COMPOSTING FOOD PROCESSING WASTES

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1 COMPOSTING FOOD PROCESSING WASTES GEOFFREY A. KUTER, PH.D. AND LEWIS M. NAYLOR, PH.D. INTERNATIONAL PROCESS SYSTEMS, INC. LEBANON, CONNECTICUT ABSTRACT Beginning in the early 1970's, composting has become widely adopted for the treatment and stabilization of municipal wastewater treatment sludges. In 1987 over 100 municipal composting facilities were in operation in the United States. However, relatively few food processing industries have taken advantage of this technology. In 1986, International Process Systems introduced a vessel type system that can be used for the economical and environmentally sound composting of a wide variety of materials. The IPS system opens up many opportunities for the food processing industry to make full use of composting as a waste management technology. This report discusses the results of two full-scale demonstrations of the successful composting of residuals from the production of (1) apple juice and (2) chocolate. A total of 127 wet tons of apple wastes (pomace, filter cake, and a biological sludge) were composted in the first study. In the second study, 8 wet tons of chocolate waste (expeller cake, bakery wastes, and a biological sludge) were processed. Sawdust was added to the waste mixtures in order to obtain an input mixture with adequate porosity and moisture for composting. In both studies, after 18 days retention in the vessels with daily agitation, the finished compost was dry, about 60% dry matter, and sufficiently stable and odor free to be used directly as a soil amendment. INTRODUCTION Composting is a traditional method for recycling agricultural wastes and animal manures into useful soil amendments. During the composting process, microorganisms metabolize readily degradable organic matter, and generate heat energy, carbon dioxide, and water vapor in an aerobic environment. Mixing and aerating the compost mass removes excess heat to "in an optimum microbial environment, and disperses excess moisture to assure an acceptable, dry finished product. Since the pioneering research performed by the U. S. Department of Agriculture in the early 1970's, composting has become widely accepted for treating municipal wastewater treatment sludges. In 1987, over 100 municipal composting facilities were in operation in the United States (Goldstein, 1987). The facilities described employ a diverse array of technologies including simple windrow, aerated static pile, and various types of vessel systems. Much of the composting research and technology that has developed for composting agricultural wastes and municipal wastewater sludges can also be applied to food processing residuals. However, virtually no published studies on composting food processing residuals exist. This paper describes the results of two full-scale composting tests with a mixture of residuals generated by (1) an apple juice producer and (2) a 1

2 chocolate manufacturer. The primary focus of the studies was to demonstrate the use of an existing vessel type system that has been used for several years to produce manure based composts for the retail soil products market. MATEW ANDMETHODS The composting facility used in the study is located at Earthgro, Inc., Lebanon, CT. The composting technology used in these studies is licensed in this country by Intemational Process Systems, Inc. The IPS composting system is described as a forced air, agitatedbed, vessel system. The IPS composting system used in this study consisted of four, rectangular, elongated, concrete bays 6 ft wide by 6 ft high and 180 ft long (Figure 1). In this system, the material to be composted is blended with the bulking agent, and loaded, using a small, one cubic yard, front end loader, into a bay at the input end. The composting mass is transported down the length of the bay by a mechanical agitator that travels along steel rails mounted on top of the concrete walls of the bays. As the mechanical agitator moves through the compost, the material is mixed, shredded, and conveyed approximately 10 ft. After 18 passes the material will have travelled the 180 ft distance to the opposite end of the bay, and is discharged as finished compost. With each pass of the machine, a space is left at the input end of the bay for a fresh charge of the material to be composted. In the normal operation of the facility the machine passes through each bay once a day to obtain an 18 day retention time. Operation of the mechanical agitator is automatic, and an operator has not been required to be present in the facility while the unit is in operation. At this IPS facility, a timer is used to automatically start the machine in the morning prior to the arrival of personnel. Transfer of the machine from bay to bay on a dolly is also accomplished without operator assistance. The composting system is enclosed in a unheated building. The facility is ventilated using large, wall-mounted fans to remove the large volumes of moisture saturated air produced during the composting process. This design eliminates operational problems related to rain and snow, and minimhes moisture condensation on the interior of the building and on the machinery. In order to maintain optimum temperatures and aerobic conditions in the compost mass, forced aeration is provided by a series of blowers set in the floor adjacent to the exterior walls of the outside bays. Air is delivered upward from the bottom of each bay through perforated piping set in gravel base. Blowers serving individual bays are operated independently with timers or by a computerized temperature feed-back system to regulate temperatures. Each of the bays is a separate and independent composting unit and can handle at least seven to nine wet tons (about 11 to 12 cu yds) of material with each charge. Because of the modular design of the IPS system, one bay was dedicated to the food processing residuals study without interruption of the ongoing manure composting operations. This bay was loaded with an input mixture of the processing residuals and bulking agent on a daily basis, and finished compost was discharged from the output end of the bay after 18 days retention in the system. 2

3 Upon delivery the raw materials were dumped directly inside the compost facility building into a staging and mixing area. In order to prepare a mixture that had sufficient porosity and dry matter content for composting, residuals were mixed with a bulking agent prior to loading into the bay. Sawdust was used as the bulking agent in these studies because of its wide availability, and absorptive pmperties. The quantity of each food processing residuals delivered to the site for composting and the quantity of sawdust used as the bulking agent was recorded. Samples were taken from the residuals upon delivery and analyzed for dry matter content, volatile solids, and ph. Samples of the input mixture and of the finished compost were also collected and analyzed. ADDk Processing Residuals RESULTS A blend of apple processing residuals generated by a juice manufacturer were used in the fiit study: apple pomace, filter cake (mostly diatomaceous earth with some apple solids), and a biological sludge. The weights of each type of material are shown in Table 1. On a wet weight basis, the pomace accounted for 49% of the total. As noted in Table 1, both the pomace and the sludge had a low dry solids concentration (14% and 12% dry solids, respectively) in comparison to the filter cake (38% dry solids). Thus, while the sludge accounted for 30% of the total mixture on a wet weight basis, it represented less than 20% of the total dry solids. Sawdust was mixed with the apple processing residuals in the ratio of about 0.5 tons per ton of the residuals. The input mixture averaged 36% dry solids. During the study a total of 67.8 tons of sawdust (equivalent to 45.9 dry tons at 68% dry solids) were mixed with 127 tons of apple residuals (equivalent to 23.5 dry tons) to yield a total input mixture of tons (69.4 dry tons). The total input mixture was loaded into the dedicated bay for 22 consecutive days. Each day the material was agitated and transferred down the bay by the mechanical agitator. At the completion of the composting period, a total of 92.4 ton of compost was produced, with a mean dry solids content of 60%. The weights of the materials processed and produced are presented in Table 2 on a daily basis. A mean of 5.8 wet tons of the apple residuals were mixed each day with 3.1 tons (about 8 cu yds) of sawdust to produce a total of 8.9 tons per day of the input mixture. After the 18 day retention period, 4.0 tons per day of finished compost was produced. Thus during the composting process 4.9 tons was lost from each days input. This loss amounts to 53% of the input mixture (Table 3). On a dry weight basis, about 20% of the input mixture was lost, suggesting that about one-fifth of the mixture was biodegraded to carbon dioxide, water, and heat. The volume of the compost was reduced by about 30%. In summary, about 0.5 tons of sawdust was requid for each ton of the apple processing residuals, and 0.7 tons of finished compost was produced per ton of the input apple residuals. 3

Chocolate Production Residuals Eight tons of chocolate production residuals were delivered to the composting facility for experimental processing in the second study.

4 Chocolate Production Residuals Eight tons of chocolate production residuals were delivered to the composting facility for experimental processing in the second study. The load consisted of 4,720 lbs of expeller cake from the chocolate extraction process, 7,000 lbs of a biological sludge (5% dry solids) f wastewater treatment, and 4,252 lbs of bakery wastes. The bakery wastes consisted of a mixture of whole chocolate, sugar, cocoa, and rice. The moisture content of these individual materials was not determined. About 9.25 tons of sawdust was required as a bulking agent to absorb the free water in the high moisture sludge. Although the other materials were relatively dry (in excess of 50% dry solids), they were not mixed adequately to absorb the free liquid in the sludge. The volume of the sawdust and the chocolate residuals after mixing, 23 cu yds, was sufficient to fiil the bay on two consecutive days with a average of 8.6 wet tons per day. Total dry solids content of the input mix was 50%; volatile solids were 92.9% of total dry solids. The ph of the input material was 5.2. During the composting period, both the weight and the volume of the mixture decreased. From Table 3, the wet weight of the input mixture, 17.2 tons, was reduced by about 40% to 10.2 tons by moisture lost. Volume of the compost decreased by about 40% due to drying and collapse of the bulky structure of the input mix. Dryness of the compost improved to 62% dry solids. The data suggest that about 2.2 tons of dry matter was degraded and lost during the composting process. This figure is close to the volatile solids weight loss of 2.9 tons. With the degradation (biological combustion) of the volatile solids, the concentration of minerals such as calcium and potassium oxides or carbonates (biological ash) increased proportionately in the finished compost. This increase in mineral concentration would be one of the factors contributing to the slight ph increase to 5.4. Overall, 0.6 tons of finished compost was produced per ton of the input mixture, and 1.3 tons of finished compost was produced per ton of the chocolate residuals. DISCUSSION Results of the studies with the apple and chocolate processing residuals indicated that both types of food processing residuals are readily composted in the IPS vessel system. Although the wastes were very different in terms of physical structure, food processed, and moisture content, both could be handled in a similar manner and produced a dry, well-stabilized finished product. Use of a dry, absorptive bulking agent, in this case sawdust, to absorb free water, very wet residuals such as the apple pomace and the biological sludges could be composted. The amount of sawdust used with the two materials differed substantially and was a function not of the overall dryness, but rather of the amount of free water in the materials. For example, the mixture of the apple processing residuals which had a mean dry solids content of 18% was mixed in the ratio of 0.5 ton of sawdust per ton of residuals. In contrast, the chocolate processing residuals which had a dry solids content of 50% was mixed with sawdust in a one to one ratio. Although not investigated in this study, other bulking agents can be used either in addition to sawdust or as a replacement for the sawdust. For example, the dry finished compost could be used as a bulking agent. This operational strategy would reduce the 4

quantities of bulking agent needed. It would also increase the solids retention time in the composting system by cycling the material through the system more than once. This would have two effects.

5 quantities of bulking agent needed. It would also increase the solids retention time in the composting system by cycling the material through the system more than once. This would have two effects. The compost withdrawn k m the system would be more stable, a potential benefit. On the other hand, with the increased degradation of the volatile solids, there would be an increase in the concentration of the mineral or salt fraction of the compost. For uses of the compost in container mixes in which salt sensitive plants would be grown, this could be a disadvantage. Weight loss during composting was a function of both moisture loss and dry or volatile solids loss. Moisture loss amounted to 40 to 50% of the original wet weight of the input mixture. Dry solids loss varied from 20 to 25% of the dry weight of the input mixture. The change in volume of the composted materials appeared to be related to the texture of the original mixture, and the subsequent collapse of this structure caused by the daily shredding and moisture loss during composting. This reduction varied from 30 to 40% of the original volume. Despite the marked difference between the two materials, both produced a finished compost of about 60% dry solids after 18 days retention time in the system. Both composts were odor-free and readily useable as a soil amendment. Although composting can be accomplished using a wide variety of technologies, the IPS system possesses a number of features that are unique and contribute to the ability of the system to compost materials of widely variable properties. The system is modular in design. This feature enables one type of material to be composted in one bay, and another in an adjacent bay. With an appropriate design, the finished composts could be collected separately for distribution and use dependent on quality. The system is highly flexible in operation. Day to day variations in the supply of the materials to be composted can be handled by regulating the operation of the mechanical agitator. As an example, by operating the agitator twice a day through a bay, the capacity of the system would be doubled. This type of operational strategy would provide drying, but a lower level of stabilization. It could be useful in processing certain materials such as horse manure or stable waste that are high in organic matter (energy), but relatively low in nitrogen. In contrast, the agitator could be operated on altemate days to increase the solids retention time in the system. This program would produce a very stable finished compost and provide enhanced pathogen kill for materials such as municipal sewage sludge. The system provides mixing and shredding with each pass of the mechanical agitator. This feature reduces mechanical mixing requirements of the raw materials used in the input mixture. Many dewatered materials tend to form balls or clumps that are not mixed easily and quickly with a front-end loader. In other vessel systems, the center of these clumps can remain unstablized even after the complete composting period, and can produce odors when broken open during use. The system provides separate aeration control of five individual segments of each bay through five blowers mounted outside the compost bays. This operational flexibility provides complete control of the composting and drying processes. Temperatures in the initial composting phase can be maintained for optimum microbial activity to assure rapid stabilization of the materials. Near the end of the composting period, aeration can be increased to enhance drying. This type of aeration in combination with the daily shredding and mixing also assures adequate heating of all particles of the compost to 55 C or above, generally recognized to be essential for optimum pathogen kill (Finstein et al.,1983, Kuter 5

6 et al., 1985, McKinley and Vestal, 1984). It also assures production of a uniformly dry and homogeneous product that is important in developing uses of the finished product. CONCLUSIONS Results obtained from composting apple processing and chocolate production residuals indicated that the IPS system was effective in producing a usable product from wet, highly degradable materials of diverse physical properties and moisture contents. Sawdust used as a bulking agent absorbed free water in the materials to produce an input mixture of 35 to 50% dry solids. After 18 days retention time, there was a loss of about 40% wet weight and 20% of the dry solids. The ffished composts were dry, 60% dry solids, and sufficiently stable to be used directly as soil amendments. REFERENCES Finstein, M.S Composting ecosystem management for waste treatment. Biotechnol. 1 :347 Goldstein, N. Nov./Dec Facilities composting municipal sludge in the U.S. BioCycle 28( 10):24. Kuter, G.A., H.A.J. Hoitink, and L.A. Rossman Effects of aeration and temperature on composting of municipal sludge in a full-scale vessel system. J. Water Poll. Contr. Fed. 57:309. McKinley, V.L. and J.R. Vestal Biokinetic analyses of adaptation and succession, Appl. Environ. Microbiol. 47:

7 Table 1. Quantities of the individual components used in the apple processing residuals composting study. Material Wet weight, Dry solids, Dry weight, Wet wt, % Dry wt, % tons % tons oftotalmix oftotalmix Pomace Filter cake 27.O Sludge Total Sawdust Input mixture Finished compost Table 2. Mean daily quantities of apple processing residuals introduced and finished compost produced. Material Wet tons/day Dry solids, % Dry tons/day Ratio, wet Ratio, dry Apple residuals o Sawdust Input mixture Finished compost ).

8 Table 3. Quantities and characteristics of materials used in food processing residuals composting study. Materials Wet wt., Dry solids, Dry wt., Volatile Volatile Volume, ph tons % tons solids, % solids, tons cuyd Apple processing residuals Input mixture Finished compost Difference Per cent change Chocolate residuals Input mixture Finished compost Difference Per cent change

Composting Principals

Composting Principals Southern New England Chapter of the Soil & Water Conservation Society Friday August 5 th, 2016 Bear Path Farm (Whately, MA) and UMass Amherst Geoff Kuter, Ph.D. Agresource Inc. www.agresourceinc.com