ORP slope and feast–famine strategy as the basis of the control of a granular sequencing batch reactor treating winery wastewater

Winery wastewater is characterized by a high variability of its organic content, and flexible systems such as granular sequencing batch reactors (GSBRs) are required for its treatment. Despite the high load capacity inherent to these systems, the operation with a predetermined cycle length is not suitable to withstand high COD fluctuations. In this study, a control system able to automatically control the HRT depending on the actual organic load has been designed. The relation between ORP slope and DO profiles with the COD consumption together with a proper periodic starvation time are the basis of the control strategy. GSBR operation using the designed system led to an organic matter removal up to 95% for a wide range of organic matter concentrations (1–8 g/L), optimizing cycle duration and avoiding unnecessary aeration costs. The reactor showed a high stability and a rapid response to sudden changes in the COD influent concentration. Biomass settleability remained almost constant around 95 m/h and aggregates showed a Feret diameter of 4–6 mm and sphericity up to 0.8.

► Organic matter from winery wastewater was removed by aerobic granulation in a SBR.
► Frequent COD fluctuations of winery effluents were properly treated.
► A SBR control system based on dissolved oxygen and ORP slope was designed.
► The control of feast/famine ratio lead to spherical, dense and fast settling granules.
► Important energy savings were achieved by implementing the control system.