Document Type

Thesis - University Access Only

Award Date

1996

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

William R. Gibbons

Abstract

Calcium magnesium acetate (CMA) has been used on a limited basis as an environmentally friendly road deicer for over a decade, and has provided excellent results in certain situations. The high cost of CMA, currently 30-40 times the price of NaCl, has prevented more extensive use. Since acetate is the most costly component of CMA, my efforts have been directed at reducing acetate-production costs by using a low-cost substrate. Thin stillage (TS) is a byproduct of fuel ethanol production from corn, and my objective was to develop a stillage-based medium which supported acetate production using the thermophilic, anaerobic bacterium Clostridium thermoaceticum. Previous research in our laboratory showed that C. thermoaceticum could be grown in a medium consisting of only 65 g/L (dry basis) TS, sodium bicarbonate, phosphate buffers, ammonium sulfate, and glucose. This medium was cheaper than the medium commonly used to culture C. thermoaceticum. In the present study, variables investigated included: 1) stillage concentration, 2) stillage filtration, 3) stillage from different sources, 4) elimination of phosphate buffers and ammonium sulfate, 5) different types of dolime (used for neutralizing acetate by forming CMA), and 6) fed-batch fermentation. Studies evaluating the effects of stillage concentration and filtration with different stillage sources determined the optimum stillage medium to be filtered Pekin stillage with an optimum concentration of 98 g/L (dry weight). In batch shake flask fermentations this medium resulted in a maximum acetate productivity of 0.34 g/L/h, an acetate yield of 93.3%, and a maximum acetate concentration of 25.1 g/L. Elimination of phosphate buffers and ammonium sulfate had no significant effect on fermentation parameters; therefore these constituents were eliminated from the medium, further reducing costs by 30%. In pH-controlled batch fermentations in a 5L bioreactor all lime sources performed equally well. These trials achieved maximum acetate productivities of 0.39-0.46 g/L/h, yields of 85.1-114.7%, and maximum acetate concentrations of 37.3-41.4 g/L. Fed-batch fermentation trials with both stillage and glucose additions showed no significant difference in acetate production compared to previous batch trials. Since fermentation efficiencies for the fed-batch trials averaged only 40%, it appeared that the initial amount of glucose could be reduced and still maintain optimum acetate production.

Library of Congress Subject Headings

Deicing chemicals
Calcium magnesium acetate
Corn
Distilling industries -- By-products

Format

application/pdf

Publisher

South Dakota State University

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Rights Statement

In Copyright