michigan State University. The sudden influx of students to the MSU campus resulted in heavy overloading of the aeration system and a rapid deterioration of the mixed liquor. Since no dissolved oxygen could be maintained in the aeration tanks, the mixed liquor turned from the brown color which it had obtained during the time between terms to a dark grey-black color. The average primary effluent BOD concentration increased from 130 mg/l to about 200 mg/l as shown in Table 28. As a result of this greatly increased BOD concentration the Specific oxygen consumption rates, kr, increased to about double the summer term rates as shown in Tables 27 and 28. Experiment No. 19: Tuesday, September 29, 1964 Table 20, Figure 20 This test series began at 7:00 AM Tuesday and ended at 8:00 AM Wednesday. The oxygen uptake rates were minimum at 9:00 AM, Tr = 21.1 and kr = 12.2. The values then increased less rapidly until at 3:00 PM, Tr and kr were 45.9 and 23.2 respectively, at which time the primary effluent BOD measured 182 mg/l. The 7:00 and 11:00 PM data show marked increases in both the BOD and oxygen uptake rates. At 7:00 PM Tr and kr were 72.0, and 37.9 reSpectively while the BOD amounted to 216 mg/l. .At 11:00 PM rr and kr were 87.5 and 17.8 respectively at a 55 TABLE 20 ANALYTICAL DATA FOR EXPERIMENT 19 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. VSS S.S. BOD Dis. BOD 00 r k ms/l % ms/l mg/l ms/l % r r 7:00 a.m. 16.5 22.5 12.3 1835 65.6 72 81 50 61.8 9:00 a.m. 16.5 21.1 12.2 1735 69.5 104 147 72 49.0 11:00 a.m. 19.0 38.9 21.4 1820 67.3 110 192 74 38.3 12:30 pom. 1908 38.7 20.9 1845 7104 "' " "’ " 3:00 p.m. 20.0 47.1 22.7 2080 87.0 88 183 84 46.0 5:00 p.m. 20.5 45.9 23.2 1975 78.6 182 174 86 49.5 7:00 p.m. 20.5 72.0 37.9 1900 76.8 216 210 106 50.5 9:00 p.m. 19.8 - - 1920 70.1 180 228 110 48.3 11:00 p.m. 20.0 85.5 24.2 1932 66.1 192 243 114 46.5 8:00 a.m. 19.0 27.0 17.8 1522 67.4 - - - - TABLE 21 ANALYTICAL DATA FOR EXPERIMENT 20 Sampling Mixed Liquor Primary Effl. Time Temp. 02 Uptake Rate S.S. VSS S.S. BOD Dis. BOD Oc r k mg/l mg/l mg/l mg/l % r r 7:00 a.m. 18.0 31.5 184. 1716 72.8 88 105 - - 11:00 a.m. 19.0 71.0 40.0 1776 72.5 104 222 157 70.6 1:00 p.m. 20.0 75.2 37.8 1966 73.1 90 186 105 57.0 3:00 p.m. 20.0 84.6 41.2 2056 70.4 98 174 130 74.8 5:00 p.m. 21.0 90.0 48.8 1848 77.1 204 234 154 65.9 7:00 p.m. 20.5 82.0 42.5 1922 76.8 186 174 115 66.2 9:00 p.m. 20.5 77.6 40.3 1926 75.8 192 180 142 78.8 12:00 a.m. 20.2 78.0 40.5 1922 — 250 21 109 50.4 2:00 a.m. 1905 73.2 3907 1840 "' " - - - 7:00 a.m. 19.2 52.7 38.8 1380 " - "' “ '- 56 C pf: H0 oHr~\H.\CO NE m \ 0 ll LR All L oHuk\ or mg O2/g SS/hr mg 02/1/hr 100 Tuesday, September 29, 1964 Ar—fia rr 90- 0—0 kr 80—w 70-* 60-“ 50— 4o— 30- 20— 10— 0 I F I 12 4 8 12 4 midnight noon .— time Figure 2CL EXperiment Number 19. 57 ——1 12 midnight lO Thursday, October 1, 1964 Ar—fia rr 90- 80- 79‘ 60‘ or mg 02/g SS/hr 50- mg 02/l/hr 20‘ 16‘ noon time — I 8 12 midnight Figure 21. EXperiment Number 20. 58 I 4 BOD of 243 mg/l. The 8:00 AM data on Wednesday indicate that sometime after 11:00 PM Tuesday the consumption rates decreased to the much lower level of rr = 27.0 and kr : 17.80 EXperiment No. 20: Friday, October 1, 1964 Table 21, Figure 21 This test series began at 7:00 AM Friday and ended at 7:00 AM Saturday. The data of this series again show the marked effect of the BOD concentration upon the oxygen consumption rate. The oxygen uptake rate rose steeply throughout the morning and afternoon, from rr = 31.5 and kr = 18.5 at 7:00 AM, to a peak of rr = 90.0 and kr = 48.8 at 5:00 PM. Then from 9:00 PM until 2:00 AM the activity of the sludge remained steady at about kr = 40.0. The value of kr at 7:00 AM Saturday was 38.8 which is rather high. 5. [Peak Oxygen Uptake Rate The purpose of these two test series was to observe the variation of the 3-4 PM sample's oxygen uptake rate over a week. It had been observed in many of the daily surveys that the peak oxygen demand occurred between 2:00 .5... 5:00 PM. Test Series No.11 From Monday, August 31 to Sunday,September 6 the mixed liquor oxygen uptake rate and suspended solids 59 were determined at 3:30 PM each day. These data are still representative of the summer term since few of the students had left before Friday night. However, nearly all of the students left on either Saturday or Sunday. See Table 22 and Figures 22 and 23 for the data of the survey. Test Series No. 2 From Monday, September 29 to Sunday, October 3 the mixed liquor oxygen uptake rate and suSpended solids were determined at 3:30 PM each day. The data reflect very markedly the arrival of the main Michigan State University student body for fall term registration which began on Monday. The oxygen uptake rates are very much higher than for series number 1 which was run when only about one third of the main student body was present on campus attending summer school. See Table 23 and Figures 22 and 23 for the data of the survey. Both test series show that the activity of the sludge, measured by kr, increases steadily from Monday to a maximum on Wednesday after which the activity decreases. 0n the basis of these two test series it can be said that the heaviest demand on the aeration system of the treatment plant occurs at mid-week, Wednesday. 60 TABLE 22 PEAK OXYGEN UPTAKE RATE SERIES NO. 1 Monday, August 31, to Sunday, September 6, 1964 Day Sampling Mixed Liquor 02 Uptake Rate Time Tr kr mg/l7hr. mg/gSS/hr. Monday 3:30 p.m. 20.7 12.6 Tuesday 3:30 p.m. 32.5 18.3 Wednesday 3:30 p.m. 42.1 23.4 Thursday 3:30 p.m. 37.2 21.7 Friday 3:30 p.m. 35.2 19.2 Saturday 3:30 p.m. 21.5 15.1 Sunday 73:30 p.m. 13.3 11.1 TABLE 23 PEAK OXYGEN UPTAKE RATE SERIES NO. 1 Monday, September 28, to Sunday, October 3, 1964 4 Day Sampling Mixed Liquor 02 Uptake Rate Time Tr kr mg/l/hr. mg/gSS/hr. Monday 3:00 p.m. 36.3 20.2 Tuesday 3:00 p.m. 47.1 22.7 Wednesday 3:00 p.m. 88.5 50.6 Thursday 3:00 p.m. 84.6 41.2 Friday 3:00 p.m. 85.2 47.4 Saturday - - - Sunday 3:00 p.m. 47.0 28.5 61 lO 90— 80‘ 233‘ ‘4‘ 9?‘ 3 oxygen uptake rate, rr, mg 02/1/hr u) ‘? 20+ 10* [km—A Test series no. I)- h September 28 to October 3, 1964 C) C)Test series no. 1 - August 31 to September66, l9 4 Sun. Mon. Figure 22. I I Tue. Wed. day I I r Thur. Fri. Sat. Peak Oxygen Demand, rr, Over a Week. 62 Sun. 6O 4: \n c? o 1 oxygen uptake rate, kr, mg 02/g SS/hr ‘6’ 1 Ar~i3 Test series no. 2 - September 28 to October 0 0 3, 1964 Test series no. 1 - August 31 to September 6, 1964 0 Sun. Figure 23. Peak Oxygen Demand, k I I I I I I Mon. Tue. Wed. Thur. Fri. Sat. Sun. day r’ Over a Week. 63 6. Determination of the Oxygen Transfer Coefficient, KLa, for the Treatment Plant's Aeration Equipment The theory of oxygen transfer to a liquid body has been discussed quite thoroughly by Eckenfelder and O'Connor (21). The rate of molecular diffusion of a dissolving gas into a liquid is a function of the characteristics of the gas and the liquid, the temperature, the concentration gradient, and the cross-sectional area through which diffusion occurs. The rate of oxygen transfer is given by: dc/dt = KLa (CS - C) where KLa is the "oxygen transfer coefficient" which is a function of the interfacial area, volume of the liquid, and other physical and chemical variables characteristic of the system, and CS - C is the dissolved oxygen gradient. Eckenfelder and O'Connor (21) modified the above equation for application in the steady-state aeration of an activated sludge system by introducing the term rr: dc/dt = KLa (CS - C) -rr (1) in which rr = oxygen uptake rate in milligram oxygen consumed per liter per hour. Under steady-state dc/dt = O and the equation becomes KLa = Egg—C (2) 64 This relation is very useful for analyzing and Operating an aeration system. By measuring the D.O. in the mixed liquor tank, C, and determining the oxygen uptake rate r at the same time, the oxygen transfer r coefficient for the aeration system can be evaluated from the 510pe of a plot of D.O. versus rr. The relation- ship is linear as is shown by rearranging the equation: rr = KLa (Cs - C) (3) : KLa C S '- KLa C then c = c - 1 (4) S KLa Tr Equation 4 can be compared to the straightline y = a - bx where: y = C a = C3, the ordinate intercept b = l/KLa, the slope x = r 1' Therefore, assuming steady-state, and by determining C and rr, the transfer coefficient KLa can be evaluated from the slepe. The measurements of C and rr shown in Table 23 and in Figure 24 were taken over a two day period during the Christmas holidays. The students had left the MSU campus thereby reducing the load on the treatment plant. Under 65 the reduced loading, the aeration system was adequate to maintain several parts per million D.O. in the mixed liquor, otherwise this survey would not have been feasible. The temperature of the mixed liquor varied from 140 to 150C which is allowable since a 10C difference will not effect KLa significantly. In agreement with data given by Eckenfelder and O'Connor (21) the D.O. saturation limit, CS = 8.7 mg/l, was taken as 90 per cent of the saturation value given in Standard Methods at 150C. This value was used as a fixed point on the ordinate when locating the line through the data. The value of the oxygen transfer coefficient determined from the graph is KLa = 2.63 per hour. Thus, for every unit (1 mg02/l) of concentration gradient, C - C = 8.7 - C, 2.63 milligrams oxygen per 5 liter per hour are transferred to the mixed liquor. Thus, the capacity of the aeration system is very low since the maximum oxygen uptake rate, rr, which can be satisfied while still maintaining a D.O. of 1 mg/l is only 7.7 (2.63)== 20.3 mg02/l/hr. A value of rr = 20.3 is very low indeed. The daily test series during the summer and fall have all shown that Tr greatly exceeds 20.3 most of the day, with the exception of weekends where rr is not greater than 20.3 for the majority of the day. 66 TABLE 24 ANALYTICAL DATA FOR THE DETERMINATION OF THE OXYGEN TRANSFER COEFFICIENT Temp Mixeg giquor Oxygen Uptake Rate (0C 0 0 Ir ) mg02/l mgOZ/l/hr. 15 0.89 20.7 14.5 1.3 19.5 14 1.8 15.1 15 2.2 15.9 15 2.2 14.9 15 2.9 14.4 15 3.3 15.0 15 3.6 13.5 14.5 4.3 12.0 14.5 4.6 11.2 14 5.2 11.4 67 dissolved oxygen, mg 02/1 saturation limit at 15 0C, c = 8.7 S l/slope = 2.63/hr O I I O 10 20 30 oxygen uptake rate, rr mg 02/1/hr Figure 24. Determination of the Oxygen Transfer COfoiCient , KLa o 68 B. Otherlnvestigations l. Tgmperature Effect Identical mixed liquor batches were prepared by mixing aerated return sludge with a primary effluent sample using the pr0portions of l to 1.5 reapectively. This procedure allowed each sample to be treated individually without any error due to aging of one sample while the oxygen uptake rate of another was being observed. Three temperature controlled water baths were available. The baths were first set at 15°, 200 and 30°C. Then the 15° and 30°C baths were cooled to 10° and 25°C respectively. Each sample was placed in its respective water bath and aerated at a high rate in order to obtain an adequately high D.O., preferably 6 to 7 mg/l, for the observation of the oxygen depletion rate over time. During the aeration the sample was stirred by means of a submersible Bronwill Mag-Jet magnetic stirrer with a teflon coated stirring bar. .After 15 minutes of aeration the sample was assumed to be in equilibrium with the temperature of the water bath. The D.O. depletion was followed by means of the polarographic oxygen electrode. As demonstrated in Table 24 and in Figure 25 the data show a straightline relationship, when a semilogarithmic plot is made of k1. versus temperature. The slope of the line is 0.0323/00. The equation of the slope is: 69 0.0323 (t2 - t1) (1) log k2 - 10g kl then k2 : k1 lo0.0323 (t2 - t1) (2) This is in agreement with data published by Eckenfelder (21), Wuhrman (22) and Phelp's (23). The slopes reported by these authors as given by Eckenfelder and O'Connor (21) were 0.0368, 0.0315 and 0.0273/0C respectively. TABLE 25 EFFECT OF TEMPERATURE ON RESPIRATION RATE Temp. Sludge to Primary Contact Mixed Liquor 02 Uptake Rate 0 Effluent Ratio time r k . r r C minutes mg/l/hr. mg/gSS/hr 10 1:1.5 15 11.8 5.4 15 1:1.5 15 17.8 8.1 20 1:1.5 15 28.6 13.0 25 1:1.5 25 30.3 13.8 30 1:1.5 15 50.0 22.7 7O oxygen uptake rate kr mg 02/g ss/hr 60- 40" 20'- 1.0 O 10 Figure 25. I I 20 30 4O temperature 0C Effect of Temperature upon the Oxygen Uptake Rate of a Mixed Liquor o 71 2. Effect of Substrate Addition The purpose of this experiment was to observe the effect of a sudden BOD loading upon a mixed liquor which had not been fed for several hours. On November 19, 1964 a mixed liquor grab sample was taken from the East Lansing Sewage Treatment Plant. The mixed liquor was black indicating that it was in a very poor condition. The sample was aerated for four hours after which time a 2 liter sample was fed 1000 mg glucose. The temperature was held constant by means of a controlled water bath at 20°C. The effect of the glucose addition was observed by determining the oxygen uptake rate at frequent intervals. The data are listed in Table 26-and shown graphically in Figure 25. In Figure 26 there are four distinct portions of the curve. In portion I the mixed liquor had reached the endogenous phase after four hours of aeration and no feed, average rr ==l4.5. Then a sudden doubling of the reapiration rate, r = 28.8, was observed in section II r which was obtained within one halfuhour after feeding. In section III there was a slow increase in the respiration rate for approximately 3 hours, after which rr = 32.4, then a more rapid rise in the reapiration rate occurred for the next two hours until a maximum of rr = 38.7 was reached. In section III an adaptive process to the glucose substrate 72 seems to have been occurring. Finally in section IV the substrate has either been completely used up or has reached such a low concentration that the organisms could no longer maintain the relatively high oxygen uptake rate and within two hours rr decreased to the endogeneous level, rr = 11.9. Since the East Lansing Sewage Treatment Plant where this thesis work was done is a "biosorption" plant with approximately 7 hours aeration of the return activated sludge, the activated sludge entering the mixed liquor aeration tanks is in the endogeneous phase, similar to section I. Then, when this starved sludge is contacted with the primary effluent an immediate reSponse similar to section II occurs. Thus by measuring the oxygen uptake rate within 10 to 20 minutes after initial contact of the return activated sludge and primary effluent, the maximum oxygen demand rate placed upon the aeration system is determined. This has been done in this thesis. In the above statement section III of the curve in Figure 26 has not been disregarded, but it is felt that it is relatively unimportant for most domestic sewage treatment plants. In such treatment plants, it is expected that the sludge is adapted to the sewage. It was observed during the course of this work that the oxygen uptake rate rapidly decreased after 20 to 30 minutes as shown in Figure 27. This would be expected since the BOD concentrations are quite low compared to 73 the activated sludge solids concentration. Eckenfelder and O'Connor (21) and Bargman, Betz and Garber (24) have reported that the oxygen utilization rate of activated sludges decreased rapidly within one half hour of aeration. 74 TABLE 26 EFFECT OF SUBSTRATE ADDITION USING GLUCOSE Run No. Time Mixed Liquor 02 Uptake Rate, rr hours mg02/l/hr. l 4.0 14.6 2 4.5 14.4 Addition of 500 mg/l glucose 3 5.0 28.8 g g.§5 28.8 . 27.9 6 600 30.3 7 6.5 31.5 8 700 31.5 9 8.0 32.4 11 11.0 27.0 12 11.5 23.4 13 12.66 11.9 40 30" :3 ,q h 20— \\ N C) 0.0 a n 2. 10— $4 0 I g I I I 2 4 8 10 12 14 time, hours Figure 26. Effect of Substrate Addition Using Glucose. 73 ki, mg 02/g ss/hr 20 l5~ temperature = 20 1 0.5 00 MLSS = 2376 mg/1 10 primary effluent BOD; == 96 mg/l 8—1 6—~ 4... 2— O I l l l 0 2 4 6 8 10 time, hours Figure 27% Variation in Specific Oxygen Uptake Rate with Time. 76 SECTION IV DISCUSSION OF RESULTS A. Oxygen Uptake Rates by the Polarographic Oxygen Electrode Technique The measurement of mixed liquor oxygen uptake rates by observation of the dissolved oxygen concentration depletion over short periods of time with the oxygen sensitive polarographic electrode has been found to be a rapid, simple, and accurate technique. The oxygen meter and reSpiration flask assembly were easily used at the sewage treatment plant due to the portability of the instrument and the simplicity of the technique in determining respiration rates. The electrode functioned well and it was only due to membrane damage incurred by accidentally bumping the membrane against a rough surface that the electrode had to be recharged after three months of service. Although the electrode functions well over long periods of time, it is necessary to check the calibration of the instrument from time to time. The electrode shows a definite aging effect which makes itself felt by decreasing sensitivity with time. The rate of aging is quite slow as shown in Figures 28 and 29. The greatest rate of aging occurs immediately following the charging of the cell with the 77 electrode sensitivity, microamps/mg 02/1 4 _. 3.. 5111/64 2_ 5/26/64 6/8/64 7/6/64 1 1 T O 10 2O temperature, 0C Figure 28. Aging Effect Upon the Electrode Sensitivity. 78 electrode sensitivity, microamps/mg 02/1 5 4' temperature == 20 0C 3‘ ‘vfig 2—4 1— 0 I I I I I 0 10 20 30 40 50 60 time , days Figure 29. Aging Effect Upon the Electrode Sensitivity at 20 0C. 79 potassium chloride electrolyte and installing a new membrane. The writer feels that the aging process involves a decreasing permeability of the protective teflon membrane, although a small reduction in the sensitivity undoubtedly occurs due to the deterioration of the batteries and the silver coil cathode. The electrode allows to measure the oxygen depletion rate over time with a rather high precision. The observed dissolved oxygen concentrations when plotted against time show a very good correlation to a straight- line as shown in Figure 30. The lepe of this type of plot is the oxygen uptake rate for the sample. The oxygen uptake rates reported in this thesis were obtained by computing the average oxygen uptake rate per 5 or 2 minute interval used in observing the D.O. depletion and multiplying by the corresponding conversion factor, either 12 or 30 respectively, in order to convert the rate to an hourly rate. B. Mixed Ligaop Oxygep Uptake Rates at the Sewaga Treatment Pleat 1. The Oxygea Uptake Rate Curve Over a Day The series of experiments 1 through 20 indicate that a characteristic loading curve exists at the East Lansing Sewage Treatment Plant. The form of this characteristic loading curve, given by the Specific 80 dissolved oxygen, mg 02/1 Tuesday, September 29, 1964 Oxygen uptake rate = rr = lepe, mg 02/1/hr 22.5 0 2 4 6 8 10 12 time, minutes Figure 30. Mixed Liquor Dissolved Oxygen Depletion Over Time. 81 oxygen uptake rate, kr reSpiration rate occurs from 7 to 10 AM after which the , is the following: (1) the minimum activity steadily increases to the afternoon maximum, (2) the maximum reSpiration rate occurs from 2 to 5 PM after which the activity decreases to an evening plateau, and (3) in the evening the reapiration rate remains quite steady from about 7 PM to about midnight, after which the activity decreases to the minimum rate for the following day. The numerical value of the oxygen uptake rates is dependent on the BOD concentration of the primary effluent. The peak oxygen uptake rate survey shows that these rates vary daily with Wednesday having the highest oxygen consumption rate. The weekend survey has shown that kr is considerably lower for the weekend than for weekdays. The comparison of data obtained during terms and in between terms shows that the whole curve is raised considerably by the increase in pOpulation during terms. 2. T e Ox en U take Rate Curve Over a Weekend In general the kr measurements show that the demand placed upon the aeration equipment of the sewage treatment plant during the summer months over a weekend, was about 1/3 less than that experienced during a weekday. The lower aeration demand exists during Saturday and through Sunday until Monday morning. The first weekend survey, see Figure 12, clearly shows that the aeration demand on 82 Saturday and Sunday is lower than on Monday although Sunday was not quite as low as Saturday. The second survey, see Figure 15, again showed that the Sunday oxygen demand is lower than on Monday and that the Specific respiration activity kr shows a rapid rise on Monday morning. The third survey, see Figure 16, shows that the Saturday demand is less than on Friday. On the basis of the above three weekend surveys, the oxygen demand on Saturday is the minimum for the entire week, with the Sunday demand being the next lowest. The BOD data for the reSpective days agree with this concept. Saturday is the period of lowest BOD concentrations, although the differencebetween Saturday and Sunday is not very great. Dissolved BOD deter- minations may have illustrated this point better but no such determinations were made for the weekend surveys. The above surveys also reveal that the rr value did not exceed 20 mg/l/hr. on Saturday and that on Sunday the portion of the rr curve above 20 mg/l/hr. was much less than the portion below this level. It is therefore evident that the mixed liquor was being adequate aerated only over the weekend. Throughout the week the aeration equipment was not capable of supplying the oxygen needed to maintain even a trace of D.O. in the mixed liquor. 83 3. Relatiopship of the Specific Respiratiop Rate, kr, to the Primary Effluent - Total and Dissolved B92 In experiments 2 through 20, BOD determinations were made upon primary effluent grab samples simultaneously with the rr and kr measurements. The majority of the BOD determinations were made on unfiltered primary effluent; these were recorded as total BOD and tabulated in Table 27 and plotted against the solids respiration rate, kr, as shown in Figure 31. The graph shows that the activity of the activated sludge increases directly with the concentration of the primary effluent BOD. The data show a wide band of variation which is probably due to differences in the dissolved BOD, which is the only part of the total BOD immediately available to the bacterial cell. Secondly, the cellular reSpiration rate, kr, is based upon the total mixed liquor suSpended solids concentration. As has been shown by several authors, (21), (25) and (20) the mixed liquor suSpended solids consist only partially out of viable microorganisms. The mixed liquor volatile suSpended solids deter- minations obtained in experiments 18 through 20 indicate that the ash content of the mixed liquor suspended solids is about 30%, as shown in Tables 19, 20 and 21. This indicates that the East Lansing activated sludge contains 84 a significant fraction of inert material since pure bacterial substance has ash contents of only about 8 - 12% as reported by Schulze (26). Even the volatile content probably still does not represent pure active cells but it is certainly closer to a more realistic value of the amount of viable cells than the total suSpended solids. The mixed liquor volatile suSpended solids(M.L.V.S.S.) of eXperiences 18 through 20 have been used in the computation of k1. for these experiments as tabulated in Table 28. This table also lists dissolved BOD data, as obtained by filtering the sample through a 0.45 micron pore size Millipore membrane filter. Figure 32 shows the plot of kr based upon the M.L.V.S.S. versus both the dissolved and total BOD of the primary effluent. The lines drawn through both sets of data are tentative. The data show that kr increases directly with the dissolved and total BODS. More data over a larger range of BOD values would be required for a more definite evaluation of the shape of the curves. The graph shows that the dissolved BOD has a pronounced effect on kr which is as expected since the dissolved BOD represents that portion of the BOD which is immediately available to the bacterial cells. 85 TABLE 27 TABULATION OF THE PRIMARY EFFLUENT BOD DATA OF EXPERIMENTS 2 THROUGH 20 BOD kr BOD kr BOD kr 36 7.3 86 11.3 114 14.1 42 6.6 87 6.8 114 18.2 45 7.3 87 9.9 115 15.0 45 6.8 87 10.1 117 13.6 45 6.4 87 12.7 117 13.8 51 7.0 87 15.7 117 14.6 51 7.2 87 15.9 117 15.0 54 5.7 92 9.2 117 15.6 54 5.7 93 7.0 120 14.4 54 8.0 93 7.4 120 18.1 57 7.0 93 9.5 120 21.0 57 7.5 93 13.4 122 8.5 60 7.8 94 15.7 122 19.9 60 8.2 96 6.4 122 20.6 60 9.3 96 8.6 123 14.6 63 13.4 96 8.9 123 15.1 66 10.5 96 9.0 124 6.2 66 5.1 96 14.8 124 13.4 66 8.3 96 18.6 124 14.4 68 8.6 99 7.9 126 10.4 68 6.2 99 8.0 126 14.9 69 8.3 99 9.3 126 15.4 72 13.9 102 7.0 126 21.9 72 9.3 102 15.9 128 15.3 72 7.5 102 18.8 129 15.9 72 5.6 105 7.9 129 16.2 75 4.9 105 14.3 129 19.9 75 9.1 105 18.4 130 11.3 75 8.0 107 7.8 130 24.7 75 14.3 107 10.0 132 12.6 76 12.4 107 13.5 132 19.1 78 13.4 107 17.8 134 16.7 80 11.3 111 5.5 134 19.2 80 5.1 111 9.9 135 15.9 82 11.5 111 13.4 135 26.0 82 15.3 111 16.4 136 23.4 84 7.3 114 8.3 138 8.7 84 8.7 114 13.4 138 11.3 BOD Total Primary Effluent BOD, mg02/1 kr Mixed Liquor Cellular ReSpiration Rate, mgOg/gSS/hr. 86 TABLE 27 CONTINUED B OD kr B OD kr B OD kr 138 13.2 147 10.8 164 42.5 138 14.2 147 12.2 183 22.7 138 18.7 150 11.9 186 37.8 140 12.6 153 20.5 190 15.9 142 17.7 156 15.6 190 21.4 142 20.7 156 28.5 201 19.2 142 19.2 159 20.6 210 37.9 144 15.1 159 22.0 216 40.5 144 16. 162 19.3 222 40.0 144 20. 164 23.3 234 48.8 144 20.9 164 41.2 243 44.2 87 TABLE 28 TABULATION OF THE PRIMARY EFFLUENT BOD DATA OF EXPERIMENTS 18, 19, and 20 Total Dissolved Mixed Liquor 02 Uptake Rate 'BOD BOD kr kr m802/1 mgoz/l mgO2/gSS/hr. mgOZ/gVSS/hr. 81 50 12.3 18.6 147 72 12.2 17.4 192 74 21.4 31.1 183 84 22.7 26.0 174 86 23.2 29.5 186 105 37.8 52.2 210 106 37.9 49.8 216 109 40.5 54.0 243 114 44.2 66.9 174 115 42.5 56.5 174 130 41.2 58.9 180 142 40.3 53.2 234 154 48.8 63.2 222 157 40.0 57.6 94 15.7 21.9 82 15.3 20.7 114 18.2 24.6 142 20.7 29.5 142 19.2 27.0 138 18.7 25.5 122 20.6 27.5 88 50 O - 54 O 5 3’, 40- 90 O 0 no \ N 0 DD 0— a 3 O " O H o x O O OO O p — g 20 0% 09000 o O o (D 0&08 O 000 O O 31 OO 0 0 00 4‘3 0 03 00 O0oO S‘ 10 %OOOO%0900 0 q 0.900 a « - (D 00 O E K o O I I O 100 200 300 primary effluent BOD, mg 02/1 Figure 31. Relationship Between Primary Effluent Total BOD to the Cellular Respiration Rate, kr, Based on M.L.S.S. 89 .L.V.S.S., mg 02/g vss/hr k based on M 80 7O 6O 5O 4O 3O 2O — 10‘— A - total BOD C>- dissolved BOD l l O 100 200 300 primary effluent BOD, mg 02/1 Figure 32. Relationship Between Primary Effluent Total and Dissolved BOD to the Respiration Rate, kr’ Based on M.L.V.S.S. 9O 4. Maaaurement of the Capacity of Aeration Egaipment UndeaOperating Conditions The use of the polarographic oxygen electrode for the rapid and simple measurement of oxygen uptake rates of heavy suSpensions such as sewage-activated sludge mixtures has Opened up a new concept of treatment plant control. As shown in Figure 23 in the experimental results, Section V-6, the oxygen transfer coefficient of the East Lansing Sewage Treatment Plant aeration equipment was determined as the inverse of the slope of the plot of the D.O. in the mixed liquor tank versus the oxygen uptake rate existing at the time of the measure- ment of the D.O. A great practical asset of this type of graph is that it tells the plant Operator what his aeration system is capable of doing. By varying the rate of air supply, the operator can obtain a set of curves showing KLa at each aeration rate. Then, with these graphs as a guide he can regulate the aeration rate in a adequate manner to meet changes in rr. If the Operator desires to maintain 1.5 mg/l D.O. in the mixed liquor but finds that he is actually obtaining 4.7 mg/l due to a low sludge activity, such as observed on the weekend, he can determine what aeration rate to use merely by extrapolating the activity, rr, at D.O. = 4.7 from the high aeration rate curve. Then by referring to the 91 lower aeration rate curves find that curve at which the D.O. is closest to 1.5 at the extrapolated r value as r illustrated in Figure 33. Eckenfelder and O'Connor (21) have reported that the logarithm of KLa V, the product of tank volume V times KLa, increases directly with the logarithm of the aeration rate within limits. Since V, the aeration tank volume is constant, KLa increases directly with the air flow rate. A graph illustrating the above relationship was given for the sparger and discfuser, hydraulic shear box, saran tubes, plastic tubes, and aloxite tube diffused aeration device. The increase in KLa results in an increase in the capacity of the aeration equipment which is equal to KLa (CS - C). Therefore at a given D.O. higher oxygen utilization rates can be supplied by increasing the aeration rate. The effect which the aeration rate is illustrated in Figure 33. The graph shows that the lower aeration rate can supply the oxygen demand rate of 12.5 mg/l/hr. and maintain an adequate D.O. concentration of 1.5 mg/l while the high aeration rate is maintaining an unnecessary high D.O. of 4.7 mg/l. 92 dissolved oxygen, mg 02/1 10 -P \n Ch ~q cn \0 Nu) _ low air flow Figure 33. I I 10 20 oxygen uptake rate, r , mg 02/l/hr I' Effect of Aeration Rate Upon Aeration Capacity. 93 6O SECTION VII CONCLUSIONS 1. The oxygen uptake rate of a heavy floc suSpension such as a sewage-activated sludge mixture can be measured rapidly and accurately by the polarographic oxygen electrode technique. 2. The portable oxygen meter and electrode assembly can be used to measure the dissolved oxygen concentration in "situ" at a mixed liquor aeration tank. 3. The rapidity and simplicity of the polarographic oxygen electrode technique for the measurement of oxygen uptake rates by the continuous observation of the oxygen depletion over short periods of time makes it feasible to study actual plant Operating conditions. 4. Experimental data indicate that the solids oxygen uptake rate, kr, for any given day increases from a minimum between 7 and 10 AM to a peak value between 2 and 5 PM after which the rate slowly decreases during the evening until at about midnight the rate decreases more rapidly to the minimum value at the following morning. Over the weekend, kr, is much lower than for a weekday, with Saturday being the period of lowest kr values while Wednesday is the period of highest kr value. 5. The oxygen uptake rate, kr, of activated sludge treating a domestic sewage has been found to vary directly 94 with the total and dissolved BOD of the primary effluent. 6. Temperature markedly effects kr' The lepe of a semilogarithmic plot of kr against temperature, 0C, was found to be 0.0323/0C. 7. The activity of a starved activated sludge doubled within one half hour after being fed 500 mg/l glucose. This immediate acceleration of the sludge activity is assumed to be analogous to the reSponse of an aerated return activated sludge such as found in the biosorption modification of the activated sludge treatment process. 8. The aeration system of an activated sludge plant can be analyzed for its efficiency and capacity by observing the D.O. in the mixed liquor and simultaneously determining the oxygen uptake rate, rr. The plot of D.O. against rr is linear; the inverse of the lepe is the oxygen transfer coefficient, KLa, and the abscissa intercept is the maximum capacity of the aeration system for the given conditions of temperature, aeration rate, and other characteristics of the aeration system. 95 l. 10. 11. BIBLIOGRAPHY water, 11th Ed. American Public Health Assoc., Inc., New York, N.Y. (1960). Ingols, R. 3. "Determination of Dissolved Oxygen by the DrOpping Mercury Electrode," Sewa e Works Journal, 13, 6, 1097 (November 1941). Moore, E. W., Morris, J. C., and Okun, D. A., "The Polarographic Determination of Dissolved Oxygen in Water and Sewage " Sewage Works Journal, 20, 6, 1041 (November 1948). Band, M. C., and Heukelekian, H., "Determination of Dissolved Oxygen in Industrial Wastes by the Winkler and Polarographic Methods," Sewa e apa Industrial Wastes, 23, 9, 1141 (September 19 1). Lynn, W. R., and Okun, D. 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F., "Aeration Requirements of a High Oxygen Demand Sewage," Sewa e and Industrial Wastes, 29, 7, 768 (July 19571. Schulze, K. L., "The Activated Sludge Process as a Continuous Flow Culture, Part 2. Application," Water Works and Sewage, 112, 1, 11 (January 1965). McKinney, R. E., Microbiology for Sanitar Engineers, McGraw-Hill Book Co., New York, (19625. 98 ,. - ("a ""Jh :, .. T . L.- i'. .. - flr‘,.’:.--*o ‘ _“ ‘L "44“.“ k‘. MICHIGAN STATE UNIVERSITY LIBRARIES I IIII III I II II IIIIIIII 3 1293 3142 5402