Start-up of an aerobic granular sequencing batch reactor for the treatment of winery wastewater

Aerobic granular sludge was cultivated in a sequencing batch reactor (SBR) in order to remove the organic matter present in winery wastewater. The formation of granules was performed using a synthetic substrate. The selection parameter was the settling time, as well as the alternation of feast-famine periods, the air velocity and the height/diameter ratio of the reactor. After 10 days of operation under these conditions, the first aggregates could be observed. Filamentous bacteria were still present in the reactor but they disappeared progressively. During the start-up, COD loading was increased from 2.7 to 22.5 kg COD/(m³ day) in order to obtain a feast period between 30 and 60 minutes. At this point, granules were quite round, with a particle diameter between 3.0 and 4.0 mm and an average density of 6 g L⁻¹. After 120 days of operation, synthetic media was replaced by real winery wastewater, with a COD loading of 6 kg COD/(m³ day). The decrease of the organic load implied a reduction of the aggregate diameter and a density increase up to 13.2 g L⁻¹. The effluent was free of organic matter and the solids concentration in the reactor reached 6 g VSS L⁻¹.