Water Research 38 (2004) 1081–1088
Physico-chemical factors affecting the E: coli removal in a
rotating biological contactor (RBC) treating UASB efﬂuent
*, Bram Klapwijk
, Joost Van Buuren
Fatma El- Gohary
, Gatze Lettinga
Water Pollution Control Department, National Research Centre, El-tahrir St., Dokki, Giza, Egypt
Agrotechnology and Food Sciences Department, Sub-department of Environmental Technology, Wageningen University and Research
Centre, P.O. Box 8129, 6700EV Wageningen, The Netherlands
Received 20 April 2001; received in revised form 13 May 2003; accepted 23 May 2003
The removal mechanism of E. coli from UASB efﬂuent using a Rotating Biological Contractor (RBC) has been
investigated. Preliminary batch experiments in a RBCindicate a ﬁrst-order removal kinetics. Variation in the dissolved
oxygen concentration and E. coli counts over the depth of the RBChas been recorded and indicates that the RBCis not
a completely mixed reactor. Therefore batch experiments were carried out in a beaker where the different operating
conditions can be controlled.
Factors affecting the removal of E. coli via a bioﬁlm system as stirring, dissolved oxygen concentration, pH, and
addition of cationic polymer were investigated. The results obtained indicated that the most important removal
mechanism of E. coli in the bioﬁlm is the adsorption process, followed by sedimentation. Die-off is a relatively minor
removal mechanism in an RBCsystem. Higher removal rate of E. coli was observed in an aerobic compared to an
anaerobic bioﬁlm system. Variation of dissolved oxygen concentration (3.3–8.7 mg l
) and pH-values between 6.5 and
9.3 did not exert any signiﬁcant effect on the removal rate of the E. coli by the heterotrophic bioﬁlm. A rapid adsorption
of E. coli to the bioﬁlm occurred during the ﬁrst days after adding the cationic polymer, after which the adsorption
r 2003 Elsevier Ltd. All rights reserved.
Keywords: UASB efﬂuent; RBC; E. coli; Removal rate; Die-off; Adsorption
During recent years signiﬁcant attention has been
focused on post-treatment of efﬂuent of Up-ﬂow
Anaerobic Sludge Blanket (UASB) reactor using a series
of algal ponds. Special emphasis has been devoted to
factors affecting the removal of pathogens. E. coli is
used as indicator of these pathogens in the pond systems
. Much less attention has been given to the factors
affecting the pathogen removal in other post-treatment
technologies such as the RBCsystem. In earlier research,
we found that the RBCis effective for the reduction of
COD, ammonia and E. coli from UASB-efﬂuent .
Since the removal of pathogenic bacteria is an important
objective in post-treatment, optimization of the RBC
performance for this purpose is of prime importance.
To optimize the removal of E. coli from UASB
efﬂuent using a RBCsystem, adequate understanding
of factors affecting the removal mechanism of E. coli is
The removal of E. coli in an RBCunit can be seen as
the sum of the following mechanisms: die-off, sedimen-
tation, adsorption and ﬁlter feeding. According to Crane
ARTICLE IN PRESS
*Corresponding author. Department of Environmental
System Engineering, Nagaoka University of Technology,
Kamitomioka 1603-1, Nagaoka, Niigata, 940-2188, Japan.
E-mail address: tawﬁk8@hotmail.com (A. Tawﬁk).
0043-1354/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.