The solid substrate cultivation (SSC) process is often limited by rapid increases in temperature as a result of metabolic activity and poor heat transfer properties of the solid substrate. High temperatures can adversely affect microbial growth and product formation. Reduction of substrate temperatures is important for improved productivity, yet effective and efficient control of heat transfer in a deep-bed SSC reactor has proven difficult. An internal cooling water coil was incorporated into a deep-bed reactor system and evaluated for its ability to reduce substrate temperature. Three operating treatments were investigated: cooling water circulation whenever the center bed temperature was above 30°C, timed cooling water operation on 10 min on/off intervals from the start of cultivation, and timed operation on 10 min on/off intervals after the expected start of microbial exponential growth. Enzyme yield, peak temperature, and net rate of metabolic heat accumulation within the substrate bed were measured during the cultivation of Trichoderma longibrachiatum on wheat bran for xylanase production. The cooling water reduced the temperatures observed in the substrate bed by 5°C on average and was effective in decreasing the rate of heat accumulation in the bed. Within a 10 min time interval, the internal heat exchanger demonstrated a net decrease in heat accumulation at an average rate of approximately 0.5°C/min. Despite the decrease in temperatures observed with the control strategies, the xylanase yields were not statistically different from the cultivations with no temperature control.
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The authors thank Alltech Biotechnology Center (Nicholasville, Ky.) for providing funds for the instrumentation used in the project. This research effort was also supported by a National Science Foundation Graduate Fellowship and a Lyman T. Johnson Fellowship.
The investigation reported (02-05-014) is part of a project of the Kentucky Agricultural Experiment Station and is published with the approval of the director.
Chinn, Mari S. and Nokes, Sue E., "Temperature Control of a Solid Substrate Cultivation Deep - Bed Reactor Using an Internal Heat Exchanger" (2003). Biosystems and Agricultural Engineering Faculty Publications. 103.