Synthesis of polyhydroxyalkanoate (PHA) from excess activated sludge under various oxidation-reduction potentials (ORP) by using acetate and propionate as carbon sources |
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Authors: | W F Hu S N Sin H Chua P H F Yu |
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Institution: | (1) College of Food Science, South China Agricultural University, 510642 Guangzhou, China;(2) Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong;(3) Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Kowloon, Hong Kong |
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Abstract: | Accumulation of poly hydroxyalkanoate (PHA) from excess activated sludge (EAS) was monitored and controlled via the oxidation-reduction
potential (ORP) adjusting process. The ORP was adjusted and controlled by only regulating the gas-flow rate pumped into the
cultural broth in which sodium acetate (C2) and propionate (C3) were used as carbon sources. Productivity of PHA and the PHA
compositions at various C2 to C3 ratios were also investigated. When ORP was maintained at +30 mV, 35% (w/w) of PHA of cell
dry weight obtained when C2 was used as sole carbon source. The PHA copolymer, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate)
(PHBV), accumulated by EAS with different 3-hydroxyvalarate (3HV) molar fractions ranged from 8% to 78.0% when C2 and C3 was
used as sole carbon source, By using ORP to monitor and control the fermentation process instead DO meter, the ORP system
provided more precise control to the PHA accumulation process from EAS under low dissolved oxygen (DO) concentrations. Adjusting
the C2 to C3 ratios in the media could control the composition such as the 3HV/3HB ratios of the PHBV. Furthermore, it might
be an effective way to adjust the 3HV molar fractions in PHBV by controlling the DO concentration via the ORP monitoring system.
The 3HV molar fractions in the PHBV declined with increasing ORP from −30 mV to +100 mV by adjusting the gas-flow rate (i.e.
the DO concentration). It is concluded that the DO plays a very important role in the synthesis of 3HV subunits in PHBV co-polymer
from the EAS. Therefore, a hypothetic metabolic model for PHA synthesis from EAS was proposed to try to explain the results
in this study. |
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Keywords: | Activated sludge oxidation-reduction potential ORP polyhydroxyalkanoate PHA |
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