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Process and utility water requirements for cellulosic ethanol production processes via fermentation pathway
Citation:
Lingaraju, B. P., J. Lee, Y. J. YANG, AND T. C. Keener. Process and utility water requirements for cellulosic ethanol production processes via fermentation pathway. Environmental Progress & Sustainable Energy. John Wiley & Sons Incorporated, New York, NY, 32(2):396-405, (2013).
Impact/Purpose:
To inform the public.
Description:
The increasing need of additional water resources for energy production is a growing concern for future economic development. In technology development for ethanol production from cellulosic feedstocks, a detailed assessment of the quantity and quality of water required, and the critical factors that can be controlled in these technologies need to be identified for maximimal water conservation. In this paper, the water requirement for ethanol production is assessed on a volume-to-volume basis (gallons of water per gallon of ethanol produced). This estimate facilitates easy estimation of the water requirements for a planned ethanol production yield. Fresh water requirement and total water requirement were analyzed and compared for each processing unit of a cellulosic ethanol plant under four production cases. Principal variables among these four cases are feedstock type, pretreatment process and quantity of recycled water used. Three feedstocks (i.e. hardwood, corn stover, and switchgrass) and two 2 pretreatment processes (i.e. dilute acid and Ammonia Fiber Expansion or AFEX) are chosen for analysis. The results showed the most significant influence of pretreatment process and feedstock on the process water requirement, while effectiveness of cooling tower design and operation significantly affects the required utility water quantity. Potential for water conservation can be achieved advanced by effective design of cooling towers where ~75% of water is lost in evaporation. For example, use of recycled water can reduce the water requirement by 50% compared to once-through operation. Recycling of water in unit processing and the improved cooling technologies are viable engineering options in conserving freshwater resources, a factor worthy of consideration in planned future cellulosic ethanol productions.
