Short-Chain Fatty Acid Production from Different Biological
Phosphorus Removal Sludges: The Influences of PHA and Gram-Staining
Bacteria
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Abstract
Recently,
the reuse of waste activated sludge to produce short-chain fatty acids
(SCFA) has attracted much attention. However, the influences of sludge
characteristics, especially polyhydroxyalkanoates (PHA) and Gram-staining
bacteria, on SCFA production have seldom been investigated. It was
found in this study that during sludge anaerobic fermentation not
only the fermentation time but also the SCFA production were different
between two sludges, which had different PHA contents and Gram-negative
bacteria to Gram-positive bacteria (GNB/GPB) ratios and were generated
respectively from the anaerobic/oxic (AO) and aerobic/extended-idle
(AEI) biological phosphorus removal processes. The optimal fermentation
time for the AEI and AO sludges was respectively 4 and 8 d, and the
corresponding SCFA production was 304.6 and 231.0 mg COD/g VSS (volatile
suspended solids) in the batch test and 143.4 and 103.9 mg COD/g VSS
in the semicontinuous experiment. The mechanism investigation showed
that the AEI sludge had greater PHA content and GNB/GPB ratio, and
the increased PHA content accelerated cell lysis and soluble substrate
hydrolysis while the increased GNB/GPB ratio benefited cell lysis.
Denaturing gradient gel electrophoresis profiles revealed that the
microbial community in the AEI sludge fermentation reactor was dominated
by <i>Clostridium sp.</i>, which was reported to be SCFA-producing
microbes. Further enzyme analyses indicated that the activities of
key hydrolytic and acids-forming enzymes in the AEI sludge fermentation
reactor were higher than those in the AO one. Thus, less fermentation
time was required, but higher SCFA was produced in the AEI sludge
fermentation system