Nocardia foaming control in activated sludge process
treating domestic wastewater
, S.N. Sin, H. Chua
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Received 22 June 2007; received in revised form 8 August 2007; accepted 9 August 2007
Available online 20 September 2007
In this study, ﬁlamentous bacteria (Nocardia amarae) were identiﬁed as the major causal microorganism in foaming sludge. The
results of growth kinetics study indicated that N. amarae had a relatively strong aﬃnity for non-readily biodegradable fatty acids.
N. amarae was able to consume various fatty acids at a constant growth yield from 0.413 to 0.487 g/gCOD. Under common F/M ratio
(less than 0.5 gBOD/gMLSS/d) used in activated sludge processes, speciﬁc growth rate of N. amarae was found to be more signiﬁcant
than that of non-ﬁlamentous bacteria. Based on this feature, a novel technique feast–fast operation (FFO) was developed for the foaming
control. The sludge volume index (SVI) rapidly decreased from 300 to 80 mL/g and further stabilized at about 70 mL/g and the system
was free from stable foam, while the BOD removal eﬃciency was maintained above 95%. This control technology eﬀectively suppressed
the overgrowth of ﬁlaments and improved the settleability of activated sludge without adverse eﬀects on the treatment performance and
the process stability.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Foaming control; Wastewater treatment; Filamentous bacteria; Long-chain fatty acids
In recent decades, activated sludge process is accredited
to be the most widespread technology for treating various
types of wastewater such as domestic sewage and industrial
eﬄuent (Martins et al., 2004). However, since its develop-
ment in 1914, operation problems and deterioration of
treatment eﬃciency due to bulking sludge have been cited
as common problems in activated sludge processes around
the world (Graveleau et al., 2005; Krhutkova et al., 2002).
Activated sludge process is a biological process which
depends on the profound balance ecosystem among the
ﬂoc-formers, such as Pseudomonas spp., Zoogloea spp.,
Alcaligens spp., and Achrombacter spp., and the ﬁlaments,
such as Nocardia spp., Rhodococcus spp., Type 1863 and
Microthrix spp. (Martins et al., 2004; Rossetti et al.,
2005; Wagner et al., 2002). They are the key organic
degraders and oﬀer the skeletal matrix for the formation
of compact ﬂocs. However, the overgrowth of ﬁlamentous
microorganisms is generally identiﬁed as the main origin of
foaming, which deteriorates sludge settleability, and results
in decreased sludge settling rate and incompact sludge
blanket (Jenkins et al., 2004; Jolis et al., 2006; Tsang
et al., 2007).
Physical factors such as process design parameters (e.g.
aeration basin conﬁguration and feeding regime) and oper-
ating conditions (e.g. high mixed liquor suspended solids
(MLSS), low sludge return rate and low dissolved oxygen)
are contributed to the growth of ﬁlamentous bacteria
(Martins et al., 2003, 2004; Metcalf and Eddy, 2003).
Chemical factors such as nutrient balance and substrate
composition also play an important role in governing the
ﬁlamentous overgrowth (Liu and Liu, 2006; Tsai et al.,
2003). The nonionic and self-producing surfactants also
signiﬁcantly boosted the foam generation and stability
(Iwahori et al., 2001; Pagilla et al., 2002; Theander and
0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +852 2766 4486; fax: +852 2334 6389.
E-mail address: firstname.lastname@example.org (Y.F. Tsang).
Available online at www.sciencedirect.com
Bioresource Technology 99 (2008) 3381–3388