Therefore preparing substrate under aerobic

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Unformatted text preview: r deleterious chemical compounds are formed. Therefore, preparing substrate under aerobic conditions, where less offensive odors are produced, is better for mushroom growers. Figure 2. Self-propelled compost turner moving through a compost rick or pile. As temperatures increase above 155ºF (70ºC), microorganisms cease growing and a chemical reaction begins. Concentrating and preserving complex carbohydrates is one goal of Phase I. The quantity and the quality of nitrogen in the system are changed to a type of nitrogen that Phase II microorganisms and, eventually, the mushroom will use as food. Adequate moisture, oxygen, nitrogen, and carbohydrates must be present throughout the process; otherwise, the process will stop. This is why water and supplements are added periodically and the compost pile is aerated as it moves through the turner. Oxygenation is achieved in conventional outdoor ricks by natural convection. The high pile temperatures draw ambient air through the sides of the stack, and as the air is heated, it rises upward through the stack—a process commonly referred to as the chimney effect (Figure 3). The sides of the pile should be firm and dense, yet the center must remain loose throughout Phase I composting. The exclusion of air results in an airless (anaerobic) environment. As the straw or hay softens during composting, the materials become less rigid and more compact while substrate density increases. Thus, less air reaches the bottom and center of the pile. A lack of oxygen may occur after the large quantities of water are added to the dry bulk ingredients and before 4 Figure 3. Cross section of a compost pile showing the different temperature zones and air movement (blue arrows) caused by the chimney effect. Outer cooler temperature e zone Hot, optimum composting temperature zone Anaerobic core zone Aerated Phase I Composting Improving community relations has led to alterations in the way the Phase I mushroom composting process is carried out. As urban areas encroach on rural farmland, residents have made odor-related complaints and legal battles have ensued, which suggest a need for more stringent odor-management practices. If the pile is not turned and aerated during Phase I composting, oxygen may become limited and anaerobic conditions may develop along the bottom of the stack. As the anaerobic core gets larger, more offensive odors are produced. In order to maintain aerobic conditions throughout the entire substrate pile, supplemental aeration is sometimes used. This aeration is accomplished by using a fan to force air up through a concrete pad with a series of evenly distributed openings and into the substrate material. This design is referred to as an aerated floor. Systems have been built with structural sidewalls, usually of concrete and occasionally of wood, to form the piles with a uniform height and depth (Figure 4). Aside from aerated floors and structural sidewalls, there is great variation among bunker systems currently being used for Phase I. Figure 4. This aerated substrate preparation system has a piped concrete floor under the substrate that forces air through the substrate to maintain aerobic conditions during the composting process. Aerated composting systems are replacing conventional ricks throughout Europe and are beginning to gain acceptance in North America as the quest to manage odors continues. Europeans were the first to regulate emissions from their agricultural operations. Therefore, most European mushroom composting operations have employed some type of enclosed or environmentally controlled Phase I system. In North America, a few systems have been built to test the technology. Eventually they may become common at commercial operations. Unfortunately, little information is available to show how these systems reduce emissions. Therefore, determining how effective aerated systems are in reducing odors is difficult. Phase I is considered complete as soon as the raw ingredients become pliable and are capable of holding water, the odor of ammonia is sharp, and the dark-brown color indicates that carmelization and browning reactions have occurred. At the beginning of Pha...
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This document was uploaded on 03/16/2014.

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