I Spy Fugitive Methane: A Look at 3-years of Leak Detection Surveys

Bioenergy programs at municipal water resource recovery facilities (WRRF) are centered around anaerobic digestion, beneficial use of biogas, and opportunities for co-digestion. These programs can help to can provide avenue for climate positive action and cost offsets or revenue generation. Although bioenergy programs provide major benefits, they can also be an unsuspecting major source of greenhouse gas (GHG) emissions. Fugitive methane is the unintended release of methane typically from anaerobic digestion and solids handling systems but can also come from upstream processes as well. Fugitive emissions are often one of the sources of GHG emissions from WRRFs along with energy use and nitrous oxide emissions. Methane is a major contributor to climate change, accounting for 45 percent of current net warming. As a potent GHG, methane is 84 times more effective at trapping heat in the atmosphere compared to carbon dioxide over a 20-year timeframe. WRRFs are estimated to contribute 5-8% of global anthropogenic methane emissions (Ocko, 2021). The significance of methane and its impacts on the climate, coupled with burgeoning interest and attention of WRRFs as a source, creates considerable opportunities within the wastewater sector to address both local and global climate action goals by reducing these emissions. The adoption of leak detection and repair (LDAR) programs can provide a means to substantially reduce emissions while addressing odors, safety, asset renewal, and other drivers. This presentation will provide an overview of LDAR programs and summarize data collected from optical gas imaging (OGI) fugitive methane surveys from 15 WRRFs over the course of two and a half years. To date, most of the fugitive emissions detection and quantification efforts have been focused on the oil and gas (O&G), landfill, and mining sectors. Additionally, only the O&G sector have mandates for LDAR programs. A vast majority of WRRFs do not deploy regular leak detection efforts as part of route maintenance or are reliant on rudimentary leak detection methods. New detection technologies and methods developed in O&G provides the significant opportunities to implement effective LDAR programs. Leak detection methods include audio, visual, and olfactory (AVO) inspections, portable monitoring instruments, or OGI cameras. Many of these methods are established as part of the Environmental Protection Agency (EPA) Reference Method 21 (40 CFR Part 60, Appendix A). The direct appropriation of some of these methods by the wastewater sector may present challenges due to the unique nature of emissions from WRRFs. WRRF emissions have high variability, broad range of quantities, and types of leaks that can deviate from O&G calibration and detection settings. However, OGI technology has translated well to its use at WRRFs where it has been effective at detecting biogas leaks and could potentially be a key component of LDAR programs. OGI relies on thermal imaging spectrometry to isolate gases that are invisible to the human eye by detecting the infrared radiation that passes through the gases. As infrared radiation travels through certain gases, energy is absorbed at specific wavelengths and changes the infrared radiation transmittance. The OGI camera is equipped with a spectral filter that limits the type of infrared radiation that can pass into the detector. This spectral filter is designed to uniquely match the gases' infrared fingerprint. A cryogenically cooled detector then translates the signal into a thermographic image of the gas. Many OGI cameras are also capable of quantification or QOGI which allows the camera to compute mass and volumetric flow rates of gases. A Konica Minolta GMP02 OGI camera was used to identify and record methane emissions at solids and liquid treatment processes. Figure 1 depicts the Konica Minolta GMP02 OGI camera and illustrates the process through which OGI detects gases. The fugitive emissions surveys took place between 2022 and 2024 at 15 WRRFs to capture unintended leaks from equipment, structures, piping, and other assets. The following locations were typical of most surveys: - Headworks, preliminary treatment - Aeration tanks and primary clarifiers - Solids thickening - Biogas/natural piping and appurtenances - Biogas system (boilers, condensate traps, co-generation, gas conditioning/upgrading) - Digesters (walls, covers, appurtenances) - Dewatering equipment, building, and cake storage - Odor control Over two hundred emissions leaks were classified in three broad arbitrary categories of small (1 - 200 g CH4/hr), moderate (201 - 1000 g CH4/hr), and large (>1000 g CH4/hr). Quantifications of methane emissions occurred at most locations, but some emissions were qualitatively classified. Photos and video were documented at all leak locations. Example sources of leaks are shown in the following figures. Additional data summaries will be provided in the presentation and the final proceedings. The outcomes of the survey found that the most common sources of leaks included pressure vacuum release valves (PVRV), floating covers, digester cover safety appurtenances, biogas compressors, biogas condensate and drip traps. One of the more common leak points were from PVRVs which were attributed to lack of maintenance, manufacturing quality control issues, and system operating pressure. PVRV are designed to be leak tight up to 75% of the setpoint and less 1 scfm at 90% of the setpoint. However, many of the PVRV leaks reflected greater than 1 scfm of biogas even when below the setpoint. Several plants had significant leaks due to corrosion and failure of the PVRVs while others were venting per normal operation where system pressures exceeded the set point. During the course of the survey, several leaks were corrected by plant staff and resurveyed to verify mitigation of the leaks. When considering methane emissions, they can be classified as either venting and fugitive methane leaks. Venting is the intentional operational and maintenance actions that leads to emissions of methane typically for system operation, safety, and performance. Fugitive methane is the unintended emissions of methane due to damage, wear, corrosion, and human error. Both fugitive leaks and venting can potentially be addressed with design improvements and innovations. Some elements include redesigning digesters for higher pressures allowing for greater buffer between PVRV setpoint and operating pressure. This study indicated that voluntary LDAR programs may be effective at identifying and reducing fugitive emissions. They also play a vital role in ensuring the safety and health of plant staff and reduction of nuisances to the surrounding communities. LDAR programs can lead to considerable cost savings by preventing the loss of biogas. Additional studies are needed to develop the framework of LDAR program included recommended technologies, frequency of inspections (annual, quarterly, monthly), documentation and workflow, and other key factors.