9th European Waste Water Management Conference
12-13 October 2015, Manchester, UK
www.ewwmconference.com
Organised by Aqua Enviro Limited
REDUCE CAPITAL INVESTMENTS AND OPERATING COSTS WITH PLANT
WIDE CONTROLWASTEWATER MANAGER-CONTROL – WASTEWATER
TREATMENT PLANT OPTIMISATION
Sørud, M., Kόzka, A.K., Vangsgaard, A.K., Önnerth, T.B.,
Krüger A/S, Denmark
Corresponding Author Email. [email protected]
Abstract
WasteWater Manager-Control focuses on operating costs-savings. The savings are achieved through
prioritisation of the best biological performance during all load situations without compromising a good
effluent quality. In the denitrification and phosphorus removal process, the advantages ranges from
reduced energy consumption, no need for chemicals, significant reduction in chemical sludge
production to improved environmental compliance.
Additionally, WasteWater Manager-Control increases hydraulic capacity while reducing the need for
process and clarifier extensions. When installed as part of a design-build project, the online control
will reduce footprints and help avoid plant extensions. Proven achievements include up to 100 percent
higher flow through the wastewater treatment plant without capital investment.
WasteWater Manager-Control is part of the product suite STAR Utility Solutions™ specially designed
with focus on safety, operating cost-savings and process performance.
Keywords
Advanced process control, online control, plant wide control, CAPEX reduction, OPEX reduction, STAR
Utility Solutions™, WasteWater Manager-Control, wastewater treatment plant optimisation
Introduction
The increasing demands by citizens and environmental organizations have initiated environmental
protection against harmful effects of urban and industrial wastewater discharges. The definition of
sensitive areas introduced by the European Union (Council of European Communities 1991) for
freshwater bodies, estuaries, lakes, coastal waters, water sources for drinking water abstraction
(surface water and groundwater) has strengthened activities related to further treatment to comply
with other regulations on fish, bathing, shellfish waters and protection of natural environment of wild
birds and natural habitats. Most of the wastewater treatment plants have been extended and
modernised for nitrogen and phosphorus removal. Subsequently, the local regulations published and
the amendment to the directive (Council of European Communities 1998), including summary report
with identification of sensitive areas by the Member States of EU, have introduced even more
stringent environmental demands for the effluent quality of the wastewater treatment plant. Therefore,
it may seem that wastewater treatment plants that do not comply with the effluent demands must be
further modernised, extended or re-designed to replace the existing technologies. But is it really the
only solution to comply with those strict demands? It is probably the most common question for many
wastewater plants with continuous focus on operational improvements.
9th European Waste Water Management Conference
12-13 October 2015, Manchester, UK
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More stringent effluent demands and expensive environmental fees usually result in high operating
costs, even for the plants that comply with the effluent demands. Here, excessive operating costs are
mainly due to energy and chemical consumption. Is there any economical and profitable solution to
reduce the operating costs with the lowest possible capital investments? Let us take a closer look at
the plants with advanced online control systems, and the results obtained and the operational
experience gained.
Reduction of capital investment
The following section describes two wastewater treatment plants where capital investments have been
reduced through the implementation of the advanced online control: WasteWater Manager-Control
(WWM-Control).
Biological plant extension – Ede Wastewater Treatment Plant (WWTP)
Ede WWTP in the Netherlands is an example of a biological plant extension with WWM-Control. The
biological treatment capacity has been increased without having to physically extend the volume of
the plant.
The plant is designed with two separate BioDenipho lines with a capacity of 300 000 PE (based on
136 g TOC/person/day) for biological nitrogen and phosphorus removal, and is operated by the Dutch
Water Board Vallei & Eem. The plant load has increased in recent years and the effluent quality has
not been in compliance with the EU demand of max.10 mgN/l. In addition, it is predicted that the load
will increase by another 20% in the coming years.
Figure 1: Ede WWTP, the Netherlands
Watershap Vallei & Eem was placed in a situation in which they had to choose between the
installation of a third biological line or the alternative solution proposed by Krüger, i.e. the installation
of advanced online control: WWM-Control. Watershap Vallei & Eem decided to implement the WWM-
Control as the costs involved were much lower than the costs required to construct a new biological
line. The WWM-Control was implemented in January 2011, and included control strategies to improve
9th European Waste Water Management Conference
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effluent quality by optimisation of the biological performance during different load situations
(Jørgensen et al. 2012).
The WWM-Control is based on data supplied by the reliable online meters from the ARCHESTRA
control system and requires stable communication between WWM-Control and the PLC/ARCHESTRA
control system. WWM-Control evaluates the quality of the online data by performing an online data
check of the sensors. In this way, only reliable data is being used to calculate the set points, which
are transmitted every 2 minutes to the PLC. In case the primary data is of a bad quality, a range of
fallback strategies are applied, which results in a robust control system that is able to maximise the
use of the reliable data available. The set points calculated by the WWM-Control include length of
nitrification/denitrification (N/DN), amount of oxygen for each of the aeration tank and return sludge
flow from the final settling tanks. The result of the WWM-Control implementation gives a significant
reduction of nitrogen from 12.1 mgN/l to 6.8 mgN/l based on a comparison of mean values from the
period of 26.01-12.08.2010 and the mode of operation in the same period – (see Figure 2).
Figure 2: Tot-N in the effluent after the implementation of WWM-Control
Implementation of WasteWater Manager-Control has given highly satisfactory results in a very short
time. Nitrogen concentration is below the EU demands also in the winter period, which has resulted in
significant savings on wastewater fees and prevented the need of two extra clarifiers.
Hydraulic plant extension – Czajka Wastewater Treatment Plant (WWTP)
Czajka WWTP is one of the biggest wastewater treatment plants in Europe, designed for 2 000 000
PE and situated in Warszawa, the capital of Poland. The plant is operated by the Municipal Water and
Sewage Systems Enterprise in Warszawa S.A., and has a great effect on its recipients: the Vistula
River and the Baltic Sea. The effluent from the existing Warsaw WWTP did not comply with the EU
effluents demands and the plant was definitely too small to treat the wastewater from the entire city,
which also included the wastewater from central Warsaw. This situation resulted in approximately
70% of the untreated municipal wastewater was discharged directly into the Vistula River. The plant
9th European Waste Water Management Conference
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extension could not be avoided due to the new construction of a wastewater transit through the
Vistula River from a new catchment area. The existing wastewater plant required an increase of the
capacity from 240 000 m3/d to 435 300 m3/d.
The Project Execution Unit of Municipal Water and Sewage Systems Enterprise in Warszawa S.A
awarded a consortium of companies the contract for the design, build and construction of the project
”Modernization and Extension of the Czajka WWTP”. The contract involved 3 subsidiaries of Veolia
Water Solutions and Technologies: Krüger A/S (Denmark), Veolia Water Systems Sp. z o. o. (Poland)
and OTV (France).
The existing preliminary and biological treatment of the Czajka WWTP was demolished and a new
plant was designed and constructed in 2010-2012 with 10 BioDenipho lines and 20 secondary settling
tanks for biological removal of organic matter, nitrogen and phosphorus.
Figure 3: Czajka WWTP, Poland
The implementation of WasteWater Manager-Control already in the design phase reduced the volume
of the secondary settling tanks. Advanced Storm Water Control (ATS) was installed to protect against
sludge escape, handle maximum flow during the rainy weather - and in combination with excess
sludge control for the plant operation with necessary sludge concentration - to ensure an increased
hydraulic and biological capacity during rainy weather conditions with smaller secondary settling
tanks. The diameter of each of the 20 tanks was reduced from 52 m to 48 m, which resulted in lower
capacity investments and a smaller footprint.
Additionally, 22 various control strategies of WWM-control secure that the effluent quality is in
compliance with EU standards without increasing operating costs. Dynamic phase (N/DN) lengths
control based on the existing concentration cooperates with an oxygen setpoint following the load on
the plant (DO control), which optimises the biological nitrogen and phosphorus removal. Return
Activated Sludge (RAS) control optimises sludge dewatering and reduces polymer consumption. The
implementation of WWM-Control has allowed the plant operators to run the plant without using
chemicals for phosphorus precipitation and without an external carbon source for the denitrification
process. The chemical phosphorus precipitation is controlled according to the actual needs and
9th European Waste Water Management Conference
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prioritizes biological phosphorus removal over chemical phosphorus removal, while the carbon control
prioritizes by-pass of the primary settling tank control over external carbon supply.
The modernised and extended Czajka WWTP has increased its plant capacity by approx. 45% which
made it possible also to treat wastewater from the central and northern parts of Warsaw by the
construction of sewage transit channels to the newly constructed plant. A significant reduction in the
discharge of untreated wastewater and dismantling of old leaking sewage storage tanks eliminated
soil and water contamination and resulted in a significant reduction of the pollution of the receiving
waters.
Implementation of WWM-Control already in the design stage has reduced the volume of 20 secondary
settling tanks by 15%, and thus contributed to a significant reduction in capital investment and the
final footprint of the plant.
Reduction of operating costs
The following section describes the results and experience gained from four wastewater treatment
plants. All cases include a comparison of operating costs between conventional PLC-based control
and advanced online WWM-Control.
Energy reduction – Central Wastewater Treatment Plant (WWTP) in Koziegłowy
Central WWTP in Koziegłowy is a recirculating wastewater treatment plant for the Poznań city in
Poland. The plant is designed for a capacity of 960 000 PE (200 000 m3/d) and is operated by
Aquanet SA. Warta River is the wastewater treatment plant´s recipient. In the 1990s, the
environmental legislation changed and discharge standards become stricter, and the requirements to
wastewater treatment technologies have increased. Therefore, Aquanet SA decided to modernise and
extend the existing wastewater treatment plant in the period from 1995-2001. Among other things, the
upgrading included the construction of a new biological section to achieve a highly efficient biological
nutrient removal.
Figure 4: Central WWTP in Koziegłowy, Poland
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WWM-Control was implemented to enhance the biological removal of carbon, nitrogen and
phosphorous, and had been running almost continuously and without supplier maintenance since
2000. In 2006, Aquanet SA deactivated the WWM-Control and returned to the first level of basic PLC
control in 2006 and 2007 due to software network issues. This provided a good opportunity to
compare plant performance and operating costs of the two control systems.
The operating costs related to the energy consumption increased by 11% during the 2 years with daily
operation based on PLC control levels. Table 1 shows the measured power consumption per m3
treated water and per kg removed pollutant. The consumption during the PLC-control for removed
BOD and Total-Nitrogen (TN) increased by 7% and 14%, respectively. The flow increased, while the
inlet concentrations of BOD and TN decreased by 2% and 4%, respectively. However, the overall
nutrient loading was still higher during the PLC-based operation than during the WWM-Control. Based
on those facts a minor increase in energy consumption was expected, but at the same time, the same
level of nitrogen removal could be expected.
Table 1: The 2-year average energy consumption from operation with WWM-Control in
2004-2005 and conventional PLC-control in 2006-2007
Energy consumption __________________Total plant_*________________
BOD removal
2-year average (kWh/m3) (kWh/kgBODremoved) (kWh/kgNremoved) (%)
WWM-control 2004-2005 0.46 1.6 6.38 99.2
PLC control 2006-2007 0.51 +11% 1.14 +7% 7.30 +14% 99.2
* No evaluation available on energy consumption for bioreactors only.
A final data evaluation also revealed a significant increase in the energy consumption by 7% of kWh
per BOD removed and by 14% of kWh per TN removed, while TN removal was almost the same for
the two control strategies. The WWM-Control focuses on adjusting the control for different load
variations based on ammonium and nitrate to optimise both denitrification and nitrification by
intermittent aeration, while conventional PLC-control focuses on low ammonium concentration in the
effluent based on the design of adequate denitrification and nitrification volumes.
Energy reduction – Aalborg Øst Wastewater Treatment Plant (WWTP)
Aalborg Øst WWTP is a BioDenitro wastewater treatment plant located Aalborg, Denmark. The plant
treats wastewater from the eastern part of Aalborg city and wastewater from a number of towns
situated north and south of the fiord, Limfjorden. Aalborg Øst WWTP is designed for 100 000 PE,
which corresponds to a daily average flow of 15 000 m3/d. The wastewater is treated mechanically,
biologically and chemically before it is discharged to 8 m depth in the fiord.
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Figure 5: Aalborg Øst WWTP, Denmark
WWM-Control was implemented in 1995 to optimise nutrient removal and reduce operating costs. The
advanced online control has been in operation continuously and only interrupted by maintenance of
hardware or online meters, as is the case for all plants with WWM-Control. Three years after the
implementation of WWM-Control, the plant operator, Aalborg Forsyning, decided to make a
comparison of operation with and without advanced online control, hence the deactivation of the
WWM-control. The plant was operated with a PLC control system for a period of one week, after
which period the WWM-Control was switched back on.
The results of the comparison of nutrient removal (in the upper graph) and energy consumption (in the
lower graph) are shown in Figure 6 below. The test performed showed a significant reduction in nitrate
concentration by 35%, from 1.75 mgN/l to 1.1 mgN/l in the upper graph when the control was on.
However, this was not the only benefit observed from WWM-Control of denitrification and nitrification
phase lengths (Önnerth et al. 2009).
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Figure 6: Ammonium/nitrate concentrations and power consumption measured over a 2-
day period with conventional PLC-control and a 2-day period with WWM-Control
At the same time, a significant reduction of operating costs from the rotor´s power consumption was
obtained. The calculation of energy consumption of the surface aeration is based on the number of
hours in operation and submersion, but in this case no direct measurement of kWh was available.
Therefore, the energy consumption was defined by surface rotor hours in operation, which is a
measurement equivalent to kWh. Rotor hours for aeration decreased from 1.52 to 1.08 hours, which
corresponds to more than 25% reduction.
Hence, both effluent quality and energy consumption improved when operated by advanced online
control compared to operation based on PLC-control.
Chemicals reduction – Mosede Wastewater Treatment Plant (WWTP)
Mosede WWTP is situated on Zealand, Denmark. Similar to other Danish plants in the 1990s, it has
been modernised and extended to mechanical, biological and chemical treatment to comply with the
environmental requirements. The plant has a capacity of 60 000 PE with a hydraulic load of 20 000
m3/d. The biological treatment handles nitrogen removal while phosphorus removal is performed by
chemical, simultaneous precipitation with iron sulphate or aluminum salts. The treated wastewater is
discharged to the bay of Køge town. The wastewater treatment plant is operated by Greve Utility
Company. In 2008, WWM-Control replaced conventional PLC-control at Mosede WWTP.
Advanced on-line controloff on
Number of rotors in
operation, 2 hr. moving average
period avg. = 1.08 rotorsperiod avg. = 1.52 rotors
4/17/98 4/19/98 4/20/98 4/22/98 4/24/98Date0
1
2
3
mgN/l
NH4 (blue)
NO3 (red)
4/17/98 4/19/98 4/20/98 4/22/98 4/24/98Date
0.5
1.0
1.5
2.0
Number
of rotors
Advanced on-line controloff on
Number of rotors in
operation, 2 hr. moving average
period avg. = 1.08 rotorsperiod avg. = 1.52 rotors
4/17/98 4/19/98 4/20/98 4/22/98 4/24/98Date0
1
2
3
mgN/l
NH4 (blue)
NO3 (red)
4/17/98 4/19/98 4/20/98 4/22/98 4/24/98Date0
1
2
3
mgN/l
NH4 (blue)
NO3 (red)
4/17/98 4/19/98 4/20/98 4/22/98 4/24/98Date
0.5
1.0
1.5
2.0
Number
of rotors
4/17/98 4/19/98 4/20/98 4/22/98 4/24/98Date
0.5
1.0
1.5
2.0
Number
of rotors
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Figure 7: Mosede WWTP, Denmark
After the implementation of WWM-Control and fine-tuning was completed, results from 2009 and 2010
with advanced online control were compared with average data from a 3-year period with PLC control
(2004-2006).
Table 2: Operating costs at Mosede WWTP in 2009
OPERATING COSTS Reference* Corrected reference
without WWM-Control**
Actual WWM-
Control
Savings
Electricity consumption***
[MWh/year]
1 511 1 652 1 321 20%
Aluminum sulphate
consumption [tons/year]
503 593 162 73%
* Average consumption from 2004, 2005, 2006
**Reference data corrected for actual load
*** Energy from aeration and intermediate pumping
Data of chemical and energy consumption with and without WWM-Control are stated in Table 2.
Significant savings are achieved in dosing with aluminum sulphate (73%) and energy consumption
(20%).
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Table 3: Operating costs at Mosede WWTP in 2010
OPERATING COSTS Reference* Corrected reference
without WWM-Control**
Actual WWM-
Control
Savings
Electricity consumption***
[MWh/year]
1 511 1 997 1 431 28%
Aluminum sulphate
consumption [tons/year]
503 661 264 60%
* Average consumption from 2004, 2005, 2006
**Reference data corrected for actual load
*** Energy from aeration and intermediate pumping
Data of chemical and energy consumption with and without WWM-Control are stated in Table 3.
Significant savings are achieved in dosing with aluminum sulphate (60%) and energy consumption
(28%).
Operational savings in both periods were calculated on the basis of costs in 2007 in order to avoid
adjustments for any price change of energy, consumables, wastewater fees and other related costs.
The reference load and reference costs from the 3-yar period without advanced control were
corrected according to the load changes during the investigated 2-year period with WWM-Control. In
one year of operation with WWM-Control, Mosede WWTP earned approximately 2 778 000 DKK
corresponding to more than 370 000 Euro. The final price includes savings on wastewater fees,
energy for aeration and internal pumping, precipitation chemicals and sludge handling.
Chemicals and energy reduction – Damhusåen Wastewater Treatment Plant (WWTP)
Damhusåen WWTP was put into operation in the 1930s and is one oldest treatment plants in
Denmark, situated on Zealand. Over the years, the plant has been significantly modernised and
upgraded to comply with today's environmental legislation and quality requirements. For many years,
Damhusåen WWTP was only a physical treatment plant. The wastewater from Damhusåen WWTP
was transferred to Lynetten WWTP for biological treatment. Already since the 1980s, Lynetten WWTP
has taken over the wastewater from Damhusåen WWTP before it was discharge to the Øresund.
Finally, in 1996 the plant became independent from Lynetten WWTP and the physical treatment was
extended by biological and chemical treatment for nitrogen and phosphorus removal. The plant
capacity has been extended to 350 000 PE (100 000 m3/d) and the treated wastewater is discharged
through its own effluent pipes to the Oresund via the pumping station Sjællandsbroen.
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Figure 8: Damhusåen WWTP, Denmark
WWM-Control was implemented at Damhusåen WWTP in 2012 to lower operating costs, lower TN in
the effluent and improve reliability. In order to evaluate all those investment goals, a comparison of
operating results under the existing PLC control and WWM-Control was performed. Data shown in
Figure 9 shows the precipitation and energy consumption from the period with PLC control: January
2009 - July 2012 and from the period with WWM-Control: August 2012- April 2014.
The results of the comparison show that the ferric chloride consumption with PLC control reached 136
tons/month, while precipitation consumption with WWM-Control decreased to 89 tons/month. A
downward tendency was also recorded for the energy consumption, which dropped about 68
MWh/month and resulted in 14% reduction in the energy consumption.
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Figure 9: Ferric chloride consumption and energy consumption at Damhusåen WWTP.
Analysed data are shown from the period with advanced PLC control:
01.01.2009 – 01.07.2012 and WWM-Control 01.08.2012-01.04.2014
Despite chemicals and energy savings, TN in the effluent also dropped about 12%, with the TN effluent
concentration dropped from 7.4 mg/l to 6.5 mg/l. Thus, all investment goals were successfully reached
on Damhusåen WWTP.
At the same time costs of ferric chloride consumption decreased by approx. 76 000 Euro per year and
costs of energy consumption dropped by approx. 77 000 Euro per year, as shown in Figure 10, which
shows the precipitation and energy expenses.
Figure 10: Comparison of ferric chloride and energy consumptions costs.
Analyzed data are shown from the period with advanced PLC control:
01.01.2009 – 01.07.2012 and WWM-Control: 01.08.2012-01.04.2014
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Discussion
The cases presented show that expensive extension of hydraulic capacity or treatment capacity can
be postponed or even avoided by implementation of advanced online control: WasteWater Manager-
Control. At the same time, capital investments and operating costs can be significantly reduced. The
extent of the cost reduction will be specific for each plant and may vary from plant to plant depending
on different conditions. By combining all advanced online control on a common platform, a central
plant wide optimisation can be performed, as opposed to local optimisation of the individual unit’s
operation, which is usually the case of conventional PLC control systems.
Someone can ask how far advanced online control can reduce the costs, since normal plant
optimisation must have reached its limits. However, WasteWater-Manager continuously intensifies
and extends the plant optimisation in cooperation with sewage system control combined with weather
forecasts, flow forecasts, reporting and overview tools for best possible control optimisation including
reduction in operating and capital investments costs. WasteWater Manager is continuously developed
through research which goes further with optimisation of energy consumption in sewage systems and
wastewater treatment plants, e.g. in relation to varying energy prices. A control strategy based on
SMARTGrid solutions has been implemented at Kolding WWTP in Denmark and is expected to adjust
the extent and timing of the wastewater treatment plant´s energy consumption and energy production,
and in this way improve its energy business. WasteWater Manager-Control focuses on operating cost-
savings, local process flexibility and actual weather forecast to plan energy consumption ahead and
thus gives priority to a cheaper, greener, and more flexible consumption of consumables.
Conclusions
WasteWater Manager-Control focuses not only on the reduction of capital investment, but also on
long-term savings by giving priority to energy production and reduction of daily operating costs from
energy and chemical consumption. The savings are achieved by giving priority to the best biological
performance during all load situations without compromising a good effluent quality. This leads to both
less energy consumption and a reduced need for chemical dosing for denitrification and phosphorus
precipitation. The advanced online control ensures plant optimisation through continuous adjustment
of hydraulic and biological treatment capacity to the current hydraulic and nutrient load conditions at
the plant. The advanced control allows an increased hydraulic capacity during rain events which
secures a higher flow through the existing plant without extra process volume, and thus reduces
overflow and bypass. The increased biological capacity corresponds to the increased biological load
and improved effluent quality. In this way, the WWM-Control can improve the effluent quality by
optimising the biological performance during all load situations. This includes the overall balances of
the plant load and sludge distribution in order to utilize all available volumes in the best possible way.
References
Council of European Communities (1991) Urban Waste Water Treatment Directive (91/271/EEC)
Council of European Communities (1998) Commission Directive of 27 February 1998 amending
Council Directive 91/271/EEC with respect to certain requirements established in Annex I (98/15/EC)
9th European Waste Water Management Conference
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Jørgensen D.H., Önnerth T.B. and Verkuijlen J.(2012) Advanced Process Control by STAR Control®
Reduces Effluent Quality to the Safe Side of Limit Values. 1st Conference on New Developments in IT
& Water, 4-6 November 2012, Rotterdam, the Netherlands
Önnerth T.B., Budych-Górzna M., Rosen C., Thomsen H.R. (2009) Energy savings from advanced
online control comes out clear when operation is disturbed by short time interruptions. Nutrient
Management in Wastewater Treatment Processes, 2nd IWA Specialized Conference, 6-9 September
2009