7: \l M» 11 HIuWil’l v r 1 .TH3 126 704 USE OF RESTRXCTED AER SUPPLY FOR TEMPERATURE CONTROL PM THE AEROBEC 9ECQMFGSWON OF SGLEZ} GRGAMC WASTES Thesis 50w Hue Degree o§ M 5. MICHEGAN STEEE UNIVERSITY John B. Zondorak 1956 IIIT WWI W1Ifiiiflfififlilfllll'lTl‘l‘l‘ll’l‘l'ElsiI| 3 1293 10705 1736 This is to certify that the thesis entitled ' . Use of Restricted Air Supply for Temperature Control in The Aerobic Decomposition of Solid Organic Wastes presented by John B. Zondorak has been accepted towards fulfillment of the requirements for ”Hillel's. _ -__degree in..._S§13.3:-ol?§11.Y_ Engineering ajor professor Date November 28, 1956 11-795 MSU RETURNING MATERIALS: Place in book drop to LIBRARIES remove this checkout from “- your record. FINES will be charged if book is returned after the date a stamped below. 'flQV? . 4 "6' 235.137“ ' USE OF RESTRICTED AIR SUPPLY FOR TEMPERATURE CONTROL IN THE AEROBIC DECOMPOSITION OF SOLID ORGANIC WASTES by John B. Zgndorak AN ABSTRACT Submitted to the College of Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Civil and Sanitary Engineering 1956 Approved JOHN B. ZONDORAK ABSTRACT A study was made on the control of temperature for an aerobically decomposing mass of solid organic matter by re- stricting the supply of air. Preliminary work indicated that a discontinuance of air flow during the decompositinn process resulted in a de— crease in temperature. Conversely, addition of air caused the temperature to rise. A unit operating on this principle of controlled air supply was constructed. A cylindrical batch-type digester with 4 gallon working capacity and no stirring mechanism was used. Forced air at room temperature was applied through a plastic diffuser plate to the unit when a solenoid air valve was energized by a thermostat set for 4500. In this way air was supplied to the solid organic material in the unit when the temperature was below 4500 and not above this level. The solid organic matter consisted of fresh food which was proportioned in such a manner as to represent a typical garbage. The sample was shredded, mixed with oven dried end product from previous runs, and stored for 48 hours at room temperature before each of three experiments was started.. One experiment did not have a storage period. Physical and chemical tests for evaluating changes which resulted during each run were made for initial and final samples. 2 JOHN B. ZONDORAK ABSTRACT A series of experiments were conducted in the manner described above and the results have been reported. The ex— periments were successful with respect to control of temper— ature by limiting the supply of air available to the material undergoing decomposition. It is considered that this success established the validity of the principle employed. Moisture content increased during experiments with both moist and dry air resulting in partial anaerobic condi- tions and foul odors. An initial air supply ranged from 17.0 to 35.9 cu ft per lb of volatile solids per day was reduced to about one— third after a temperature of 450C was reached. Volatile matter was reduced 36 to 46 per cent and nitrogen loss was 11.1 to 5A.6 per cent. The greatest volatile solids reduc- tion and nitrogen loss was at 17.0 cu ft of air per lb of volatile solids per day. After initial heating all experiments required about 10 days time at 450C for stabilization of the material. The material then cooled to within lOOC of room temperature in 2 days. Initial heating to ASOC required about 24 hours in experiments with food stored 2 days at room temperature after grinding. In the run made with freshly ground material 3 days time was required for initial heating. USE OF RESTRICTED AIR SUPPLY FOR TEMPERATURE CONTROL IN THE AEROBIC DECOMPOSITION OF SOLID ORGANIC WASTES by John B. Zondorak A THESIS \ Submitted to the College of Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of ' \\. MASTER OF SCIENCE Department of Civil and Sanitary Engineering 1956 ACKNOWLEDGEMENT The author wished to express his sincere appreciation to Professor Robert F. McCauley for his valuable guidance and assistance in connection with this thesis. The suggestions of Doctor Karl Schulze concerning the principle of operation utilized in this study is also greatly appreciated. Thanks is also extended to Professor Frank R. Theroux for his interest in this work and reading the thesis. ii TABLE OF ACKNOWLEDGMENT. . . . . . LIST OF FIGURES . . . . . LIST OF TABLES. SECTION I. II. III. IV. VI. VII. BIBLIOG APPENDI INTRODUCTION . . . . . . LITERATURE REVIEW . . . . . . . . THEORETICAL CONSIDERATIONS . . . . EA; Energy and Living Cell B Influence of Temperature Upon Reaction Rates . . . . . . (C) The Effect of Forced Air on Moisture Content . . (D) The Effect of Evaporative Cooling. . EXPERIMENTAL EQUIPMENT AND PROCEDURE . . A Principle of Operations . . B Description and Function of Equipment C Raw Material. . . . . . D Procedure. . . . . . E Sampling and Testing Procedure. . EXPERIMENTAL RESULTS . . Experiment Experiment Experiment Experiment 4:me DISCUSSION OF RESULTS CONCLUSIONS . . . . RAPHY O C O O O 0 CES . . . . . iii CONTENTS Page ii iv Figures 1. LIST OF FIGURES Examples of Velocity Constants for Various Chemical Reactions and for the Growth of Some Bacteria. . . . . . . . The Generation Time of B.coli as a Function of Temperature . . . . . . . . . Detail of Digester Unit . . . . . . Flow Diagram--Use of Restricted Air Supply for Temperature Control in the Aerobic Decomposi- tion of Solid Organic Wastes. . . . Diagram of Electrical Circuit with Temperature Below] 4500. o o o o o o o o 0 Diagram of Electric Circuit as Temperature in Unit Exceeds 450C Closing Air Supply . iv Page . ll . l2 . 18 . 19 . 2O 21 LIST OF TABLES TABLES Page 1. Experimental Conditions for Runs 1 through A. . 3O 2. Moisture Levels, Runs 1 through A . . . . . 3O 3. Dry Weight, Runs 1 through A . . . . . . . 31 A. Volatile Matter and Ash, Runs 1 through A. . . 31 5. Total Nitrogen, Runs 1 through 4. . . . . . 31a 6. Summary of Runs 1 through A . . . . . . . 31a SECTION I INTRODUCTION The aerobic decomposition of organic matter can be accomplished successfully only by providing an environment favorable for efficient biological activity. The control of these environmental conditions is of paramount importance if the decomposition process is to attain a satisfactory degree of stabilization. Several of the factors which constitute a favorable environment have been established and a limited amount of progress made towards their regulation. Knowledge concerning the effect of oxygen supply upon a mass of solid organic matter undergoing decomposition by biological activity is lacking in the field of sanitary science. Such physical factors as temperature, moisture, and air supply upon a mixed population of aerobic and facul- tative aerobic organisms govern the decomposition process. This author has found no reports upon the control of one of these factors by varying another and the effects of this control upon the decomposition process. The purpose of this work has been to investigate the control of temperature during decomposition ofa.synthetic gar- bage by limiting the air supply. The effect of this limited air supply upon nitrogen loss, ordor and rate of decomposi— tion has been carefully noted. SECTION II LITERATURE REVIEW The aerobic and anaerobic decomposition of organic wastes occur in nature continuously. The degree of stabili- zation and type of by—products depend upon the type of organic matter present and the environmental conditions existing. If aerobic decomposition is to exist, such factors as air supply, temperature, and moisture must be made favorable to the organ- isms. Efficient biological activity and “breakdown" of the complex organic compounds then results. Waksman [6] in his studies on the aerobic decomposi- tion of manure and vegetable residues stated: The temperature of the organic matter is one of the most important factors in the controlling the rapidity of the decomposition and the conservation of nitrogen. The most rapid decomposition of horse manure sets in at 6500, followed by that at 5000. After the first stages of rapid decomposition the process was found to proceed more rapidly at 500C. Whenever decomposition was delayed either be- cause of too high or too low temperature, losses of the volatile forms of nitrogen occurred. This study was made in earthen-ware pots which were maintained at constant temperature by incubation and aerated by mixing when samples were removed. The relative degrees of decomposi- tion were measured by correlating on a dry weight basis the amounts of material in the process remaining and lost. 2 In a report on a study of the composting of garbage and other solid organic wastes at Michigan State University[5], studies were made on the effect of temperature and moisture upon the oxygen uptake of the composting mass. The data col- lected in these studies seemed to indicate that the maximum oxygen uptake was at a moisture content of 40-45 per cent for the first 27 hours in the laboratory digesters. From this time on, the maximum oxygen uptake was at a moisture content of approximately 56 per cent. At the conclusion of the experiments the material in the digesters containing a moisture content of 56 per cent appeared to be well composted material. The material with a moisture of 40-53 per cent was only partially composted. Material containing a moisture con- tent of less than 40 per cent was very dry and very little if any composting had taken place. Material with a moisture con- tent above 60 per cent was anaerobic and in very bad condition. Studies on the optimum temperature, utilizing a mois- ture content of approximately 55-60 per cent, were made within the range of 25-4500. The greatest oxygen uptake measurements were recorded at 450C with a rate of 420 x 10—4 moles per 100 gm of dry weight per hour at standard temperature and pressure. Converting this value to cu ft of air at 20 psi and 4500 yields approximately 0.166 cu ft of air per hour per 100 gm dry weight or 18.1 cu ft per lb of dry weight per day. Ludwig [A] in a thesis for a Master's degree (1952), made a similar study on the effect of various temperatures it upon the aerobic digestion of garbage. This paper indicated that thecptimum temperaturefbr the most rapid aerobic diges— tion and stabiization of the garbage samples, under the con- ditions stated, was A5OC. The maximum rates of oxygen uptake occurred at this temperature along with the greatest volatile matter reductions. A synthetic garbage composed of meat, potatoes, carrots, celery, and apples, containing a moisture content of 85 per cent, was employed. The maximum oxygen uptake rate was 0.129 cu ft of air at 450C per 100 gm of dry weight per hour or 13.7 cu ft per lb of dry weight per day. The results of Ludwig and Michigan State University concern— ing the oxygen uptake rates did not disagree markedly and good agreement was found regardizg the temperature at which the oxygen uptake rates were maximum. Differences may have been due to the variance in moisture contents and to the types of material tested. Laboratory, batch—type mechanical composters to deter- mine criteria for high rate composting of solid organic wastes were employed by Wiley and Pearce [7] in 1955. Phy- sical and chemical tests for indicating the degree of decom- position were outlined and the results reported. The units were of an ll—gallon working capacity with a stirring mech— anism and with insulation. Low pressure air, 10 psi, was used for aeration with provisions for regulating air rate. The raw material was a mixture of garbage and refuse with the non-compostable items removed. The end of a run was reached . , , L . ,. .. 0 when the temperature of the material returned to within 10 F of room temperature. Average moisture of the composting material used in these experiments was 54.5 per cent. In general, losses in volatile solids varied between 17 and 53 per cent with an average of 30 per cent. This result indicated that nearly one third of the organic matter was decomposed. Varying the rate of aeration produced marked differences in the course of decomposition. Low aeration, 4.0-6.4 cu ft per day per 1b volatile solids in the initial charge, resulted in a late peak temperature (seventh day) and unfinished compost by the ninth day. Medium aeration 9-29 cu ft per day per lb volatile solids, resulted in a peak temperature on the fourth day with a slow decline until the ninth day when the digestion was considered complete. Higher aeration values than those mentioned caused reheating of the compost after it was considered complete. It was concluded that low aeration provided either insufficient oxygen or in— sufficient sweeping out of waste gasses, resulting in a pro- longed period of composting. Medium aeration values, in the range of 10-30 cu ft per day per lb volatile solids, resulted in a relatively stable climb to peak temperatures (lMOOF), and a slow decline to room temperature with the inability to reheat. High aeration resulted in rapid cooling and dehydrated compost, with seeming completion of the process in a very short period, but with reheating upon subsequent mixing. Results of a series of tests indicated that optimum aerobic decomposition of organic material occurred when the moisture content was maintained within the limits of 55-69 per cent. The activated sludge process of sewage treatment in- volves oxidation of the adsorbed organic matter by the aid of bacteria during aeration of the mixed liquor containing sewage and activated sludge [1]. Therefore, this process is biological utilizing forced air. Bloodgood [8] determined the oxygen utilization rate of normal activated sludge pro- cesses to range from 14 to 20 mg of oxygen per gram of sus- pended solids per hour. This figure agrees with more recent data presented by Wuhrmann [9] of 11 to 20 mg of oxygen per gram of suspended solids per hour. Standard aeration equip- ment used today in activated sludge plants has an approximate ‘oxygen transfer efficiency of 5 per cent, Assuming that all of the oxygen supplied is utilized 26 cu ft of air is required per lb of suspended solids per day. With an efficiency trans- fer of 5 per cent of the oxygen supplied it is necessary to supply 520 cu ft of air per lb of suspended solids per day. The data presented by Michigan State University [5] for the maximum oxygen uptake measurements of 420 x lO-L'L moles per 100 gm of dry weight or 13.5 mg of oxygen per gm of dry weight agrees with that of Wuhrmann [9]. This comparison of activated sludge and composting seems valid because oxygen supplied to the organisms is dissolved in water in both cases. SECTION III THEORETICAL CONSIDERATIONS 19) Energy and Living Cell Only two sources of energy for living cells are known to exist, light and chemical energy. Light can be eliminated from this study as a source of energy because the nature of the work did not permit its utilization. Heat, electricity and mechanical energy can also be ignored because the bacter- ial organisms involved lack appropriate"transformers.II Heat, in the form of a rise in temperature, may cause in- creased growth and metabolic activity of a cell, but affect the process only in so far as the chemical changes (which supply the essential energy) are speeded up by a rise in temperature. A starving cell, for instance, derives no bene— fit from a rise in temperature. It follows that the energy liberated in one cell is of no value to any other cell; neighboring cells, even those closely linked in one tissue, have no direct energy exchange system. The chemical energy necessary for growth must be liberated within the cell, therefore, the only foods of value to the organism are those which can diffuse through the sur- rounding moisture layer. Complex proteins, fats and carbo— hydrates like starch and cellulose, are not directly available to the organism, but must first be broken down or hyrolyzed to appropriate soluble, and diffusible compounds. The work ~ of breaking down food to a usable form is carried on by a class of exo-cellular enzymes or hydrolases which are secreted into the medium by the organisms. The reactionscatalysed by these exo-cellular enzymes involve only relatively small energy changes, while reactions brought about by the endo- enzymesinside the cell, where the energy liberated is of real value to the organism and involve large energy changes. The value of a compound as a food or energy source also depends on the degree of oxidation which it undergoes; the more complete the oxidation the greater the energy made avail- able. Glucose may be taken as an example, and the energy liberated with varying degrees of oxidation compared: (a) Complete aerobic oxidation + o 0613206 + 602—... 6002 6H2O + 674 Cals. (Kilo cals.) (b) Partial aerobic oxidation . oxalic acid 2C6H1206 + 9024>.602H204 + 6H20 + 493 Cals. (c) Anaerobic oxidation _ lactic acid ethyl alcohol acetic acid C6H1206 —>- 3 CHBCOOH + 15 Cals. It follows that with less complete oxidation more of a given substance must be broken down to supply the needs of an OPganism. From the above mentioned considerations (which are generally true due to the heterogeneous organic matter and organisms present in the synthetic garbage) it can be stated that an increase in temperature of a biological active mass of organic matter can be expected if an adequate supply of oxygen is available and aerobic conditions prevail. This statement should hold true in spite of the cooling effect of evaporation because biological activity is an exothermic reaction. (B) Influence of Temperature Upon Reaction Rates The majority of known chemical reactions are increased in rate by increase in temperature. In biological systems this increase in rate is limited because at higher tempera- tures the enzymes begin to be denatured. We, therefore, find an increase of reaction rate up to a certain "optimum” tem- perature, and then generally a rapid decrease is noted due to enzyme destruction or denaturation. The effect of temperature upon a homogeneous chemical reaction can be expressed by its effect upon the velocity constant, K, of the reaction.1 The simplest case is that of a monomolecular or "first order reaction.” Thus if we start with (a) molecules of a substance and (x) of these molecules 1The derivation and values concerning the velocity con- stant K are taken from Kenneth V. Thimann, The Life Of Bacteria, The Maxmillan Company, New York, 1955, pp. 148. IO have reacted after time (t), the rate then depends upon the remaining molecules which have not reacted, i.e., the rate of chaxge of (x) with time depends on (a-z), or: Ex _ K (a-x) dt — x t by integration 1 dx _ dt K a—x K = % 1n a equation (1) The value of K increases with an increase in temper- ature as illustrated by the following equation: K2 Tr - T log = 2 1 equation (2) K1 T2 x Tl The velocity constant, therefore, is a measure of the activity of the biological reaction. In equation (1) it can be seen that if the value of K increases (x) (the molecules which have reacted after a time (t) ) must also increase. Figure 1 shows the values and variations of K with tem- perature for various chemical reactions, and for the growth of some bacteria. The effect on growth is also illustrated by the data of Barber (1908) on B.coli (Figure 2). In this graph the time plotted is the actual time required for an organism to divide once, i.e., the “generation time." This time is infinitely great both at low temperatures and when the temperature is so high that the bacteria are destroyed faster than they can grow. ll DECOMPOSITION COAGULATION l l N 0 N 0 + — O ,HFO e-HFO Of milk by Of Hemoglobin 2 5*, 2 A 2 2 d 2 ‘ +202 Rennet by Heat Temp.Kx103 Kxio3 Temp. v K OC 00 0 0.05 25 l 10 30 1 . 69 20 1.17 1.06 35 3.15 25 2.03 40 5.40 30 3.08 50 35 8,08 5.16 60 0.009 40 7.90 62.6 0.019 45 29.9 13. 65.6 0.044 50 17.3 67.6 0.074 55 90.0 70.4 0.15 HYDROLYSIS GROWTH 0f Propyl 0f sucrose Acetate by Of Lactobacillus by Invertase KOH Temp. Ka K x 105 Temp. K .434 0C 0C 0 1.03 18 15 10 2.15 25 0.084 20 4.23 120 30 0.184 30 8.10 163 35 0.365 40 14.95 216 40 0.62 50 302 45. 0.84 Fig. l. EXAMPLES OF VELOCITY CONSTANTS FOR VARIOUS CHEMICAL REACTIONS AND FOR THE GROWTH OF SOME BACTERIA 160 I I I I I I I I 120 F 100- GEI‘JERATION TIME IN MINUTES 10 20 ' 30 40 50 TEMPERATURE 0 Fig.2. THE GENEIUITION TIME OF B. cell AS A FUNCTION OF TEMPERATURE (Data of m. A. Barber, from 3.92% fiBaggfla by Thimann, Kenneth v., (1955). By courtesy of The Mamillan Company, page 151.) 12 13 It was shown above that increase in temperature in— creases the rate of all the reactions involved in growth, i.e., temperature accelerates not only those reactions which constitute normal metabolism, but also those reactions, like enzyme inactivation and protein denaturation, which are damaging to the cell. Therefore, the optimum temperature for growth must be defined loosely as that temperature above which the damaging reactions just produce a discernible effect. Correspondingly, the maximum temperature is that at which the rates of damaging reactionsbecome just equal to those of the metabolic processes so that no growth takes place. (C) The Effect of Forced Air on Moisture Content Saturated air contains a given amount of water vapor at a specific temperature and pressure. Therefore, when dry air flows through a moist mass it becomes saturated, and in doing removes the vapor of saturation. In mixtures of perfect gases, the partial pressures of the components may vary without limit. A vapor, however, cannot exist in a mixture at a pressure higher than the satur— ation pressure for the vapor at mixture temperature. This fact is useful for obtaining a measure of the relative quantity of vapor present in a gaseous mixture. If the vapor has a partial pressure equal to the saturation pres- sure, the mixture is said to be saturated. The humidity ratio M is defined as the mass of vapor associated with 1 1b of S dry air to form a mixture of l + MS 1b. The specific volumes 14 of the air and water vapor may be expressed by the perfect gas law: Ra Ta . . va = .______ Va = specific volume of air P a Ra = gas constant of air Ta = temperature of air Pa = air pressure R T vS = S S VS = specific volume of water PS vapor RS = gas constant of water vapor TS = temperature of water vapor P = vapor pressure The mass of moisture associated with 1 lb of air is the mass contained in a volume equal to the specific volume of air (since in mixtures all components occupy the same volume). Ta and T8 are of course equal.2 R P MS=Va = a S —_5_§_;§3§__—o.622_§_ vS s Pa 85.7Pa P a Equation (3) The experiments described here were conducted at approx- imately atmospheric pressure, 14.7 psi at a temperature of 114OF. If the relative humidity was assumed to be 100 per 2Charles L. Brown, Basic Thermodynamics, McGraw-Hill Book Co., 1951, p. 204. 15 cent in the unit when the temperature reached 114OF, then, from vapor pressure tables [3] the corresponding saturation pressure for the vapor was 71.88 mm of mercury or 1.39 psia. Therefore, the humidity ratio for saturated air at 114OF was: Psat. = 1.39981a = PS = 4. .__ l. = l . l ' Pa 1 7 39 3 3 p31a equation (3) M = 0.622 ii = 0.065 lb/lb dry air 3 13.31 From the above it can be seen that for every pound of dry air (14 cu ft) which entered the unit 0.065 lb of vapor could be carried out the exhaust if the humidity in the unit was 100 per cent. (D) The Effect of Evaporative Cooling The cooling effect of evaporation was a significant factor in the experiments performed. The heat of vaporiza— tion is the quantity of heat required to change one gram of liquid to vapor without change of temperature. From the tables of the properties of saturated steam (3), 571 calories of heat are required to vaporize one gram of liquid water or 1028.4 B.T.U. are required per pound at 450C. Therefore, it can be seen that forced air effected the rate of cooling of the decomposing mass of organic material by removing the vapor, thereby causing a loss of heat in the mass by the pro— cess of vaporization. SECTION IV EXPERIMENTAL EQUIPMENT AND PROCEDURE (A)_Principle of Operations When organisms utilize oxygen and organic food as a source of energy heat is produced and a corresponding rise in temperature ensues. This exothermic production of heat was the subject of the study reported here. In the devise used a reduction of the oxygen supply to the organisms was used to reduce the rate of heat production to cause an attendant cooling. In this way the rate of air supply was used to con- trol temperature of the digestion unit. The operation was similar to a furnace utilizing natural gas as a fuel. The furnace utilizes the gas as a source of heat energy by combining it with oxygen in an exo- thermic reaction—thus producing heat. When either the gas or the oxygen ceases to be supplied to the furnace heat energy is no longer produced and a reduction in temperature will result (the rate of reductiOn being dependent upon the degree of insulation). With a thermostat the temperature of a room can be controlled by regulating the injection of fuel when the room is heated above or drops below a designated limit. The above analogy applies directly to the experimental unit employ— ed in this study as the identical operation was utilized. 16 17 (B) Description and Function of Equipment The type of unit employed to study the effect of re- stricted air supply upon temperature of solid organic waste was a laboratory batch—type digester without mechanical stirring as shown in Figure 3. It consisted of a cylindrical drum 8.5 inches in diameter and 21 inches in depth. The working capacity was approximately 4.0 gallons or 16 lb of solid organic waste. A temperature sensing element for con— tinous recording was placed in the unit as shown in Figure 3. The drum was covered with 1—1/2 inches of fiber glass to prevent excessive heat losses and because the maintenance of a constant temperature would have been difficult without insulation. Air supplied to the digester was controlled by a sole- noid valve as shown in Figure 4. Forced air was allowed to enter the unit containing the solid organic waste when the solenoid valve was energized from the thermostat set for 4500, therefore, the solenoid was energized until the unit reached this temperature as shown in Figure 5. In this way air was supplied to the material up to 450C. Above 450C the air supply was cut off by the thermostat as shown in Figure 6. The temperature therefore remained at 450C throughout the de- composition process after the initial heating. The 4500 tem- perature was selected because the work of Waksman [6], Ludwig [4], and Michigan State University [5] suggested that this was the temperature at which the most aerobic decomposition and maximum oxygen uptake of solid organic wastes occurred. 18 EXHAULT TO WATER BATH I I 8. IL A, I I 7 1]“ web . OPENINGS \\ “I ORGANIC , ,‘ /I‘I{FhiAL . 1F— - ‘ _,'~~ ' atom PLAN VIEW g PLASTIC DI.‘1"U;_.ER [ i-LATEILIAL a $ DI‘JCOf'lPObING l ' g 51/“ TW i“? T.-_._...5~ -4 \ E, ELEVATION DIFFUSER PLATE SECTION OF .fiLl‘xtLTIC "Ill“"ll'"III""IIIIIIIIIIIIIIIIIIH INSULATION DIFFULLIL F ALoE BOTTCM IJDmLINAGL‘ LIL,UOR (OUT) FORCED AIR (IRIS3 Figure 3. DETAIL 0F LICESTOR UNIT .19 $923 0Hz§o gem ho ZOHBHmomZOQmQ 0H3 Mme zH A8828 ”$593898 m8 HamABm de naked—”mag ho mg§c' AIR SUPPLY T0 UNIT (Closed) J SOLENOID? VALVE |(Closed) J A W IM’ (Off) GENERATOR L—A THEE :10 STAT? ////////{ Thermostat opens circuit as temperature in unit exceeds 45°C. Figure 6. DIAGRAE-i or ELECTRIC CIIVLCUIT AS as Tarwmum IN UNIT moss s. 45°C CLOLING AIR warm Low pressure air, 5 psi. was supplied to the false bottom of the digester as shown in Figure 3. The forced air entered the organic matter through the plastic diffuser plate composed of 1/64 inch diameter orifices spaced 1/4 inch on centers. This design of the diffuser plate resulted in uni- form dispersion of forced air throughout the decomposing mass without "channeling." The rate of forced air supplied to the sample of organic matter was the single variable studied in this investigation. Aeration rates were varied depending upon the results obtained during each test, and the rates used in this study varied between 17.0-35.9 cu ft per 1b of volatile solids per day. When the solenoid valve was energized the air passed through a flask containing calcium chloride and a Daigger continuous gas flow recorder and then entered the digester. The calcium chloride removed any moisture which may have been present from the air source, and the gas recorder indicated the time and rate of air flow. The gas recorder served to indicate whether or not the solenoid valve was energized and permitted computations of the amount of air fed to the unit, be made. (C) Raw Materials The solid organic matter used for aerobic decomposition was composed of fresh food from the Food Stores at Michigan State University. The specific constituents of food used were representative of Mallison's [5] data for a typical sample 23 of garbage from East Lansing, Michigan as follows: Per Cent on Wet Wet Weight Food Constituent Weight Basis lb Meat (ground beef) 12.8 1.50 Bread 10.5 1.25 Green Vegetables 26.2 3.25 Coffee grinds 11.1 1.50 Fruit 21.8 . 3.00 Potatoes 17.3 2.00 Paper negligible 12.5 Decomposed matter from previous run (oven dried 1030C) 3.00 Total weight of sample— 15.5 The main variation of the above constituents from those reported by Mallison was the reduction in the per cent of paper and miscellaneous constituents. The moisture of the synthetic garbage was 75 per cent. Wiley and Pearce [7], Michigan State University [5] and the University of Calif- ornia [2] have suggested that for this type of organic matter a moisture content of approximately 60 per cent would be de- sirable for aerobic decomposition. Such moisture content was obtained by adding approximately 24 per cent of oven dried compost; that is, 24 per cent of the total wet weight of fresh food used or 19.3 per cent of the 15.5 lb sample. Each experiment contained identical amounts of the specific constituents. This procedure permitted a valid comparison of the end results of different experiments. 24 The fresh food was thoroughly mixed and chopped manually before grinding. An Enterprise Engine Company vertical mill grinder with 3/8 inch screen openings was employed for the shredding. The food and the oven dried compost were put through the grinder twice. The ground material was collected in a bucket and inverted onto a screen where it was allowed to set for about 48 hours to drain. This procedure produced a sample of organic matter with a moisture content of about 60 per cent. (D) Procedure The thoroughly-mixed and shredded sample containing ap- proximately 12.5 lb of food constituents and 3 1b of dried compost was placed in the digester unit. The sample occupied a volume of about 2.6 gallons with a moisture content of about 60 per cent. Samples for initial analysis were takenfrom the original weight. Air was supplied to the unit until it reached a temper- ature of approximately 4500 at which time the thermostat opened the electrical circuit, closed the solenoid valve, and ceased to supply air to the unit. he reverse occurred when the unit cooled below 4500. The rate of air supplied during each run was constant. Aeration rates ranged from 4 to 8 cu ft per hour or 17.0—35.9 cu ft per day per lb of volatile solids. Usually, 24 hours of aeration were required to raise the temperature of the sample organic matter in the unit to 25 450C. Once the temperature reached 450C in the unit, it re- mained there (within i 30C) for 9 to 11 days. The unit then cooled to within 50 to 100C of room temperature at which time the experiment was stopped.3 Samples for analysis were taken and the remaining material dried at 1030C for 48 hours to beixxuthaif0r~use as seed for moisture control in the _next run. (E) Sampling and Testing Procedure Preliminary studies on sampling techniques indicated that variable results were obtained if samples removed from the decomposing mass were taken from one level in the unit. Samples were, therefore, collected only at the beginning and end of a run. Initial samples were obtained by spreading the entire mass of organic material on a large surface and extract- ing small segments of a whole sample from various parts of the mass. That is, if a 20 gm sample was to be collected, then, about ten 2 gm random samplings were made to comprise the whole 20 gm sample. Samples were collected from the en- tire end product in a similar manner except that the material was first mixed thoroughly by hand. This procedure minimized the errors which would have resulted from variations in mois- ture and type of material due to the fact that the material in the unit was not stirred or disturbed during the experiment. Also, this allowed a closed system during the entire run. 3A series of air and temperature charts are included in the appendix. 26 ‘ Moisture was determined gravimetrically by drying in an oven at 1020—105OC for about 48 hours. Drying periods of 24 hours were sufficient for 15 gm samples, but when larger samples were used 48 hours was employed. Some of the more readily volatilized compounds such as ammonia, volatile acids, and carboydrates were probably reported as moisture. The moisture was reported as the per cent of wet weight. Total volatile and fixed solids (ash) were determined by igniting the approximately 6 grams of total dry solids remaining from the moisturetests.Ignition was in an electric muffle furnace for 3 hours. The per cent volatile and fixed solids were reported on a dry weight basis. Carbon dioxide and volatikaminerals may have beenreported as volatile solids,a1though volatile solids represent primarily organic matter in the solid organic matter considered. The determination of total nitrogen by Kjeldahl re- quired the development of a different technique from that mentioned in Standard Methods, tenth edition, because of the sample of the organic matter used. The procedure employed was developed with the aid of Dr. Erwin J. Benne of Michigan State University and is outlined below: 1. Weigh out 1-4 gm of sample and place into a 800 m1 Kjeldahl flask. 2. Add 1-2 gm of CuSOu 3. Add 4-5 gm of K2S04 4. Add 25-30 ml of H2 804 and begin to digest using a low flame until frothing ceases. 5. Increase flame after frothing ceases and boil until a clear solution appears (green color). 6. Digest for 1-1/2 hours at a high flame after solution clears. 7. Cool and add 200 m1 of water. 0’) Add 2 or 3 pieces of granulated Line (to decrease bumping). Add sufficient NaOH to make solution alkaline (about 40 to 60M1). It is most important that the solution is alkaline at this point. 9. Distill off about 150 m1 into a measured quantity of standard acid (the amount of standard acid de- pends upon the amount of nitrogen present and the normality of the acid). 10. Titrate with NaOH using methyl red as an indicator. In the experiments performed here an automatic Beckman titration meter was used. The calculation is as follows: % N 1°4X N° 301d x ml acid used by NH gm of sample* 3 N base N acid m1 of acid used by NH3 m1 of acid used - x ml base * Gm of sample is on a dry weight basis. Samples of approximately 5 gm were collected at the beginning and end of a run, diluted in distilled water, and mixed thoroughly before the pH was measured with a Beckman meter. SECTION V EXPERIMENTAL RESULTS Experiment 1. This experiment was made to demonstrate whether temper- ature control of aerobically digesting material with a re- stricted air supply was feasible. The air valve was set to supply 6 cu ft of air per hour with the thermostat adjusted to open the electric circuit when the temperature in the unit reached 450C. The amount and type of organic matter supplied to the unit was the same in this and each subsequent experi- ment; namely, 12.5 lb of fresh food and 3 1b of the oven dried end product from a previous run as escribed in Section IV. Saturated air was provided in this run by bubbling air through a flask of water installed in the inlet air line. The flow diagram of Figure 4 applied to this run except for the provision for moist air. The initial temperature of the organic material was 250C when saturated air at a rate of 6 cu ft per hour was fed to the unit. Within 24 hours the temperature rose to approx- imately 300C. The air supply was then discontinued for 2 days but no further increase in temperature resulted. Therefore, the air was again supplied to the unit at the previous rate. Within 24 hours a level of 450C was reached, thereby causing the thermostat to close the air supply line. In approximately 28 29 30 minutes the material cooled about 20C and the air supply came on again, This air feed rate continued for approximately two days with the air remaining on about 15 minutes and off for about 30 minutes. Gradually, the interval between off and on times decreased. After the third day the air was on and off every two or three minutes for a period of approximately seven days after which time the period of air flow began to increase. At the end of nine days the material began to cool and reached a room temperature within two days. The experi- ment was then concluded. This experiment proved that temperature could be con- trolled by restricting the air supply. Tables 1 through 5 contain the individual results of the four experiments of the study with a summanrin Table 6. For this first experiment the initial dry weight of 3350 gm was reduced by 32 per cent to 2292 gm and thexolatile matter of 2830 gm was reduced by 36 per cent to 1820 gm. These weight reductions were in line with those reported by Wiley and Pearce [7] and by Michigan State University [5]. The water loss was 331 gm or a 6.7 per cent reduction with initial moisture of 60 per cent and final moisture of 67 per cent. The dry weight reduction of 32 per cent and water loss by only 6.7 per cent accounts for the increase in per cent moisture from 60 to 67 per cent. The small water loss was probably due to the use of saturated air thereby decreasing the amount of water vapor which could be carried away by the air. The 30 TABLE 1. Experimental Conditions for Runs 1 through 4. Experiment No. 1 2 3 4 Air Rate (cu ft per hr.) 6 6 8 4 Air_Rate (cu ft per 1b of volatile solids per day) 23.1 29.5 35.9 17.0 Condition of Air Entering Unit Saturated Dry Dry Dry Thermostat Set (temperature) 4500 450C 450C 4500 Days Unit Remained at 4500 11 10 10 9 pH (initial) 6.8 6.8 6.4 6.1 final) 8.6 8.2 9.0 9.2 TABLE 2. Moisture Levels, Runs 1 through 4. Initial Final Total Total Experiment Per Weight Per Weight Loss Number Cent Grams Cent Grams Per Cent 1 60 4985 67 4654 6.7 2 62 4202 64 2920 30.3 3 ‘ 62 4584 67 3625 20.8 4 60 4278 68 3490 18.3 31 TABLE 3. Dry Weight, Runs 1 through 4. Initial Final Total Total Experiment Per Weight Per Weight Loss Number Cent Grams Cent Grams Per Cent 1 40 3350 33 2292 32 2 38 2580 36 1650 36 3 38 2740 33 1785 35 4 40 2852 32 1640 42 TABLE 4. Volatile Matter and Ash, Runs 1 through 4. Initial Final ,L_ . Total . Total Experl- Weight Grams Weight Grams LOSS ment Per Per Per Number Cent Vol.Matter Ash Cent Vol.Matter Ash Cent 1 84.3 2830 520 79.5 1820 472 36 2 86.0 2210 370 82.0 1350 300 38 3 88.5 2420 320 82.5 1470 315 ’39 4 89.8 2560 292 85.0 1390 250 46 31a TABLE 5. Total Nitrogen, Runs 1 through 4. Initial Final Total Total Experiment Per Weight Per Weight Loss Number Cent Grams Cent Grams Per Cent 1 4.05 135 5.30 120 11.1 2 4.02 112 5.80 96 14.3 3 3.40 93 3.70 63 32.8 4 3.03 91 2.60 41 54.6 TABLE 6. Summary of Runs 1 through 4. Volatile Air Dry Weight Matter Water Rate Experiment Loss Loss Loss Nitrogen cu Number Per Cent Per Cent Per Cent Per Cent ft/hr 1 32 36 6.7 11.1 6 2 36 38 30.3 14.3 6 3 35 39 20.8 32.8 8 4 42 46 18.3 54.6 4 32 initial total nitrogen was 135 gm or 4.05 per cent and the final 120 gm or 5.30 per cent. This is equivalent to a nitro- gen loss of 11.1 per cent. The initial and final pH was 6.8 and 8.6 respectively. A very strong putrid odor characterized the end pro- duct. The excessive moisture was attributed to the use of saturated air. This suggested that dry air might alleviate this condition and dry air was used in the three subsequent experiments. Experiment 2. Dry air was fed to the solid organic matter in this run at a rate of 6 cu ft per hour. The use of dry air re— sulted in a loss of 1280 gm of water or a reduction of 30.3 per cent. The initial and final dry weights were 2580 and 1650 gm with a reduction of 36 per cent. A volatile matter reduction of 38 per cent was the result of initial and final volatile matter weights of 2210 and 1350 gm respectively. The nitrogen level increased from 4.00 per cent to 5.80 per cent although over-all nitrogen loss was 17.8 per cent as com— pared to the previous run with a 11.1 per cent loss. The initial ph was the same as the first experiment, 6.8, and the final 8.2. The material undergoing decomposition remained at a level of 450C for approximately 10 days before cooling. About one day was required to reach a temperature of 450C at the beginning of the run. The rapid increase in temperature as 33 compared to the first run was attributed to a two day storage period at room temperature as explained in Section IV. A less putrid odor was noticed in the end product than for the first run although a strong ammonia odor was notice- able. The bottom and top of the finished materialhad a one inch layer of bluish white actinomycetes with a very musty odor. A sample of this growth, which was tested, showed a moisture of 10 per cent and a total per cent nitrogen of 4.86. The final moisture of the end product was 64 per cent. There- fore, the use of dry air did not reduce the final per cent moisture materially although the total moisture loss was high. This fact indicated that more water was produced and that the decomposition process probably more effective. Experiment 3. A higher rate of dry air, 8 cu ft per hour,was utilized in this run in an attempt to produce an end product with a lower moisture content and less putrid odor. The organic material heated to a temperature of 450C in about 24 hours and remained within 200 of this temperature for 10 days before cooling. This rapid temperature rise was again attributed to the two day storage period previous to placing the organic material in the unit. The initial moisture in this run was 62 per cent and the final 67 per cent with a total loss of 959 gm of water or a reduction of 20.8 per cent. The initial volatile matter of 2420 gm was reduced to 1470 gm for a total loss of 39 per cent, 34 This was greater than the two previous experiments and in- dicated that a higher degree of stabilization had occurred in this run. In this experiment an initial nitrogen content of 93 gm was reduced to 63 gm for a total nitrogen loss of 32.8 per cent. Theappearance and odor of the end product were similar to experiment 2 except for an even stronger ammonia odor. Actinomycetes growth at the top and bottom was largely absent due to high moisture content of the end product. This experi- ment showed that a higher rate of air did not decrease the moisture level during the decomposition process and did not increase the rate of stabilization. Experiment 4. Per cent moisture increased from 60 to 68; the highest final moisture recorded in these experiments. The water loss from 4278 gm to 3490 gm, a reduction of 18.3 per cent, was approximately that of the previous experiment. The initial and final volatile matter of 2560 gm andl39O gm was a reduc— tion of 46 per cent. The nitrogen loss of 54.6 per cent was the result of reducing the initial weight of total nitrogen from 91 gm to 4l gm. These high values indicated that the stabilization process proceededamzanigher rate in this run than in any of the preceeding experiments. The odor of the end product was foul and the appear- ance of the material was similar to very moist humus. When the lid was taken off of the unit at the end of the run the 35 ammonia odor was overwhelming. From this general condition of the material and odors emanating from the unit during the process, it was concluded that at least partially anaerobic conditions prevailed in this run. In general good relationships were noted between initial and final total and volatile solids. However, a variation of between 3 to 15 per cent in initial and final ash was noted. This variation must be attributed to sampling errors and the fact that when obtaining the dry weight of a sample to be used for ash determination, exactly identical periods of time were not employed.for drying the material. SECTION VI DISCUSSION OF RESULTS These studies demonstrate that the temperature of a decomposing mass of solid organic matter can be controlled by restricting the supply of air. The fact that a level of 4500 was reached bysngnflgfilmgair at lower temperatures and that it was possible to maintain this temperature by restricting the air supply indicated that certain organisms utilized oxygen in their metabolism and produced heat. Aerobic organisms were therefore undoubtedly present. Probably a mixture of facultative aerobes and anaerobes also existed. The putrid odor of the end products suggests that an- aerobic decomposition took place. In general, odors produced were typical of the end products of anaerobic decomposition of protein. The strong odor of ammonia also suggests that an- aerobic "break down“ was occurring during the degradation of amino acids which was favored by the anaerobic conditions. The experiments which utilized dry air produced the highest reduction in volatile matter, and no difficulty was encountered in raising the temperature to 4500 initially-~as was the case when saturated air was used. The use of saturated air throughout the entire first experiment may have prevented the growth of aerobic or facultative anaerobic organisms at the beginning of the run. However, it is more probable that 36 37 temperature lag was due to omitting the two day aging process at room temperature which was utilized for experiments 2 through 4. Because aerobic organisms produce a greater quantity of heat during their metabolism than anaerobes a sizeable population of aerobes were undoubtedly present in order to raise the temperature to 4500 at the beginning of the experi- ment. Experiment 4 supplied the least amount of air to the solid organic matter and produced the highest degree of vola- tile matter reduction, 46 per cent. This high loss of volatile matter was accompanied by a 54.6 per cent loss of total nitro- gen and very putrid odors which indicated that decomposition had taken place at a high rate. If all this ammonia is con? sidered to have been in the form of protein, then a 51 per cent reduction took place. This 51 per cent value was ob- tained by multiplying the per cent nitrogen in the initial and final samples by a factor of 6.4, since protein is com— monly about 16 per cent nitrogen. he fact that this large per cent of ammonia was lost to the atmosphere suggests that very little, if any, of this free ammonia was oxidized to the nitrite or nitrate form. Anaerobic conditions definitely accompanied this run but in spite of these conditions a higher volatile matter reduction was observed in thisexperi— ment than in any other. Experiments 2 and 3 appear to have undergone a lower degree of decomposition as shown by the reduction of volatile 38 matter. These two experiments were conducted at higher rates of air supply indicating that anaerobic conditions tend to result in more rapid decomposition. Further investigations will be necessary in order to establish the relationship be- tween anaerobic decomposition and rate of stabilization. The rates of air were 4, 6, and 8 cu ft per hour or 17.0, 29.5, and 35.9 cu ft per lb of volatile solids per day. Actually, these rates existed only when the temperature was below 450C. Due to the fact that the air was on one-third of the time after the initial heating, the above air flows should be divided by three. Therefore, the rates of air discussed in Section II in connection with the studies made by Wiley and Pearce [7], Michigan State University [5], Ludwig [4] and an activated sludge process correlate closely to those used before and after,but not during the heating process. In Section III it was shown that at 100 per cent humidity and 450C 0.065 lb of water vapor could be carried out through the exhaust for every 14 cu ft of dry air which entered the unit. Applying these figures to experiment 4 approximately 2.2 lb of water could have been lost during the entireexperiment. Only 1.7 lb of moisture was lost in the run probably due to condensation on the lid of the unit which was not insulated. SECTION VII CONCLUSIONS A study was made to investigate the control of tempera- ture for solid organic material undergoing aerobic decomposi- tion by limiting the supply of air. A six gallon capacity unit with a plastic air diffuser was constructed for the study using a thermostat and solenoid air valve to control air flow. Raw material used was fresh food mixed with oven dried end product from previous runs. Inlet air was at room temperature. Conclusions pertaining to four runs and to other factors involved in this thesis are listed below: I. A satisfactory method was devised for controlling the temperature of an aerobically decomposing mass of solid organic material at 4500 by restricting the supply of air. 2. Once the temperature reached a level of 4500 and the '”on and off" process of air flow started, flow rates were re- duced to one-third of the initial level. This rate of air flow continued for approximately 10 days. 3. The end products of the experiments were putrid in all cases indicating that partially anaerobic conditions ex- isted. 4. Experiment 4 produced the greatest reduction in volatile solids and total nitrogen loss. These losses of 46 39 40 and 54.6 per cent respectively occurred at an initial air rate of 4 cu ft per hour or 17.0 cu ft per lb of volatile solids per day. Experiments 1; 2, and 3 with higher initial air rates showed lower reductions in volatile solids and in total nitrogen as follows: Initial Air Rates Reduction of Total (cu ft per hr) Volatile Nitrogen Experiment cu ft per lb of , Solids Loss Number Volatile Solids (per cent) (per cent) per Day 1 23.1 (saturated) 36 11.1 2 29.5 (dry) 38 14.3 3 35.9 (dry) 39 32.8 4 17.0 (dry) 46 54.6 The above table also shows that increased nitrogen loss accom— panied a high reduction in volatile solids. 5. Because of the moist condition of the end products the optimum moisture for aerobic decomposition was probably exceeded. Moisture contents were as follows: Experiment Initial Moisture Final Moisture Number (per cent) (per cent) 1 60 67 2 62 64 6O 68 4 60 68 4l 6. The use of dry air in experiments 2, 3, and 4 resulted in a greater loss of water, volatile solids and total nitrogen than when using saturated air in experiment 1. 7. Material stored for 2 days at room temperature after grinding heated to 450C in 24 hours. For one run in which no initial storage period was allowed three days initial heating was required. BIBLOGRAPHY Babbit, Harold E., Sewerage and Sewage Treatment, John Wiley and Sons, Inc., New York, 7th Edition, p. 649, 1952. Gotaas, Harold B., Composting Sanitary Disposal and Reclama— tion of Organic Wastes, World Health Organization, Geneva, 1956. Handbook of Chemistry and Physics, Chemical Rubber Publishing Company, 34th Edition, 1952—1953. Ludwig, Gordon W., The effects of Various Temperatures upon the Aerobic Decomposition of Garbage, Master's thesis May 1954, Georgia Institute of Technology, Atlanta, Georgia. Preliminary Report on a Study of the Composting of Garbage and other Organic Wastes, July, 1955, Civil and Sanitary Engineering Department, Michigan State University. Waksman, S.A., and Gordon, T. C., and Hulpoi, N., "Influence of Temperature upon the Microbiological Population and Decomposition Processes in Compost of Stable Manures,” American Soil Science Journal, 47:83, 1939. Wiley, John S., Pearce, George W.,‘"A Preliminary Study of High Rate Composting,” Proceedings American Society of Civil Engineers,8l:846, Paper N . 846, December,1955. Bloodgood, D. C., "Studies of Activated Sludge Oxidation at _ Indianapolis,” Sewage Works Journal, 10:26, January,l938. Wuhrmann, K., "High Rate Activated Sludge Treatment and Its Relation to Stream S nitation,‘l Sewage and Industrial Wastes, 26:1, January, 1954. 42 APPENDICES 43 PMENT {00¢ co can. ’80 RECORDER % Am Eu” 847-433(49) $ 7 5 O '6 :3 ' z ( \ 9 "V AIR FLOW RECORDER CHART ( 0944/6 I’m/ark / reacbea’ flaw/0. of/5‘C 4,41,,- 45,, ,1 (g ,5 ,. ‘5. n . . a K‘“ 75/17’0./?‘%l//7cod (Wig/I7 :2 5 A 3 £4. 4 .3 EM 3 4 "’ Z 9 ’2” 7/'/77€ —-/Vw//v ’4' JIFFJQETUHE ELCOHDEF. C HART TYPICAL AIR FLOLT AND TJL’LLHTUI‘L CHART». 20 HOUES AFTER bTAiLT OF EXPEMLHENT ME 00W NT CO Q RECORDER 0 v ‘p M 5..., eel—5:5. ms. 5 . a 0 MODEL A-IOO .9 AIR FLOW 5.2300533}. CHAhT Mr )» //cé/ Jew/x2}! flay. rp/ao/fl’d a / {9‘ Z ‘3‘ 2% i6 , WQK$NJIV H 45‘P4-Z/\/\_//\/’\/’\//\/ Tux. M/pg ‘ Z2 gag/7’ ago/m $.34 i‘fi%f a, ‘(4 fly [ff/0d My” V, - Q" E) I! 2.33“ l 3.. R’ + wé a” 3%?- 2 53 ,2” 3w- 41- 2 a ,2 7”»? 7694/4; ——-7 TE: PLENUM. Loom-Ar. CHAM' TIPICJJJ an. my magmas 03L ms: Mir; mmozzrmzr. 10 my PhIOD AT 45°C mammm LEVEL Demco-293 Date Due HICHIGQN STRTE UNIV. LIBRRRIES 31293107051736