1a. Objectives (from AD-416):
To identify membranes that can reduce the microbial activity and antibiotic residues in the liquid processing streams from fuel ethanol processing facilities; Study the heat transfer fouling characteristics of the processing streams after membrane treatment; Evaluate the processing and economic effects of membrane incorporation by modification of ERRC’s ethanol processing model.
1b. Approach (from AD-416):
Several types of membranes will be used to filter process streams such as thin stillage obtained from commercial fuel ethanol production facilities. Permeate and retentate streams from the filtrations will be characterized for microbial activity and antibiotic residuals. This will be done using a non-hazardous challenge organism and commercially used antibiotics. Permeate and retentate will be evaluated for heat transfer fouling tendencies. Modification of ERRC’s existing fuel ethanol processing model. Membrane processing steps will be added using the data generated. Upon completion of the work, knowledge gained from this research can be expected to lead to development of process strategies that will serve to avoid or reduce microbial contamination, remove antibiotics from coproducts, and mitigate evaporator fouling. With the new knowledge gained, processors potentially will have opportunity to separate microbial and antibiotic components prior to evaporator operation that, in turn, would allow opportunities to significantly improve process efficiency.
3. Progress Report:
The commercial processes used to produce fuel ethanol from corn, wet milling and dry grind, use evaporators to remove water from process streams. Proteins, carbohydrates, fats, ash and fiber in thin stillage and steepwater are involved in causing deposition of materials onto evaporator surfaces, a process called fouling. It is not understood which components increase fouling rates. Since there are more than 200 biofuel facilities that use evaporators, fouling is a major concern. Costs associated with fouling include labor and equipment needed to clean fouled heat transfer surfaces, increased capital, antifoulant chemicals and production losses. Research during the last fiscal year has focused on using model systems to simulate thin stillage to better understand which components contribute to fouling. It was found that a simple sugar solution had lower tendencies to foul heated surfaces than a mixture that contained granular starch. When starch and simple sugar was added to commercial thin stillage (at equal total solids concentrations), starch had a significantly strong effect on fouling characteristics, whereas sugar had limited effects. A smaller experimental apparatus is being constructed that will allow using smaller batches (5 L) to study fouling characteristics of process streams from biofuel production. A presentation covering this work was given at the International Conference on Heat Exchanger Fouling and Cleaning in Budapest, Hungary in June of 2013.