Chemical Engineering September 2014 - 54

Cover Story
1) increase and control solids dryness at the beginning of the drying stage by
adding (recycling) final dried product to the dewatered cake, to increase solids
dryness beyond sticky phase before entrance in dryer
Authors
Bart Peeters is a manufacMechanical
dewatering
Sludge
feed
Cake
STICKY
PHASE
Thermal
drying
%DS
2 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Final dried
product
2) lower and control solids dryness at the beginning of the drying stage by lowering
the cake dryness after mechanical dewatering to postpone and, hence, avoid
sticky issues at the beginning of the (flash) dryer
Mechanical
dewatering
Sludge
feed
Thermal
drying
%DS 2 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Cake
STICKY
PHASE
3) reduce sludge's intrinsic stickiness by adding PACl additive
Mechanical
dewatering
Sludge
feed
Thermal
drying
%DS 2 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Cake
STICKY
PHASE
Final dried
product
Figure 4. Practical control strategies to tackle sticky issues during the course of
sludge drying
(depicted in the middle of Figure
4), the drying sludge behaves as a
sticky paste only at a less critical
place in the dryer, such that no operational
issues are encountered
3. Finally, an additive can be introduced
into the raw sludge feed
to mitigate, or even almost completely
eliminate the stickiness of
the sludge (conceptually presented
at the lower part of Figure 4). This
can be accomplished by adding
polyaluminium chloride (PACl) -
a technique thoroughly tested and
validated by the authors [10, 15,
20]. The addition of rather small
amounts of PACl to the raw sludge
feed of a combined centrifuge-dryer
system (only 10-20 L on a volumetric
sludge flow of 7 m³) has become
common practice at the Monsanto
WWTP in Antwerp for more than
four years. The beneficial effect of
PACl conditioning of waste sludge
is explained by the bound hydration
water associated with the super-aluminium
structures of PACl
solutions, attached to the exterior
of the sludge flocs upon dosing
of PACl to sludge. These shields
of hydration water act as a type
of lubrication (aquaplaning) and
guide the underlying sticky biopolymers
through the dryness range,
where they otherwise would cause
the sticky issues of partially dried
sludge [10]. Also lime addition pretreatment
of sludge would reduce
the sludge buildup on dryer walls,
based on recent laboratory results
of Li and others [23].
Acknowledgments
The authors gratefully acknowledge
the mapping of the sludges' sticky
phase by Luc Vernimmen from the
Monsanto Laboratory.
Edited by Scott Jenkins
54 ChemiCal engineering www.Chemengonline.Com September 2014
Final dried
product
turing technologist at Monsanto
Europe N.V. (Haven
627, Scheldelaan 460, 2040
Antwerp, Belgium; Phone:
+32 3 568 5762; Email: bart.
peeters@monsanto.com),
where he has been working
since 1998. He first served
as a process improvement
engineer at Eastman's PVB
polymer
manufacturing
plant on site, till 2004. Since then, he has been
working at the environmental department of
the company, with particular responsibilities in
improving the wastewater treatment plant and
the combined sludge centrifuge-dryer installation.
Being a Master Black Belt he is also the Six
Sigma program leader at the Monsanto Antwerp
site. While working at Monsanto's WWTP, he
obtained his Ph.D. in Engineering from the KU
Leuven (Belgium) in 2011 on the research topic
" Effect of activated sludge composition on its dewaterability
and sticky phase " . Prior to that, he
received his M.S.Ch.E. degree in 1998 from the
KU Leuven, plus his M.Bio.Ch.E. degree in 1996
from the university college De Nayer. He is the
author of 20 papers in scientific journals, technical
magazines and international conferences.
Raf Dewil holds a M.S. Ch.E.
(KU Leuven, 2003) and a PhD
in Bioscience Engineering
(University of Antwerp, 2006).
Currently, he is an assistant
professor with the Chemical
Engineering Department of
KU Leuven, where he heads
the Process and Environmental
Technology Laboratory.
Within the Faculty of
Engineering Technology of
the same university, he chairs the Sustainable
Chemical Process Technology Cluster. His main
research domains include (i) (bio)chemical conversion
methods for the valorization of biomass
and organic wastes (currently main focus on
anaerobic digestion), and (ii) the integration of
physicochemical treatment methods in wastewater
treatment (such as, advanced oxidation
processes, ultrasound, microwave). He has authored
or co-authored over 60 publications in
peer-reviewed international journals and about
90 presentations at international conferences.
He is an associate editor with the Journal of
Environmental Management, a member of the
editorial board of several international journals
and a regular invited speaker at international
conferences.
Ilse Smets holds a Master
in BioSciences Engineering
and a Ph.D. in Engineering:
Chemical Technology, both
of the KU Leuven (Belgium).
She is currently associate professor
at the Department of
Chemical Engineering of that
same university. She heads a
team of about eight doctoral
researchers and focuses on
monitoring, modeling and
■
optimization of biological wastewater-treatment
systems ranging from classic activated sludge
systems to membrane bioreactor (MBR) systems,
with a specific focus on the bioflocculation
aspects of activated sludge. Her teaching activities
also lie predominantly in this field. She is
a board member of B-IWA, the Belgian branch
of the International Water Association and is
the chair of the Bioprocesses and Biosystems
Technical Committee of IFAC, the International
Federation in Automation and Control. Her active
contributions to the field of wastewater
treatment, and bioprocesses in general, are further
witnessed by several review duties, many
memberships of International Programming
Committees and the co-organization of several
conferences and workshops.
http://www.Chemengonline.Com
Chemical Engineering September 2014

Table of Contents for the Digital Edition of Chemical Engineering September 2014
