Performance of a low-cost full-scale wastewater treatment system: Tubular digesters combined with granular filtration for domestic wastewater in the Ecuadorian Amazon

This study evaluates the performance of a full-scale, low-cost wastewater treatment system combining sequential tubular digesters (LCTDs) with a granular filtration system (GFS) to treat domestic wastewater in the Ecuadorian Amazon. Over three monitoring periods, the system achieved significant pollutant reductions, including COD removal of up to 83 %, with robust nitrate, nitrite and sulphate reductions. Organic loading rates (OLRs) ranged from 0.0326 to 0.0593 kg COD/m³.d for the LCTDs and 9.5 to 52 g COD/m².d for the GFS, demonstrating adaptability to varying operating conditions. The system also effectively stabilized solids, with total suspended solids (TSS) removal exceeding 87 %. Biogas production was monitored in the first and third digesters with daily averages of 0.555 Nm³/d and 0.039 Nm³/d, respectively Therefore, the system's capacity for energy recovery is demonstrated. Specific methanogenic activity (SMA) tests showed an average of 0.0312 gCOD/gVS.d, consistent with reported values for anaerobic digesters. While limited efficiencies were observed for phosphate and ammonium removal, the treated effluent consistently met Ecuadorian discharge standards for most parameters. These results highlight the system's potential as a cost-effective, scalable solution for decentralized wastewater treatment, resource recovery and environmental protection in tropical, resource-constrained environments.