While numerous studies report methane emissions from wastewater treatment plants (WWTPs) in developed countries, few address emissions from plants in developing countries, where outdated technologies, such as the lack of enhanced primary and sludge treatment, are common. Moreover, these studies often rely on indirect calculations rather than direct measurements. Our study fills this gap by providing unit-process-level direct measurements of methane emissions in a conventional WWTP in Mexico, serving as a case study for developing countries. A standard plant was selected and visited on five occasions. It includes a primary settler, an aerated reactor, and a secondary settler, with no sludge treatment in place. Our findings revealed a CH