How Columbus Used Fugitive Methane Quantification to Implement Fugitive Methane Abatement Solutions as Part of a Major Bioenergy Program

Methane is a major contributor to climate change, accounting for 45 percent of current net warming. As a potent greenhouse gas (GHG), it is 84 times more effective at trapping heat in the atmosphere compared to carbon dioxide over a 20-year timeframe. A global effort to reduce methane emissions was inaugurated by the Global Methane Pledge (GMP) with 150 countries committing to reduce methane emissions by at least 30 percent from 2020 levels by 2030. Its reduction is crucial to mitigate near-term warming and to avoid the worst effects of climate change. Municipal water resource recovery facilities (WRRFs) have been estimated to contribute around 5-8% of global anthropogenic methane emissions (Ocko, 2021) which are largely attributable to fugitive, or unintended, releases. These emissions are associated primarily with anaerobic digestion and associated solids handling. The significance of methane and its impacts on the climate, coupled with burgeoning interest and attention to WRRFs as a source, creates considerable opportunities within the wastewater sector to address both local and global climate action goals by reducing these emissions. Recently, new measurement technologies developed in other sectors (oil, gas, and landfill) have provided WRRFs with the ability to more accurately quantify and identify sources of emissions. In addition, new abatement technologies and knowledge to reduce fugitive methane has emerged that allows solutions to be implemented. This abstract covers one of the first efforts to reduce fugitive methane as part of a major bioenergy program based on new technology quantification and represents the second part of a two part presentation. As part of the Bioenergy Project at Southerly Wastewater Treatment Plant (SWWTP), the City of Columbus embarked on a field campaign to quantify fugitive methane emissions. The field campaign was the first US multi-technology effort to quantify fugitive methane at a WWTP using commercial services and products. This included drone flux measurement (DFM), an optical gas imaging (OGI) camera and discrete sampling with a flame ionization detector (FID). The field investigation spanned several days and included an evaluation of the solids handling facilities, waste gas burner (WGB), digestion facilities, and the BLAF. The OGI camera was used as a qualitative method for source identification. The DFM is an ISO 17025-accredited top-down method and was used as the primary method for quantification. The DFM was used to collect area emissions from various parts of the plant and a representative DFM. The total amount of fugitive methane measured via drone at SWWTP at the time of the investigation was approximately equal to 15 percent of the total biogas production or 70 kg/hr as seen in Figure 1. The outcomes of the campaign lead to an alternatives evaluation looking at a comprehensive list of abatement options. A fugitive methane model was developed to estimate fugitive methane emissions based on the quantification campaign results and future flows and loads for years 2028 and 2048 see Figure 2 and Figure 3. In the no-action scenario, the total FM would increase 87 percent. Due to the severity of the FM issue, the City decided to take initial actions to reduce fugitive methane emissions by developing a beneficial biogas program, implementing digestion system improvements, and replacing the methane phase digester floating covers with concrete fixed covers. These actions would result in a fugitive methane reduction of 74 percent based on 2048 flows and loads see Figure 4. The remaining FM needed to be mitigated were from the solids handling facilities and the BLAF (see Figure 1). Solutions that were evaluated included augmented biofiltration, vapor combustion units (VCUs), regenerative thermal oxidizers (RTOs), an Elovac system, and replacing the BLAF cover to capture the gas. A cost-benefit analysis based on cost per metric ton (MT) CO2e reduced was used to evaluate the alternatives. RTOs were selected for the BLAF and VCUs for the solids handling facilities as shown in the costs in Table 1 and 2. The end solution resulted in a 96 percent decrease in FM emissions from the solids handling and treatment processes at SWWTP see Table 3.