The New Alchemy Institute, East Falmouth, Massachusetts
Reprinted from Proceedings of the First International Conference on the Composting of Solid Wastes and Slurries Leeds, England
September 28 - 30, 1983
Our prevailing methods of waste disposal, resource management, and agriculture are ecologically unsustainable. The soil is being drained of its fertility and eroded at unprecedented rates while an abundance of nutrients are allowed to leach from organic waste products and contaminate precious water resources. Unless profitable means of conserving topsoil nutrients are developed, standard waste management practices will continue to sacrifice the inherent value of these renewable assets. The composting greenhouse is a physical shell and economic mechanism through which the symbiotic technologies of thermophylic composting and greenhouse horticulture are united. Composting within commercial greenhouses can increase plant yields and reduce production costs by capitalizing on the thermal and gaseous cogenerants of the composting process. This provides an economic incentive to recycle underutilized and problematic organic recources. In the past, biothermal energy has made major contributions to the agricultural self-sufficiency of population centers in cold and temperate climates, and holds the potential to do so again. Several recently constructed composting greenhouses have proven to be technically and economically feasible. This promising biotechnology will require expanded research and development for it to root in its crucial niche, and can benefit from the contributions of a diverse and sophisticated composting industry. The successful evolution of the concept could markedly affect the implementation of sustainable methods of agriculture and waste treatment.
The food system that stocks most supermarket shelves in the United States relies on escalating inputs from shrinking reserves of fossil energy and fertilizers to maintain production from chemically farmed soils. Recent crop failures due to drought, insect infestation, and disease, point to the frailty of modern western agriculture. These problems are compounded by, and at least partially resulting from, the continued loss of the topsoil. A growing centralization of the agricultural industry has decayed regional agrarian economies and leaves areas such as the industrial northeastern United States heavily dependent on ecologically unsustainable farming practices. The re-establishment of agricultural vitality in these areas is hindered by a shortage of economic means of returning locally generated organic resources to agriculturally productive soils.
In terms of soil health and vitality it is prudent for farmers to compost abundant and underutilized organic resources. However, there is no economic incentive to do so. The economic value of compost depends heavily on the estimated quality and yield response due to the addition of an organic material. The economic benefits of higher crop yields or lower fertilizer and energy inputs usually have a time-lag that cannot be afforded by most farmers. Prevailing economic conditions place a high relative value on current crops, and a preference for an immediate income to pay off high overhead, at the sacrifice of future returns. There is also a distinct lack of affordable farm-scale machinery to make composting commercially viable on the medium and large scales that apply to most agricultural producers of organic wastes. The net result is the inefficient use of agronomic assets to the detriment of soil, water quality, and regional economic stability.
The adoption of locally based and regenerative agriculture is additionally hampered by short growing seasons that make it difficult for temperate climate farmers to compete with growers in warmer regions. Greenhouse vegetable production has been used for centuries to offset climatic limitations to food production, but that industry in the United States has declined to near extinction. Rising costs of energy and labor plus competition from corporate food producers centered in warmer climates have reduced total greenhouse food production to less than 260 hectares(1). Highly automated hydroponic greenhouse operations are encouraging some new-entry growers, but their inherently high energy and synthetic fertilizer inputs contribute little to local economies and nothing to the regeneration of the soil. The success or failure of greenhouse food production, like farm scale composting, hinges on short term profitability.
In the past decade sharp increases in energy costs have dictated that greenhouse operators adopt more thermally efficient structures. Greenhouses designed to cut energy costs by reducing air infiltration losses suffer from low CO2 concentrations, as plants can deplete concentrations to photosynthesis-limiting levels within several hours following sunrise (2). In order to maintain plant productivity, such greenhouses must either lose thermal energy by ventilating to bring in ambient CO2, generate it internally by burning special fossil fuels, or utilize compressed CO2 (3).
The role of CO2 in plant growth is frequently underestimated. Atmospheric CO2 concentrations are the most limiting factor in the growth of terrestrial plants (4). Carbon dioxide is as essential to plant growth as are water, light, and soil nutrients. Plants average about 50% carbon by dry weight, deriving most of this carbon from atmospheric CO2 via photosynthesis. Without CO2, plants cannot photosynthesize, regardless of all other growth factors being adequately met.
Carbon dioxide has given the most spectacular yield increases of any growth factor yet discovered in the culture of greenhouse crops (5). A remarkable increase in yield, improvement in quality, and accelerated maturity in all crops has been demonstrated in research and commercial application (6).
Much research has been done to determine the content and value of the products of high rate composting, including CO2, nitrogen compounds, heat, and soil amendments. Likewise, a long history of research and commercial application has separately demonstrated the effects of these same products in increasing plant productivity. The composting greenhouse may provide an optimal ecosystem in which the composting process is facilitated and its byproducts recycled to greatly enhance plant growth.
The composting process generates impressive quantities of horticultural essentials. Sardinsky's findings reveal the probable outputs from a metric ton of compost at 3,375,000 BTU (13,510,000 KCal), 290 kg CO2, and 47 liters of H2O vapor during a 21 day thermophylic stabilization period (7). Under standard composting practices, most of these valuable products are lost to the atmosphere. Production of quantities of these elements is impossible to standardize, given the diversity of feedstocks and methods of composting, but these figures provide reasonable estimates to work from in designing systems to contain them.
The composting greenhouse addresses both the lack of economic means to return nutrients from organic wastes to agricultural use and the lack of economic means to operate greenhouses to grow food year-round in cold climates. It holds the potential to make ecologically-imperative practices viable by deriving a marketable return from the invisible outputs of the composting process. This could effectively remove many organic wastes from the ecological and economic liability positions they currently occupy and use them as the feedstock for year round agriculture in regions now heavily dependant on imported foodstuffs.
Biothermal energy has played a major role in maintaining stable agrarian economies in the past. The composting greenhouse has its roots in the Paris market gardening movement that lasted from the early 1600s until the early 1900s. The horse provided the raw fuel, fertility, and transportation for a year-round agriculture that returned almost all horse manure directly to the soil via hectares of glass-enclosed hot beds (8). The heat and gases from decaying horse manure under a topdressing of finished compost supplied the necessary elements for the winter cultivation and season extension of a variety of vegetables. The energy and nutrient value of the plentiful biothermal resource were maximized in the low-technology ancestor of today's composting greenhouse, forming the foundation of a robust agrarian economy. The French hot bed system fell into disuse when the advent of the automobile displaced the horse and consequently, its biothermal feedstock, from the Parisian agricultural scene by the 1920s. Most of the soils that once supported Paris and its hinterlands have since been depleted and developed out of food crop productivity, and that region has become heavily reliant on imported foodstuffs.
From the hot bed evolved straw bale culture, where nutrient-saturated bales of straw were enclosed to capture thermophylic process heat and gases for uptake by plants on top of the bales. This method became popular with Dutch and English growers with cold and poorly drained soils to produce off-season crops of cucumbers, tomatoes, and lettuce (9). The practice flourished from the 1940s until the mid 70s, when the escalated price of straw made the practice no longer cost effective. Although straw bale culture and the French hot bed technique are still employed on a limited basis, they both are victims of their very specific feedstock demands. The composting greenhouse can be tailored to suit a variety of feedstocks and composting practices, and is likely to adapt to market and resource fluctuations more easily than its predecessors. Its flexibility of design, low initial construction cost, and rapid payback potential are elements crucial to the implementation and durability of any new agricultural technology.
The biothermal energy database has been greatly expanded in the last decade by number of researchers who have advanced the composting greenhouse far beyond its hot-bed ancestry to the present state of the art.
Jean Pain developed methods of composting woodchips and brush, deriving heat, methane gas, and compost for domestic and agricultural use while improving forests in the Mediterranean Provence region of France. Pain utilized the heat from massive piles of composting woodchips to maintain spring-like growing conditions in his quonset-style plastic glazed greenhouse. Pain's research has shown that a 50 ton heap is capable of producing hot water at a temperature of 60oC (entering at 10oC) at a rate of 4 liters/minute for 6 months without interfering with the decomposition process. An insulated "umbilical cord" carries hot water to a network of subterranean tubing, where the heat is released to the plant root-zone for maximum thermal benefit (10). At Pennsylvania State University, White has conducted comparative trials of mechanisms of biothermal heat exchange. His findings have determined that EPDM tubing, an extremely durable synthetic rubber, is superior to PVC plastic, polyethelene, or copper pipe for biothermal heat transfer. White estimated that in using an EPDM heat exchange mat, a ton of externally located compost would heat from .6 - 2.2m2 of commercial greenhouse per year, depending on the thermal properties of the specific structure (11).
Graefe and Knapp investigated and reported on biothermal systems that included direct air exchange between greenhouses and compost to make use of the CO2 component of the biothermal process. Graefe focused on the use of residues of wine pressing to enhance greenhouse productivity, crediting the increased CO2 concentrations and volumes of water vapor generated by the compost mass as much as the heat factor in producing valuable winter vegetable crops in inexpensive greenhouses in Austria (12).
Graefe's findings are paralleled by Knapp's, who observed significant frost protection properties of the biothermally generated vapor in inexpensive, single glazed structures. As temperatures inside the greenhouse dropped, vapor from the compost condensed on the foliar surfaces of the plants, releasing the kinetic energy stored from the evaporative process. Upon reaching 0oC, the water undergoes a second phase change and forms an insulative layer of hoarfrost, preventing plants from further heat loss and resultant cell rupture. Greenhouse interior temperatures dropped as low as -8oC without negative effects on the plants within (13). This phenomenon mimics commercial applications of phase change physics used by fruit growers to save their crops from freezing during fruit-set.
The Ecotope Group of Seattle, Washington, has succeeded in raising greenhouse CO2 concentrations to commercial enrichment levels up to 2,000 ppm (6X ambient) using insulated external reaction chambers and simple thermosiphoning mechanisms for gas generation and transport (14).
The Biothermal Energy Center (BTEC) was founded in 1981 to encourage the development of compost-energy recovery systems, primarily focusing on the composting greenhouse. The organization has established a network of researchers and practitioners of biothermal energy systems, and has contributed to the body of research and design work that has spurred the growth of this budding biotechnology. Since its inception, BTEC has built three composting greenhouses and inspired the construction of a number of others. Most of BTEC's research to date has been on small scale experimental greenhouses which have yielded crucial data that serves as the basis for improved designs (15).
A greenhouse based in part on BTEC designs and publications has successfully demonstrated the adaptation of the composting greenhouse to the typical American small farm. A minimum of investment capital and labor inputs were required to generate a profitable vegetable seedling crop and 5 tons(WW) of finished compost in its first three months of operation in 1983. An extremely low-cost shell enclosed a 12m3 biothermal feedstock of mixed farmyard manures and crop residues that maintained root zone temperatures of 21oC while exterior temperatures dropped as low as -8oC. High quality seedling development continued through extended periods of low light levels when comparable crops in standard commercial greenhouses in the area experienced retarded growth rates despite high labor and energy inputs (16).
BTEC is now collaborating with the New Alchemy Institute (NAI) to test a prototype that has evolved from the past three years of research and experience. NAI researcher Robert Sardinsky was among the first to advance the composting greenhouse concept through his studies there between 1977 and 1980. During the winter of 1977-78, composting experiments were conducted in the NAI's 200m2 solar heated bioshelter to determine the effects of biothermally generated heat and CO2 on a variety of vegetable crops (17). His investigations laid the technical foundation for work now being continued by the Institute.
The sandy soils on Cape Cod and the heavy nutrient drain on the intensively cultivated soils of the market gardens and three bioshelters require some 50 metric dry tons of compost per year. Insufficient on-farm sources of nitrogen and the lack of appropriate mechanized composting equipment have mandated labor intensive composting methods that have not adequately met annual demand. In an effort to rebuild the depleted soil, generate year-round crop income, and continue to pioneer integrated bioshelter research, NAI has undertaken the construction of its own composting greenhouse. This facility is being monitored and operated as a commercial enterprise to produce cash crops and large volumes of compost that are the mainstay of the Institute's garden project. The greenhouse is of modular pole construction and plastic glazing that is standard in the commercial greenhouse industry. Construction and operational costs are expected to be amortized within the first year. NAI will be marketing vegetable crops, bedding plants, and the compost in which to grow them in order to offset production costs. A percentage of the compost will be returned to the farm's soil to insure its lasting fertility.
To aid in the design process, NAI will use the Dynamo computer model software package tailored to model systems interactions in the closed environment of the composting greenhouse. This research and monitoring program will greatly increase the technical understanding of the interactions of the biological, chemical, and thermal phenomena in the composting greenhouse.
The amount of CO2 required to maintain specific enrichment concentrations is largely dependant upon air exchange rates with the outside atmosphere. Saxton cites 90g CO2/m2/day to meet optimal photosynthetic requirements (18). The preferred enrichment technique in the Netherlands requires the combustion of natural gas at aproximately 8m3/1000 m2 of greenhouse/hr to supply levels of 2000 ppm (19). At an average 8 hrs/day X 180 days/year, this consumes 11,520 m3 annually for a cost of $9561.60 @ $.83/m3. If summertime enrichment were employed, as has been recommended by the British Glasshouse Crops Research Institute, this figure could double.
Traditional greenhouse designs dictate that solar thermal gains be vented during midday, when CO2 demand is peaking. In enriched greenhouses, this results in the loss of precious CO2 in order to prevent overheating. The inefficiencies inherent in typical enrichment regimes are greatest when kerosene or natural gas are burned for their CO2 value alone, producing unusable surpluses of heat which must then be vented along with the CO2 contained in the combustion gases (20). Growers in the Netherlands now maintain daytime temperatures an average of 7oC higher than the previous maximum in order to optimize uptake of CO2 without venting (21). Species tolerant of the elevated temperatures and increased CO2 levels are becoming standard crops in the Dutch greenhouse industry (22) which has traditionally adopted new methods of cultivation much more rapidly than its American and European counterparts. These developments indicate that composting greenhouses should be able to enrich CO2 to above-standard concentrations with a minimum of venting, resulting in greater efficiencies in CO2 and water utilization.
A significant body of research indicates that CO2 enrichment should not be confined to the atmosphere alone, but should involve the root medium as well. Berquist reports that from 40%-60% of the gains in hydroponic tomato production were attributable to root absorption of CO2 (23).
The channelling of reaction process exhaust gases through the planting beds aerates the soil, maintains critical root zone temperatures, delivers water directly to roots, filters potentially toxic ammonia concentrations and fixes them for plant use, and releases CO2 in the immediate root and leaf environments for most efficient uptake.
Soil aeration speeds nutrient uptake by plants. Root zone heating is a more efficient method of maintaining plant integrity and productivity under low temperature conditions than attempting to maintain high air temperatures (26). Root zone irrigation assures efficient uptake of the H2O evaporated during composting, and can eliminate most other direct watering requirements. Filtering the nitrogen compounds through the soil bed/biofilter provides a ready feed source and optimal temperatures for nitrifying bacteria to mineralize potentially toxic concentrations of NH3 or NH4+ into plant soluble nitrate. If venting is required to reduce overheating, the fact that CO2 and H2O vapor are introduced within the planting bed and through a biofilter insures that much of it will be used before ventilation can carry it away. Most of the water vapor is condensed in the planting bed, and much of the remainder is condensed on foliar surfaces as it is carried past them on the steady thermal updraft. Should greenhouse air temperatures drop seriously, vapor can be vented from the reaction chamber directly into the greenhouse atmosphere for the phase change thermal protection properties reported by Knapp and Graefe.
Yet unknown in the design is the ability of the biofilter to remove potentially toxic quantities of nitrogen compounds from the process exhaust gases. NO2 levels of more than 5 ppm are considered unsafe for humans, and NH3 concentrations of more than 10 ppm are frequently damaging to plants (27). During thermophylic oxidation, nitrogen is also released as N2, N20, and (NH4)2CO3 (28). Quantities generated, transport dynamics, and ultimate destination of these gases within the enclosed greenhouse environment must be fully comprehended for the system to be considered safe from the standpoint of workers' health.
Another health aspect to consider is presence of high spore counts of Aspergillus Fumigatus likely to be present in the favorable conditions of the composting greenhouse (29). Following Oliver's findings, increased levels of A. Fumigatus spore will not pose a problem to healthy individuals, but persons with a history of respiratory ailments should avoid the humid microclimate of the composting greenhouse (30).
Commercial greenhouse operation is a full time job that requires specific knowledge and a degree of horticultural expertise. Most farmers are unlikely to be able to successfully meet the diverse requirements. It is more likely that composting greenhouse operators would become processors of agricultural and municipal residues that could then be marketed as finished compost following the extraction of the biothermal cogenerants. Farmers could supply composting greenhouse operators with the feedstock in exchange for a percentage of the finished product. Municipalities could reduce waste disposal burden by off-loading the organic fraction of their MSW to composting greenhouse operators who would profit from both composting process and end product.
As the demand for compost increases, the commercial viability of such an enterprise could be greatly improved. Compost is becoming more popular with greenhouse operators as the price of traditional potting mixes and soil amendments escalates. Many growers are switching to compost-based mixes for their superior ability to hold water and supply slow-release nutrients. Commercial growers in Europe frequently use compost at a rate of 80 T/ha/yr in biologically managed greenhouses (31). Given a practical means of production, the on-site demand for compost is a strong incentive for growers to produce their own from locally available feedstocks and use the byproducts and the end products of the composting process to make a whole system that is at once profitable and sustainable.
Biothermal energy's potential is amplified through marriage of commercial greenhouse and large scale composting practices. Recent innovations in these related biotechnologies is being coupled with an expanding data base on their merger to assist the development of the composting greenhouse. Commercialization will be eased by the fact that virtually all of its components are presently commercially available. The composting industry can lend considerable technical sophistication to the composting greenhouse design. Standard composting tools such as forced pressure static pile ventilation and in-vessel composting have been incorporated in several recent composting greenhouse designs. In-vessel composting offers the ideal mechanism for transporting compost through the greenhouse and generating uniform quantities of gaseous products for known uptake rates. The BAV Tunnel Reactor and Dano Biodigestor are two commercial units ideally adapted for this purpose. They could be enclosed within the greenhouse or in an adjacent insulated building, and the gaseous byproducts ducted to the greenhouse for crop enhancement.
The implementation of the composting greenhouse depends on its ability to adapt to site-specific conditions ranging from feedstock fluctuations to limited investment capital. The wide spectrum of agricultural and industrial equipment that may be incorporated into composting greenhouses makes it possible to assemble workable designs for a variety of situations.
It is ecologically imperative that profitable means of nutrient and organic waste recycling be developed. Without locally based fertility and economically viable food production, dependencies on unsustainable energy and fertilizer inputs will continue to drain regional economies and global resources until they are exhausted. The composting greenhouse could become an essential link between our presently disjointed food and waste production systems. Though still in its technical adolescence, it already shows promise of maturing into a valuable tool for a renewable and permanent agriculture. The degree of sophistication which the composting industry could lend to the development of this and other biothermal energy recovery systems may be critical to their ultimate success. With an expanded research commitment, the composting greenhouse could become a vital economic pathway out of the ecological dead-end that our waste treatment industries and agriculture now faces. Given the options at hand, further development of the composting greenhouse warrants serious consideration.
1. Lieberth, J.A. 1982 "Greenhouse Industry Survey Reveals..." The American Vegetable Grower and Greenhouse Grower, Nov. 1982
2. Bierhuizen, J.F. 1973 "Carbon Dioxide Supply and Net Photosynthesis", Acta. Hort. 32, p.120
3. Sardinsky, R., 1979 "Greenhouse CO2 Dynamics and Composting in a Solar Heated Bioshelter", Proc. 2nd Nat'l. Energy Conserving Greenhouse Conf., ASES: Newark, Del.USA
4. Wittwer, S.H., and W.M. Robb, 1963 "Carbon Dioxide Enrichment of Greenhouse Atmospheres for Crop Production", Michigan Ag. Exp. Sta. Journal; Article No. 325, p. 311
5. O'Kelley, J.C., 1965 "Culture of Protosiphon Botryoides in Ca- and Sr- media with CO2 Enriched Atmosphere", BioScience 15: Pp. 595-596
6. Wittwer and Robb, p. 312
7. Sardinsky, Pp. 13-16
8. Aquitas, A., 1913 "Intensive Culture of Vegetables on the French System", Solar Survival Press: Harrisville, NH, USA
9. Loughton, A., 1977 "Strawbale Culture of Greenhouse Crops" Proceedings of the International Symposium on Controlled Environment Agriculture; Pp. 208-215
10. Pain, I. and J., 1972 "Another Kind of Garden...The Methods of Jean Pain", Domaine "Les Templiers": Villecroze, France. p. 49
11. White, J., 1982 "Letters to BTEC" Biothermal Update (BTU) BioThermal Energy Center: Portland, ME, USA. Vol. 1, No. 2
12. Graefe, G. 1979 Energie aus Traubentrestern. Bundesministerium fur Wissenschaft und Forschung: Vienna, Austria. Pp. 69-74, 81-91
13. Knapp, D., 1978 "Composting in a Solar Greenhouse for CO2 and Heat", The Solar Greenhouse Book, Ed; J. McCullagh, Rodale Press: Emmaus, PA, USA. Pp. 287-292
14. Brown,D., et.al.,(Ecotope Group) 1979 "Operating Performance of a Solar Aquaculture Greenhouse". Proc. 2nd Nat'l. Energy Conserving Greenhouse Conference. ASES: Newark, Del. USA
15. Fulford, B., 1982 "The Composting Greenhouse; A Biotechnical Fix" Proceedings of the 3rd Energy Conserving Greenhouse Conference ASES: Newark, Del. USA
16. Fulford, B., 1983 "Low Tech-Profitability for North Country Permacultures Composting Greenhouse", BioThermal Update (BTU) BTEC: Portland, ME, USA. Vol.2, No.2
17. Sardinsky.
18. Saxton, M., 1978 "Production of Carbon Dioxide and Heat from Compost" (unpublished report available from the author, 1620 Pole Line Rd., Davis, CA. USA 95616
19. van Berkel, N., 1967 "Some Technical Aspects of CO2 Enrichment" Proceedings of the 12th Internat'l Hort. Cong. Vol.3 p. 338
20. Ibid.
21. Wittwer and Robb, p. 50
22. Klougart, A. 1967 "A Look Ahead based on Research on CO2 and Horticultural Plants in Europe" Proc. 12th Int. Hort. Cong., Vol. 3, p. 324
23. Kretchman, D., and F.S. Howlett, 1970 "CO2 Enrichment for Vegetable Production" Transactions of ASAE, Vol.13, No.2, p. 255
24. Berquist N.O., 1964 "Absorption of Carbon Dioxide by Plant Roots" Bot. Not. 117: 249-261
25. Pomeroy, R.D., 1982 "Biological Treatment of Odorous Air", Journal of Water Pollution Control Federation 54:12
26. Warren, G., 1983 "Designing for Odor Control" Biocycle May-June 1983
27. White, J., 1978 "Growing Basics", The Solar Greenhouse Book Ed. J. McCullagh. Rodale Press: Emmaus, PA, USA. p. 240
28. van Berkel, N., 1967 "Some Technical Aspects of CO2 Enrichment" Proc. 12th Int. Hort. Cong. p.334
29. Vogtmann, H., and J.M. Besson 1981 "European Composting Methods: Treatment and Use of Farmyard Manure and Slurry" Composting Theory and Practice for City, Industry and Farm JG Press: Emmaus PA, USA. Pp. 214-216
30. Raper,K.B., and D.I. Fennel 1965 The Genus A. Aspergillus" Williams and Wilkin Co.: Baltimore,MD., USA.
31. Oliver, W. Jr., 1981 "The Aspergillus Fumigatus Problem", Composting Theory and Practice for City, Industry, and Farm JG Press: Emmaus, PA, USA.
32. Blair, D. 1977 "Organic Food Production Under Glass in Europe" Winston Churchill Memorial Trust: London, England
Copyright 1983, The New Alchemy Institute, Inc.
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