Mogden upgrade demands improved automatic data reporting

By David Brearley

Adsyst Automation Ltd integrated Wonderware's Pantek-supplied InSQL real-time database to new logic controllers for new sludge digesters at the Thames Water wastewater treatment plant in Mogden, Twickenham, one of the largest facilities in the United Kingdom. The real-time database provides semi-automatic completion of a standard Thames Water reporting spreadsheet that is used for plant reporting and proof of regulatory compliance. This report is large and contains manually entered data from laboratory sampling.

The current upgrade of the Thames Water facility required improved and automatic data gathering and reporting. Wonderware's InSQL real time database is also helping with regulatory compliance and commissioning of new digesters.

UK companies Thames Water, Paterson Candy and Binnie Black & Veatch are working together to upgrade the treatment works at Mogden, with real-time computing subcontracted to Adsyst. The facility is being upgraded to comply with the latest standards and regulations, and to increase energy production by stabilising the process; thus optimising production of generated biogas.

The process involves passing raw sewage through settling and aeration before the resulting sludge is fed to digesters. The digesters ensure that digested sludge is safe for output. The plant previously had 20 digesters; these are now being refurbished and modified. Sixteen are back in service. The plant has continued operating throughout the programme, the new digesters being integrated with the existing processes on a step-by-step basis.

The digesters break down the sludge using bacteria. The sludge must be heated to 35°C, this temperature being held through the process. The sludge must be retained for 12 days for the process to be efficient and meet regulations. The process is continuous with controlled extraction and inflow. The digestion process produces large amounts of gas. Gas is pumped back through the sludge to provide agitation to ensure that sludge has a uniform temperature of 35°C. Surplus biogas is pumped off in large volumes and the remaining material is free of harmful content such as pathogens.

The site powerhouse has four large dual-fuelled engines and generators. Engines are run mainly by the biogas from the digesters. The system is now running at a level that allows 92% of the energy to be exported owing to favourable rates for renewable energy.

Heat is extracted from the engine's cooling system and from exhaust to keep the sludge at 35°C. Without the engine, boilers would have to be used to supply heat to the process. Instead, the extracted heat warms the supply water that is used to heat the input to the digesters, creating a true model of energy efficiency.

The long-term upgrade of facilities at Mogden soon revealed that more information was required from the process than the existing SCADA system could provide. The Trend and Alarm information within the SCADA system has been supplemented to give additional functionality by Wonderware's Pantek-supplied InSQL real-time database. Adsyst Automation Ltd integrated this to the new logic controllers that they supplied, installed and programmed for the new digesters. This provides semi-automatic completion of a standard Thames Water reporting spreadsheet that is used for plant reporting and proof of regulatory compliance.

Using the InSQL information from the new digesters helps in commissioning and stabilising the process. The PLCs that control energy recycling will eventually provide data sources for InSQL. The information from InSQL will then provide reports that will show the energy balance of the site.

Author's note
David Brearley is an industrial journalist who works for Pantek Ltd, based in Stockport, Cheshire, England.