Methane emissions from stabilization ponds for municipal wastewater treatment in Mexico

Abstract: Wastewater treatment (WWT) is applied for environmental protection and water reclamation. However, this activity has been identified as a source of methane (CH₄), contributing to climate change. WWT (municipal and industrial) is estimated to produce 8 to 11% to overall CH₄ emissions. In order to apply effective mitigation strategies in the water sector, a more precise inventory of CH₄ emission should be accomplished. The application of the Tier 1 methodology in the Guidelines for National Greenhouse Gas Inventories of the Intergovernmental Panel on Climate Change (IPCC) results in rough estimations, as default emission factors are used. An effort should be done for determining actual emission factors for the more representative treatment processes in a given region or country. In this work, a detailed inventory of CH₄ emissions form municipal wastewater management in Mexico was obtained, based on the Tier 1 IPCC methodology. In addition, on-site CH₄ emission measurements in five stabilization ponds (SP) were realized. The total CH₄ emissions generated by municipal WWT in Mexico were 600.4 Gigagrams (Gg) for year 2010. Also, the IPCC (theoretical) estimations showed that CH₄ emissions were overestimated if compared with the results obtained in the five sampled facilities. The on-site emission factors obtained showed wide variation as they are specific to each sampled system and to their particular environmental and operating conditions. In Mexico, the value of 0.431 kg CH₄/kg BOD removed (0.110 kg CH₄/m³ treated water) may be used for SP with good operational practices.