REDUCE CAPITAL INVESTMENTS AND OPERATING COSTS WITH PLANT WIDE CONTROLWASTEWATER MANAGER-CONTROL WASTEWATER TREATMENT PLANT OPTIMISATION

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1 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 . 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.

2 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 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

3 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 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 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

4 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 m 3 /d to m 3 /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 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

5 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 PE ( m 3 /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 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

6 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 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 m 3 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 and conventional PLC-control in Energy consumption Total plant_* BOD removal 2-year average (kwh/m3) (kwh/kgbodremoved) (kwh/kgnremoved) (%) WWM-control PLC control % % % 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 PE, which corresponds to a daily average flow of m 3 /d. The wastewater is treated mechanically, biologically and chemically before it is discharged to 8 m depth in the fiord.

7 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).

8 mgn/l 3 Advanced on-line control off on NH4 (blue) NO3 (red) /17/98 4/19/98 4/20/98 4/22/98 Date 4/24/98 Number of rotors 2.0 period avg. = 1.52 rotors period avg. = 1.08 rotors Number of rotors in operation, 2 hr. moving average 0.5 4/17/98 4/19/98 4/20/98 4/22/98 4/24/98 Date 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 PE with a hydraulic load of m 3 /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.

9 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 ( ). 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] Aluminum sulphate consumption [tons/year] % % * 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%).

10 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] Aluminum sulphate consumption [tons/year] % % * 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 DKK corresponding to more than 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 PE ( m3/d) and the treated wastewater is discharged through its own effluent pipes to the Oresund via the pumping station Sjællandsbroen.

11 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 July 2012 and from the period with WWM-Control: August April 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.

12 Figure 9: Ferric chloride consumption and energy consumption at Damhusåen WWTP. Analysed data are shown from the period with advanced PLC control: and WWM-Control 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 Euro per year and costs of energy consumption dropped by approx 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: and WWM-Control:

13 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 costsavings, 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)

14 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