Automating wastewater treatment to meet regulatory standards

Paul Boughton

Automation is becoming ever more important when it comes to wastewater treatment, especially in terms of control and monitoring, increasing capacity, improving effluent quality, and meeting environmental compliance standards.

Emerson Process Management has been selected to automate equipment and processes for two innovative environmental projects at DC Water's Blue Plains advanced wastewater treatment plant in Washington, DC, USA.

Blue Plains is the largest plant of its kind in the world, with a capacity of 370million gallons/day. DC Water is undertaking two major capital improvement projects - enhanced nutrient removal, and thermal hydrolysis and anaerobic digestion - that will help it comply with evolving environmental regulations and protect the Chesapeake Bay watershed while serving an expanding population. Emerson's Ovation control system will help DC Water optimise operations of these new facilities (Fig.1).

The plant currently utilises a sophisticated nitrification/denitrification and filtration process to reduce the amount of nitrogen in the water. Excess nitrogen causes an overgrowth of aquatic plants and algae, robbing water of the oxygen fish and other aquatic life need to survive. The US$950million (EUR719 million) enhanced nutrient removal project is designed to reduce almost to the limit of technology the level of nitrogen that DC Water discharges to the Potomac River.

Ovation technology will monitor and control all major equipment and processes related to the project which, once complete, will enable Blue Plains to produce effluent with some of the lowest levels of nitrogen in the country, especially for a plant of its size.

The second project, thermal hydrolysis and anaerobic digestion, will enable DC Water to reduce biosolids by 50 per cent. This will not only slash carbon dioxide emissions associated with hauling biosolids away by up to 60 tons, but will also allow DC Water to burn the methane gas by-product to generate electricity that will help offset power by one third for its operations. Additionally, the remaining class A biosolids will have greater commercial value, because they offer more reuse options as a fertiliser than the plant's current biosolids.

The control system will monitor and control the anaerobic digesters, final dewatering and other equipment and processes related to this major initiative, as well as interface to the combined heat and power plant.

Real time data visibility

Recently, a Canadian water/wastewater operation that encompasses six separate treatment plants recognised its need to not only increase visibility into existing systems, but spot trends that would help better predict its production needs. Because a range of issues might diminish a plant's ability to deliver water supply - from flow issues and spiking electrical usage to greater-than-average demands by one water user on the network - the operation needed real-time visibility into factors that affect flow. Gaining this information would allow the facility to react to specific issues affecting the fluctuation in demand, without having to risk inaccuracy by 'guessing'.

The water/wastewater operation enlisted Grantek, an Ontario-based systems integrator and its partner, Rockwell Automation, to identify areas in need of improvement and implement a manufacturing intelligence strategy that could help it reduce risk of downtime and optimise operations.

Grantek's solution is centered on FactoryTalk VantagePoint software from Rockwell Automation. FactoryTalk VantagePoint software taps into information from systems across operations that has been automatically identified, gathered and stored by FactoryTalk Historian software - including systems developed by a number of different vendors and varying widely in age. The FactoryTalk VantagePoint application provides visibility into production by putting all this data into context through a Web-based reporting tool that gives users a comprehensive picture of the factors contributing to the performance of their operations.

By marrying FactoryTalk VantagePoint software with the specific information demands of the water/wastewater operation, Grantek modelled the physical units of the facility such as high lift pumps and intake pumps, and plant processes such as chlorination and filtration, logged those names into a library, and created drag and drop functionality that provided for a quick and easy migration. The software was scalable and compatible with the operation's legacy systems, and leveraged the enhanced visibility and reporting capabilities inherent in the application.

Grantek's solution also provided easy-to-use reporting on key performance indicators, enabling users - whether operator, line supervisor, plant manager or executive - to hone in on the suitable level of detail for their role. Because the FactoryTalk VantagePoint user experience is very intuitive, the water/wastewater operators can now access role-appropriate information with a simple click-through on the Web-based system.

"Role-appropriate visualisation is critical to creating value for our customers," says Rick Hargreaves, Grantek regional manager. "While an operator needs particular information to make quick decisions on the floor, a manager may only seek high-level dashboard displays that allows taking measure of the whole system with a quick glance."

The software also reduced the amount of operator time spent on information gathering for regulatory purposes, and highlighted a US$100,000 (EUR76,000) billing error that had gone unnoticed in the company's original manual entry spreadsheet system.

Yokogawa Indonesia has received an order from Waskita Karya to supply the automation system for the Petanu water treatment plant that it is building at the Sanur beach resort area on Bali's southeastern coast for a municipal water utility.

The Petanu water treatment plant will produce 300litres/s of clean water for Gianyar Regency, Denpasar City, and Badung Regency. It is scheduled to start operation in late 2013.

Indonesia is the world's fourth most populous country, and its infrastructure is being rapidly developed to meet the growing needs of its urban population and the tourism industry. The Petanu water treatment plant is a key to ensuring a stable supply of clean water for south eastern Bali.

The automation system that is to be installed at the Petanu water treatment plant includes the FAST/TOOLS SCADA 3 software package, the STARDOM network-based control system, analysers, and a variety of field devices such as ADMAG series magnetic flowmeters. Yokogawa Indonesia will be responsible for the entire project.

Wastewater transfer pipelines

Meanwhile the central wastewater treatment plant of Lapuan Jätevesi, a Finnish company located in Lapua, west of Finland, treats the wastewater from three locations: Lapua, Nurmo and Kuortane. It also maintains municipal wastewater transfer pipelines from Nurmo and Kuortane to Lapua and the central wastewater treatment plant in Lapua.

The process starts with the primary treatment where the influent sewage water is strained to remove all large objects and the oxygen level of the water is increased to facilitate microbe activities. During this biological treatment phase, the microbes in the wastewater are given suitable growing conditions in terms of temperature, oxygen level and nutrition.

The next phase includes chemical secondary sedimentation, where aluminium-based chemicals are added to the water from the biological treatment to prompt flocculation of slowly-degrading organic and other materials. In the last phase, the remaining sludge is treated by removing water from it. The water separated from the sludge is taken back to the beginning of the treatment process, and the solid sludge is taken to the Lakeuden Etappi biogas plant.

The central wastewater treatment plant at Lapua has just been upgraded. In terms of automation, the new solution includes six Modicon Premium controllers that are implemented with Monitor Pro v7.6 and are using Modbus TCP/IP over wireless via nine ProSoft Technology RadioLinx industrial Ethernet radios. About 2000 process variables are transiting over the wireless network.

The company says this solution has helped it meet the four targets of the project: ease of installation and maintenance; flexibility to adapt to fast changing regulation; improvement of the overall solution; and compliance with existing applications and methodologies.

EU hails water treatment moves, but more to be done

Released in August, the EU Commission's Seventh Report on the Implementation of the Urban Waste Water Treatment Directive to the European Parliament is a measure of how each member state is progressing towards compliance with the Directive and covers the period 2009/2010.

The report measures the percentage of compliance that each country has achieved in wastewater collection, wastewater secondary treatment and more stringent wastewater treatment.

Its main findings include: collection rates were at a very high level, with 15 member states collecting 100 per cent of their total polluting load. All had maintained or improved previous results, although compliance rates remained below 30 per cent in Bulgaria, Cyprus, Estonia, Latvia and Slovenia; compliance rates for secondary treatment are 82 per cent, up four points since the previous report.

However there were huge differences between the EU-15, where rates were in the range 90 per cent to 100 per cent, and EU-12, where average compliance was 39 per cent; compliance rates for more stringent treatment to combat eutrophication or reduce bacteriological pollution that could affect human health were 77 per cent overall. EU-12 member states averaged only 14 per cent, whereas Austria, Germany, Greece, and Finland reached 100 per cent compliance

The report also finds that the share of EU territory designated as a sensitive area increased by two points since the previous report, reaching almost 75 per cent. The biggest increases took place in France and Greece.

An annex to the report comparing the situation of 27 European capitals cautioned that only 11 of the 27 had an adequate collection and treatment system in place - despite the fact that the standards were set more than 20 years ago

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