Production of polyhydroxyalkanoates by <Emphasis Type="Italic">Azotobacter vinelandii</Emphasis> UWD using swine wastewater: Effect of supplementing glucose,yeast extract,and inorganic salts |
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Authors: | Hee Wook Ryu Kyung Suk Cho Philip R Goodrich Chang-Ho Park |
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Institution: | (1) Department of Chemical and Environmental Engineering, Soongsil University, Seoul, 156-743, Korea;(2) Department of Environmental Science and Engineering, Ewha Womans University, Seoul, 120-750, Korea;(3) University of Minnesota, 1390 Eckles Avenue, St. Paul, MN 55108, USA;(4) Industrial Liaison Research Institute, Green Energy Center, and College of Environment and Applied Chemistry, Kyung Hee University, Yong-in, 446-701, Korea |
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Abstract: | This study examined the effect of adding glucose, yeast extract, and inorganic salts to swine wastewater (SWW) in a batch
culture on the production of a biodegradable plastic, polyhydroxyalkanoate (PHA). A bacterial strain, Azotobacter vinelandii UWD, was used to produce PHA without limiting the non-carbon nutrients. The addition of glucose (30 g/L) to the SWW medium
increased the level of cell growth (4.4∼7.0 times) and PHA production (3.8∼8.5 times) depending upon the dilution of SWW.
A 50% dilution of SWW was found to be optimal considering the dry cell weight (9.40 g/L), PHA content (58 wt%), and hydroxyvalerate
(HV) mol fraction in the PHA (4.3 mol%). A 75% SWW medium was more advantageous for producing PHA with a higher HV fraction
(7.1 mol%) at the expense of losing 22% of PHA production. The undiluted SWW medium produced less than one third of the PHA
compared with the 50% SWW medium, but the HV fraction was the highest (10.8 mol%). Regarding the effect of the glucose concentration,
at 20 g/L glucose, the dry cell weight and level of PHA production increased to 9.34 g/L (0.63 g PHA/g dry cell weight) and
5.90 g/L, respectively. At 50 g/L glucose, there was no significant increase in PHA production. For the glucose-supplemented
(30 g/L) 50% SWW medium, the addition of a nitrogen source (1 g/L of yeast extract) did not increase the level of cell growth
or PHA production because the C:N ratio (23:1) was already close to the optimal value (22:1). Better aeration increased the
productivity of PHA. External nitrogen supplements (1 g/L of yeast extract) and other essential mineral salts was not necessary
for bacterial growth because they were contained in the SWW. These results suggest that SWW is an excellent feedstock for
producing larger amounts of the value-added material, PHA, if it is combined with carbohydrate-rich organic waste. |
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Keywords: | polyhydroxyalkanoates swine wastewater Azotobacter vinelandii glucose |
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