Garbage Composting for Mushroom Production

Transcription

1 APPLIED MICROBIOLOGY, Jan., 6 6 American Society for Microbiology Vol., No. Printed in U.S.A. Garbage Composting for Mushroom Production S. S. BLOCK Department of Chemical Engineering, University of Florida, Gainesville, Florida Received for publication June 6 ABSTRACT BLOCK, S. S. (University of Florida, Gainesville). Garbage composting for mushroom production. Appl. Microbiol. :-. 6.-Laboratory and pilot-plant composting of garbage mixtures of newspaper and vegetable waste has demonstrated that garbage can be converted to a medium that produces mushrooms (Agaricus campestris) in good yield. Sewage sludge was less satisfactory than newspaper, gumwood sawdust, or vegetable waste as a compost material for growing mushrooms. A sample of commercially produced compost was found to yield mushrooms in the same quantity as was produced in the laboratory experiments. In this paper, experiments directed toward the conversion of garbage and other organic wastes into edible mushrooms are described. Mushrooms have traditionally been produced from composted horse manure and straw. The procedure followed in this work has been to compost garbage and other wastes and to evaluate these composts as media for mushroom production. In earlier publications (Block, Tsao, and Han, 8; Block and Rao, 6), it was demonstrated that certain wastes such as sawdust could be satisfactorily composted in small-scale experiments and would support mushroom growth. Garbage composting has been practiced as a sanitary measure in different parts of the world (Gotaas, 6), and studies have been conducted in small-scale composting of garbage mixtures (University of California, ). Research has shown the value of composted garbage as an organic fertilizer, but no research has been reported on composting garbage for use in mushroom production. MATERIALS AND METHODS The study of garbage presents a special problem because of the widely varying composition of garbage. In the present study, we adopted a simple formula of 6% newspaper and % (by weight) fresh vegetable waste, and produced a garbage of this composition. To avoid having a wholly "synthetic" product, the vegetable waste was obtained from the University cafeteria and undoubtedly differed in composition in the runs that were made. Newspaper and other paper makes up a large proportion of American household garbage (as compared with European garbage); therefore, it was felt that the use of such a large percentage of paper was desirable. Furthermore, preliminary experiments indicated that there was little problem in composting vegetable matter but much more of a problem in degrading paper to compost. Paper aids composting of the vegetable matter in a physical way, since it serves as a fibrous absorbent to take up the water from the wet, digesting vegetable wastes and to provide structure and porosity for the composting mixture. The paper and vegetable matter were ground in a W. W. Grinder hammer mill, with bars set at. in. used in place of a discharge screen. The mixture was put into an open tank, and sufficient water was added to bring the moisture content to approximately 8%. The following mineral salts were added to fortify the compost for mushroom growing and to lower the carbon-nitrogen ratio:. lb of NHNO,. lb of CaSO-H, and. lb of KCl, per lb of dry compost materials. The mixture was allowed to remain in the tank for day with occasional mixing to allow all the material to absorb the water and salts; then it was again passed through the mill and packed into the composter. Two types of composters were employed in these tests. The laboratory size (Fig. ) was made of two cylinders of hardware cloth separated by. in. of coarse sawdust. The inner cylinder was. in. tall, in. in diameter, and held. ft of material. When filled with compost, the cylinder was covered with a sawdust-filled pillow, giving insulation all around the compost but still permitting gases to diffuse through the container. The laboratory composter was used in a constant-temperature room heated with live steam (Block, in press). The pilot-plant composter, used outdoors, was designed on the same principle as the smaller unit. It was a cubical, sawdust-insulated bin holding 7 ft of material (Fig. ). Composting progress was measured by changes in temperature, ph, free ammonia, and the ability of the compost to support growth of mushroom mycelium (Rao and Block, 6). Free ammonia was detected by a simple, standardized test with phenol red indicator paper, and was reported on an intensity scale to to. The readiness of the Downloaded from on November, 8 by guest

2 6 BLOCK APPL. MICROBIOL. HARDWARE CLOTH SAWDUST FIG.. Sawdust-insulated composter for laboratory composting studies. FIG.. Sawdust-insulated composting bin for pilot runs. compost as a medium for mushroom growth was determined by sampling g and inoculating it with mushroom spawn (mycelium). After weeks of incubation at 76 F, the growth of mycelium in the compost was rated on an increasing scale of to. Mold was also recorded as present () or absent (-). After composting, the material was placed in wooden trays 8 by by 6 in. and cooled to room temperature. The trays were then moved to the mushroom-growing house (Fig. ), and the composted material was inoculated with.% (v/v) commercial mushroom spawn. The inoculated compost was kept in a:foom maintained at 76 F and 88% relative humidity for about weeks. A spray of water was applied as necessary to keep the material moist but not wet. When the spawn had run through the compost, the trays were FIG.. Experimental mushroom-growing house with temperature and humidity controllsfd rooms. transferred to the growing room (6 F and 88%G relative humidity) and covered with a -in. layer of "casing matter" made up of equal parts by volume of sand and ground peat moss. After about weeks the first mushrooms appeared on the casing matter, and after an additional week they were large enough for harvesting. The bottom portion of the stipes (stems) was trimmed off, and the weight of the mushrooms was recorded. Mushrooms continued to appear at irregular intervals and were harvested until the compost was exhausted, a period of about 6 months. RESULTS AND DIscussioN Table presents composting data on two runs with the mixture of newspaper and vegetable waste. The mushroom yields from these two runs are presented in Table. Table shows mushroom yields on compost with gumwood sawdust substituted for paper in the above mixture, on composts produced from dried sewage sludge mixed with either paper or gumwood sawdust, and on a sample of compost from a commercial composting operation. In run with the mixture of newspaper and vegetable waste, the garbage mixture was composted in the steam room maintained at F. Owing to rapid microbial activity on the readily available nutrients of the vegetable matter and to the insulating properties of the composter, the temperature of the compost rose rapidly to 68 F. In this run, the compost was mixed and watered daily, which may explain some of the fluctuations in temperature, although the fermentation may be cyclic as a consequence of attack by different groups of microorganisms. For example, when vegetable waste was employed, yeast was noted first, then an odor of acetic acid, and then free ammonia. The ammonia test in both runs showed no ammonia release until the fifth day. The early production of acid was better noted in the second run, in which the initial ph was 6.6 but after the first day had dropped to 6.. Thermophilic mold was prevalent in the compost about the time the Downloaded from on November, 8 by guest

3 VOL., 6 GARBAGE COMPOSTING FOR MUSHROOM PRODUCTION TABLE. Composting data on a garbage mixture of 6% newspaper and % vegetable waste Temp (F). Growth of Run no.* Days ph NHt Ambient Compost Cs I. * Run was conducted in a laboratory composter; run, in a pilot-plant composter for the first 6 and in a laboratory composter for the remainder of the test. t On a scale of to. t On a scale of to. ammonia release began, but in the later stages of composting actinomycetes, known to the mushroom grower as "fire fang," prevailed. Signs that composting may be terminated are lowering of the temperature and ph, and a reduction in ammonia production. The indication of spawn growth on the compost is delayed; thus, it is useful only in analyzing the results after com- TABLE. Yield of mushrooms from mixture of newspaper and vegetable waste Run Tray Avg Avg * Fresh wt (g) of mushrooms produced per tray after 6 77,8,,,7,,,6,8,8,7,88 8,,86,7,,,7,,,,,66,,87,,66,87,,8 Yieldt Ratio (lb/ft) (t * Days of harvesting. t To convert to kg/m, multiply by posting. During the last of run (Table ), there was a slight rise of both temperature and ph and evolution of ammonia did not subside, but the compost became progressively more favorable as a medium for mushroom growth from the th day on. In composting other materials, we have found that the growth of mold was suppressed as the mushroom mycelium became established, but this was much less the case with garbage. On the other hand, composting removes the soluble components that favor the growth of bacteria, yeasts, and lower fungi, and improves the competitive advantage of the mushroom, which can obtain its carbon from hemicellulose, cellulose, and lignin. Thus, it may be observed that mushrooms could be produced in the presence of mold on the - day-old compost but could not on -day compost (run, Table ), unless it were to be sterilized and mushroom growth were thereby established under noncompetitive conditions. In run, the pilot-plant composter with 7 ft of garbage mixture was used. The recorded outdoor air temperature was an average of maximal and minimal daily temperatures taken by the weather bureau at a nearby station. As with run, the compost heated rapidly, the differential between the ambient and compost temperatures being much greater, however, due to the large quantity of material employed.- Nevertheless, the maximal temperature was about the same, demonstrating that the fermentation is self-limiting due to temperature restrictions on the proliferation of microorganisms and the activity of enzymes. After 6, the compost temperature had decreased to the first day's reading but the high ph and the commencement of ammonia emission suggested that the compost was not ready. This was confirmed by the failure of spawn 7 Downloaded from on November, 8 by guest

4 8 BLOCK APPL. MfICROIBIOL. TABLE. Yield of mushrooms from various garbage mixtures composted in the laboratory and from commercially composted municipal garbage Fresh wt (g) of mushrooms produced Garbage composition Garbage copositiontay Tray - per tray after - (lb/f Yield t) (Wt/Wt) Ratio 6 * 8 Vegetable waste (%) and gumwood saw-,76,.8. dust (6%) 8,6,6.. 76,67,7.. Avg 87,788,..7 Newspaper (%) and sewage sludge (6%) 8,7,.7.,7,,.7.7,,8,.7.7 Avg,6,8,76.7. Gumwood sawdust (%) and sewage sludge,7,68.. A (6%),66,.. Avg,6,.. Gumwood sawdust (%) and sewage sludge 8,87,.6. B (6%) 77,6,6..7 Avg 878,68,87.. Commercially composted municipal gar- 7,77,86.8. bage,6,887,.6. Avg,8,..7 * Days of harvesting. to grow in the compost. During these 6, a shrinkage of the compost to about one-half the original volume was noted. The decision was made to transfer the compost to laboratory composters and to maintain a high ambient temperature in the steam room to promote activity. The compost temperature quickly rose to the peak of 6 F and remained in this region for several (run, Table ). With the passage of time, the temperature, ph, and NH gradually lowered, but only during the last did the compost support mushroom spawn. Apparently several more of composting would have been desirable, but in both runs the mushroom spawn did establish itself and mushrooms were produced in good yield, as is shown by the data in Table. The two runs show the garbage mixture to be an excellent medium for mushroom growing. The mushrooms were distributed to people familiar with fresh mushrooms and were considered to be no different in appearance or taste from those grown commercially on conventional compost. In the first run, the mushrooms grew more slowly than in the second run, but final production was almost the same. This difference in rate of production probably resulted from the use of manure spawn in the first run and grain spawn in the second run. Although grain spawn is more active than manure spawn, manure spawn was used in all the experiments reported here, with the stated exception, because it is less susceptible to contamination by foreign microorganisms. Two calculated yield indexes are presented in the tables. The first gives the pounds of fresh mushrooms produced per square foot of compost surface, and is a practical index of production used by commercial growers. The second gives the weight of fresh mushrooms produced by an equal weight of moisture-free compost, and is useful in comparing the relative value of different compost materials. The yield per square foot was a little greater in the second run than in the first. This was due to a little more compost having been packed into the trays, for the weight of mushrooms per equivalent weight of compost averaged nearly the same for both runs. When gumwood sawdust was substituted for paper in the mixture, a slightly greater average weight of mushrooms was eventually produced (Table ), but the sawdust was less efficiently converted to mushrooms as shown by the yields on an equivalent weight basis. This was again demonstrated in the runs in which sewage sludge was mixed with paper or sawdust (Table ); the yields per tray were similar, but a pound of paper produced more than twice the weight of mushrooms produced by a pound of gumwood sawdust. Different kinds of sawdust also caused considera- Downloaded from on November, 8 by guest

5 VOL., 6 GARBAGE COMPOSTING FOR MUSHROOM PRODUCTION ble differences, with oak producing very good results and pine very poor (Block, in press). Two sources of sewage sludge were evaluated with the gumwood sawdust. Sludge A was from the University plant, and Sludge B was from the city of Gainesville. Expressed on either yield basis, production of mushrooms differed little regardless of the source of sludge. Sewage sludge, although a source of nitrogen, vitamins, and trace metals for the microorganisms involved in composting, is a poorer source of carbon for the mushroom than is paper, gum sawdust, or vegetable waste. This is not altogether surprising, because sewage sludge has already been subject to prolonged microbial attack, no doubt eliminating nutrients that could have been assimilated by the mushroom. Since our experimental compost had produced mushrooms in good yield, it was of interest to learn whether compost from large-scale municipal or commercial composting operations would function similarly. Compost from the city of Williamston, Mich., was obtained which had been constituted as follows: to each parts of garbage, parts of corncobs, 7 parts of undigested sewage sludge, and parts of lime were added. This mixture was ground and composted in passing through four bins for a period of in each bin. The material was said to maintain a temperature of F for. From the City of El Paso, Tex., samples were received of a composted mixture of half sewage sludge from the drying beds and half pine sawdust which had been composted outdoors in windrows for 6 months with turning approximately every weeks. Dano of America, Inc., of Sacramento, Calif., submitted another sample of compost. It was stated that in the Dano operation refuse and garbage are rotated in a large steel drum, known as the biostabilizer, where they are simultaneously mixed, ground, and aerated for a little over hr. They are then spread over the ground for the final stages of composting. The only treatment given to these samples was to add water and activate them by steaming at to F in our composting room for to. The compost from Williamston, Mich., grew mold but not mushroom spawn. That from El Paso, Tex., was inert, supporting neither spawn nor mold. The Dano of America compost, however, did support the growth of the mushroom spawn, and the weight of mushrooms produced (Table ) was equivalent to that produced in our experimental composts. Yields on an equivalent weight basis were considerably lower. Although efficiency of conversion was much lower, the compost was much more dense so that much more material filled the trays. From the standpoint of the commercial mushroom grower, the major criterion is overall production per tray; efficiency of conversion is of little concern. From the results obtained, it appears that the compost from Williamston, Mich., was insufficiently composted to serve as a substrate for mushrooms, whereas the material from El Paso was excessively composted so that it was exhausted of nutrients. This very property of inertness, which is highly desirable in an organic fertilizer supplying humus to the soil. is undesirable for a compost to be utilized in mushroom growing. Thus, composting for these two different applications obviously requires different treatment. It is gratifying, however, to have found that a commercially produced compost can serve as a base for growing mushrooms. Composting as a means of waste management conserves and reuses mineral resources that are employed in food and fiber production. Composting is only marginally economical in this country at the present time, because most farmers favor mineral fertilizers over compost. Any additional outlet for municipal compost, even though small as compared with the quantity available, could help to put composting practice on a firmer economic footing. The process of aerobic composting with its high temperatures, plus pasteurization of the compost as is practiced in mushroom growing, should eliminate pathogens that might be introduced with the wastes. Careful regulation would, of course, be required as in the production of any food. ACKNOWLEDGMENT This work was performed with the technical assistance of S. N. Rao under Public Health Service grant EF-8 from the National Institutes of Health. LITERATURE CITED BLOCK, S. S., AND S. N. RAO. 6. Sawdust compost for mushroom growing. Mushroom Sci. : -. BLOCK, S. S., G. TSAO, AND L. HAN. 8. Production of mushrooms from sawdust. J. Agr. Food Chem. 6:-7. GOTAAS, H. B. 6. Composting sanitary disposal and reclamation of organic wastes. World Health Organization, Geneva, Switzerland. RAO, S. N., AND S. S. BLOCK. 6. Experiments in small scale composting. Develop. Ind. Microbiol. :6-. UNIVERSITY OF CALIFORNIA.. Reclamation of municipal refuse by composting. Sanit. Eng. Res. Proj., p. 8. Downloaded from on November, 8 by guest