Coupling of sponge fillers and two-zone clarifiers for granular sludge in an integrated oxidation ditch

Abstract

Considering that aerobic granular sludge (AGS) exhibits a long granulation time in continuous flow and that the poor removal effects on N and P have severely restricted its large-scale application, a novel strategy was developed involving sponge fillers to construct an anoxic zone coupling two-zone clarifiers to promote granulation in an integrated oxidation ditch. The different pores in the sponge fillers were used to accelerate the accumulation and formation of aggregates under the impetus of water flow, meanwhile, the A/O operation mode and the formation of AGS were also improved the denitrification and phosphorus removal capacity of the reactor. The experimental results indicated that AGS was shaped in the anoxic and aerobic zones on day 30 and on day 43, respectively. When running for 90 days, the mixed liquor suspended solids (MLSS), sludge volume index (SVI5) and average particle size in the anoxic zone and aerobic zone were 5848 mg/L and 4812 mg/L, 31.2 mL/g and 35.8 mL/g, and 329.2μm and 362.3μm, respectively. During the granulation process, the EPS content in the anoxic zone was significantly higher than that in the aerobic zone, indicating that the sponge fillers played a dominant role in granulation. After the reactor reached steady conditions, the removal efficiencies of COD and N were 87.29%±2.61% and 60.11%±4.68%, respectively. The TP removal efficiency gradually increased from 26.90% on day 1 to 77.54% on day 90. Moreover, the microbial community transformed conspicuously throughout granulation, including an enrichment of microorganisms exhibiting EPS secretion and pollutants degradation.