H !i W H ‘ HIM l 1 H II" I 1 r \ t \ WNW 1| an s 4 \‘ f n: r; "J t n a: A ‘l. { ('13 (a! «in; :4: L-.».5 w v'\ i 3:: k‘K ‘¥ Raw ..‘- .I’dcgg 3‘ ' Pd,‘ '5 r.“ ’3‘?‘ V‘ L 9 "t' a ‘J ‘ ‘, ' 3 o \.\a‘ \. -~. .L an. \3-4 1“ 4.; " \"Jks Thesis far "the Dagmar of M. S. MCHEQAN STATE UMVE-RSI‘W Robert L. Biraii'iwwaite 3956 THESlS This is to certify that the thesis entitled A Study of Garbage Composting in Controlled, Insulated barrels presented by Robert I... BraithI-Iaite has been accepted towards fulfillment ' . of the requirements for 37.8. degree in Civil Engineering 0-169 fv, ‘ 31 v as . Iii L U 1* ? 00C ‘fi A STUDY OF GARBAGE COMPOSTING IN CONTROLLED, INSULATED BARRELS By ‘Robert L. Braithwaite A THESIS Submitted to the School of Graduate Studies of Michigan ’State University of Agriculture and Applied Science 'in partial fiulfillment of the requirements for the degree of MASTER OF SCIENCE ’Department of Civil and Sanitary Engineering Year 1956 ACKNOWLEDGEMENTS This thesis was only possible with the sincerely ap- preciated guidance of Dr. John R. Snell, former Head of the Civil Engineering Department, Professor Frank Theroux, and Dr. Robert McCauley. The tireless and concientious laboratory assistance of Mr. S.W. Kao, supported by an N. I. H. grant, is also deeply appreciated. The author is indeed grateful to Dr. W. L. Mallmann for his valuable assistance in the field of bacteriology, and to Dr. Harold Hart for his valuable suggestions per- taining to organic chemistry. .'A II I]... I‘ll ABSTRACT Composting is a sanitary and potentially, an economic method of municipal refuse disposal. The end-product may provide a valuable fertilizer and soil conditioner. Al- though the process has been used for a nwmber of years in other countries, scientific knowledge concerning the pro- _ ceases of decomposition is still limited. Before adequate design criteria for commercial plants can be established, many fundemental problems must be solved. It was the pur- pose of this thesis to aid in the unraveling of a few of these enigmas. In order to simulate field conditions in such way as to provide sufficient controls and measurements, a small in- sulated fiber barrel was used as a container for ground gar- bage. Compressed air was circulated through the barrel. The contents were subjected to various physical and chemical measurements; such as air flow, volume, weight, temperature, pH, moisture, ash, volatile acids, and nitrogen. The per- centages of carbon dioxide and oxygen at the outlet and in the material were also determined. To demonstrate the relationships that were found to exist, some of these results have been plotted directly. In other cases further calculations were made to determine -iii- the weights of the dry material, gases utilized and evolved, and the water evaporated. One of the major findings was that the temperatures sometimes reached in the composting process can be detri- mental to rapid composting. Also, the anaerobic fermentation of sugars during the initially wet period seemed to account for the decrease in pH; and lastly, by utilizing the moisture content, the approximate weight of a certain volume of homo- geneous, finely ground compost could be determined, regardless of the stage of decomposition. Moisture imparted very little swelling to the material. TABLE OF C ONTENTS Page LIST OF TABLESOOOOOOOOOOOOOOOOOO.0.OOOOOOOOOOOOOOOOOOOOV11 LIST OF PI‘ATES...OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOVj-i LIST OF FIGURESCOOOO00.00.00.000....0.OOOOOOOOOOOOIOOOOV11 No. II. III. IV. INTRODUCTIONOOOOOOO0.0.00COOCOOOOOOOOOOOOOOOOOO A. B. C. Advantages Of CompOStingoeee00000000000000. comPOSting MethOdSoeeeeeooeooooeeeeeeeeeeoe Purpose Of this ThOSiBoooooeeooeeeeeeeeeeoe APPARATUS AND PROCEDURE........................ A. B. C. D. E. THE A. B. C. D. E. F. Experimental ApparatuSeoeooo000000000000000 Material USBdoeooereoooeoeeeeeeeeeeeeeooeeo Experimental Procedure..................... Laboratory Procedure....................... Calculations............................... CONDITIONS OF COMPOSTINGOOOOOCO0.....000000 The pHeoeeeoeeeeeeeeeeeoeeeeeeeeeeeeeeeeeeo A Comparison of Air Rate, Moisture, and Temperature................................ Oxygen Utilization and Carbon Dioxide Evolution.................................. The Effect of Heat on Biological Activity.. Amount of Water Evaporated................. Change in pH...00.000000000000000...0000000 PARAMETERS OF DECOMPOSITION..................;. A. B. C. D. E. VOlatlle A01d800000000000000000000000000000 v018t110 SOlidSoeooeeooeeeoeeoeeoeoeeeeeeee Nitrogen................................... Respiratory QUOtientooceooeeoeeoeoeeeeeeeoe The Decomposition of Cellulose............. #4 r4 n4 a) no <3cnowr¥f $r \mroha t4 P‘ +4 \o \a 20 22 25 26 26 31 32 3 3 No. V. VI. VII. VIII. TABLE OF CONTENTS (continued) Page WEIGHT RELATIONSHIPS DURING DECOMPOSITION....... 38 A. Analysis of Weight During Decomposition..... g8 B. The Relationship of Dry Weight to Volume.... 0 CONCLUSIONSOOOOOOO00.000000000000000...00000.... uz APPENDIXOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO [+14- A. The Determination of Total Organic Nitrogen by the Kjeldahl Method............. AS B. The Procedure for Determination of Ammonia Nitrogen............................ ’46 LITERATURE CITED................................ h? -vi- N0. N0. 1. Figure 1. LIST OF TABLES Page The Total Bacteriological Count on Tryptose-Glucose-Eosin Agar of Garbage COMPOSteeeeoe00000000000000eeeoeeeeeeeeoeoeo 23 LIST OF PLATES Page Experimental Apparatus......................... 6 LIST OF FIGURES Page Conditions of Decomposition in Barrel h -- Fresh Garbage................ 1h Conditions of Decomposition in Barrel 5 -- Pilot Plant End-Product...... 15 Conditions of Decomposition in Barrel 6 '- Fresh Garbage................ 16 Parameters of Decomposition 1n Barrel u -‘ FTGSh Garbage................ 28 Parameters of Decomposition in Barrel 5 -- Pilot Plant End-Product...... 29 Parameters of Decomposition in Barrel 6 -- Fresh Garbage................ 30 Analysis of Weight During Decomposition in Barrel h ‘- FrOSh Garbage................ 39 The Relationship of Dry Weight to Volume....... Ll -vii- I. INTRODUCTION Composting refers to the decomposition of solid or- ganic material, by microorganisms, to a relatively stable humus. A. Advantages of Composting The advantages of composting garbage are twofold. It provides a method of disposal of refuse and a means of ob- taining a suitable fertilizer. As a method of disposal, it must be compared to ex- isting methods in the United States. Incineration is a cost- ly process resulting in a complete loss of all the valuable organic solids. Landfill is an unsightly method, requiring the acquisition of land remote from the municipality. Composted garbage may in some cases be regarded as a suitable fertilizer, and in certain respects may be superior to commercial fertilizer. While the commercial fertilizers may have much larger amounts of the principle nutrients, composted garbage has a greater variety of nutrients that may be more readily available to plants. In contrast to the commercial fertilizers, nutrients contained in the or- ganic material will not readily leach out of the tepsoil. Composted garbage, because of its organic nature, will im- prove the soil by promoting better aeration and moisture re- tention. The possibility of disease resulting from the use of the composting end-product is extremely remote. It is doubtful that any pathogens would be found in a municipal garbage. If so, the organisms would undoubtedly be destroy- ed during the composting process, because of the very high temperatures encountered. The maximum growth temperature for most pathogenic bacteria lies between NO and 50 C. Temperatures of 60 and 70 C. are not uncommon during gar- bage composting. B. Composting Methods There are two general processes employed in the com- posting of municipal refuse. One of these, the anaerobic process, is slow with objectionable odors. The second, aer- obic composting is presently being investigated in this country. It is a rapid process and can be conducted under controlled conditions in a manner free from stench problems. ‘ Systemized anaerobic composting began about thirty years ago. However, the recent trend in this country has been toward aerobic decomposition. The two principle meth- ods of the aerobic composting process advocated in the United States are the windrowing method, and the silo or digester method. The high-rate composting plant at Mich- igan State University was of the digester type, with pro- cessing periods ranging from four to six days. C. Purpose of this Thesis Until recently, very little scientific data could be found concerning the composting process. A great deal of the literature was highly Opinionated with very little supporting scientific facts. However, certain industries, governmental groups, and universities are currently carrying out constructive research programs. The decomposition phenomena and the various conditions encountered in the garbage throughout the process are not yet fully understood. It is the purpose of this thesis to contribute information within the limitations of the methods‘ employed. II. APPARATUS AND PROCEDURE A. Experimental Apparatus‘ In a study of these problems, on a scientific basis, a volume of material large enough to be representative of actual composting conditions, yet small enough to facilli- tate daily shredding was required. Since loss of heat was a critical factor in simulating the central portion of a large mass of material, insulation was needed. An insulat- ed barrel seemed satisfactory in meeting those requirements. The barrel used was composed of fiber, of the type used to ship dried milk. The container measured about 21.5 inches in diameter and 26 inches high. Small pipes were fitted along the side of the barrel, at the extreme tap and bottom, to permit the circulation of air. To allow uniform circulation of this air through the material, a screen was installed four inches from the bottom. The available space for the material was 3.8 cubic feet. To record the temperatures of the material, and the percentages of oxygen and carbon dioxide at different levels, three additional short pipes were installed 3, %, and 1h inches above the screen. Several coats of shellac were applied to the inner and outer surfaces of the barrel. One inch spun glass insulation was glued to the outside surface and to the top of the tight fitting metal cover. Aluminum 4,- foil was applied to the inner surface of the barrel to re- sist the attack of moisture and acids. This foil also served as an added insulating material. Air leakage around the cover was prevented by incorporating a snap-ring sealed with roofing compound. The barrels were placed on a low rack in a heated building. The source of air was a compressed air reservoir tank. Air passed through a pressure reducer and regulator, through rubber tubing to an air flow preportioning device, and into the inlet of the barrel (either at the t0p or bot- tom). Usually the apparatus for measuring air volume was attached to the outlet pipe. This air metering apparatus' consisted of a wet flow meter together with a commercial gas meter. The insulated barrels and air meters are shown in Plate 1. To reduce particle size of the garbage, two types of grinders were used. The screw type Ray-Mo grinder, util- izing a crushing-squeezing action similiar to a household grinder, was used for the initial grinding of the fresh gar- bage. The resulting material possessed a very small parti- cle size. A Kemp soil shredder was principally used to break up wet chunks that formed during the composting pro- cess. This shredder was a semi-portable machine possessing a shredding-throwing action, developed by heavy blades ro- tating at a high speed. The particle size resulting from this operation was quite large, with a certain percentage -6- PLATE 1 EXPERIMENTAL APPARATUS Tap view of barrel Tap view of barrel with screen support with screen Insulated barrels and gas A preliminary air supply meters (without the con- arrangement necting air tubing) of garbage passing through unmodified. However, the part- icles were progressively reduced in size through success- ive shreddings. B. Material Used In each experiment, fresh garbage was the source of organic material for composting. Garbage was either shred- ded in the Kemp soil shredder, or ground in the Ray-Mo grinder. If the latter method was employed, the result- ing dense-wet mass was subsequently shredded to provide ad- equate aeration. Seeding was accomplished with partially 'or nearly composted end—product of former windrow and bar- rel experiments. C. EXperimental Procedure During the periods of observation of barrel eXperi- ments, measurements were made and observations noted each day prior to disturbing the contents. Gas was sampled at the three levels of the barrels by inserting a glass tube, sealed with a rubber stOpper, about eight inches into the material. While compressed air was entering the barrel, the gas was allowed to displace salt water in a filled sam- ple bottle. Precautions were taken to blow the tube free of air prior to sampling. Temperatures were recorded at the three levels at an eight-inch penetration. The temperature of the inlet air was usually around 18 C. Each gas meter reading and the -8- time were recorded. The volume and weight of the compost material were also noted. The material was then removed and shredded to disen- tegrate the wet clumps that tended to form. II'oward the latter part of each eXperiment, the material was dry enough to omit grinding and was raked and turned. Water was some- times added at this point of the experiment in an attempt to reestablish the Optimum.moisture content. After a thor- ough mixing, a small sample was removed for laboratory analysis, and the remaining material returned to the barrel. D. Laboratory Procedure The gas sample was analyzed to determine the percent- age carbon dioxide and oxygen present. This analysis was accomplished in the usual manner; that is, passing the sam- ple through potassium hydroxide, then through pyrogallol, measuring the gas absorbed in each case. The compost samples were subjected to varied analyses. Percentage moisture was computed on the basis of the moist weight of the material. Moisture was first determined by employing a Cenco Moisture Balance, using a five-gram sam- ple. The determination was later carried out by drying a sanple for 2h hours at 102 to 101; 0., and obtaining the loss in weight on an analytical balance. Percentage of ash, on a dry-weight basis, was ascertained by burning the dried sample in an electric muffle furnace at a temperature of 650 to 700 c. for at least three hours. Percentage of volatile acids (as acetic acid) was determined by employing a modified procedure of the tenth edition of Standard Methods for the Examination of Water and Sewage. Approximately 10 grams of wet sample was used; 5 milliliters of concentrated sulfuric acid and 200 milliliters of water were then added, and 100 milliliters of distillate was collected. Percentage volatile acids were based on the dry-weight sample. Results were report- ed as total volatile acids (as acetic acid), including the volatile acids and their salts. A further determination was made to differentiate the salts of volatile acids from volatile acids as such. A sample was first dried, then subjected to the same pro- cedure described just above. Results from this analysis were reported as salts of volatile acids (as acetic acid), upon the assumption that the volatile acids would evapor- ate during drying, leaving the salts. The pH of the fresh sample was determined by using a Beckman pH meter. A sample was placed in a closed.test tube, moistened, then incubated for 2h and AB hours. The pH and odor were then noted. Foul odors after incubation and excessive drOp in pH were considered to be indicators of incomplete composting. -lO- Ammonia and total nitrogen (see appendix), expressed as nitrogen, were determined by the Kjeldahl method. Three 1 to h-gram samples were used in each determination. E. Calculations Since only the volatile solids (organic matter) was oxidized during decomposition, all weights and volumes plot- ted were based on the weight of the initial dry volatile solids in the particular barrel. The weight of the dry vol- atile solids was the difference between the dry weight of the garbage and the weight of the ash in the barrel. The dry weight was computed from the moisture content and the weight of the moist material. The bulk density was deter- mined by dividing the dry weight by the volume occupied by the moiat compost. The weight of the water evaporated daily was calculated by the difference of the measured moist weight and the calculated dry weight. Percentage nitrogen, expressed as percentage of initial dry volatile solids, was obtained by multiplying the percent- age nitrogen of the sample by the factor: the percentage of initial dry weight of the sample divided by the percentage of initial dry volatile solids of the barrel contents. The volume of air was the difference in gas readings each day. Since the average barometric pressure was 761 mm. and the average temperature of the air was 18.h C., the cor— rection for standard conditions was negligible (1.01). The -11- percentage of oxygen utilized by the material was deter- mined from the assumption that the atmosphere contained 21 per cent oxygen (although a blank was collected each day to determine the reliability of the chemicals). On the premise that one mole of the gas was contained in 22.h liters, the weights of the respective gases were calculated from the percentage carbon dioxide evolved, percentage oxygen utilized, and the volume of air passing through the barrel. The respiratory quotient was calcuhated by dividing the percentage carbon dioxide evolved by the percentage oxygen utilized. III. THE CONDITIONS OF DECOMPOSITION As a preliminary test, two barrels, Barrels l and 3, were filled with fresh garbage and composted. Typical tests were run throughout, but due to inexperience with the method, serious questions were raised regarding validity of data. This data is therefore omitted from this discussion. The second experiments were with three new barrels, designated as Barrels h, S, and 6. Barrel h contained fresh garbage, finely ground in a Ray-Mo grinder. It was seeded with approximately 10 per cent end-product from the previous barrel. The seeding material contained a moisture content of 35.3 per cent and a pH of 7.8; and was alkaline for about two weeks before being used as a seeding material. End-product from the high-rate composting plant (com- posted fresh garbage) was utilized in Barrel 5. Finely ground fresh garbage in Barrel 6 was composted after Barrel h was completed. This material was seeded with approximately 10 per cent of the Barrel h end-product. A. The pH The pH, in general, denoted the progress of aerobic decomposition. Strictly fresh garbage had a pH of around 6 or 7, depending upon its contents. Upon being ground, bro- ken vegetable cells released a large amount of free water. -12.. -13- The moisture contents of the material were plotted in Figs. 1 through 3. High moisture levels, which inhibited aerobic activity and favored anaerobic decomposition, were noted during the first few days in Figs. 1 and 3. Among the by-products of this type of decomposition were organic acids. These acids were apparently utilized (the pH climbing to an alkaline range) by the aerobic bacteria when the moisture content dropped enough to permit oxygen to permeate between the particles. The condition of higher pH was reached on the seventh day in Barrel h (Fig. l) and on the fifth day in Barrel 6 (Fig. 3). This initial stage had already taken place within the material of Barrel 5 (Fig. 2) while still in the pilot plant. ‘ B. A Comparison of Air Rate, Moisture, Temperature The prevailing temperatures of the compost were plot- ted versus time in Figs. 1, 2, and 3. In Figs. 1 through 3, a recurring temperature cycle was evident. The first cycle in Fig. 1 occurred between Days 0 and 17 (with the exception of Days A, 11, and 1h -- low air supply); the second cycle, between Days 17 and 22; and the beginning of a third cycle, after the twenty-second day. Four or five cycles are shown in Fig. 2. The peaks of these temperature cycles occurred on the second, eighth, fourteenth, and p03- sibly the twenty-third day, respectively. One cycle is ev- ident in Fig. 3; the lower temperature on the fourth day I H. In W ”M. 3 D I. _ 7 5 w m R E . a m m F N B I v - i N. O O R m _ mm .| A S H E S T G P _ T Clo E A N H L — M O O s n — I P E A A T M R L mm 0 F w N i O M _ v R m. _ C 4 .o u w i a L W 5 ~ R m M 0 .l M .H E M s D . a m 0 - P E G 2 m. M ~ w. m... . m u. i m i d. . i K / \h lullr A \l a L I ll | ’ ‘0 v! s _ k n O 2 l w 7 w m m . 0. Q 0 magefizwo .emo . 33.55.33 3534. ms.o._.ox>3\.ox.om8< «was; azuo awn magma: .m.>.o._.ox\>3\.ox.m<>m $.53 F n n P b m w . m o o 3 5 impassmsd 45:2. .3. >23 mama... iod x2 m.>.o 45:2. .3. >3 Emma... 533E. ~~o m.>.o 45:2. .8. \ sax mama: .8526 3 — .- 9 . o «a 4 K S . a m U . T m L E \L m M N m n. M i m m o m A 8 TI! m 0 M N w P v 0 D Y I D. N R m s. D O N. a F N C W a m w m s w A _ D L E m w R S , P._ m n. m d u E .0 mo. U .F T _ m. 0 _ M + w \ r 0 _ W i: i! -, \ ( (Lililw EL! v _ (1.] -1 (IE- \ P Q _ O l B . n4u 2 MW aw— 0. ”.545:qu .omodmaqmmazm: me< 0:6 mosaic m>.o._.ox\>.o._.ax\>m amt; P! P b L w m m 3 5 5252655.. ex\>.o .zEz. .oxxioxmmup: .omNDF: Moo 38 43:2. ex\>eum oweaopd amomzoo mmemmae no mess zqmom -mmoooqe-mmoem~ma zo azboo q<0Hcoqummao.o....m>o. ao pzmo mun. .2 3.23052 .... oz<.mo.u ...o ...:mzofijwm F . mu. . , m w e m Emu mun. . 3:8 3:39 SALTS OF VOLATILE ACIDS TOTAL BI SALTS TOTAL VOLATILE ACIDS O o . . m0_0< 445.0% ZO_.P 30 m END PRODUCT F om mm TILS em MM mm E MD BARREL 5 — ASSUMED INITIAL DRY VOLATILE souos- 43.4 Kg FIG. 5 IO 0 m 0:6 “5.20 .5253 >moa8 z. 3353 amt-2:28 o_m:o\m2:mzmo 5-6 p — O O 4 I. O 8 IZOP Emu «...-a .m23..o> z. mm