Quantifying Emissions from Wastewater Sludge Digesters

Today’s Plume of the Week is courtesy of Severn Trent Water. The QLM Quantum Gas Lidar installed at their Minworth Sewage Treatment Works in the UK was able to detect, image and quantify this emission source and confirmed what was suspected about the methane emissions from the sludge seals on a legacy asset known as a floating roof digester. This has not been a standard digester design for decades, but several such assets are still in use. The seal around the base of the anaerobic digester tank is supported by the sludge to be digested. This has benefits when it comes to the simplicity of design and balancing sludge levels but has a downside in terms methane emissions. Continuous monitoring with QLM was able to 1) confirm methane emissions do occur from the sludge seal, 2) quantify and track the continued nature of the emission, and 3) to build an understanding of how any variation in emission rate may be affected by changes in the digester process. At Minworth STW, a program to replace the roofs is underway and QLM also enables monitoring the newly fixed roofs to confirm the solution’s emission benefits. This allows Severn Trent to understand the benefits to emissions in upgrading the floating roof digesters to fixed roofs, supporting investment decisions across all these assets.