Water security and methane reduction in Ganga riverfront STPs: a comparative analysis of advance treatment technologies

Wastewater discharge exerts a profound influence on riverine fluxes of dissolved organic matter and methane (CH4) emissions; however, the contrasting impacts of treated versus untreated effluents remain poorly characterised. Here, we present a comprehensive assessment of CH4 emissions from 122 sewage treatment plants (STPs) along the Ganga River, examining variability across treatment technologies and regulatory compliance status. Annual CH4 emissions ranged from 2.9 to 1.82 × 106 kg CH4, with anaerobic systems, particularly UASB reactors, exhibiting the highest emission intensities. Among the surveyed facilities, 81 STPs complied with the Ministry of Environment, Forest and Climate Change (MoEF & CC) discharge norms, while 41 non-compliant plants accounted for a disproportionately high CH4 load (1.39 × 106 kg CH4 year−1), compared to 1.11 × 105 kg CH4 year−1 from compliant counterparts. Advanced aerobic technologies, including FBBAS, FBS, and A2O processes, achieved >92% reductions in CH4 emissions, underscoring their mitigation potential. These findings highlight the dual importance of stringent regulatory compliance and continuous technological advancement in minimising wastewater-derived CH4 emissions. As river basins across Global South experience rapid urbanisation and rising wastewater loads, future mitigation efforts must prioritize region-specific strategies to lower STP carbon footprints and support climate-resilient infrastructure.