Water Research 36 (2002) 3473–3478
Polyhydroxyalkanoates form potentially a key aspect of
aerobic phosphorus uptake in enhanced biological phosphorus
removal
Andrew Amis Randall*, Yan-Hua Liu
Department of Civil and Environmental Engineering, University of Central Florida, P.O. Box 162450, Orlando, FL 32816-2450, USA
Received 1 June 2001; received in revised form 1 January 2002
Abstract
Eighteen anaerobic/aerobic batch experiments were conducted with a variety of volatile fatty acids (VFAs) on a
sequencing batch reactor (SBR) population displaying enhanced biological phosphorus removal (EBPR). A statistically
significant (P50:01 for all variables) correlation between aerobic phosphorus uptake and polyhydroxyalkanoates
(PHAs) quantity and form was observed. The results suggest that poly-3-hydroxy-butyrate (3HB) results in significantly
higher aerobic phosphorus (P) uptake per unit mmoles as carbon (mmoles-C) than poly-3-hydroxy-valerate (3HV). The
results showed that acetic and isovaleric acids resulted in higher P removals (relative to propionic and valeric acids)
during EBPR batch experiments not because of higher PHAs quantity, but largely because the predominant type was
3HB rather than 3HV. In contrast propionic and valeric acids resulted in 3HV, and showed much lower aerobic P
uptake per unit PHAs. r 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Enhanced biological phosphorus removal (EBPR); Phosphorus accumulating organisms (PAO); Volatile fatty acids
(VFAs); Polyhydroxyalkanoates (PHAs); Biological nutrient removal (BNR)
1. Introduction
For over 10 years there have been reports in the
literature where a higher P removal was observed for
acetic and isovaleric acids in enhanced biological
phosphorus removal (EBPR) batch experiments than
the other 1–5 carbon volatile fatty acids (VFAs) (e.g.
[1,2]). In all cases each of the C2 to C5 VFAs supported
EBPR, but acetic and isovaleric acids were simply more
efficient (i.e. resulted in more P removal) per mmole as
carbon or per mg COD than the other VFAs analyzed.
Hood and Randall [3] conducted an extensive literature
review to try and determine what acetic and isovaleric
acids had in common that might correspond with the
higher P uptake observed. From this search two
possibilities were found; (1) both VFAs were thought
to result in negative contributions to the overall cell
redox balance during transformation to polyhydrox-
yalkanoates (PHAs) (i.e. reducing equivalents were
required to transform acetic or isovaleric acid to PHAs),
and (2) both VFAs were thought to result in poly-3-
hydroxy-butyrate (3HB) as the predominant PHAs
form. At the time the hypothesis was proposed the
transformation of acetic acid to 3HB had been
experimentally observed in numerous studies (e.g. [4]);
however, the PHAs formed from isovaleric acid had
never actually been observed in an activated sludge
system. The hypothesis for isovaleric acid was based
purely on information from the biochemical literature
and pure culture PHAs studies [3].
In this study 18 batch experiments were conducted to
test key aspects of the hypotheses of Hood and Randall
[3]. The PHAs types resulting from glucose, acetic,
propionic, valeric, isovaleric, and succinic acids were
*Corresponding author. Tel.: +1-407-823-6429; fax: +1-
407-823-3315.
E-mail address: randall@mail.ucf.edu (A.A. Randall).
0043-1354/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0043-1354(02)00047-7