BIOTECHNOLOGY AND BIOENGINEERIXG VOL. VI, PAGES 403-418 (1964)

Composting Conversion of Solid Wastes for Mushroom Growing

S. S. BLOCK, Department of Chenzical Engineering, University of Florida, Gainesville, Florida

Summary hlethods for coinposting small quantities of tjrganic. materials have been de-

veloped in order to be able to better study the cornposting process. A composting bin was developed which holds 27 cu. f t . of compost and which provides uniform conditions of temperature, moisture, and aeration within the compost mass. A system for indoor composting of less than one cubic foot of material has been developed and is described. The methods have been shown to be reliable and reproducible. The composts were evaluated for their suitability for mushroom growing and were found to give high yields of mushrooms.

INTRODUCTION

The expanding population and its urbanization have produced great accumulations of solid wastes. Disposal of these wastes in the United States costs an estimated three billion dollars a year.’ It is evident that any utilization of such wastes would help to reduce the expense for disposal. Composting is a procedure for treatment of organic, solid waste to reduce its disease potential and nuisance value, and at the same time to convert it into an organic fertilizer. The author and associates have reported their experiments demonstrating that different organic wastes upon cornposting will serve as a medium for growing niushrooni~.~-~ The present paper describes the facilities, equipment, and procedures developed for our pilot plant studies of composting and niushrooni growing.

OUTDOOR COMPOSTING

In ordinary windrow coniposting, organic matter is wet and heaped into piles, whereupon it undergoes natural “fermentation” and decom-

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Fig. 1. Insulated bin for small scale composting.

position. The outer 2-6 in. layer of the pile is cool and may be dry or wet depending upon the weather.6 Deeper in the pile there are zones of medium and high temperature, and at the base of the pile there is a cool zone characterized by anaerobic fermentation and bad odors. Since the desirable, aerobic fermentation occurs only in the medium and high temperature zones, it is necessary to turn, water, and mix the pile frequently for all of the material to be properly composted. This is termed the “nut and shell” system of coniposting6 and it is the method used by mushroom growers. This method is relatively slow, requires large quantities of material, and necessitates considerable labor or machinery for the turning operation. Further, the cool outside portion of the conipost heap gives flies and other insects the opportunity to lay their eggs and proliferate.

In the course of this work a special composting bin, Figure 1, was developed for the purpose of composting relatively sniall quantities

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COMPOSTING CONVERSION OF SOLID WASTES 405

Fig. 2. Temperature profile and pH changes in paper-garbage mixture in composting.

of materials quickly and efficiently. The bin, which had 3 X 3 X 3 ft. inside dimensions, provided the compost material with 6 in. of porous insulation on all six sides. The sides of the bin were hardware cloth and these were surrounded by a frame covered with hardware

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cloth. The Gin. space between was filled with sawdust and shavings so that gases would diffuse through but that more of the heat of fermentation would be retained in the compost. The bin was erected to permit an air space of several inches between the ground and the sawdust insulation at the bottom of the composter. A sawdust-filled cushion, constructed like the sides of the coniposter, rested on top of the compost so that it lowered as the compost shrank in volume during the fermentation. To prevent cooling of the compost due to winds blowing against the bin, baffles were placed around the bin but l /2 in. away from it and the ground to allow air circulation around the compost.

In making compost, the dry ingredients were ground in a Wiley mill (W. W. Grinder with screening bars at in. separation), then weighed and mixed in a tank with enough water to give 80% moisture. The mixture was allowed to stand overnight to permit all the water to be absorbed and the wet mixture was passed through the inill again and then transferred to the composter. Figure 2 presents the tem- perature profile in the composter during a run of a mixture of 60% newspaper and 40% wet vegetable garbage. This material was fortified with 1% KC1, 2.5% CaS04. 2Hz0, and 2.5% NH4N03. The key gives the distance from the bottom of the bin at the center, and in one case, at 1 in. from the outside edge a t the center of one of the sides. It will be noted that the pile was rather uniformly heated throughout the mass of the compost, and even the outside edge rose to the high temperatures necessary to destroy pathogenic micro- organisms and insects.’ Furthermore, no part of the compost became anaerobic and the outside surfaces remained moist as well as warm. As is seen in the plot, Figure 2, pH increased with increasing tempera- ture, as ammonia was produced, and then declined as the temperature declined. Unlike other composts, garbage fermentation produces acetic acid in the early stages of composting causing the pH to lag somewhat behind temperature.

For any procedure to be useful for research investigations, the results must be reproducible. This is definitely not the case in or- dinary compost piles. Therefore, we set up an experiment to test the reproducibility of coniposting in our bin. Figure 3 gives the tem- perature records of two identical runs on the same composition mate- rial in separate bins several days apart. Considering that the fer- mentation is a natural process in which different types of microorgan-

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COMPOSTING CONVERSION OF SOLID WASTES 407

Fig. 3. Temperature records of two identical runs of oak sawdust compost.

isms successively take part, the similarity of the temperature patterns of the two runs is quite remarkable. The uniformity in yields of mushrooms from pilot plant and laboratory composts, as will be

S. S. BLOCK

Fig. 4. Temperature records of corncob-hay and horse manure-straw composts.

presented later, further deliionstrates the ability to reproduce condi- tions and product. In the runs illustrated in Figure 3, the compost was a mixture of 80% oak sawdust, 20y0 dried sewage sludge, 5% brewers’ grains, plus the minerals given previously for the paper- garbage coinpost. This mixture eomposted very rapidly achieving a peak heat of almost 180°1J. in 7 days.

In Figure 4 are fourid trniperature records produced iii coniposting two mixtures co~nnwily used in corniriercial ni~shroon1 growing. The traditional compost for niushroom growing is horse manure with

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COMPOSTING CON\*ERSIOS O F SOLID WASTES 409

bedding straw, and the newer or “synthetic” coinpost is ground corn- cobs with hay. The manure-straw compost was fortified with only the minerals, while the synthetic mixture received the same additions as the oak sawdust, already mentioned. The temperature pattern of the nianure-straw compost differed froin the other composts in that it went through two temperature peaks, the second being higher than the first, but both lower than with the corncob-hay or the sawdust. Even after the two peaks, the compost was not finished, as indicated by the failure of the mushroom spawn to grow in it. This compost might have been benefited had it been turned and mixed during composting. With the composting bin, turning and mixing had been found to be unnecessary with the other materials since sufficient aeration was obtained throughout the compost and the conditions in the compost were uniform. The use of the wind bafRes had the un- expected, beneficial result of retarding the loss of moisture a t the high temperatures, so that with the additional water produced as a fermen- tation product, there was no need for disturbing the compost to water it.

INDOOR COMPOSTING

Since the outdoor composting bin required about 1500 lb. wet weight of material along with its handling and treatment, the number of treatments with it were necessarily limited by considerations of labor and material. Indoor composting of small samples was accom- plished in a steam room, Figures 5 and 6. The room, 7 X 9 X 8 ft., was walled and floored with cement-asbestos board and insulated with rock wool. Steam was supplied by a homemade steam boiler, consisting of a 55 gal. drum and a heating source. For the latter, a forced-draft kerosene heater was employed. The fire pot (Fig. 7) was constructed of stainless steel after several commercial units made of ordinary steel were burned out by the heat of the flame. A clay flower pot resting on crumbled fired brick in the fire pot acted as a wick and helped to obtain a clean blue flame. Since the hot flame burned through the bottom of the water drum, a in. stainless steel plate was placed under the drum and prevented this burnout. Aux- iliary electric steam and dry air heaters were employed for precise temperature and humidity control. The air was recirculated from bottom to top within the room, with provision for fresh air intake.

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Fig. 5. Steam room used for experimental composting trays of different materials.

As was described earlier, in indoor coinposting the materials to be composted were niixed, wet, and placed in composters made of hardware cloth cylinders surrounded by sawdust insulation as in the outdoor coniposter. Three sizes, holding approximately 1, 2, or 5 cu. ft. of inateria1 were employed. In addition to these insulated composters, it was later found that satisfactory composting for mush- room growing could be obtained by placing the material in wooden trays 18 X 12 X 6 in. and maintaining the ambient temperature at about 140°F. The depth of the coinposting material in the trays was not critical, but tests showed poor results with 3 in. and good results with 6 in. of compost. The data in Table I were taken on material in a box 20 X 14 X 12 in., whereas a box 18 X 18 X 39 in. was un- suitable since the material in it soon became anaerobic. The trays

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CORIPOSTIXG CONVERSIO?; OF SOLID WASTES 41 1

Fig. 6. Design and materials for temperature and humidity control in steam room (I) Dry heater blower, 11 g. (electric model B9), 2350 cfm '/s in. S.P. ( 2 ) Dry heater, 5400 watts, 220 v. resistance heater. (S) Butterfly valve. ( 4 ) Outside thermometer (0-150°C.). ( 5 ) Thermostat and indicator light, 2 required, one for dry heater, and one for auxiliary electric steam boiler. Honeywell temperature controller type T415A, range 80-210°F. ( 6 ) Return air grille. (7) Auxiliary electric steam boiler, Chromalox replacement immersion water heating element TRF-245 BX, 4500 watts, 236 v., Edwin L. Wiegand Co., Pittsburgh, Pa. (8) Level controller tank, 2 required, one for main steam drum, and one for auxiliary steam boiler, 10 gal. toilet bowl with float. (10) Kerosene heater, stainless steel. (1 I ) Auxiliary steam boiler water drum, 55 gal. (12) Heater vent. (14) Xero- sene metering valve, needle valve. (15) Forced draft tans, 2 required, Dayton shaded pole blower, 4K--903, 1520 r.p.m., 1/100 hp., 118 cfm, 0.2 in. S.P.

(9) Main steam drum, 55 gal.

(IS) Kerosene supply drums, 2 required, 55 gal.

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10" STO W T ST STL PIP

CI A Y FLOWER

2" STD W T

i 1/4" S T S T L P L A T E

CRUS HE0 FIREBRICK

Fig. 7. Fire pot for small kerosene-fired steam boiler.

were most economic of space and easy to handle but required frequent waterings because, even at humidities close to saturation, water evaporated due to the higher temperature in the compost. Covering the compost with layers of thick, wet burlap reduced the loss of water and kept the surface moist.

In Table I, data are presented on a corncobhay mixture, fortified as already specified for this mixture, and composted in a small box in the steam room. It will be noted that the fermentation proceeded more slowly and at a lower temperature than with the outdoor com- post. At its peak the temperature was only 18'F. above ambient. This is because the heat of fermentation of this small amount of conz- post was easily dissipated. At these lower temperatures the compost was much lighter in coIor and not as thoroughly digested as in the outdoor composting. As noted in outdoor coniposting, pH followed the course of the fermentation as indicated by the temperature.

BIOTECHNOLOGY AND BIOENGINEERING, VOL. VI, ISSUE 4

TABLE I Indoor Composting of Corncob-Hays

Compost Ambient temp., Temp.,

Days "F. OF pH S H 3 Mycelium

1 122 134 7 . 1 0 0, Mb 7.4 0 0, M

0 0, M 2 142 144 3 128 146 7.8 4 142 149 8.1 1 0, M 5 143 159 8 .2 1 0, M 6 143 159 8 .1 2 0, M 7 143 158 8 .2 2 0, M 8 143 154 8.1 2 0 9 143 1.58 8 . 2 2 0, M

10 143 159 8 .3 2 0 11 142 160 8 .2 2 2, M 12 143 158 7.9 2 2, M 13 141 154 7.8 2 4, M 14 142 154 7 5 2 3 15 143 151 7.2 2 4 16 143 149 7.1 2 5 17 143 146 6.9 2 4 18 143 148 6.9 2 5

a Wooden box 20 X 14 X 12 in. b M = mold.

Since ammonia was given off during the course of the coniposting a simple test for ammonia was made daily. Ten grams of compost was placed in a test tube and a piece of filter paper wet with phenol red indicator was suspended 1/4 in. over it for 1 min. The intensity of red color produced by the aniinonia was estimated on an arbitrary scale of 0-3. Another test of the conipost was for the purpose of deter- mining when it was ready to support growth of niushrooni mycelium. Thirty gram samples were taken daily and inoculated with mushroom spawn. After two weeks incubation, the samples were stored in the refrigerator until all samples taken from that run were ready for comparison at the same time. The extent of growth of mushroom myceliuni in the compost was estimated on a scale of 0-.5. The pres- ence of mold was also noted.

As the data show, for the first 10 days of coiiipostiiig the colnpost would not support the mushrooin myceliuni but mold grew readily.

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A4fter that time, the inushrooni niyceliuin grew progressively better and the mold was excluded. In the case of the nianure-straw com- post, Figure 4, the niyceliuiii tests were zero, with mold throughout the run, demonstrating that the conipost was not ready. Since this test takes two weeks to run, it is valuable only in forecasting future runs with the same material.

MUSHROOM GROWING

In coiniiiercial inushrooin growing the finished compost is trans- ferred to the growing house where it is allowed to heat up naturally or it can be heated with steam to initiate a second feriiientation called ‘(sweat out,” which iiiay continue froin several days to a week or more. In our experiinents, this proccdurc was not practiced. The compost

Fig. 8. Mushroom growing room. BIOTECHNOLOGY A N D B1OENC;INEERING. VOL. VI, ISSUE 4

COMPOSTING CONVERSION OF SOLID WASTES 415

MP. INDICATOR L

THERMOSTAT

RELAY

220". CONDITIONER

VEL CONTROLLER GAL. TOILET BOWL

STEAM POT - 18'' WNG X 4"DIA.

HEATING ELEMENT

2 20 LCONTSOL BOX

Fig. 9. Humidity controlling system for spawn running room and mushroom growing room.

from the outdoor or indoor cornposters was put into trays and trans- ferred to the spawn running room, where it was allowed to cool to room temperature (76-78OF.). The trays were made from two soft- drink boxes by using the bottom and sides of one box and adding the sides of another. They were the same as were employed in indoor coniposting. As soon as the compost was cool it was inoculated with spawn of the common, coinniercial mushroom, dgarzcus bisporus. The spawn was then allowed to run through the conipost for a period of 1@14 days, during which time it was watered with a fine spray to keep it moist but not wet. After two weeks the trays were trans- ferred to the growing room (Fig. 8) , which was maintained at 65°F. The growing and spawn running rooms were 18 X 9 X 8 ft., having concrete block walls faced inside with 2-in.-thick styrofoani insulation. The dry bulb temperatures were thermostatically controlled with one ton refrigeration units, installed in the window of each room. In the

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spawn running room it was occasionally necessary to heat the room to maintain the desired temperature and this was done with a small, electric room heater equipped with blower fan and thermostat.

The system used to maintain humidity a t 88% in both rooms is pic- tured in Figure 9. An electric steam generator connected to a wet bulb thermometer supplied steam to the room as the wet bulb temperature increased. The steam generator employed the heating element from a domestic hot water heater placed inside a 3-in. pipe and connected to a water supply tank through a constant-level float valve obtained from a toilet flush mechanism. In our first steam generator, the heating element was inserted in the top of the pipe and the steam was bled off from the side. After burning out several elements, however, the design was modified, with the element inserted a t the bottom. In this way, the element was always covered with water and did not burn out.

In mushroom growing, the compost is covered with “casing soil” when the spawn has run through the compost. A layer of clay loam soil one inch thick is used. Since such soil was not available in our area, we developed a substitute casing layer made up of equal parts by volume of building sand and ground peat moss. This casing material was compared with good casing soil and was found to give equivalent yields of mushrooms from the same compost. It had the advantage of always being uniform and it did not puddle as soil may do if not watered properly. The trays were watered as needed to keep the compost moist.

About two weeks after being put in the growing room the first “break” of mushrooms appear. Four to six days later the mushrooms are full grown and are picked in the “button” stage before the veil breaks and the cap expands. The bottom of the stem which is dirtied by the casing matter is cut off and the mushrooms are weighed. In our experiments picking was continued until the trays were practically exhausted, a period of 4-6 months. Yields of mushrooms were calculated on a practical basis of pounds of fresh mushrooms per square foot of compost surface 6 in. thick, and on a scientific basis of weight of fresh mushrooms per equal weight of dry compost.

The compost on which data were presented in Table I was used to grow niushroonis and the yields are given in Table 11. The yield data show that the conipost produced indoors with this very small quantity of material is of very good quality, as was indicated earlier

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TABLE I1 Yield of Mushrooms from Corncob-Hay Compost Produced Indoors*

Fresh weight, g., of mushrooms produced in days Yield

30 60 90 120 180 lbs./ft.2 wt./wt."

Tray I 960 1818 3030 4439 5523 8.95 5.02 Tray I1 1066 1889 3078 4608 5654 9.16 5.14 Average 1013 1854 3054 4524 5589 9.05 5.08

a Dry weight of compost per tray, 110 g.

0 Weight of fresh mushrooms per unit weight of dry compost. Six inches deep.

by the mycelium growth test. The yields from the small trays were very high and were equivalent to yields from the same composition compost produced in the outdoor composting bin (Table 111). The weight of fresh mushrooms per unit weight of dry compost demon- strates the value of this compost compared to an equal weight of composts of other raw materials4

TABLE 111 Yield of Mushrooms from Corncob-Hay Compost Produced Outdoors"

Fresh weight, g., mushrooms produced in days Yield

30 60 90 120 180 lbs./ft.2b wt./wt."

Tray I 859 1600 2163 4787 5360 8.68 4.87 Tray I1 821 1560 1989 4958 5437 8.81 4.94 Tray 111 1024 1608 2049 5208 5436 8.81 4.94 Average 901 1589 2067 4984 5411 8.77 4.92

a Dry weight of compost per tray, 110 g. b Six inches deep. 0 Weight of fresh mushrooms per unit weight of dry compost.

This work was performed under National Institute of Health Grant EF-00085.

References

1. Steed, Henry C., Jr., paper presented at Natl. Conf. on Solid Waste Utiliz.,

2. Block, S. S., G. Tsao, and L. Han, J . Agr. Food Chem.. 6,923 (1958). 3. Rao, S. N., and S. S. Block, Develop. Ind. Microbiol., 3, 204 (1961). 4. Block, S. S., and S. N. Rao, Mushroom Sci., 5,134 (1962). 5. Lambert, E. B., and A. C. Davis, J . AgT. Res., 48, 587 (1934).

Dec. 2-4, 1963, Chicago, Illinois.

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6. Witt, W., Das neue Champignonbtcch, 1932 (through E. B. Larnbert, Bvtun.

7. Gotaas, H. B., Coniposting, Sanitary Disposal and Iieclamation of Organic Rev., 4, 397 (1938).

Wastes, World Health Organization, Geneva, 1956, p. 81.

Received May 19, 1964

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