Environmental and Energy Sustainability in Wastewater Transportation: Integration of ISO 50001 and ISO 14040/14044 in the Replacement of Diesel with Compressed Natural Gas, Lima, Peru

Evidence combining energy management and life cycle assessment of diesel-to-CNG substitution under real fleet operation remains limited. The energy and environmental assessments were jointly applied over a common functional unit—the transport of 30 m3 of non-hazardous wastewater per documented service—with an annual reference flow of 82,422 m3·km derived from 38 services (1140 m3; 5905.2 km) in Lima, Peru. A single primary dataset fed both the energy baseline (characteristic monthly consumption of 22,828 ± 1435 MJ month−1; service-level intensities of (Formula presented.) vs. (Formula presented.) MJ (m3·km)−1, (Formula presented.), (Formula presented.)) and the life cycle inventory, assessed in SimaPro v9.6.0.1 (ReCiPe 2016 Midpoint (H)) under an extended tank-to-wheel boundary with Pedigree–Monte Carlo uncertainty propagation. The transition—fuel substitution combined with Euro V-to-Euro VI platform renewal—reduced energy intensity by 45.3% and direct-combustion GWP100 by 61.1%; this integrated effect is not attributable to the fuel change alone. Methane slip contributed 1.3% of the CNG GWP100, and only an upstream leakage of 15.5% of the delivered gas would cancel the climate benefit. Tire replacement remained the dominant hotspot (64.5%/51.7%); immediate 30-vehicle fleet conversion would avoid 2530 t CO2-eq over ten years.