High-strength anaerobic digestion wastewater treatment by aerobic granular sludge in a step-by-step strategy

To reduce the instability of aerobic granular sludge (AGS) caused by high-strength anaerobic digestion wastewater, a strategy of increasing proportion of anaerobic digestion wastewater step-by-step was adopted in this study. High-performance stable AGSs were successfully cultivated with sequencing batch reactors by this strategy, which could efficiently treat high-strength anaerobic digestion wastewater with an influent chemical oxygen demand (COD) up to 5090 mg⋅L−1. After six phases of stepwise increasing COD loads, the sludge sizes increased from 0.5 mm to 1.5 mm, with the final mixed liquor suspended solids increased to 13,814 mg⋅L−1, and the final sludge volume index decreased to 15 mL⋅g−1. The extracellular polymeric substance (EPS), which is crucial to keep the stability of AGS, increased continuously from 85.1 mg⋅g−1 SS to 307.8 mg⋅g−1 SS with the increase of COD loads. Moreover, the removal efficiency of COD and TN could reach 92% and 87% for real high-strength anaerobic digestion wastewater treatment. The bacterial community analysis revealed that the family Rhodocyclaceae, Flavobacteriaceae, and Xanthomonadaceae were the major microbes of AGS, and were responsible for COD and TN removal, as well as EPS secretion. These findings may provide novel information and enrich AGS treatment of high-strength real wastewater. •Aerobic granular sludge was used for the treatment of high-strength anaerobic digestion wastewater.•Stepwise strategy was adopted to reduce the high-strength wastewater shocks.•Compacted and stable high-performance aerobic granular sludges were successfully formed.•High chemical oxygen demands and total nitrogen removals were achieved for high-strength wastewater.•Family Rhodocyclaceae and Flavobacteriaceae were dominant during the treatment.