Evaluation of the anaerobic digestion process of arrudas wastewater treatment plant (conventional activated sludge)

Abstract

This research aims at assessing the characteristics and behavior of the anaerobic digestion units, which treat sludge at the Arrudas Wastewater Treatment Plant (2.25 m3/s design flow). The plant is located in Belo Horizonte, Brazil, and operates as conventional activated sludge, with anaerobic digestion of the sludge and further mechanical dewatering by centrifuges. The plant went through three different operational phases in relation to the thickening, thus affecting the following stage of anaerobic digestion: Phase 1: digestion of thickened primary sludge; Phase 2: digestion of thickened mixed sludge; Phase 3: digestion of thickened.secondary sludge and of primary sludge. During the first and second phases, values of removal efficiency of volatile solids of 37% and 36% respectively occurred. In the third phase, the average efficiency of removal of VS was higher (43%). The VS/TS ratio was maintained, in the three phases, around 0.60. The pH values were always within those reported by the literature. The longest hydraulic detention time occurred in the second phase (47 days), while in the first phase it was 35 days, and in the third phase 22 days – a value near that assumed in the design.