The invisible hand
Aalborg Vest wastewater treatment plant, Denmark
Dealing with polymer consumption
The Danish municipality of Aalborg operates two wastewater treatment plants to serve the needs of its approximately
200,000 inhabitants. It is the third-largest municipality in the
country, with a sophisticated overall policy for efficient, costeffective wastewater treatment.
The Aalborg Vest plant processes approx. 19 million cubic
metres of waste water annually, and has a daily capacity of
approx. 60,000 cubic metres.
Case story
Octopus Lite assistance
The Octopus Lite polymer dosage control system is a
part of the Alfa Laval Decanter Core Controller (DCC).
This communicates with the polymer pump via the
Octopus Lite module.
Octopus Lite helps the staff at Aalborg Vest adjust the polymer dosage to correspond to the particular solids load at any
given time, with the aid of an easy-to–use touch screen.
As part of the sludge dewatering process, the plant uses two
Alfa Laval G2-80 decanter centrifuges, both equipped with
Alfa Laval Decanter Core Controllers (DCC).
The operator manually sets the polymer dosage needed for
the sludge dewatering process to proceed effectively. The
Octopus Lite system records this set point and monitors any
changes in solids load, based on feedback from the decanter
unit.
The sludge flow to these dewatering units normally amounts
to approx. 25 m³/hour, with an average of 3% dry solids.
By the time the sludge leaves the G2-80s, and prior to the
sludge being sent to the drying plant, this figure has been
increased to approx. 30% dry solids.
Using the “Active polymer control” function, Octopus Lite
then supplies a quantity of polymer that is proportional to the
amount of solids fed into the decanter centrifuge.
Primary sedimentation
Primary/raw sludge
Secondary sedimentation
Aeration
Secondary/waste activated sludge
Digester
Water
Achieving more with less
The Octopus Lite system means that operating staff at the
Aalborg Vest plant spend less time on manually monitoring
and adjusting the flow of polymer to the decanter centrifuge.
The Octopus Lite has consistently provided satisfactory
results despite seasonal variations or day/night load
fluctuations.
Achievements
• Polymer consumption reduced by 3–5%
•E
asily capable of dealing with seasonal
and day/night load fluctuations
• Ensures consistent dewatering with maximum efficiency
• “Peace of mind” for both management and operating staff
Dewatered mixed anaerobically
digested sludge
The system also does away with the natural tendency to add
extra polymer to cope with load variations that might occur
during the evening, the night and weekends, when the plant
operates unattended. Instead, the Aalborg Vest staff know
they can rely on Octopus Lite to make sure the amount of
polymer added always corresponds to the level of solids in
the flow passing through the decanter centrifuge for dewatering. Increased percentages of solids in the cake are expected
in the long term, but are as yet undocumented.
Thoft Andreassen, the operations manager responsible for
the Aalborg Vest plant, estimates that by helping to match
the amount of polymer used to the actual level of dry solids in
the flow to the Alfa Laval decanter centrifuges, Octopus Lite
can provide reductions in polymer consumption of as much
as 3–5%.
The Alfa Laval Octopus range
Octopus Lite
Octopus Monitor
Octopus Plus
An active polymer control feature
that also reduces the amount of
operator attention required.
Enables the user to monitor and
control the entire dewatering
process, and to make sound
operating decisions that result in
stable processing conditions and
lower operating costs.
The most advanced Octopus
model, which automatically
optimizes the entire process and
thus achieves the lowest possible operating costs. Octopus
Plus ensures drier cake, cleaner
centrate, lower polymer consumption, fewer alarms and less
downtime.
PEE00169EN 0612
How to contact Alfa Laval
Up-to-date Alfa Laval contact details for
all countries are always available on our
website at www.alfalaval.com