Two-Step Upflow Anaerobic Sludge Bed System for Sewage Treatment Under Subtropical Conditions with Posttreatment in Waste Stabilization Ponds

SEGHEZZO, L.; TRUPIANO, A.; LIBERAL, V. I.; TODD, P.; FIGUEROA, E.; GUTIERREZ, M.; DA SILVA WILCHES, A.; IRIBARNEGARAY, M. A.; GUERRA, R.; ARENA, A.; CUEVAS, C.; ZEEMAN, G; LETTINGA, G.

APPLIED BIOCHEMISTRY AND BIOTECHNOLOGY

HUMANA PRESS INC

Lugar: Oregon; Año: 2003 vol. 109 p. 167 - 180

0273-2289

A pilot-scale sewage treatment system consisting of two upflow anaerobicsludge bed (UASB) reactors followed by five waste stabilization ponds(WSPs) in series was studied under subtropical conditions. The first UASBreactor started up in only 1 mo (stable operation, high chemical oxygendemand [COD] removal efficiency, low volatile fatty acids concentration inthe effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kgof CODremoved). Removal efficiencies up to 90% were obtained in the anaerobicsteps at a hydraulic retention time of 6 + 4 h (80% removal in the first step).Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobicsteps and 99.98% in WSPs). COD balances over UASB reactors are provided.A minimum set of data necessary to build COD balances is proposed.Intermittent sludge washout was detected in the reactors with the COD balances.Sludge washout from single-step UASB reactors should be monitoredand minimized in order to ensure constant compliance with discharge standards,especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions.