Simultaneous biological nutrients removal from wastewater with high ammonium and phosphorus loading using aerobic granular sludge

In this study, two SBRs were inoculated with biomass from a flocculant biological nutrient removal facility and operated for the biological treatment of synthetic wastewater to explore the impact of low influent COD/TN/TP ratio on the start-up, performance, and development of stable, matured AGS. AGS maturation and simultaneous nutrient removals were investigated for 422 days under applying limited DO (1.5-2.0 mg L-1); after that, an optimization period was performed till day 558 to study the influence of applying high DO levels (5.0-8.5 mg L-1). Initial observations at day 118 indicated high settling velocities for granules with a size >= 1.5 mm, with 90 % COD removal achieved since day 35, while exhibiting moderate levels of ammonium (68-71 %) and phosphorus removal (42-44 %). By day 422, the maturation of granules continued, reaching sizes exceeding 3 mm, with a 70 % increase in biomass growth (14.3 g L-1). P-release and P-uptake rates of 52 and 12 mg-P/g-MLVSS<middle dot>h, respectively, resulted in reduced effluent PO4-3-P (1.5 +/- 0.2 mg-P L-1). TN removal performance reached 82 % (NH4-N removal of 88 %), and SND of 99 % was achieved by matured granules maintaining effluent nitrite/nitrate concentrations <= 0.5 +/- 0.3 mg-N L-1 (days 330-422). The optimization period was conducted by enhancing biomass mixing conditions and increasing DO, resulting in improved nitrification, with oxidation rate reaching 19.2 mg-NH4/g-MLVSS<middle dot>h at DO 6 mg L-1. However, DO > 6.5 mg L-1 adversely affected EPS secretion, and granules exhibited poor settleability.