Articles & Case Studies

Modern sewerage management system for the city of Vienna

Posted: Friday 4th July 2008

Local authorities have to provide a wide range of services for residents and these must operate affectively and efficiently. The public sewerage system serving the Austrian capital, Vienna, is regarded as state-of-the-art throughout Europe, because it can be actively controlled. The ultra-modern automation systems installed in the distributed network control the sewerage streams in real time.

Municipal Department 30 (MA30), responsible for Vienna’s sewerage system, takes care of the systematic drainage, monitoring and treatment of surface water and sewerage. It has an advanced sewerage management system that links around 120 plants by means of a control system network – based on Rockwell Automation technology – and guarantees the controlled, continuous flow to the main sewerage plant.

The system uses the combined storage capacities of the sewerage network and its main drains, which can retain up to 600,000 cubic metres of mixed water. The current and forecast water streams are controlled from a control room using a real time control (RTC) system so that there is a constant 18 cubic metres a second flow into the sewerage plant. This has enormous economic advantages, because the volume of sewerage can vary quite considerably, depending on the weather. The 18 Wienerwald streams alone, which flow through the city underground and into the sewerage network, can swell 2,000 times in heavy rainfall.

Because of the innovative sewerage volume management system, the main sewerage plant serving Vienna is actually equivalent to one serving a much smaller population equivalent (PE) than had been the case with the traditional system; the PE being the measure for the waste burden from homes, industry and commerce. In this case the value is around 3.25 million PE. Without the modern sewerage management system, the maximum flow would have had to have been 24 cubic metres a second. Essential savings have been made through the omission of expensive storage basins and reducing the necessary mixed water throughput of the sewerage plant, meaning that the plant located to the south-east of the capital could be dimensioned much more economically.

Expert system in the network control room

The control room housing the RTC system is located in the southern part of the Danauinsel, just upstream of the point where the left Danube main drain discharges into the main sewerage plant. At the control console, all the information pertaining to the Viennese sewerage system converges into a format that can be easily surveyed by a plant operator. The heart of the RTC system comprises several computers (SCADA systems). They receive data from 20 precipitation measuring stations and from 25 volume measurement devices, which record the current situation in the sewerage network. An expert system then analyses the current and likely progress of the sewerage streams, which can change quickly in certain rainfall situations. The control room personnel can monitor all the processes and values at any time at four control stations with RSView Supervisory Edition (SE), from Rockwell Automation, and take any specific action. Up-to-date weather information is also provided by Austro Control. Because of the data pool, the expert system can therefore generate a forecast two hours in advance.

Consistent communications

At information and control level, the system modules are connected to the system level via Gigabit Ethernet (TCP/IP, 1000Mb/s). Consistency – in relation to the field level – is assured by networking via Fast Ethernet (TCP/IP, 10/100 Mb/s). System components such as ControlLogix, FlexLogix, MicroLogix1500 and RSViewSE Server/Client, from Rockwell Automation, are used at all levels.Rockwell Automation technology was chosen in the planning stage, because its extensive capabilities for networked control and process control environments were regarded as the best. The client also praised the competent management of the Austrian Rockwell Automation team during the implementation of the project. The design office Neukirchen ZT-GmbH has overall control of the RTC project as part of the Neukirchen-Enviroplan-ITWH-Steinwender joint venture.

Efficient architecture

One of the essential details of the sewerage network management system – which is impressive through its sheer size alone – is the modern data transmission. This is achieved with a ring of optical waveguides installed in the sewerage network. The pioneering RTC ring, with a total length of around 30km, makes 24 optical waveguide single-mode fibres available. Consequently, MA30 is equipped for all events and has an independent information highway as the backbone. The connection of the system level in the main MA30 pumping station, on the Donauinsel, is made via Rockwell Automation PLCs and optical waveguide couplers, which make the connections to the distributed plants via optical waveguides.

Because of the size of the RTC installation, around 20,000 data points have to be handled on the hardware side (sensors and actuators). Measured values are loaded or polled into the database at one-minute intervals. Rockwell Automation’s RSSQL technology plays a leading role in structuring this volume of information.

Stations in areas further away are remotely connected via GPRS data connections, using VPN tunnel technology. Access to the Internet also exists, and is securely protected by means of firewalls.

The RTC system architecture is designed for consistency and transparent communications. By means of an OPC Client (via RSLinx) and web browsers, the plant components that are distributed throughout the area of the city can be monitored and parameters set on all network levels from practically any point. This is an enormous advantage for the installation and service activities performed by MA30. As a result, the features of the Rockwell Automation PLCs implemented in the central control area and in the distributed plant topology ensure an integrated architecture resulting in problem-free processes.

Every situation

A tour of the pumping station, which houses the control console and many of the different components at the system level in long rows of switch cabinets, clearly illustrates the cleverly devised processes. Richard Plank, MA30 project manager, explains what happens when the flows increase: "Wet weather means an increased volume flowing into the mixed water system. If limits are exceeded at measuring points, the system switches to the banking-up mode in preparation." All the control valves in the main drains move to a defined starting position that represents 50% of the end value (closure). With an increase in rainfall and corresponding forecasts, the electro-hydraulically operated valves block the main drains to bank-up the sewerage. This means that the flow into the main sewerage plant remains constant, even with many times the normal volume.

As soon as the full bank-up capacity of 600,000 cubic metres of mixed water is reached, a controlled 'dump' takes place. "In this case, the powerful spiral pumps at the Simmering pumping station discharge 16 cubic metres of mixed water a second into the Danube. More than 99% of this water is surface water and relieves the pressure on the bank-up area," Plank continues. As a result, the maximum bank-up target can be maintained for each main drain. When the situation improves again, the volume from the bank-up areas is pumped successively to the sewerage plant.

Investment in the future

All the processes run transparently and reliably at any time. Thanks to the intelligent process control system technology from Rockwell Automation, the people in charge in the control room can perform their supervisory functions without any problem and can intervene in the process manually if necessary. Each measured value and each action can also be evaluated later from an historical data store. Through the implementation of the very latest European sewerage management system, the municipal authority of Vienna has provided a service that guarantees maximum safety for the population while also representing a highly economic solution.

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