Partida de um sistema de lodo granular aeróbio em escala plena: avaliação da formação de biomassa e de seu desempenho no tratamento biológico de esgoto sanitário

Abstract

Aerobic granular sludge technology has been shown to be promising for wastewater treatment. Despite the several investigations applying this process for the treatment of industrial and domestic wastewater worldwide, there are still few studies in full-scale settings. The aim of the present work was to evaluate the development of the aerobic granulation process and the biological treatment performance during the start-up of the first full scale aerobic granular sludge plant in Latin America for the treatment of sanitary sewage. The Deodoro treatment plant, located in the city of Rio de Janeiro, was designed to be operated in two distinct stages, with flows of 750 L.s-1 (current) and 1000 L.s-1 (future). The unit is composed of three sequencing batch reactors, and its operation began in July 2016. For this study, the plant was monitored for 272 days by physicochemical and microscopic analysis. The inoculation of the biological reactor was carried out with activated sludge from an existing conventional plant. The influent sewage exhibited great concentration oscillations due to the dynamics and local characteristics of the collection network. The mean values of BOD, COD and SST in the influent were 61 mg.L-1, 152 mg.L-1 and 71.5 mg.L-1, respectively. Despite the oscillation of the influent characteristics and the low organic loads applied to the reactors (approximately 0.5 kg COD.m-3.d-1), the system was able to withstand such conditions while maintaining stability. The average percentages of COD, SST, phosphorus, ammonium and total nitrogen removal were 85%, 84%, 55%, 92% and 73%, respectively, even without legal requirement and design premise for nutrient removal. During the monitoring period of the start-up phase, the legal requirements of the current environmental legislation were fully met in the first weeks of operation, resulting in average effluent BOD, COD and SST concentrations of 6 mg.L-1, 22 mg.L-1, 7.5 mg.L-1, respectively. Even without legal requirement and project premise, high percentages of ammonium and total nitrogen removal were achieved, with mean values of 92% and 73%, respectively. The beginning of the granulation process was evidenced, and the formation of some granular structures was noticed. However, due to the low organic load applied, the percentage of granulation during the entire reactor operating period was only 5.5%. Finally, this study demonstrated that, despite the challenges to be faced, especially due to the characteristics of sewage in Brazil, aerobic granular sludge technology can be effectively implemented in the treatment of domestic sewage in the national context, achieving excellent quality of treated effluent.